ELECTRIC DINGHY 
Will pay for itself in a few years .....
An electric Dinghy is an economical and clean proposition for long term cruising yachties or hard core fisherman. I went through a long learning curve over many years to come up with a good set up. I now spend almost no money on maintenance and fuel. Importantly I expect good longevity. Main trick is to use a submersible motor but keep it above the water as detailed below. Second trick is to work on your connectors (see below) cause nearly everything you try will rot out in the damp dinghy environment (electrolysis).
What I have come up with as an "ideal" cruising electric dinghy
Dinghy should be long and slender (perhaps split/nesting so it packs away neatly on the deck) so it gets a good speed up with minimum of current daw on the batteries and a small cheap light weight motor can be used.
Economics: Don't over invest. I prefer to keep the dinghy contstuction philosophy to be rough and ready fibreglass. That way if you lose it you have not lost too big an investment. Also no doubt there will be modifications as you learn and improve things so just slap the glass around and chop away.
If its too pretty it may be more of a target for theft. Such an electric dinghy that looks like "a mad proffessors experiment" is less likely to be a target for theft.
Motor
- Specifications. I use a minn kota 100 lb thrust electric outboard. The trick is that whilst this is a submersible dinghy, i use it above water ie the actual motor rests in a cradle at the back of the dinghy with an extended motor/prop shaft at a down angle of 15 degrees. The whole assembly is a little over a meter long with the 9" x 9 pitch 2 blade prop just beneth the water surface.
- Steering is achieved using the standard swivel assembly that comes with the motor. It is clamped on a bridge beam placed at a suitable location to suit the dinghy. (see photo for my choice)
- No risk of water entering the motor. It is my excperience that unless you service the "oil seal" on the drive shaft that it will fail sooner or later thus giving only a few years service before send it to bin when the motor is used in its normal submersed mode. So for my set up....... expect 10 - 20 years before water even gets close to go inside. Actually the greater risk area is the motor support shaft where the power wires enter. At that location i have silicon glue protect.
- Use a "long tail" prop shaft. a simple hard sleeve type coupling connects the motor shaft to the prop shaft. To prevent it from slipping out a grub screw nests into mating detent on shafts. My prop shaft is 15mm stainless and 700mm long. The bending of this is minimal and after 2 years of mistreatment (hit rocks hard etc) no damage results. If you were to use a smaller motor with smaller shaft then you may get probs.
- Over heating is surprisingly not a problem considering the motor is meant to be used underwater. For extended trips on a hot day i sit a towel on the motor and drop a cup of water on it every few mins.
Batteries
2 x fully sealed AGM 70AH batteries. Used in series to give 24 volts. Whilst the motor is rated at 36 volts the dinghy is plenty fast enough (6 knots) at 24volts (draws only 20 amps). So that gives me 2 - 3 hours running conservativley.
Connectors. Half the battle here is to use maintenance free connectors. The best I find the welding connector common throughout the world as follows: Solid brass body 25 mm diameter accepts the cable thru 15 mm drilling one end (grub screw holding of cable) other end either male or female. Geometry of M/F is a taper stub approx 30 mm long 12mm dia. There is a "twist lock" pin on the male stub.
Advantage with these connectors is once you seal the cable end with "putty" and heat shrink/rubber vulcanising tape they can be submersed without harm. Any corrosion deposits simply sand away. Years of sanding later i still have workable connectors just the depth of swallow of male into female is greater now. This justifies the $15 price tag per set in my mind. Try dropping any other elec connector live into sea water for years on end ..... you won't.
Speed Control
Achieved by using the standard controller of outboard while it lasts (not long). Then just simple on/off. Remember we are dealing with 1/2 horsepower silent motor. For beginners or slow stealth mode i put the battery to 12 volts plug in.
The on off switch can simply be stabbing the male connector to the battery mounted female half or as i do use a $10 battery isolation switch available at most chandleries (1/4 turn on). The will need a corrosion cleanout twice a year (approx), though its a quick job.
Photos
Such an
SOME CLIP ART FOR CONSTUCTION OF THIS SITE
