Thursday, 2 February 2023

Our Tender Experiences

The best tender for a yacht has to fulfill a whole range of criteria and that will partly be dictated by your own personal needs and experiences.

There are so many different styles and shapes of tender on the market, some lend themselves to being work horses hauling the food supplies and beverages out to a yacht at anchor with ease.  Then there are the show ponies, centre console and a large outboard. These are more suited to a quick run to the beach, most of the time they are heavy due to the configuration and dragging them up to the high water mark while ashore is likely to give you a hernia or heart attack whichever comes first. We have found due to the configuration its hard to do a resupply thanks to the lack of space, and these boats are not really suited to remote location cruising.  It can be done of course by hiring a run about to bring out the supplies. Then there are of course the tenders that spend a second life as a fishing boat.  We have found waterline length certainly makes a difference to speed, and while there are those who are fine with a small out board when venturing into remote areas, it could be a lot safer to have a bit of horse power under the hood so to speak.  We have been in areas where the currents can run at 6-7 knots, so a bit of horse power is needed to get around. I also remember zooming over a large sandbar strewn bay near sunset to take photos before the light changed too much. If we were not able to get up on the plane then we would have missed the opportunity, of course we could have started our trip earlier but we would not have been back until well after the sun had set. These are the things to consider when purchasing a tender, we found the bigger the tubes the better, a bit of length certainly helps get on the plane, a flat floor or a floor added over a deep V floor is good and is a lot safer getting in and out of the tender when tied along side.  

While its a difficult ask these days, a two stroke engine can be a useful addition to a cruising yacht when going offshore. This is our experience, we went off shore with a nice new four stroke engine and after a few short months of relying on it we were celebrating when we sold it and purchased a two stroke. Yes there will be a lot of people thinking we are environmental vandals, how ever our safety and the ability to head ashore and actually make it were high on our list of desirable things an outboard should be capable of.  The only thing and this is the only plus is the fuel economy was good, unfortunately the four stroke wasn't reliable, it had a poor weight to HP ratio, and the ongoing repairs and need for maintenance was cutting into the cruising budget. So what was the problems, consistent condensation in the carburettor fuel bowl causing the engine to stop when a drop of water blocked the jet. In a one year period the rubber drive in the propeller(s) was replaced or the propeller replaced eighteen times  (18). Changing the oil was a real pain in the neck due to design. The next safety issue was the slightest kick back when starting would smash the plastic pieces in the pullcord mechanism. Then to add to the grief of the pull cord becoming unoperational, the way the flywheel was cast did not lend itself to easily using an emergency start cord.  Then to add insult to injury if you didn't use the outboard for a week or fortnight the interior of the carburettor would start to corrode when the fuel evaporated. The white powder from the corrosion would then block the jet in the carburettor when you next start the motor. Yeah happy happy times! All that aside I hope some of the info collected here is of use. 

As we have become more knowledgeable through our own experiences we have also learnt from others. I would like to share some of what we have learnt about reducing the risks when using tenders. These little boats really are our connection to the outside world and hard working pack horses come resupply day. Unfortunately the risks are real and some have paid the ultimate price by not recognising the potential danger. 

When we are sailing around our local bay enjoying the anchorages it’s a very rare occurrence to be there alone.  In the bay most anchorages allow us to anchor close to the beach and it’s possible to easily row back to the boat or summon help from passing or anchored vessels.  When we started exploring out side the bay we didn’t give a great deal of thought to how easy it would be to become like Robinson Crusoe using the tender to go ashore.  

We found it’s not hard to become stranded in sight of your own vessel.  In some cases it has been much worse for a few people. Since moving further afield, talking with others and after our own personal experiences we have been wakened out of our complacency.  You know Complacency:   a feeling of contentment, especially when coupled with an unawareness of danger.  So what’s the danger?  If you haven’t thought about it here are a few. 

We have heard through the grapevine and read several stories about others experiences both good and bad; these have ranged from forced overnight stays on mosquito infested beaches to being washed away on a tide. What if the weather turns? and you are not able to return to your anchored vessel. Or you could become stranded if the motor fails and you’re against the tide or it’s too far or perhaps you are injured and are unable to row back.  Those that have been washed away on the tide and have travelled for miles with no water and little protection from the elements, luckily in these cases they were found by passing ships but it was several days later. One couple we read about was almost washed from a mid ocean coral cay when their tender motor wasn’t powerful enough against the outgoing tidal flow.  They found themselves standing barefoot on coral holding their tender to stop it from being washed away while waiting for the tide to turn. Then once the tide turned it allowed them to motor back to their vessel on the little remaining fuel they had.  

One other danger that was highlighted during a recent incident was that a person using a tender fell over board. If being in the water wasn’t bad enough the real trouble began when they could not reboard their tender from the water. It is a worthwhile experiment to test your tender has sufficient stable buoyancy to accommodate a person being able to climb back on board from the water.  I know that with some inflatable’s even moderately unfit persons can reboard over the stern using the outboard as a step, if the out board is fitted with a wing. Unfortunately this may not be possible for all combinations of motor and tender.  What if you cannot reboard your tender from the water? It is certainly in your best interests to look at ways to make it possible to get back on board.  This is especially important if you are in the higher latitudes, hypothermia will quickly set in once you’re in the water and make it almost impossible to swim back to shore or climb up on to the main vessel.  While there are ever growing lists of problems people find themselves in, I think this small cross section should have given you an idea of the multitude of perils if you ignore the hazards. Since writing this we made a fold up ladder  to keep in the tender just in case we  or someone else fall overboard. 

