Pedal Powered Boats

[Tiny Turnip]

hi Burnley
Building Crusher for the raft race was a total blast - has got me hooked on boat building. I'd do it just as Rick says- butt the ply and use an internal splice (we lapped the ply and needed a fair amount of puraflex bodging to get the lap joints not to leak.) we Kerfed the chines and gunwales at the bending points which was worth the extra half an hour of carefulish sawing.
On the length thing- have you considered a single long hull built in a front and back half that bolt together, ( Close each half with a watertight bulKhead and bolt them together.) and break down for transport and storage? I'm not going to bang on, but if it werent for navigation problems and some rule bending, 4 very little boys in a 15foot outrigger mono hull would have totally trounced 4 serious Karate heads in an 8 foot cat.
Where's the raft race? We might have to popover and have a tilt

[Guest625101138]

Originally Posted by burnleyfc

Yeah, I realise that longer hulls would be faster, but for building, transport, and storage reasons I think that 15.5' (2 sheets of ply) would be long enough.

So the prop I made already would be a bit small. The diameter is only 450mm and the chord is only 35mm at its widest point. http://www.recumbents.com/home.asp?U...l/hpb/boat.htm

I assume we would be spinning too much if the prop is too small. If you don't mind, I'll be in touch again for a prop design when the hulls are built. I'm fairly sure I'll stick with the 15.5' plywood hulls with a shape similar to your attachment. What other info would I need to provide?

For the drive train I plan on using two universal joints so that the prop is driving in the direction of motion. I've seen your strutless prop but I've no idea where to get spring steel around here.

Thanks again.

Your prop would be OK for a test. Give you some idea of potential and can be compared with an optimised design on paper to see if it is worth the trouble of making another. The hull length is the man limitation on performance.

One thing you could do is have the two engines do some performance testing. Get to a gym on a recumbent machine and see what power level you can sustain for 3 minutes. Also find the preferred cadence. Most machines can be set in power mode and the load can be adjusted to get the best feel. I was assuming 300W each at a cadence of 80 based on what you said.

The universals will be OK if strong enough. The should be rotationally offset by 90 degrees to get smooth even torque. Also the cranks should be offset by approximately 90 degrees so the dead spots do not coincide.

Rick W

[portacruise]

Tiny, good points on the length issue. The concept could be extended to make a versatile combination of boats. If the two pieces that make a long 30' hull could be built to nestle inside one another, you could get a lot of possibilitiies.
1.1 Very long narrow hull racing boat when bolted together lengthwise.
2. 2 individual separate narrow hull runabouts.
3. A high stability catamaran with two narrow pontoons when bolted sideways.
4. Inner and outer hulls nestled together could be easily transported by auto or over water.
5. There may be some others, if fitted in a clamshell fashion?

Porta

Originally Posted by Tiny Turnip

hi Burnley
Building Crusher for the raft race was a total blast - has got me hooked on boat building. I'd do it just as Rick says- butt the ply and use an internal splice (we lapped the ply and needed a fair amount of puraflex bodging to get the lap joints not to leak.) we Kerfed the chines and gunwales at the bending points which was worth the extra half an hour of carefulish sawing.
On the length thing- have you considered a single long hull built in a front and back half that bolt together, ( Close each half with a watertight bulKhead and bolt them together.) and break down for transport and storage? I'm not going to bang on, but if it werent for navigation problems and some rule bending, 4 very little boys in a 15foot outrigger mono hull would have totally trounced 4 serious Karate heads in an 8 foot cat.
Where's the raft race? We might have to popover and have a tilt

[portacruise]

On your spring steel question, we have 4' lengths of what is called piano wire or music wire in very large diameters available at hobby shops here. It is very springy, but I don't know if the specks measure out to what Rick uses. The upper section of the shaft can be regular high strength tube and does not need to flex as referenced in a previous post by Rick.

Hope this helps.

Porta

Originally Posted by burnleyfc

Yeah, I realise that longer hulls would be faster, but for building, transport, and storage reasons I think that 15.5' (2 sheets of ply) would be long enough.

So the prop I made already would be a bit small. The diameter is only 450mm and the chord is only 35mm at its widest point. http://www.recumbents.com/home.asp?U...l/hpb/boat.htm

I assume we would be spinning too much if the prop is too small. If you don't mind, I'll be in touch again for a prop design when the hulls are built. I'm fairly sure I'll stick with the 15.5' plywood hulls with a shape similar to your attachment. What other info would I need to provide?

For the drive train I plan on using two universal joints so that the prop is driving in the direction of motion. I've seen your strutless prop but I've no idea where to get spring steel around here.

Thanks again.

