Why are my rudders so ineffective ? (pwc converted to propeller)

Welll said Charmc avi8r comment was screeming out for an even whittier reply. I tried but nope,-- you got it ,--good one.

EDIT ---nope no rep points today Charmc youlle have to wait a bit.

 

The last time I checked, the PWC speed record was 88mph, jets become overstuffed at those speeds, and it's difficult to get them to go any faster.

Unless that has changed, you have the fastest PWC in the world. Very impressive. Congratulations!

Lance.

 

Sweet ride, need to stick with the wedge rudder,maybe give some thought about counter-rotating props to eliminate prop walk. Think top fuel drag boat, each blade in the water equals stability and acceleration. Racheting propshafts would be good also for (thumb off) freewheeling, would like to see more pics of the bottom. Did you change the intake section of the old pump? What size prop is it?(pitch-dia.)

 

87 is the guinness world speed record set by riva racing but since that was set, there have been lots of improvements. I have gone 88 with jetpump with nitrous/methanol fogger setup, and there are 6-7 pwc's that I know of running in the 89-91 range. Fastest on radar was Dan with jetdraft racing pwc and he has gone 97mph (which puts me in second) The intake grate ripped out at 96 when he was shooting video , the ski was heavily damaged and his rider broke leg and ribs. (this happened a couple weeks ago)

you are correct about overstuffing the pump being the limiting factor and its incredibly dangerous. It has put several friends in the hospitol and I hope a solution surfaces that puts end to overstuffing.

I ran into a brick wall at 88 and my hats off to the guys who got past that with jetpump. Word on street is Dan is running a dual impeller setup like the drag jetboats run, he is a proven performer and is deservedly top of heap. He fiercely clings to the title of words fastest and knows of my project. Just yesterday he invited me to come race his ski for $$ (i think its to prove that he is still fastest) I havent accepted or turned down his offer yet, but if this new rudder works out, I most likely will give it a run.

So no congrats for me for being fastest.... I am just trying to do my personal best, if that gets me out front, thats cool.. if it doesnt, I wont lose any sleep over it.
David

 

I have an idea that may not work, but it's on my projects list to try when the kids are grown. Instead of a kort nozzle that the prop turns inside of, mount a ring around the edge of the prop(Part of the prop). If it can be made to work as a surface prop, it should stop the awful sideways thrust. I'm sure it will work underwater, not sure about surface piercing. Main drawback I forsee is weeds would be more likely to clog since they can't sling off the edge.

I have a dollar I'd bet on you hitting the century mark your next time out.

Thanks again for validating an idea I had and didn't have time to pursue.

Lance.

 

I bet the propgaurd if didnt create too much drag would really help with torque.

 

Propguard is a tube that the prop turns inside of...Same idea as a kort nozzle. We made one like that for a 12 foot boat I used in the Caribbean. It helped a lot at low speed, not much if any at high speed.

I'd like to mount a less massive ring on the tips of the propeller blades. It would turn with the prop, since it is part of the prop. It would be smaller than Propguard, too

Prop blades could be thinner, since they'll be supported at the tips. No prop-to-hull vibration as blades pass near the hull. Much less stern walking on single screw vessels. I'm thinking a minute funnel-shape might be helpful to lower speed vessels, probably not so good on high speed craft.

I'm thinking better thrust, less vibration, better shaft angle because you'll need much less hull clearance, less stern-walk... It might even work.

Sorry for the hijack. Can't wait to hear you've hit 100 mph.

Just curious, what speed do you think you have the power for? How much throttle was left on your last pass? If you can keep this thing tracking straight, how fast are you going to go? Is it "Faster, Faster, Faster" or do you have a personal goal you hope to reach? If you peg the throttle, will you put the nitrous back on and try for more?

Lance.

 

I'd like to mount a less massive ring on the tips of the propeller blades. It would turn with the prop, since it is part of the prop. It would be smaller than Propguard, too

Has this been done before on higher speed boats? That sounds like an excellent idea if it would work to reduce torque . Do you have any links to where its been done?

I have enough power assuming handling is correct for 105-110. Its doubtful I would ever put nitrous on it to try for higher speeds, or even whether or not I would hold throttle to those speeds. I personally hope it feels acceptable at 100mph.... any past will be left for next guy

 

I've never seen it done, just seems like it ought to be tried.

I have plenty to keep me busy these days, so things like this just rattle around in my head. If someone picks up one of my ideas and makes it work, that's fine with me. I have so many little things I'd like to try, I couldn't do them all if I lived to be 400.

I have a big smoker to build, a fence to build so my wife can have a garden, and she just told me that she wants my 12 year-old son to have a boat of his own. We'll probably build him an outboard canoe. Maybe I'll build me one like I want and tell him it's for him.

Good luck on your project. Photo documentation is always appeciated

Lance.

 

Why are my rudders so ineffictive?

The image shows a prop with a disc fitted to prop tips.This was tried mainly to stop prop from digging into the sea bed (mud and sand) and was good for that purpose but created a lot of extra drag.Any appendages add extra drag so a great deal of extra performance is needed to of-set that drag.

 

Rudder came in, so I installed it today, nothing is painted or tightened, but its mounted solid to transom.

Looks huge on this ski. I am going to run just like it is first time out for some easy passes and see how it does.

Its 3/4 on back and goes to 1/8 round in front. Should the front be sharpeneed to a wedge?

Before I had water pickups welded to my rudders, can I mig weld steel lines to bronze rudder for water pickups to this rudder or bore a hole in it and have internal water pickup?

 

David

Leave the front edge alone for now. If it's too sharp, it'll dent easily on debris, plus, the idea is to keep the water in contact with the rudder so it can steer. If you sharpen the front, the transition line from the side to the front will be more like a ramp at speed causing cavitation as the water jumps off the face of the rudder. (a lesser version of what was happening before)

You can't mig weld steel to bronze, but you can tig bronze to steel using silver solder or silicone bronze filler rod.

How much water flow do you need? I doubt it's necessary to make your pick-up tubes as complicated as your first ones. A tube sticking straight down with an angle-cut end should do the trick. (Back edge lower than front) I like your idea of a hole through the rudder, but how much hole can you put in a 3/4" rudder?

The aft edge of the rudder should be sharp and square, if you attach a round tube, it will increase drag. I have no idea how much, but a little is a lot at those speeds.

 

Hit "post message" a little too soon. Can't wait to hear how it works. Good luck!

Tom Kane, thanks for the info and pic. Do you have any more info on the experiment?

Lance.

 

Why are my rudders so ineffictive?

I think it would be a good idea to limit the turning effect of that rudder,like some inboard/outboards for safety.At least for trial runs.

 

Tried rudder this weekend and it pushes bow down way too much. I need to shorten it ( too deep in water) but was looking at it.....

My ski needs to run at approx 5-7 degree angle to get keel out of water (very important)

Looking at rudder, if it has flat bottom, then it would try to keep ski level (so bottom of rudder could run level in water.

If I put a 10 degree angle on bottom ( like in second picture) it seems like this design would be less likely to push front end down.... the ski could rotate to 10 degrees for the bottom of rudder to run level in water.

Is this thinking correct? Also the rudder was very draggy.. I have been suggested to sharpen front and bottom to razor sharp to help prevent the rudder from pushing bow down.. does this sound correct?

thanks
David