We now carry additional gear in our tender as well as a safety box so we can summon help or do minor repairs should they be necessary.  However the safety box is only good if you take it with you. We didn’t once and when we had finished our walk and swim at the beach we couldn’t get the motor back down.  Luckily we were able to flag down a passing fisherman. Incredibly he didn’t have any tools on board but was kind enough to run us to our vessel and back with the tools for the repair. I have listed the contents of our tender safety box and what we carry in our tender.  While the lists may look excessive it’s a matter of adjusting it to suit the situation. 

Our tender safety box and the contents of what we carry. 

Our safety box is a medium size commercially available water resistant box. Into the box we put our outboard spares and these include dewatering fluid, start rope, shear pins, split pins, stainless plier, adjustable spanner, spark plugs, screw driver, propeller and the spanners to change them. We do carry a spare propeller as we have had one experience where the rubber drive sheared when we hit a rock and we lost drive. While it appears to be a bit of an over kill by the manufacturer to have a shear pin and rubber drive fitted to the propeller to protect the gearbox.  In this instance the rubber protected the shear pin. We also have room for a V sheet, knife, a couple of flares, handheld VHF, a whistle, torch, small first aid kit, water, sunscreen, insect repellent.  Someone said to add some waterproof matches to the list in case you need to light a fire on the beach, it’s a good idea and they take up next to no room.  We have the basic tools to undertake minor motor repairs, and these have come in handy on a number of occasions.  While carrying out the repair we were able to protect our selves with the basics like sunscreen and insect repellent.  Having a drink of water didn’t go astray on those warm days either. While I hope we never need to use them we do have the basic signalling equipment to summon help or aid a rescue for ourselves or render assistance to some one else.

Don’t be tempted to use the V sheet as shelter from the rain if you do not need help.  I heard of a case recently where a couple of guys out fishing put their girlfriends under the V sheet to keep the light rain off, a passing aircraft saw the V sheet and alerted the authorities, who arrived to find the embarrassed fishermen and girlfriends.  However in situations where you require help use the V Sheet as protection while you are waiting for help to arrive. If we were going to the outer reef or find a remote anchorage empty I would also pack the vessels EPIRB in case we run into trouble. Trouble need not necessarily be related to the tender but could be a medical emergency, for example if one of the crew falls and injures themselves while ashore. The uninjured party may not be able to move the injured crew into the tender or for that matter get them from the tender back on to the main vessel.  

While hard to see in the dark green pouch the small repair tool kit tucked away in under the cowl of the motor. 

The small tool kit supplied with the motor, we store ours under the cowl of the motor, better there when needed than on the boat rusting away in one of the lockers. While there is an emergency start cord you have to remove the pull start mechanism to use the cord, just keeping the cord on board the tender isn't enough
Tender anchor chain and rode connected and ready to deploy, we keep ours in a bucket so if we don't get all the mud or sand off it doesnt coat the floor of the tender. 

Stainless steel cable fitted with a plastic hose to stop chafe should it rub against the tender tubes while in use. We like a large combination lock so we don't need to worry about losing the key.

The additional gear we carry in the tender is, shoes, anchor, oars/paddles and bailer. The bits and pieces we keep in the tender are all secured on lanyards in case the worst happens and the tender capsizes. PFD’s can be secured into the tender with a stainless steel cable and padlock when you tie up at the dock while going ashore. Our anchor is rigged for use at a moments notice should it be needed to hold position. We keep shoes in the tender so we can wear them while stepping ashore. It’s better to find there are things on the beach that could slice your bare feet apart while you’re wearing shoes or sandals than if you weren’t. 

Additional water proof storage attached under the seat

Made from cheap easily available storm water plumbing pipe and glue. Sewerage pipe will also work but is more expensive and slightly heavier gauge wall thickness.

To prolong your outboard motors life it’s a good idea to carry out monthly checks and engage in some proactive maintenance.  Firstly buy or make a cover for the motor and fuel tank, keeping the sun and weather off can certainly extend the life of exposed components. A plastic fuel tank left exposed to the weather has a very limited life before it will become brittle and capable of splitting from internal pressure if the vent is closed.  It’s worthwhile to get a small grease gun and marine grade grease and identify grease points and squeeze in fresh grease regularly. Learn how to check the gearbox oil level and condition.  It doesn’t take long to give the outboard ten or fifteen minutes of your time once a month to do some preventative maintenance. I also try to flush the motor with fresh water after use, that’s not every day if using it daily but before storage for a week or more. It’s not always possible to do a fresh water flush when the water tanks are getting low, however if you have sufficient fresh water it is well worth the effort. When you can spare ten to fifteen litres of water, small motors can be held and run in a bucket but with larger motors you will not need much more water but a little ingenuity and mechanical help may be needed. I have seen a larger size bucket filled with water held in place with the motor lifting davit and clever cruisers have made electric camping showers connect to the flush port or ear muffs and use a bag to collect and recycle the water.  I think it’s a case of finding an easy way to do an engine flush on your vessel and use it before storage. 

Check over your inflatable tubes for nicks and scratches, again buy or have a cover made if you can afford it, the UV damage starts the moment its outside.  While we didn’t understand the significance at the time, our inflatable was slowly being destroyed by the sun and was wearing away.  The signs were a white/grey stain on our pants after sitting on the tubes, as it turns out this was the UV damaged layer coming off. The damage was happening for several years; eventually the outer cover was worn away and was almost down to the fabric.  We didn’t really notice the wear until we had to replace a patch and found the height difference between the area under the patch and the surrounding area was very noticeable. On closer inspection of the tubes we saw just how thin the outer cover had become. 

