New "disappearing propeller" system for small boats ...

[kengrome]

I've always been impressed by the simplicity inherent in the design and function of the original "disappearing propeller" system for small boats:



http://www.disappearingpropellerboat.com/history.html

Unfortunately it seems no one manufactures such a system any more on this planet, so I'm thinking of designing and manufacturing a new one -- a smaller and lighter one that can be installed in most any small boat.

I've created this thread to seek opinions on the most desirable features for such a system, as well as opinions on the commercial viability of such an effort. Your thoughts and suggestions are welcome, thanks in advance.

[kengrome]

By the way, here are my initial thoughts on this project:

I might use GRP for the case instead of cast or machined steel or aluminum. A grass trimmer (weed whacker) engine and flexible drive shaft might spin a small propeller no larger than 6 inches in diameter. The flex shaft would eliminate the complication and expense of a gearbox and/or universal joint so it would keep the cost down and save weight.

If I use a sealed oil-filled shaft tube connected to an oil reservoir inside the boat, water should never make its way into the shaft tube or to the flex shaft itself, which means this part of the unit would be constantly lubricated and theoretically no-maintenance -- at least until the flex shaft breaks.

Grass trimmer engines can be purchased with or without centrifugal clutches. In this type of boat an engine without a clutch might make sense for slow trolling speeds. The system won't need a clutch for neutral anyways since the prop can be lifted out of the water for neutral -- and of course it would lift naturally when its guard hits an underwater obstruction.

Another engine option (for fresh water use only) might be those used in R/C model boats which use water cooling. I could enclose this engine in a box to make it super-quiet, a very nice feature in any power boat. What's more, the captain could sit anywhere in the boat and control its speed remotely since these engines are designed for remote control -- not a very useful feature without remote steering to go along with it but "fun" nevertheless ...

The original disappearing propeller boats did not have reverse from what I understand, and neither would this one. Simple and affordable would be my goal here, so reverse would be accomplished with paddles or oars.

Given the fact that it only take 1 HP to push 500 pounds at hull speed, an engine of 1-2 HP would be fine for most small boats with total displacements of 500-1000 pounds, and this covers many small boats. Later I might build one for bigger boats that need more power or speed, but the small low-powered system is the one I'm considering at the moment.

Your constructive (or destructive) criticism is welcome!

[FAST FRED]

I think a simple universal joint from any source will prove cheaper than a specially manufactured flex shaft.EZ er to fix locally to.

Oil in the water gets the sheene police really excited so a simple bronze pillow block with Zerk grease fitting should handle the up/down shaft movement .

Rototillers are 4 stroke and usually have a 4-1 or 6-1 gear box built in.

Quieter and more reliable than weed wacker , although heavier.

Better muffler too.
FF

[artemis]

The FAO (Food and Agriculture Organization - an international group) Corporate Document Repository - Fishing Boat Designs has 4 small plywood or timber open fishing boat designs for 3rd world countries. All of them are for use with outboard motors. But the 7.4M and 8.5M disgns make provision for an inboard motor. As these boats are "run up on the beach", the design incorporates a "swinging/lifting" propeller and shaft. The concept is very similar to that of the disappearing propeller boat but, using modern materials and techniques - craftsmanship and materials readily available in 3rd world countries - a fixed, non-flexible shaft with propeller on one end and motor on the other allows up to 8HP of motor/prop. combination to be used.

I used to have a copy of the plans sheet available for this, but if you google "FAO Corporate Document Repository, fishing boat designs" you should get in close. The elevations for the 7.4M and 8.5M give an idea of what is going on. I'll try to find the construction details if you're interested.

[kengrome]

Hi Artemis, I'm familiar with the FAO concept but I don't like it as well as the dispro concept, I think it's too big and complicated for Western boats.