# Pedal Powered Boats

Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

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### upchurchmrSenior Member

Do you have a picture of the parabolic shape?
What do you mean by a wedge bow - can you provide an illustration.
What led you to the belief that the proper crosssection was a triangle? I assume you mean instead of rectangular, elliptical, or circular.

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### SchenyJunior Member

@ upchurchmr:
Parabolic shape means it looks like an american football. With "wedge bow" I meant a sharp bow rather than a blunt (round) nose like a raindrop has.

@ portacruise:
I tried to run that program for an ideal form with 3 meters length and it showed also an elliptical cross-section with a waterline which looks quite like the YS-900.

I tried to understand how the YS-900 was calculated and came to following conclusion:

The pressure gradient (the amount how fast the pressure rises) is the highest at the bow and at the stern. This is the reason why a bow and a stern wave build up.

A laminar flow profile does nothing else, than distributing the pressure gradient in a nearly flat curve, resulting in the bow wave being distributed along the hull and therefore being smaller.

The problem is the blunt nose, being only efficient for small speeds. We want to ride our boats at a high Froude number to to the limited size. This requests for a Biparabolic shape instead.

If a (Bi-)parabolic shape is optimized to a better laminar flow, it quickly goes to forms resembling the YS-900. So I think the YS-900 was calculated to be something like a "best of both worlds" between a parabolic and a laminar profile.

I have seen airfoils being invented for the engine pods of aircraft flying in a very high sub-Mach range. And guess what I found when googling "low drag hull":

This project uses this shape for minimized drag

Below I have attached:
• foil shape
• pressure distribution along shape
• graphical pressure representation
for a parabolic shape and below for NACA 66-007 shape.

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### WavewackerSenior Member

To me, that looks alot like my kayak.

For all you engineers out there, is it possible or practicle to have a heavy flywheel as a bike front sproket, large diameter running to a small diameter sprocket on a generator to charge batteries that run a small electric motor? I realize that it would not produce the current required to run, but to charge the banks? I was a cyclist, so a heavy flywheel could be started and thereafter easier to keep rotating...Would that be pedal power?

4. ### Submarine TomPrevious Member

Startng to look like a Carmicheal Bulb!

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### portacruiseSenior Member

Yes, this can be done, and it has been done to produce the current to RUN a bike with some efficiency eliminating shifting!

http://www.hupi.org/HPeJ/0015/0015.html

Porta

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### portacruiseSenior Member

Thanks, Scheny.

I was looking at 2 meter lengths, so NACA looks best? Esoteric slow speed applications, like survival capsules, small boat trans navigation records, etc.

Porta

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### SchenyJunior Member

@ Porta:
According to Godzilla, the best form for 2m long also goes to this kayak form for slow speeds. The problem is, that for such small lengths you are planing already at below 2m/s (4kt).

My calculations show, that you need 100N to overcome the drag hump and 130N to sustain 10kph. That resembles 400W for normal cruise speed.

The wave interference boat I am currently working on (as soon as my flat renovation is finished) has only one third of drag for comparison, making it possible to sustain at least 10kph at 150W.

The key is, that at 2.6m length, it uses a minimum drag displacement hull for 65% of the displacement and the rest is planing. As the planing reuses some of the wave's energy and also only 35% have to be dynamically lifted it can be achieved by human power.

There may be other ways to build a boat of 2m length, but they all will be tricky. I could imagine building a catamaran with 2 submerged hulls with the exact same form of the Seaglider (the pic I have posted) and struts with NACA 67-00x form will do the trick too, but it will be not quite as easy to build as my boat which can be done stitch'n'glue.

Best regards, Andreas

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### SchenyJunior Member

I have an urgent question and hope to get as much replies as possible:

Most of you use the "flexible driveshaft" method. How many of you would consider a steerable "Z-drive" instead, as shown in the pic below?

Pro's:
• Rudder with no additional drag (compared to a strut for the shaft)
• 360° manouverability
• No drag of a driveshaft
Con's:
• Less efficiency because of two additional bevel gears

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### Jeremy HarrisSenior Member

I wouldn't opt to use bevel gears for a low power right angle drive, as they are expensive and harder to use well in a DIY drive. I've found that a double universal joint works very well, is relatively cheap to buy and fairly easy to build in to a right angle drive leg.
Here's one of the drive legs I've made using these double UJs, albeit for a motor powered boat but with a big prop turning slowly:

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### Dennis AJunior Member

Steerable Z-Drive

One of the biggest advantages of the flexible shaft drive is that the boat can be beached and launched with the shaft lifted up to clear.

Question . What is the steel strut in front of the shaped drive housing.

Dennis

11. ### Submarine TomPrevious Member

Dennis,

I zoomed in and it appears to be a brace that allows pivoting of the vertical fin.

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### MLampiJunior Member

Z-Drive vs. Flexible Shaft

The greatest advantage of the Z-drive is the vastly improved maneuverability.

Unfortunately, that is about the only advantage over the flexible shaft drive, especially if the flexible shaft drive has the propeller accessible to the pedaler; i.e., positioned adjacent to the cockpit.

That position makes it possible for the pedaler to check the propeller for fouling, allows them to easily raise it and lower it when beaching and launching, and reduces the proclivity for aeration when pedaling in heavier seas.

Michael Lampi

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### portacruiseSenior Member

Seems to me that the maneuverability advantage would be decreased somewhat if one can pedal in reverse using a non-folding prop. Flex shaft can be run without a supporting strut to be more efficient...

Rudders don't work well in certain situations and a steerable prop would have an advantage for precise control. Situations of low RELATIVE speed would favor a steerable.
A rudder is useless when running a boat through river rapids in the direction of water flow as an example. A steerable flex shaft would excel in that specialized application, seems to me....

Porta

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### Jeremy HarrisSenior Member

Manoeuvrability with a steerable leg drive is certainly excellent, the boat that the pictured leg was used on can turn around practically within its own length.

I've found that the problem with reverse not working effectively with the folding prop can be alleviated to some extent by limiting the blade fold angle. The blades don't need to fold back far to shed weed, they only need to swing back by around 20 degrees of so. Although astern propulsion is still far less effective than ahead, even with the blade fold angle limited, it does work to some degree.

If a way could be found to transmit drive to a steerable leg and allow it to flip up if it hit an underwater obstacle then I think it might well be a pretty good system overall. Although it'd still be slightly less efficient than a flexible shaft drive this might be offset to some extent by not needing a rudder/rudders and having good manoeuvrability.

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### Dennis AJunior Member

Z-drive

I have found with my twisted chain drive systems that the weed catches on the drive housings& not the propeller.
On the Z-drive will the steel support strut lift the weed over the shaped drive housing so it does not catch at this point.

Dennis

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