Other things to look at are if you have a tender with an inflatable floor it’s possible to get a build-up of sand and grit under the floor and over time this will damage the fabric. I have seen the inflatable tube under the floor cut to pieces after the boat was used to collect shells. Broken shell fragments worked their way under the floor boards and in no time the damage was done.  The space between the hull and tubes of a RIB can also do with a clean out once a season or more depending on how you use your boat. Let down the tubes slightly and with a hose, spray in between hulls and tubes to clear out any sand and grit then reinflate the tubes.  

Tender Checklist 

Motor monthly between services 
Remove the outboard motor cowl and inspect starter rope, spark plug wires and the fuel lines for wear, cracks, splits or tears also visually check the  fuel filter for any signs of water and clogging. • Check for salt water or oil weeping at gaskets
Check Gear box oil
Check propeller shaft and seal for fishing line (remove propeller)
Grease as per manufactures instructions
Lightly spray power head with protective coating (dewatering fluid/anti –corrosion, lanoline or inox) 

Hull monthly
Check inflation level of tubes
Clean sand coral and or shell fragments from inside, RIBs between hull and tubes
Check over hull & tubes for chafe, scratches and corrosion (repair chafe using patches, if hull is aluminium touch-up paint might be necessary on scratches to minimize corrosion
Check paddles / oars & rowlocks for UV damage

Before use check:
Fuel tank – full
No fuel leaks
Kill switch – MOB lanyard connected
Start the motor and check that it spurts water
Safety strap attaching outboard to tender (to keep motor on if the clamps work loose)
If an inflatable, ensure it’s properly inflated
Paddles / Oars & Rowlocks
Long painter - for towing, tying it to a dock.
Cable with marine padlock – for locking to jetty when leaving it unattended
Safety equipment in water resistant box or bag, V sheet, knife, signal mirror, 1 orange smoke, 1 red flare, handheld VHF, whistle, torch/strobe, small first aid kit, water, sunscreen, insect repellent, water proof matches. Outboard spares: dewatering fluid, shear pins, split pins, multipurpose plier & adjustable spanner, sparkplugs and spanner, screwdriver, propeller, MOB lanyard, secured with padlock & cable.

After use:
Close fuel tank vent and cock on fuel tank.
When the motor cools refuel, helps stop condensation in fuel tank. 
Flush and rinse/wash motor with fresh water to minimize corrosion.

If the outboard motor won't start:
Kill switch – MOB motor stop lanyard not plugged in?
Gear shift in wrong position? (Shift into neutral) 
Choke in wrong position? 
Throttle in wrong position? (Too far open or not open at all, experiment)
Perhaps flooded? if flooded unclip fuel hose or turn fuel off, open throttle and pull cord until motor starts then reconnect fuel hose and try to start (possibly no need for choke now)
Fuel: Check fuel level?  Is Fuel tank cap vent open?  Is fuel tap on?
Fuel supply line connection loose or is hose kinked?  Fuel line bulb should get hard when squeezed
Is there water in the fuel?  Check fuel filter next
Clogged fuel filter? Visually inspect filter, remove and flick contents into a dry bucket for inspection 
Fuel not primed? With engine cowl open see if fuel moves in filter when bulb is squeezed
Pull fuel line from carburettor, crank motor to see if fuel flows evenly (catch fuel in can)
Clogged / water in carburettor?  Not easy to check unless experienced   
Got spark? Not easy to check and dangerous unless experienced   
Dirty spark plug?  (When changing spark plugs check for correct gap) 
Damp ignition components (spray high tension leads & ignition wires with dewatering fluid)
No compression? (Loose spark plugs, broken or jammed reed valve, previously over heated)
Pull cord not turning over motor, problem with recoil spring. Use spare start cord, check operation manual

Tender outboards are usually simple small engines and thankfully have not gone the way of their larger brothers with complex computer controlled engine management systems and fuel injection or specialist carburetion. The reason a tender outboard motor will not start is usually not a complex problem.  While having said that, it’s probably not the time to check out the motor when it’s on the tender tied off behind the vessel.  Get the engine on to a stable level work area on the main vessel. This is a better place to work and a dropped tool will hopefully mean it’s not lost forever into the large blue tool box. 

If you don’t know what you’re looking at have some one skilled in engine repair go over some of the basics with you. Work safely; it can be dangerous when checking for spark on an outboard that will not start. Get to know and understand the safety aspects of dealing with high voltage and sparks around highly flammable fuel. 

Carburettor, the drain screw is easy to see, the use of the screw does not guarantee any contaminates will drain out of the bowl 

After market fuel filter fitted to the fuel tank hose, this clear filter housing can give an  instant up to date visual of the state of fuel in the tank and hose.

Standard equipment fuel filter under the motor cowl, some only filter out large particles 
Water droplet in the carburetor fuel bowl.

Checking the fuel system isn’t complicated once you know the lay out; but work carefully and don’t spill fuel. Most problems we have encountered are from water in the fuel or a clogged filter. If you remove the fuel filter flick the contents of the filter into a container, this will let you see the contents of the filter. Water will ball up in beads in the fuel and any debris will also be visible. Don’t just blow the filter out as this will not give you any idea of what’s causing flow problems.  If you suspect water in the fuel and find small amounts in the filter, remove the fuel bowl off the carburettor and clean and dry it out before reassembly. Water in the fuel may also mean the whole system needs to be cleaned out, draining the fuel tank and lines then refilling with fresh fuel.  How does water get into the fuel? In our experience it was from the vent on the tank cap. Because we were not transporting our motor in a vehicle we would leave the vent open. It appears rain showers or spray during rough weather would be enough to find a way into the tank. As a visual check a pre filter was inserted in the main fuel line, water was easy to see in the large filter housing.  Now that we turn the vent off when we leave the motor on the tender or secured to the bracket on the back rail we no longer have the problem.  

