An apology: While updating this article I realized that I had published an earlier version that had not been spell checked or edited. Here is the somewhat cleaned up version.
Types and comparisons of Boat Tenders.
There are 2 Main types of tenders: variations of RIGID construction and variations of INFLATABLES.
Rigid boats are the hard sided wood, fiberglass (or cabon/kevlar) and vinyl boats.
inflatables can be all soft materials or incorporate some rigid components such as hulls or floors. There are also inflatable styled rigid plastic boats that incorporate features of both.
InflatablesBrig inflatable boats on the left.
Stability is THE major advantage of using an inflatable. No matter where you stand including the tubes, you are not likely to tip the boat. They are hugely buoyant and getting a side underwater is almost impossible. Most inflatables are quite wide and this helps improve stability. They are also flexible and this helps diffuse a force so that there is not so much force pushing the dinghy to tip. If you manage to dip one side under the water, the boat is so buoyant that it remains stable even with quite a lot of water in the bottom. Since inflatables are so buoyant they rarely take on enough water to swamp, unless they are leaking air of course. Weight distribution is not as critical as in a hard shelled dinghy.
An inflatable will carry more weight safely than a similar sized hard dinghy. It will also be safer if the weight moves around a lot such as big dogs or kids.Solstice Sportster 3-Person Runabout
Many inflatable companies have recognized that the traditional inflatable shape has limitations and several hybrids have been developed. Notably rigid bottom boats with improved hull shape but equipped with large flotation rings above the water line. This means that the boat benefits from the buoyancy of an inflatable with a better underwater hull.
Hard sided Dinghies
Walker Bay has a wide range of rigid, inflatable, and rigid inflatable dinghies.
Photo on far left from the Toronto Boat Show. Rigid plastic Dinghy is listed at about 750 US. Sailing rig can be used.
Because of the different types of hull shapes it is difficult to make a sweeping statement on the stability. All hard dinghies are more sensitive to weight distribution than the inflatables. Too much weight out of balance can bring the gunnel dangerously close to the water and increase the risks of swamping and tipping. There is an element of skill and care that needs to be taken when entering and exiting a hard dinghy. Most tenders are quite small and this makes balancing more critical.
Hull shape is very important and most dinghies intended as tenders have wide bottoms. Some people at my club are using canoes as tenders. These are tender crafts and never intended for this, it suits the needs of these sailors because they are experienced boaters and skilled enough to handle their tippy but maneuverable canoes.
Hard sided dinghies shaped as InflatablesWhaly boats make reliable tenders
We have Whalies at our club which are polyethylene moulded boats with hard sides but shaped as inflatables. Although there have been many complaints about them, mostly relating to their rowing ability, their stability and durability has never been in question. They have huge air chambers which makes them unsinkable and they can tolerate just about any weight distribution. It would take a concentrated effort to tip one over. They are very stable. They move very well with a small outboard.
What makes a boat stable?
There have been whole books written on stability so this is a short version. Keep in mind that a tender is usually used in relatively calm waters. Wider beamed dinghies are more stable than narrow boats. Compare a canoe and a rowboat, both are the same length but the narrow beamed canoe is much tippier.
Wall sided boats are more stable than boats that narrow as the side goes down. Wider sterns are more stable than pointed sterns. Higher freeboard also increases stability. V shaped hulls are less stable than flat hulls in calm water. They have other qualities though. The lower the centre of gravity the better the stability.
An experienced boater will not be worried if the boat shifts when he moves while a more inexperienced person might be quite frightened.
A boat might give the appearance of high initial stability and hardly move but have little residual stability if further destabilized. Another boat might feel very tender at first and shift with any move of the passenger but have high secondary stability.
There is some compromise between having a perfectly stable boat and having a boat that can be happily rowed. At one end of the scale the inflatables are about as stable a boat as you want in calm water but are despicable rowboats.
Similarly a nice stable wide boat might be very unhappy in high waves where it is more likely to tip than a more rounded or v shaped boat. I said that it was a complicated subject.
Moving or powering the tender
Motor powered tenders
How you plan to move your tender will be a determining factor in the kind of hull you will be most happy with.
