Sport 20 build. S bend in flex shaft, or no S bend.

[James Schmidt]

How many of you all use the S bend on your flex shaft. I don't think I would be a fan of this set up, but on the other hand I never tried it. I like that I can mount the engine flat which will make it fit under cowel with room to spare. what have you all experienced. S bend or no S bend.

Jim Schmidt

 

[anthony_marquart]

I've done both. No advantage either way. The single bend is less work to set up.

 

[Samuel Hagan JR]

I have a S bend in my Sport 40 and Sport 20. It is a pain in the ass to replace the tube if it gets damaged.

I've seen boats with the single boats go just as fast as anyother. I would do just the single bend. Less work.

 

[James Schmidt]

I was thinking that you would get less shaft life because with 2 bends you might get harmonic oscillations. I did not think about how much work it would be to do a change out.

Samuel, I noticed you built the whip sport 20. Frame 4 has to be right where the starter belt grove is on fly wheel. I know I can notch it out but I sure hope the hull dose not lose its rigidity. this is where the sponsons take all the abuse. I know I can slide engine mount forward or backward, but that might mess up CG.

 

[Hydro Junkie]

Just some food for though. The directions for the Whip 40 call for a double bend so that the motor can sit flat just above the bottom. Not saying it's right or wrong, but if it works and people have won with it built per the directions.......................

 

[James Schmidt]

so true mark, thanks

Jim

 

[Samuel Hagan JR]

I was thinking that you would get less shaft life because with 2 bends you might get harmonic oscillations. I did not think about how much work it would be to do a change out.

Samuel, I noticed you built the whip sport 20. Frame 4 has to be right where the starter belt grove is on fly wheel. I know I can notch it out but I sure hope the hull dose not lose its rigidity. this is where the sponsons take all the abuse. I know I can slide engine mount forward or backward, but that might mess up CG.

I laid the motor flat as possible and low as possible. I had to grind that frame out for the flywheel and starter belt. You can angle it if you want. They prefer the S bend because it helps with Flex Shaft Whip. Suppose to make the boat go faster.

CG is easy is change on those boats I have the motor as far forward on the Sport 20 and I changed the Sponsons.

 

[Jerry Dunlap]

I've build a few Sport 20s and have just run a bent tube. Guys have explained the S-bend theory, but it violates my KISS theory.

JD

 

[Bill Gibson]

By far ......the KISS theory ABSOLUTELY RULES in the game of life!........Works purty danged good for model race boats too!

 

[Don Ferrette]

I was thinking that you would get less shaft life because with 2 bends you might get harmonic oscillations. I did not think about how much work it would be to do a change out.

Samuel, I noticed you built the whip sport 20. Frame 4 has to be right where the starter belt grove is on fly wheel. I know I can notch it out but I sure hope the hull dose not lose its rigidity. this is where the sponsons take all the abuse. I know I can slide engine mount forward or backward, but that might mess up CG.

It's actually the opposite, shallow S bend set ups control cable whip better. This was proven out years ago when a very well known boater did studies on parasitic drag (I'll leave his name out for now but he's more than welcome to chime in on the topic). I've used S bends for years without issue on scales, sport hydros and riggers.

 

[anthony_marquart]

Seems I also remember that study. I switched to s bends in riggers. I'm back to one bend in my sport boats now. Maybe I'm on the down hill side of it but the single bend is easier for me. And running oilers these days the drag is low enough for me

 

[James Schmidt]

Many thanks guys, this is my first sport hydro, and while looking at this I notice the flex shaft is very long, much longer than monos and Cats. So the theory of shaft whip started making sense. I can see where the S bend would give support to a long shaft. I don't think the S bend would be necessary on boats that don't need long shafts. well I am starting to see this a little better. the thing I like about one bend is KISS for sure!!!!! thanks for helping me think through this guys..

 

[Jim Caldwell]

For electric 35,000rpm Sport hydros I put the S bend in the tube under the boat between the hull exit and the strut. Very slight bend 1/16" each side spaced about 1/3 and 1/3 of the exposed tube.

 

[Warren Tremblay]

I notched out the frame at the starter belt all the way to the hull for about half inch in center and have been racing the boat 6 years without any issues

 

[Warren Tremblay]

I was thinking that you would get less shaft life because with 2 bends you might get harmonic oscillations. I did not think about how much work it would be to do a change out.

Samuel, I noticed you built the whip sport 20. Frame 4 has to be right where the starter belt grove is on fly wheel. I know I can notch it out but I sure hope the hull dose not lose its rigidity. this is where the sponsons take all the abuse. I know I can slide engine mount forward or backward, but that might mess up CG.

 

[Roy Munoz]

​ see from your picture that your header is rubbing on your flywheel.. That could be more of a problem that the S bend..

 

[Samuel Hagan JR]

You should be fine. The radio box being right there should help it out.

 

[Hydro Junkie]

I was thinking that you would get less shaft life because with 2 bends you might get harmonic oscillations. I did not think about how much work it would be to do a change out.

Actually, James, harmonic oscillations, in a car's driveline, are caused by having two universal joints with unequal angles. Since there isn't a mechanical joint, other than the collet, I'm not so sure that would be an issue that would have to be dealt with. Now, if you were running an articulated shaft with dual U-joints..............................

 

[James Schmidt]

Well I just went with the S bend. I need to try it since I seen evidence Like the you tube video demo, and that got me doing a little more research. I can see where it can be helpful with a lone shaft. thanks a bunch fellas.

Jim

 

[Eric Bourlet]

On the bench in a static environment a single bend sets up power robbing standing waves. I doubt that if you move that into the dynamic situation of a bouncing hydro with the load and rpm changing that would be the case. I have done both but run a shallow single bend in my Sport 40.