Unleaded fuel containing ethanol should not be used in outboard motors as it has been found that the ethanol can separate from the base fuel if left to sit for a while.  Most fuel supply outlets now have instructions on the fuel pumps notifying customers not to use unleaded fuel containing ethanol in boats.  

Make sure your two stroke outboard is running the correct oil fuel mixture (motor manufactures recommendation); there is nothing to be gained by using extra oil in the fuel, if there is too much oil in the fuel the motor will not perform as it should and can run lean as the oil replaces the fuel in the mixture and running lean can increase maintenance costs.  

MOB Stop Lanyard

A motor safety lanyard, in this case made from a short length of dyneema with a stainless steel clip for quick attachment 

What else?  Make sure you have a safety lanyard attaching your motor to the tender (not to be confused with a motor stop MOB lanyard); just recently we witnessed the loss of an outboard. The owner didn’t have a lanyard attaching the motor to the outboard bracket, from what we saw it was a small motor that could be started in gear, while giving the motor a mighty pull on the start cord it jumped off the bracket, the owner held the throttle handle in his left hand. As the motor twisted the throttle opened up while the owner desperately tried to wrestle it back onto the outboard bracket. Unfortunately the motor won the tug of war and off it went to a watery grave spitting and spluttering as it sunk.  This safety lanyard could be a short cable and padlock so your motor is still there when you come back with the shopping on re-supply day.    

Use an additional safety lanyard when you remove the outboard, make sure that you have a safety line tied from the engine to the main vessel. Outboards can be heavy and if you lose balance or some crazy zooms into the anchorage while you’re doing the transfer and drop it in the water, you will be very glad to have that safety line in place.

Start the outboard first before casting off from the boat or jetty, not after. If you don't and the motor doesn’t start, you may firstly look silly, and secondly the tide will determine how hard you have to paddle against the current to get back to the boat. If the current is flowing strongly and your not making head way drop the anchor and you may need to wait it out. 

Put on a life jacket before boarding; make sure that kids and people who are not strong swimmers do the same.  Is climbing into the dinghy difficult for you or your crew? If it is you will need to plan your trip or work out ways to make it easier. To board use the painter to bring the dinghy as close as you can to the boat. I get in first and bring the dinghy up and across the boat's transom to make it easy to board for kids or those with short legs. When you step in the dinghy, try to get straight inside it putting your feet on the floor. Use a balancing rope, I have even see people use an extended topping lift or rope hung from the davits to hold while climbing aboard. Don’t stand on the on the side tube to get in, depending on the design of the vessel stern, it may be better to get the little ones and older people to sit on the tubes or swim deck then slide into the tender.  Once one of the crew is on board ask others to hop on board but don’t jump in as this can be unstable.  It can certainly make people stumble around in the boat, there is a strong possibility falling on to others in the tender, or stubbing toes or standing on things on the floor. Make sure to spread the load and not have all the weight on one side or in the aft, and do not overload the tender read the capacity label.

For the first trip of the day warm the motor up, get in the tender first and run the motor on low RPM for a couple of minutes to make sure it starts and is running smoothly while you load the passengers and luggage.  Like any other trip, plan ahead, make sure you have enough supplies, fuel, water, food for the trip your about to embark on. 

When using the tender at night it’s a legal requirement to carry a torch at a minimum to mark your presence or attract attention. We store a torch and a few other bits in an under seat storage canister made from 90 millimetre stormwater pipe and fittings.  A good torch can be used to spot obstacles like anchored boats, crab pot floats, mooring buoys and to help find your boat in the dark.  Mark your boat before heading to the beach for the night, we have put several bands of SOLAS reflective tape high up on the mast to give us a good visual which is our boat in the anchorage by shining a torch around.  If you know you’re not going to return before dark turn on a few lights and don’t forget your anchor light.

Quiet Sundowners Towed Stern Too stops the gargling and the dog lapping at water noises 

So when it’s time to be enjoying sun-downers in the cockpit or you’re headed off to bed we have found a tender will make all sorts of noises. It might gently or noisily tap against the hull or make slapping sounds like it’s a dog noisily drinking water.  In the past we would pick ours up out of the water of an evening so it didn’t ruin the serenity as we were enjoying our drinks. On investigation we found that like a lot of RIB’s there is a pocket or tunnel that forms where the tubes join the hull, it’s the motion of the waves in this pocket that makes all the noise. The solution that works for us is to tie the dinghy with its bow the other way. That’s right facing away from the boat, turn it around 180˚ from the usual towing position and secure it from the stern on one or two short painters while you’re enjoying your time in the cockpit. The tender stern with the motor on is heavier and rides deeper in the water, so there are no pockets for the waves to slap and slosh into.  Problem solved the drinking water noise disappears and with two painters securing it we found that it didn’t sneak up the side of the boat and tap on the hull at O’ dark thirty.   

Large inspection port used as a quick drain for when the tender is on the davits, could also double as an anti theft device if removed when on the beach. 

Ready to go the large stern drain has the cover in place the motor is locked and has a safety lanyard. 

