Pedal Powered Boats

If the CoG is above the metacenter there is no stable roll angle for the center hull.

 

Good point. How about SWATH with foils. Roll at zero head-way would be minimal and greatly reduced once making way.

-Tom

 

No, lets make that a SWATH foil. Providing lift (static and dynamic), roll damping (big time). So, a buoyant wing, on each side of course. Or, maybe not. Perhaps just one with vertical fins to dampen roll...

The clock on my forehead is spinning as I process... smoke is starting to come out my ears...

-Tom

 

Swath might provide roll dampening but it will not provide the initial resistance to roll, cause the buoyancy is already underwater.

A buoyant wing would work but with a huge increase in surface area when it was supporting, that is why a long skinny ama is used - less resistance a the beginning of a roll.

Vertical fins would pick up buoyancy at the cost of lots of surface area, but I can't see any roll dampening.

 

Interestingly, Rick W did experiment with submerged hull bouyancy, but not in a twin hull arrangement.



IIRC, he didn't ever expect to be able to balance his later more normal outrigger boats, just to use one outrigger or the other.

Thanks for posting your continued progress Ian, its interesting reading, viewing.

 

Upch,

Vertical fins on a submerged wing would provide roll damping via a lever arm.

-Tom

 

My mistake, I forgot SWATH meant twin hulls. I'm thinking only one with self stabilizing ailerons.

-Tom

 

Tom,

I assume you meant horizontal fins for roll damping, like an aileron on an aircraft wing. Single or double should work the same. A minor nit picking point on my part, sorry

Marc

 

Marc,

No, I meant vertical as in rudder or keel. Yes, that's it, an extended keel if you will. Roll damping.

The horizontal wings on the bulb would provide roll stability via ailerons, but little to no damping.

-Tom

 

Just ran into this series of posts and saw lots of the shaft discussion over a long period of time. Carbon fiber is much better in tension than in compression. A 45 degree spiral wind in one direction on a mandrel to achieve tensile stress only would give max torsion strength and minimum torsion flex. The fact that all carbon fibers are at the same orientation that is 45 degrees to centerline greatly reduces bend stiffness. Low bend stiffness is a real plus for this application.

Given the stiffness of carbon fiber, the mandrel would be under minimal stress in service (mostly in compression due to being "squeezed" by the carbon fibers). Therefore most any material that will work during fabrication should hold up well driving the prop.

Carbon Fiber tow can be had at a good price if you are patient and shop around (I got a 5 lb spool for $80 a while back). Running a loop of tow down into a container of epoxy and then winding tightly on the mandrel can give very good fiber density. The good density from tight wound fiber applied "wet" probably comes pretty close to pre-preg for strength. Quicker but more expensive would be carbon uni "tape" wound at the same 45 degrees.

The 8' length could be a challenge. Probably need to keep the mandrel stretched tight during the winding.

 

Rick has gone back to a spring steel shaft in his latest boat, after experimenting carbon fiber. He has accomplished 20kph with the V15 design pictured below:

http://www.rickwill.bigpondhosting.com/V15_58.htm

His CF shafts were considerably larger diameter than the spring steel.

Some of his comments:

"The reason I can get higher speed from this boat is the low torsional compliance of the drive train. I am spinning a lower pitch prop at 7X cadence. The prop is on an 8mm diameter spring steel shaft that is only 1.4m long. The drive dynamics are much improved over my V15-6m boat with the aft mounted prop on the CF shaft.

The CF shaft has worked very well but it is so long and at 4X cadence spinning a high pitch prop the torsional compliance is noticeable above 14kph. It eventually limits top speed due to shaft recoil at the crank deadspot."

Rick sometimes posts to the hpb list.


Porta

 

Porta,

I understand the trade offs between the options.

Looking back, I see that I did not emphasize what I was really trying to point out. A CF shaft that uses Carbon Fiber (CF ) with alternating 45 degree orientation is good for a shaft where you want good torsional strength and you WANT bending stiffness. For long - high speed shafts, bending stiffness is a plus. This improves dynamic stability which limits how fast you can spin the shaft. Some cases even warrant a layer or two of lengthwise uni fibers.

I have seen no discussion in this thread of 45 degree single orientation CF. Spiral wound steel cables with the load carrying outer layer in single orientation are used for flexible drive shafts on things like weed eaters, dremel tools, automotive speedometer cables, etc specifically to get maximum torsional strength with minimum bend stiffness.

If existing CF shafts for pedal boats have only been of the alternating orientation type, I would challenge that the existing results are not bounding and that significantly improved performance may indeed be possible.

 

Flados:

There was some discussion on using braided tube jackets instead of windings. Here's a commercial product along the lines http://dragonplate.com/ecart/product.asp?pID=4107&cID=79 I know this is different than winding on a mandrel.

Yes, anything is possible with carbon fiber, BUT at the expense of time and skill of the builder. Sometimes it is trial and error that is involved. Rick's CF drive shaft was custom built by a pro to Rick's mathematical specks at great $ expense and still didn't hit the target. I'm sure a perfect one could be better built on a second try. But it is faster, simpler, and cheaper to use off the shelf spring steel rod that doesn't require some artistry. Of course, CF would be the only choice in weight critical applications.

Hope this helps.

Porta

 

Rick has just uploaded a new V15 video

http://youtu.be/RQs6YgO93RY

 

There is another video of V15 with a more extensive fairing and single aka supported amas. Just look at the other videos when you see the one above. Now (or then) painted blue.