Twisted belt/chain drives

[I57]

Dennis A
Got a video of the flex shaft in action over the weekend, might give you a better idea of how it works. The clip starts off with the shaft hanging straight in the water and as it starts to spin you can see it level itself. Video a bit grainy as I had to compress it down to post.

Ian

[portacruise]

I would guess maybe under a dozen or so flex shaft craft exist in the world at this time. This is a very limited audience, but since Dennis has brought the question of weed, it gives me a place to post what I have read and done regarding the issue.

Yes, the shaft does catch weed which works its way down to the prop under water flow pressure as the craft goes forward.

I believe Rick has developed the best solution to the weed issue in the form of a folding prop which sheds weeds. There are pictures and discussion of the folding prop in the human power section of this list as I recall.

I have tried several different things to try to solve this issue using normal one piece props since '95. Weedless small props work with some types of weeds, but give up a great deal of efficiency in the process. Another thing that works sometimes, is to lift the prop up in the air and spin rapidly to fling off collected weed. Sometimes you just have to remove accumulated weed by hand.

My latest idea is to place a long, smooth, helical ridge on the prop shaft itself so that the weed contacting the shaft is augered up against the water flow pressure as the shaft turns. Ideally, that would keep it from being fed down to the prop as the boat moves rapidly forward. I tried a very small scale experiment using the concept this past week, and I believe there is some promise. The helix has something like a repelling effect on short, chunky surface debris and weed that is not stringy. The trick is to get the pitch of the helix aggressive enough so that the movement of any stringy weed works its way upward at a rate faster than the flow rate tries to pull it down. Didn't have the right pitch for that action with my small experiment.

Hope this helps.

Porta

Originally Posted by Dennis A

Ian

The one thing that confuses me on this system, is additional support for the shaft. Looking at your thumb nails of your proa it does not show any additional support.
Rick however says he uses a light folding tension strut to prevent the prop swining around and hitting the hull due to waves or turning. Do you have one of these installed and does it not catch weed.

Dennis