Tenders hanging from the aft davits or for that matter any tenders stored upright on deck or over the side need some way of clearing the water quickly so as not to put a large strain on the davits, deck chocks or halyards.  During a heavy down pore it doesn’t take much to overwhelm the small drain hole most tenders have. A leaf, loose line or just the shear volume of water during a storm can quickly see a tender fill with water.  To help clear water from inside the tender we installed an inspection hatch in the transom. If we are in a heavy downpour or take a large wave over the stern the water can quickly empty. Also when we tie up at the beach and are going to be out of sight of the tender we can take the inspection plate with us, anyone wanting to steal the tender is going to have to try and row a water filled inflatable away unless of course they carry their own motor kill switch lanyard. 

Another lesson learnt. During a trip south to Tasmania we lost our tender one evening while anchored in Twofold Bay. Following along with the proverb: the battle was lost because of a nail.  Our story started in Jervis Bay when I injured myself; I had a fall while over extending to get one of the davit lifting lines. When in Eden I returned to the vessel one afternoon the worst for wear due to the injuries I sustained in Jervis Bay rather than lifting the tender up out of the water I secured just the painter to the back of the boat.  Some time during the evening the clip securing the painter came apart.  Off went the tender on a nocturnal trip finishing upside down on the rocks at the southern end of the bay. We did get the tender back and after a new motor, some patches and work tidying up the numerous scratches we had a tender again.  So what was our nail? A short length of line was all that was needed so I didn’t need to over extend to start picking up the tender into the davits.   We now have extended both davit lines so we don’t have to over extend to start the retrieval process. Now we secure the tender in two places to the vessel if we don’t pick it up out of the water. 

A simple fuel tank cover made from sunbrella canvas and sewed on board using a house hold sewing machine we keep as much of the hoses under cover as well,

Fuel tank secured in place so it will not fall out, this tank is starting to show sun damage, its best to cover the tank from new to stop the sun damage.

What else? Securely mount (tie or strap) your loose items including the fuel tank into the tender. We were hoisting the tender up into the davits one windy afternoon as we got ready to sail back across the bay. About half way up into the cradle a strong wind bullet caught the tender turning it onto its side trying to spill the contents into the bay. Everything but the fuel tank was secured in some way. To cut a long story short we were able to up anchor and give chase to the tank as it was quickly disappearing on the outgoing tide.  Luckily the only loss was the fuel in the tank that we had to dispose of on shore at a disposal station due to contamination, sea water had trickled in the vent as it floated away semi submerged.

  Something that has fallen from grace over the years is the use of a long painter to tie up at the local jetty; the reason to do this is to allow others to get in to the jetty by being able to move your tender off to the side. If you tie up tight then only a very limited number of tenders can tie up and use the jetty at one time, and as we know that with beach parties the more the merrier. 

Lastly and very important, when you finally get to the anchorage or jetty and before you start manoeuvring your boat, shorten the painter until the dinghy almost touches the boat. This should stop the painter from getting fouled in the boat propeller.

Global Navigation Satellite System and Satellite Based Augmentation Systems

 GNSS GPS and SBAS So what do these acronyms stand for?  

Handy to know if your headed out to buy a new satellite navigation system. 

GNSS stands for Global Navigation Satellite System, and is an overarching term that encompasses all of the global satellite positioning systems. This includes constellations of satellites orbiting over the earth’s surface continuously transmitting signals that enable users to determine their position. These satellite constellations are owned and controlled by the governments of different countries. Due to design and operation, the signals and frequency's from the different systems are individual. Purchasing a system that is purported to be capable of processing the signals from a variety of systems must be backed up with an antenna capable of receiving the signals different frequencies. Keep in mind there are few receivers capable of using more than two constellations at the one time.  In a lot of cases the constellations can be selected using the receivers software, however as I have noted your unit must be connected to antenna capable of receiving the signals.  

Constellations of satellites orbiting over the earth’s surface continuously transmitting signals that enable users to determine their position. At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time), this is also why more satellites equal more precision.

GPS  Global Positioning System is but one component of GNSS (the Global Navigation Satellite System). GPS specifically refers to the NAVSTAR Global Positioning System, a constellation of satellites developed by the United States Department of Defence. Originally GPS was developed for military use, but was later made accessible to civilians and industry. GPS is now the most widely used component of GNSS in the world, and provides continuous positioning and timing information globally even under the most arduous weather conditions. This is the system that started the satellite positioning revolution. The term GPS does get used a lot to explain satellite navigation, like the term iPad is used to describe a tablet computer. 

In addition to GPS, other systems are in use or under development. These systems make up the other orbiting constellations of satellites. Several governments are developing or have operational their own systems due to the fact the US government can selectively deny access to the GPS system or degrade the system performance at any time. This has happened in the past and it is possible it could happen again in the future. 

GLONASS the Russian Global Navigation Satellite System (GLONASS) was developed at the same time as GPS, but suffered from incomplete coverage of the globe until recent years.  GLONASS signals can be added to GNSS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, sometimes to within two meters. 

Galileo is Europe’s Satellite Navigation System constellation, providing improved positioning and timing information with a significant positive impact for many European services and users. Until now, GNSS users have had to depend on American non-civilian GPS or Russian GLONASS signals. With Galileo, users now have a, reliable alternative that, unlike these other programs, remains under civilian control.

BDS is China's BeiDou Navigation Satellite System. In 2015, China started the latest generation BeiDou system for a global coverage constellation. The first satellite of the latest generation was launched in March 2015. As of October 2018, fifteen BDS satellites had been launched. The constellation will eventually consist of 35 satellites and is expected to provide global services upon completion in 2020. When fully completed, BeiDou will provide an alternative global navigation satellite system to the United States owned Global Positioning System the Russian GLONASS or European Galileo systems and is expected to be more accurate than these.

