Design Challenge - Fastest Water Craft

[Guest625101138]

I have an engine that can pump out 150W continuously and weighs 70kg.

I want a water craft to operate in, on or over calm, deep water as fast as possible using the engine I have.

The questions are:
1. What is the continuous speed?
2. What does the craft look like?
3. How reliable and practical is the solution?

Rick W.

[kach22i]

I have an engine that can pump out 150W

Is it loaded to a surface propeller now or a water jet?

Water cooled? From outside water or radiator?

[yipster]

and if W is for watts check HP to WATT to THRUST

[kach22i]

Originally Posted by yipster

and if W is for watts check HP to WATT to THRUST

I hope he meant KW.

[fcfc]

Originally Posted by kach22i

I hope he meant KW.

Not sure. I guess that kind of engine often drive paddle wheels. And is frequently beer cooled.

[Guest625101138]

The engine can be water cooled or air cooled (beer cooling reduces continuous output) and it runs at 80rpm but can obviously be geared to suit.

It is only 150W or say 0.2HP.

The best boat I can make for the engine gets 7kts. I am wondering if there is any clever way of getting an improvement. Things like low drag surfaces, foils, wings, submerged buoyancy, combination of these etc.

Rick W.

[Willallison]

Easy.

http://www.foilkayak.com/

I think you'd have to lay off the beer though...

[Guest625101138]

Foilkayak in current form requires more than 150W.

Would it be possible to fly with 150W and be still faster than displacement mode?

Rick W.

[Willallison]

I don't really know a great deal about the foilkayak, other than a little that I seen here or there. I do know that it requires a considerable burst of power to get foil-borne, then a reduced amount to stay there, but just how much I couldn't say..

[Guest625101138]

Will
I think the power level can be sustained by a top athlete for the time to do 1000m. So say 5 minutes. I think this would be up around 400W.

Rick

[alan white]

A gas engine (20cc weed-wacker unit of approx. 700 watts max output) could run at moderate rpm to drive a large diameter slow-turning prop that would attain and maintain foil lift. I don't know if 150 watts would maintain foil speed, but 350 watts surely would (would be interesting to see). Craftsman (Sears) now sells a 4 stroke weed-wacker, believe it or not, and I wonder how such an engine would fare aboard a micro-motor-foiler.
Food for thought. And how fast could it go?

Alan

[Guest625101138]

Alan
It is amazing what can be done with efficient craft. I am trying to find the limits of human power for average joe. Once you find this then there are lots of ways of changing power source to solar, wind, fossil etc.

There is no doubt that foils have proven best in high effort applications but I am wondering what is best for 150W.

I have thought about a large buoyant foil but the numbers seem to still favour displacement at 150W.

The question is about exploring this issue or if there is another avenue of merit worth exploring.

Rick

[Willallison]

Well in that case, we're back to the old addage... very long, very light, minimum wetted surface....
I guess pedal power is the easiest to sustain, and turning a prop is probably the most efficient...

[alan white]

Originally Posted by Rick Willoughby

Alan
It is amazing what can be done with efficient craft. I am trying to find the limits of human power for average joe. Once you find this then there are lots of ways of changing power source to solar, wind, fossil etc.

There is no doubt that foils have proven best in high effort applications but I am wondering what is best for 150W.

I have thought about a large buoyant foil but the numbers seem to still favour displacement at 150W.

The question is about exploring this issue or if there is another avenue of merit worth exploring.

Rick

Yeah, the 150 watt limit is the focus. No, I don't believe that small amount of power is going to go beyond displacement except with a kid aboard--- it probably couldn't maintain a foil craft even if it were pulled up by a motorboat.
Last weekend, my heavy daysailer (15 ft, 1500 lb dspl) handily outdistanced a hobie in light air. I wonder what wattage powered me? Less than 150, probably--- maybe half that. Point is that the Hobie was slow because its hulls are long and narrow--- lots of wetted area compared to my chunkier hull.
A waft of a breeze came up and the Hobie whizzed off. How much wattage was that wind making?

[Guest625101138]

Alan
The light air performance comparison is probably more to do with patience of the skipper, stability (through inertia), sail cloth, sail cut and sail set than the actual hull wetted surface.

I can remenber racing in quiet air and it was the only time I encouraged my friend, and crew member, to have a smoke. It was very handy knowing exactly what the wind was doing. Once you get a bit of inertia in a heavy displacement hull it seems to run on nothing. If you can get the apparent wind up then they do quite well. It takes very little power to move a heavy hull through the water at slow speed if the hull is clean.

So I would prefer to be in the Hobie than your day sailer with my 150W if I wanted to get somewhere in a relative hurry. That said a monohull does have a significant advantage over a catamaran of equal displacement, both optimised for a given speed. The monohull requires about 40% less power.

Rick W.