[portacruise]

Some quick links that may be of interest:

Spring stainless steel: http://www.joediveramerica.com/page/JDA/PROD/736-S

Model prop? spin fin at 9.5 knots:http://microship.com/bobstuart/spinfin.html

Nomadic research labs partial solar boats: http://microship.com/

Porta

[burnleyfc]

Originally Posted by Tiny Turnip

On the length thing- have you considered a single long hull built in a front and back half that bolt together,

Good idea.

I still don't think that I'll go with longer than 16'. Anything longer than that will look silly compared to the other rafts. You have given me an idea that I could make the 16' hulls in two 8' sections. That way I could easily add more length later by adding another section between the two. I'm not sure how I could bolt them together though; since the hulls are sealed it will be hard to get inside for access to the bolts.

The race is in the west of Ireland so it would be a bit of a trek for you. It's not too far from the sea so if you're feeling brave you could take to the irish sea in Crusher.

[Submarine Tom]

burnleyfc,

Wouldn't look silly at all if it was crossing the finish line first now would it?

Go longer and bolt it together.

Only my opinion, but you do want to win don't you?

Good luck, Tom

[Tiny Turnip]

An interesting patent on an electric assist pedal powered boat here, post 204 of the efficient electric boat thread

[burnleyfc]

Originally Posted by Rick Willoughby

Rudder is easy. I would go for one under one of the hulls. This leaves the other hull free to get closer to the beach. A rudder under the hull will be more effective. I would have a rudder say 250mm deep and 80mm long; a NACA0020 section.

Rick, when you say "under one of the hulls", how important is it that the rudder is actually UNDER the hulls? Is it ok for it to be off the back but deep enough so that the rudder is only acting under the hull? I hope this makes sense.

[Guest625101138]

You need a larger immersed blade if it is hung off the back of the hull. Say 300mm deep and 120mm long will work OK.

Rick

[Skipjackrick]

Has anybody ever thought about using the Drive cable from a Gas Weed Trimmer to drive the prop? A flexible Drive shaft..

We could eliminate the need for a gear box if we went this route correct?

However, would it hold up to the stress?

I found a source here.

https://sdp-si.com/eStore/Direct.asp?GroupID=454
https://sdp-si.com/eStore/Direct.asp?GroupID=422

Oh, and this is my first post. I have enjoyed reading all of the comments. I am just now getting into HPB's.

[portacruise]

Drive cable does not eliminate need for a gear box if using efficient low speed propellers. Even when used with a gear box, there will be frictional losses when using a drive cable, plus corrosion and muck seeping into the sheath area, and the need for structural support so the bends don't pinch too tight...

Hope this helps.

Porta

Originally Posted by Skipjackrick

Has anybody ever thought about using the Drive cable from a Gas Weed Trimmer to drive the prop? A flexible Drive shaft..

We could eliminate the need for a gear box if we went this route correct?

However, would it hold up to the stress?

I found a source here.

https://sdp-si.com/eStore/Direct.asp?GroupID=454
https://sdp-si.com/eStore/Direct.asp?GroupID=422

Oh, and this is my first post. I have enjoyed reading all of the comments. I am just now getting into HPB's.

[burnleyfc]

Originally Posted by Rick Willoughby

You need a larger immersed blade if it is hung off the back of the hull. Say 300mm deep and 120mm long will work OK.

Rick

Thanks Rick.

When hung off the back, should the top of the blade be level (or lower) than the bottom of the hull so that the blade operates in clear water? How would a rudder in between the hulls work?

If the rudder were placed under the hull, where would be best place to put it?

[Dennis A]

Burnleyfc

On my 10 ft pedal cat I have mounted the rudder between the hulls and the stearing is very sharp. The size of the rudder is what makes the differance, to large generates drag, to small and you can not turn tightly

Dennis A

[Guest625101138]

Originally Posted by Skipjackrick

Has anybody ever thought about using the Drive cable from a Gas Weed Trimmer to drive the prop? A flexible Drive shaft..

We could eliminate the need for a gear box if we went this route correct?

However, would it hold up to the stress?

I found a source here.

https://sdp-si.com/eStore/Direct.asp?GroupID=454
https://sdp-si.com/eStore/Direct.asp?GroupID=422

Oh, and this is my first post. I have enjoyed reading all of the comments. I am just now getting into HPB's.

Yes has been considered.

With speed step up around 4 you get a nice size prop to run around 300rpm. Working a prop at cadence, say 75rpm, would require a large pitch and quite large diameter.

The torque on a crank is quite high, typically around 20Nm and will peak 4 to 5 times this. So the cables are on the limit but workable for a while.

The biggest problem will be the feel and power delivery. Any torsional compliance results in high RMS power level compared with average power level. It can take an eternity to get the pedals through the flat spot in the crank as the shaft unwinds. It is like pedalling in mush.

It could be worth a try in conjunction with a speed step to avoid a right angle drive.

Rick W