NAVIC The Indian Regional Navigation Satellite System (IRNSS), with an operational name of NAVIC. NAVIC is an independent regional satellite navigation system that provides accurate real-time positioning and timing services. It covers India and a region extending 1,500 km around it, with plans for further extension. The system currently consists of a constellation of seven satellites. NAVIC will provide two levels of service, the "standard positioning service", which will be open for civilian use, and a "restricted service" (an encrypted one) for authorised users (including the military). NAVIC is planned to become available for civilian use in the first half of 2020. There are plans to expand the NAVIC system by increasing its constellation size from 7 to 11.

To sum up the main satellite constellations are GPS (USA), GLONASS (Russia), Galileo (EU), BeiDou (China) NAVIC (India). These five satellite systems are the major players under the umbrella term GNSS.  So a global navigation satellite system (GNSS) is a group of synchronized satellite constellations working collectively transmitting radio signals used for position navigation and time solutions. The position navigation and time solutions provided by these GNSS are used for a wide and growing variety of applications covering most industry sectors including agriculture, aviation, construction, consumer, resources, road, rail, maritime, mining and water utilities. Time solutions for the synchronisation of communication including cell phones, and electrical networks to name a few.  


The GNSS concept is based on time and the known position of GNSS satellites. The satellites carry very stable atomic clocks that are synchronized with one another and with the ground station clocks. Any drift from true time maintained on the ground is corrected daily. In the same manner, the satellite locations are known with great precision. GNSS receivers have clocks, but they are less stable and less precise.

At a glance its easy to see the benefits of having a number of available sources of data. However that said most receivers use GPS as the primary source of positioning, so that has to be saying some thing about the robustness of the system as a whole. 

GNSS Receivers

GNSS satellites continuously transmit data about their current time and position. A GNSS receiver monitors multiple satellites and solves equations to determine the precise position of the receiver and its deviation from true time. How many satellites a receiver can track or monitor, I have seen up to 99 listed however this varies with brand. Another technique becoming common is to deliver position aiding data to the GNSS receiver via wireless networks or the Internet. Supplying information such as ephemeris, almanac, approximate last position, time and satellite status and an optional time synchronisation signal significantly reduces Time to First Fix (TTFF) and improves acquisition sensitivity.

At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time), this is also why more satellites equal more precision. The information provided by a generic GNSS receiver can be used by a wide range of applications. Most systems use the receiver's solution, the receivers computed position, velocity and time to run the task assigned.

Keep in mind most GNSS receivers can pick up GPS signals (if configured), however a GPS receiver can not pick up signals from the other constellations of orbiting satellites. This can be a hard to comprehend due to the way most systems are loosely referred to as GPS, I have even seen systems that use triangulation of phone towers to find a positioning solution called GPS.  

If one system is down, most of the newer GNSS receivers will already be using signals from all the other systems. Just look for the number of satellites your receiver will track, fifty six is common but more is now the norm.   And of course, the more satellites your receiver is looking at and acquiring data from the more likely that if your line of sight to one satellite is obstructed by a mast, boom, Bimini frame or other obstacle, it can receive signals from another satellite.

GNSS Accuracy

In open sky conditions, standard accuracy GNSS receivers are accurate to around two meters, however, because GNSS receivers rely on the time it takes a satellite signal to reach them, even the slightest errors like a millionth of a second can impact accuracy. 

Errors in satellite orbit position can lead to around 2.5 meters loss of accuracy. Satellite clock errors can add another 1.5 meters. Atmospheric disturbances can add another five meters, plus throw in the occasional intense burst of solar activity or multi path effects like signals bouncing off the sea surface, mast, boom or spray dodger frames, and this accuracy can easily bump the error out to 10 meters or more. 

GNSS systems in Australia

Australia is one of few countries in the world with high visibility to six GNSS due to our geographical location. These include not only the main global systems of GPS, GLONASS, Galileo, BeiDou, NAVIC but also Japan's Quasi Zenith Satellite System (QZSS).


A simple RTK system the rover can be backpack or vehicle mounted

Real-time kinematic (RTK) positioning technique is used to enhance the precision of positioning data received from global navigation satellite systems such as GPS, GLONASS, Galileo, NAVIC and BeiDou. Luckily, high precision GNSS systems dramatically improve precision using GNSS correction data to cancel out the errors. One way to do this involves monitoring GNSS signals at a base station set up on a known location (surveyed). Deviations from the base station’s position are observed and sent via radio link to the mobile vehicle (AKA rover). The rover is equipped with a GNSS receiver and radio link receiver for the deviation corrections. When the deviation corrections are received at the rover they are applied in real time to the GNSS position to obtain a more accurate position reading. In favourable conditions, this approach can be used to achieve centimetre level accuracy, provided that the base station and the rover are not too far apart. Real-time kinematic (RTK) positioning technique is widely used by the geospatial industry for increased accuracy in surveying and mapping (navigation).

Welcome to the wonderful world of Satellite Based Augmentation Systems 

This coverage map may mean more after reading the description below. 


We hear the term *augmentation system or SBAS thrown around a lot these day so what does SBAS stand for?

SBAS stands for satellite-based augmentation system. A Satellite Based Augmentation System is a wide area differential Global Navigation Satellite System (DGNSS) signal augmentation system which uses a number of geostationary satellites, able to cover vast regional areas. These geostationary satellites don’t move, in other words they stay in sync with the rotation of the earth as opposed to the GNSS satellites that orbit the earth continuously.

