Pedal Powered Boats

Ian:

Thanks for posting.

How does the deployment/engagement work on Rick's CF prop? Are the two sides interlocked with gears like some sail boat folder props?

I have used a similar folding prop concept with carbon model rc props and found they can sometimes open unpredictability, because of the light swing out weight if only a simple hinge is used. Sometimes one side would open more than another causing a wobble. Also the hinge/deployment can hang up in slime algae which is similar to gooey pond scum....

Putting a dab of lead weight on the ends and spacers/washers on the hinge pin did help some with deployment. Protecting/hiding the hinge area behind a leading spinner seemed to help with the fine pond scum.

Mine has been a vast improvement over fixed props, but is still not weed free. It is faster to clear upon entanglement though....

Porta

 

Porta
The carbon fibre prop is about 300mm in dia with the blades pivoting from a nylon hub. Two slots are cut in the hub with the blades fixed with a pin, when the prop spins the blades straighten out. When you stop the blades fold back due to the water flow pushing them, if they stick a fast spin on the pedals will push them out and you can feel the blade bite. Rick has a mould he makes the blades from, they are designed for 1:7 ratio. Being carbon fibre they are very light and strong.

Ian

 

Just spotted these hulls in another thread and immediately thought of them as the centre hull for a typical trimaran pedal boat, Rick Willoughby style: http://www.expandacraft.com/products.html and some pics here: http://www.flickr.com/photos/74826513@N06/sets/72157629778594659

Not super light, but fairly practical. Add a couple of lightweight foam amas and a removable seat/pedal drive and I reckon you'd have a fairly compact, yet reasonably high performance pedal boat. Rotomoulded boats tend to be pretty tough, too.

 

Ian, thanks for your comments.

My design is just a heavy duty version of this folding prop:

http://masterairscrew.com/12x8foldingpropeller.aspx

I cut back the protruding hinge, so that is is flush with the nose cone, and redrilled/remounted the hinge pins further toward the shaft. The hinge area is then well protected from weed jam. Since there is nothing behind the folded prop blades, they fold together completely and have issues with getting a bite on water. A rear fairing that would keeps the blades apart and partially deployed helps. Same concept could be used on a larger scale for HP props, with a larger, cut back piece of aluminum box and say 16X16 rc props (not CF though)....

Porta

 

I have tried if I can design a custom prop according to my needs. It has 300mm diameter, should be good at weed shedding and is optimized for driving at 12kph.

Efficiency is 90% and thrust at 150W and 560rpm (70rpm cadence x8) input is 75N @ 7kph, 50N @ 9kph and 30N @ 15 kph. The best thing about it, with a maximum thickness of 7mm, it can easily by milled out of wood and is virtually indestructible with carbon coating.

I have used Javaprop for sizes and angles and rearranged all that in height and circular position in CAD. I will try to calculate a CFD analysis end of this week and post the results. This will prove if the rearrangement has effects on efficiency.


What do you guys think about it? Do you have suggestions for improvement?

 

Looks OK to me, but I suspect that the efficiency will drop as a result of sweeping the blades and increasing the wetted area a little. Also, you may find that increasing the tip chord might improve performance, as others (including Dennis A on here) have found that a wider tip chord tends to give a lower slip factor, useful for a pedal boat where you have to gear up the pedal cadence to get a suitable prop rpm.

 

Thanks for posting the Expandacraft site Jeremy, this might be just the answer for my sister who lives in a condo in the big city, and my 87 year old father who wants to get back on the water. And it would give an excuse to byild a light two wheeled cart to transport and store it!

Glen

 

Somebody give us a users report.
They might be convienent, but I would like to know how they are after you have lived with them.
Looks like you might be spending some time building the boat each time, something that most people dislike.

Actually I just dislike rotomolded hulls. The quick connect joint is clever, but I want to see the joint on the side of the hull. The rest of the assembly looks slow. How much do you think it will flex with that hull joint? Anything looks great with no waves.

 

My wave interfering hull had its maiden voyage in a digital tank at 12kph. I may remember, that at 2.6m length, thats 170% hull speed.






Waterflow seems to be really nice and pictures 4, 5 and 6 show, that even at gliding speed, the bow wave is negligible (pic 5) and the stern wave too (pic 6). Picture 4 shows, that there are no big pressure rises (wakes) around the boat. The last picture is a 3D-rendering of the upmost 3cm of the water surface, how wave pattern may look like.

Skin friction is the same as of a 4m catamaran.

 

Pity about the high viscous drag, but pretty inevitable with that large wetted area.

It looks like you have a 2.6m long boat that will perform similarly to a 4m long catamaran, but how would it compare with a typical ama stabilised monohull HPB, I winder?

 

I compared that and from viscous drag alone, it is not so much worse (2,2m²). But for sure, the stabilized monohull is the best and outruns in performance.

I wonder why no one has ever copied the Tasman rower from www.dannysunkel.com in a smaller scale. It seems to me that this is the best stabilized monohull / trimaran around nowadays.

My boat has to be small for a good reason. Our summer season is rather short in Vienna/Austria and we have to pay for the dimension of the boat. Rick`s V15 would cost around 600$ for 4-6 months in the marina, while mine will be the lowest fare of about 250$.

You can see the "Old Danube", a former side arm of the river danube which is now the biggest lake in and around Vienna in maps. google.com when you enter 48.237594,16.427808. Marinas are rather small and therefore expensive.

 

Hi folks,
Getting to the point where I am collecting props to try for my cat. Probably another month before it is complete. I have a few APC props including a 16 x 12 and a 16 x 16. Looking around I see they have electric props as big as 20 x 13. Will that larger diameter really be of benefit? Cat is 18 feet and hulls are 6.5 feet center to center. I just want a handful of inexpensive props to give me some idea which direction to go...
Thanks,
Glen

 

Hi Glen! I think, the benefit will be in the area like whether you have for example 92% or 94%. So it is quite something, but it will not change the world with about 3 Watts difference.

The advantage of a big diameter is higher thrust at low speeds, the disadvantage is a higher draft.

 

Do you have an idea of the hull wetted are for your cat? With that I could do a quick estimate of likely hull resistance for you and then run each of those props through Javaprop to see how they would perform with the sort of power you're going to be able to deliver. That's then give you some numbers for gearing and prop selection.

 

Thanks guys, The hulls are 18 feet long, 10 inches wide and 10 inches deep. I am hoping to keep the wetted area at a maximum of about 46 square feet in total. This could go up if I keep adding things but that's a good place to start. Eventually I expect this to becaome a 2 person craft with two drive units. Current drive plans are to use the Rick W. long shaft method.
I don't have numbers for my sustained power output but let's call it average for now?
Thanks, Glen