If you plan to always use a motor and NEVER use oars unless the motor dies, then you need not worry about tracking or rowing ability. You want a stern that is wide enough to support the weight of the motor, battery or gas, and not tip if you turn sharply, a reinforced transom to support the motor and a rigid bottom that facilitates motoring including planing. If you want to go fast you will want a planing hull otherwise, in a displacement hull, the nose will point up in the air and efficiency will drop. Keep in mind that in a small dinghy the driver is often sitting at the back handling the motor so a great deal of the weight gets shifted to the rear. A nice wide transom is helpful.
Inflatables are poor sailing or rowing boats and function best as motor boats.
Rowing dinghiesChesapeake Light Craft Eastport Pram
is a popular wood pram. Epoxy and fiberglass help seal the wood for a light tender that rows and behaves well. It helps that it is a lovely looking boat and a sailing rig can be added.
Duckworks Plan Index has a number of models of wooden tenders by many designers. If you plan to make a tender it's well worth the visit.
There are many factors that make a good rowboat. At one extreme, very narrow and long hulls with almost no freeboard, are the absolute fastest row boats. This will not do in a small tender so there has to be some compromise. A tender will row reasonably well if it is wide enough to accommodate the oars. If you have to cross your oars in excess it is difficult to row. A small keel or skeg is a great help in tracking. Some rocker helps make the boat easier to turn and maneuver. Rocker also helps keep the bow out of the water. High enough sides will help prevent the oars from hitting the legs when rowing. High sides will increase windage however. A pointed bow allows the tender to cut through the water but this might interfere with towing. A very short boat with a pointed bow might also have reduced capacity because a pointed bow cannot support as much weight as a wider pram bow. Many prams row well in spite of the flat bow because the rocker keeps the bow out of the water. Longer boats row better than shorter boats but in a short tender length is a rare luxury. A bit of weight helps the boat keep its momentum between strokes.
If you plan to row your tender for any distance it is well to get oars that are long enough. Short oars are easier to store but not as nice to use. Nice oars are a joy to use while poor ones are unpleasant and ineffective.
Rowing an inflatable or an inflatable shaped boat is a depressing experience. It does not help that they usually come equipped with terrible tiny short plastic oars. Low weight and relatively high sides makes an inflatable subject to windage. This is made worse by the fact that inflatables do not usually have keels or skegs. Most inflatable have essentially flat bottoms and relatively blunt bows. They tend to plow through water inefficiently.
Some hybrid inflatables/hard shell have a v bottomed hull with inflatable sides. This improves their rowing ability considerably.
Tenders can double as sailing dinghies
Many designers have added simple sailing rigs to their tender dinghies with varying degrees of success. Features that make a good tender such as stability and carrying capacity tend to impair the sailing ability of a boat. At best a small sail can help move a tender if mooring is far from shore. It's asking a lot of a 6-7 foot boat to double as a useful adult sailing dinghy. It can be more successful as a kids sailing boat. Larger dinghies can be a better success.
Several designers have created plans for take apart or sectional boats. Here is my page on take apart boats.
Sectional Boat from Bateau. It can be rowed, sailed or motored.
Take apart boats can be stored on deck when not in use and assembled when required. Because they come apart and take up less space, they can be longer and can be a more useful sailing or rowing dinghy.
Some inflatables also come with a sailing rig. It is folly to expect any kind of performance from such a rig but sometimes great fun can be had anyway. Here is an Aquaglide inflatable multisport boat. sells for about 1000 US.
Towing a Tender
If you plan to tow a tender you will do well to choose one that has a skeg to help control the stern and stop it from fishtailing. Avoid deep keels along the whole length of the boat, which will make the boat resist turning and allow the keel to dig in a wave and possibly tip and make the boat less docile when being pulled. Rocker helps the boat keep its nose out of the water. Avoid prams which have very flat bottoms with no rocker because there is a chance the bow will go under and make the boat difficult to tow and potentially plow under while being towed.
If a tender is to be towed under high power special care should be taken. Higher speed often causes water to spout in from daggerboard slots if the tender is used for sailing. High speed also causes non planing hulls to put their noses in the air after they have reached their hull speeds.
Inflatables are often towed behind a mothership. Many manufacturers suggest using a towing bridle that connects to both sides of the bow. This helps distribute weight on 2 spots rather than on only one attachment spot which can be pulled out or damaged. A bridle also helps keep the inflatable from fishtailing.