To calculate GNSS position errors, GNSS data received from satellites is compared against the precise location of each land based ground station. Discrepancies are measured and the corrections, called deviation corrections, are transmitted to the geostationary satellites.  These satellites then broadcast primary GNSS data which has been provided with the received integrity, ranging, and deviation correction information sent from the regional SBAS ground stations. 

While the primary purpose of SBAS is to provide integrity assurance, use of the system also increases accuracy and can reduce positional errors to less than 1 meter.

So in a nut shell SBAS is a regional network of ground stations and satellites that work together to boost the accuracy and dependability GNSS data. The increased accuracy is critical for aviation and is another technique widely used by the geospatial industry for increased accuracy in navigation and mapping.

Here is a drawing of a basic SBAS set up. On the left bottom is a number of receivers collecting positioning data from the orbiting satellites. The signals are then passed to the central processing unit that calculates what corrections are required for what satellite. That information is then available via the internet or it is transmitted to one of the GeoStationary satellites. The GeoStationary satellites then transmits these corrections to our mobile (ship car airplane) GNSS receiver to correct our position making for very a accurate location (lets hope the map is as accurate to make it of use) . 

While all this sounds great, how do we benefit. The GNSS receiver you purchase will hopefully be able to use the correction data that has been sent to it from the regional geostationary satellites. Your GNSS receiver may then display that you are navigating with DGNSS.  I think most of us have heard of WAAS and how it will transform our GPS in to a super accurate navigation device. Well WAAS can do wonderful things,  however for those of us who live in Australia or sail around the Pacific  it won’t help give us any better positioning accuracy. 

Now the bad news, while we here in Australia are lucky enough have high visibility of up to six GNSS constellations due to our geographical location. We do not have the use of a Satellite Based Augmentation System at present. The tests have been done and hopefully it will become fully operational in the near future.  If the documentation I have researched is correct our corrections will be broadcast by Japan's Quasi Zenith Satellite System (QZSS). I have seen this pop up on my GNSS from time to time and my receiver does indeed switch to DGNSS. 

So if the sales man trying to sell you a GNSS receiver starts letting you know about the added accuracy of the various systems like WAAS, EGNOS, MSAS and GAGAN.  You have the heads up that none are any good to you unless your headed off around the world, and really you don’t want to be paying extra for systems you will never need or use. Its nice to know those in other parts of the world can enjoy dynamic positioning however in Australia its getting there.  SBAS is regional and the regions and systems are listed below.  

Now for some good news.  The Australia test (not cricket) transmission has been extended and will be available until 31 July 2020. This will provide continuity of SBAS signals to support R&D, industry testing and encourage early adoption. Ya gota hope so. 

*Augmentation the process of increasing the size, value, or quality of something by adding to it.
*To augment is to increase the amount or strength of something 

Regions that have SBAS coverage, for a better visual look at the coverage map at the begining of this section

WAAS United States, Canada, and Mexico,  Wide Area Augmentation System, or WAAS, is operated by the United States Federal Aviation Administration. Development for WAAS began in 1994.

EGNOS European Union: European Geostationary Navigation Overlay Service, or EGNOS, was developed by the European Space Agency.

MSAS Japan: The Multi-Functional Satellite Augmentation System, or MSAS, is operated by the Japan Civil Aviation Bureau, a division of the Ministry of Land, Infrastructure, and Transport. The QZSS service area covers East Asia and Oceania region and its platform is multi-constellation GNSS. The QZSS system is not required to work in a stand-alone mode, but together with data from other GNSS satellites.

GAGAN India: GPS-Aided GEO Augmented Navigation, or GAGAN, was developed by the Indian Space Research Organization and Airport Authority of India.

MTSAT Satellite Augmentation System (MSAS) is the Japanese Satellite Based Augmentation System System a GPS Augmentation system with the goal of improving its accuracy, integrity, and availability, and that uses the Multifunctional Transport Satellites (MTSAT) owned and operated by the Japanese Ministry of Land, Infrastructure and Transport and the Japan Meteorological Agency. First tests were accomplished successfully, and MSAS system for aviation use was declared operational in September 27, 2007, providing a service of horizontal guidance for en route through Non-Precision Approach.

SBAS systems under development

SNAS China: Satellite Navigation Augmentation System, or SNAS, is in development.

SDCM Russia: System for Differential Corrections and Monitoring, or SDCM, is in development. When completed, SDCM will offer corrections for GPS and GLONASS, the Russian satellite navigation system.

WADGPS South Korea: Wide Area Differential Global Positioning System, or WADGPS.

Here are a couple of links from us that may be of interest:
One mans datum is another mans shipwreck a discussion about chart Datum 
The way we navigate in the digital age  a discussion about the tools we use to navigate
An over view of  AIS An overview about how AIS works and the weird and funny (not ha ha) things we have seen

Tuesday, 31 January 2023

OpenCPN Tracks Routes Waypoints

When we first started cruising I wish that I had been more careful with recording and backing up our Routes, Tracks and Waypoints. For the first couple of trips I thought that I was saving the tracks on my handheld GPS receiver. I thought this was working well until we started to do longer trips and due to the small memory in the unit the previous track files eventually started to get over written. It wasn't until we saved the tracks off on to the computer I found to my horror there were great number of tracks missing. 

After becoming more familiar with the handheld on the longer trips I found a way to save the active tracks on to the unit as we went along so they didn't get overwritten. I thought this was a solution until I found to save storage space on the unit the files were stripped of data and only a shell of the original track was saved. These were OK but trying to extract statistical data from them later didn't work.

After talking to some cruisers and discussing how I wanted to keep a record of our travels, we were told about OpenCPN. We downloaded and installed a copy, connected it up to the onboard instrument WiFi and away we went with positioning and AIS data. We found OpenCPN easy to use and before long this was where we did our passage planning and created waypoints, routes and clearing lines and were easily able to save off our tracks in GPX format.

So why go to all that effort to save the information. To state the obvious travelling through reef or sand bar infested waters is so much easier when you’re travelling on a track or route you’ve already successfully navigated. Anchoring is also a lot easier when you know where you or others have actually been able to get into and have dropped the pick.

This is why we keep tracks, for the return journey. 
Moonshdow sitting ever so peacefully at anchor in Damo Bay, Flores, Indonesia, yep the same bay as on the chart above. 

If we hadn't been through, or anchored, there were other cruises in similar draft and size vessels that are more than happy to share this sort of information. This can come in really handy when you know that the path was clear when they went through and didn't hit anything, or the bottom wasn't foul for anchoring. We have even negotiated several river entrances and then were able to pass on either the track or the waypoint information so others were able to enter with a reasonable level of confidence. A link to a library of  waypoints and sat charts are available on the net head here for a good start. 

While this may sound like a lot more work, after every passage when finalising the logbook we rename the track and give any waypoints created meaningful names and fill in any necessary information into the waypoint description box. With the tracks we enter the start and end port/town/anchorage and from experience we have found this certainly makes it easier and saves time to find the track if we want to do the trip again. We have been given waypoints and or tracks contained in large GPX files others have made, and it can take a bit of detective work to work out the right track and waypoints just by the numbers the system uses as default.

The three following screen grabs are not from the OpenCPN program.

Tracks routes and waypoints identified by a number. Unfortunately these are not very explanatory and needed to be tidied up and named before use. Yes it would have been possible to import them into the chart however some of the tracks were broken or parts were missing.

The tracks tidied up and partial tracks joined or removed. After naming they are good to go and we can import them into the Layer directory for use when needed. 
The routes were also tidied up and we insured they didn't cross any obstacles' by overlaying them on Google Earth. 

If you interested to see what programs are available to tidy up these navigation data files here is a link:
Programs to Manipulate GPS Navigation Files

OpenCPN Route and Mark Manager

OpenCPN access to the Route and Mark Manager on the toolbar

To save off the tracks is fairly easy, firstly open the Route and Mark Manager on the toolbar.

If you would like to save all the waypoints, routes and tracks off then use the Export All Visible button. **As a word of warning ** this will save all routes tracks and waypoints including any files in the Layers Tab that are selected for view.

If you want to be selective, and for example only want to save off the Tracks then high-lite the Tracks that you want to save off and select the Export Selected button, the same can be done for Waypoints and or Routes.

So now you have a library of Routes, Tracks and Waypoints backed up and you are now travelling back into the area. Perhaps you want to do some passage planning. What is the best way to display the data quickly and easily without merging the it with your current trips. We use the Layers function and this way we do not have to import the GPX file or files into the working directories. By using the Layers function the backed up contents is also safe from being corrupted or changed.

Keep in mind that when saving off your GPX files you don't have to save off tracks routes and waypoints in the one file. I find on a lot of occasions its easier to make three files, the three are smaller and importing or displaying them in layers is the same.   

While the import GPX will do the job, we just don't unless we want to edit the information. This work often entails moving waypoints adding information into the properties or even changing the display scale. Any sort of edit we need to do, then we do save the data back into a new file and after checking its readable we will delete the imported information and use the file(s) as Layers.  

If you want to import a GPX file you want to do an edit on or use and during the import you are questioned about duplicate entry's and you  know there isn't any entry's in any of the tabs other than Layers you will need to remove the file from the Layers Directory, to import the whole file. 

Navigating in the digital Age

Monday, 30 January 2023

OpenCPN Selecting default waypoint Icons

On the toolbar go to the Options/Ships/Routes/Points tab. 

On the page it's a good idea to set the default waypoint Icons that are created for New Routes. This is when using the Create Route option selected on the toolbar or (ctrl R). Normally the waypoint for this is a black circle with a dot in the middle, and while this is OK it can become hard to see, it depends on how cluttered the chart is. 

On the same page is the set the default waypoint Icons for new waypoints. I don't really have a preference for this I normally set it as an anchor, if I am doing chart work marking in anchorages. So choose something of your liking, remember it's not hard to select a new waypoint from the dropdown  list when making a new waypoint. 

Select the default icons, it's really a personal choice that can speed up your work if your making several waypoints of the same types. 

OpenCPN Add Waypoints Into A Route

 A quick and easy way to put in additional waypoints into a ready made route. 

Route created running across the land, not much thought to what's in the way.

Right click on the route in a location you feel a new waypoint should be, don't be too precise as these can be easily moved later. Then select insert new waypoint, in this example I will insert two waypoints but due to the scale of the chart they were not displayed.

After zooming in the new waypoints are visible, the default route waypoint icon is displayed 

To move the waypoint into a location so the route will pass the obstruction the waypoint properties box will need to be open (this is dependant on the setting of the lock waypoint option in Options/Ships/Routes/Points). With this option set accidental movement of any waypoint will not be possible unless the properties box for that waypoint is open.

Waypoint properties box is open waypoint can then be moved by click and dragging into a place to miss the obstruction, and place us in the East Coast Current. 

Both the new waypoints have been moved, this part of the route is now clear and other obsticals cane be looked for. 

At a scale similar to the first example.

You may also like to look at:

OpenCPN Add Waypoints Into A Route