Towing with a motor adds considerable weight to the tender and increases the strain and weight of the towed boat. There is also the danger that the towed boat will tip damaging or even losing the motor.
The front attachment ring should be solidly put in if you intend to tow your tender. If using an inflatable then its better to distribute the load between 2 towing rings.
Hard sided boats such as fiberglass
When it comes to maintenance fiberglass and epoxy covered boats have very good track records. Small fiberglass dinghies can be found everywhere with their wooden parts looking worse for wear but their fiberglass hulls still seaworthy.
Fiberglass is a highly repairable material and scrapes and rare holes can be fixed with readily available polyester resin or better still with epoxy. Epoxy sticks readily to polyester but NOT polyester to epoxy. Polyester resin is the stinky resin set off by the few drops of Ethyl Methyl Ketone Peroxide. Mikpik. Epoxy is measured in 1 to 1 or up to 1 to 5 ratios depending on the brand.
Polyester is used in most commercially available fiberglass boats while epoxy is more common in high end or custom dinghies. Where polyester resin is very resistant to UV, epoxy must be kept covered with paint or UV resistant varnish or the epoxy will loose its strength and become chalky as it breaks down. Wooden boats covered with fiberglass are much the same as fiberglass boats when it comes to maintenance.
Wooden boats not made with fiberglass have a regular need of maintenance and painting. Scrapes and bumps that expose wood allow water to penetrate and rot and other damage can set in. Any varnish needs to be thick and UV protected. The finer more carefully built custom boats require specialized repair techniques.
If you are travelling to tropical areas and your wooden tender is to be stored on land for even a few weeks, termites are an issue.
All rigid boats are sensitive to hard knocks and sharp blows. Gunwales are particularly vulnerable and for that reason are often padded. Keels and skegs are also often scraped against launch ramps and parking lots.
Aluminium boats are highly resistant to damage and to UV degradation. Paint finishes sometimes flakes, fades or rubs off, which is more of a problem of looks than durability.
Aluminium boats are subject to metal fatigue and denting. Metal fatigue occurs when a section is not properly braced and moves or oilcans as the boat is used. This eventually leads to failure. Denting and puncturing occurs when a sharp blow is inflicted on the boat. Any metal damage will need to be either welded using specialized aluminium techniques or riveted.
Rigid Plastic Boats
Plastic boats are very resistant to mistreatment and rarely get serious damage under normal use. Sharp blows and scrapes are deflected by the semi rigid sides. Repairs can be made. Usually done by specialists, the plastic essentially gets welded back together sometimes with a patch. These boats resist most adhesives so it is usually not possible to glue on a patch. A TEMPORARY fix can be made using a high strength duct tape such as made by Scotch or Gorilla.
Inflatables are made of PVC or Hypalon fabric. PVC is less resistant to UV degradation. It will degrade over time. Most Inflatables have an expected life of 5-10 years. IF left in sun, or roughly treated then life expectancy goes down. Hypalon is more resistant to UV and stronger but more expensive.
There is a very large range of quality in inflatable boats. As in all things you get what you pay for. You can find single thickness pvc boats intended for playing and very light use for under $100. Less if you include the pool boats (absolutely unsuitable as a tender). A good Hypalon inflatable can set you back $3000. You can get a pvc multi-layer fabric inflatable for around 1000.
The main problem of inflatables is punctures and tears and UV damage. To avoid catastrophic deflation while underway good boats will have baffles or separate air compartments. With use the air chambers can be punctured. Saturn warns of possible puncture by fish pectoral fins which can be sharp and strong. Other manufacturers warn users about glass shards in shoe soles or sharp edges such as screws on docks and boats. Fish hooks and tools are also potential hazards. Scraping against sharp rocks, coral or oysters can also damage the boats. In the past some seam failures were due to inferior adhesives, but I think this has been solved in more modern inflatables.
Every boat club has a collection of somewhat limp inflatables. Pinholes can be tricky to find and more annoying than dangerous.
Other issues with inflatables are attachments such as towing rings, or oar locks pulling out or the hard transom getting damaged. If the boat is regularly folded and re inflated, stress can damage the shell where the folds occur.
All manufacturers have a brisk trade in inflatable repair products and adhesives.
Choosing a Tender Article A must read if you are thinking of getting a tender.
email me if you find mistakes, I'll fix them and we'll all benefit: Christine