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

Not my domain, just using a bit of caution, suggests you try 0 degree (parallel to keel) but cut off to first angle... then the second cut is another option, rather than lop off too much first go... With observational interest and good luck...

 

When I saw the photo, my first impression was that it was too much rudder for your PWC and speed. Your results confirmed it. Based on some earlier posts, grinding the leading edge to be very sharp should reduce drag and lift. Shortening the rudder will help. For the best angle at the bottom of the blade, I'd suggest: 1. Look again at the photos of Slo Mo Shun and Miss Bud. 2. Make any changes in the present bottom angle small changes, with a test run after each.

 

In the opening post of this thread you were asking why you had no rudder. The answer given was that of the side walk from the surface prop. The boat is also being lifted at the back by another anomoly of surface props and that is lift. As the blades are constantly entering the water lift is generated.

 

One difference between my setup versus slomoshun and miss bud is they want to run flat where I need to run nose a little higher. Will sharpen and shorten, but I think the bottom of rudder is a planing surface also? The angle on bottom of rudder would help?

Frosty, where ski was running and would torque to right before, now it pulls to the left from the drag of rudder. I now steer slightly right to compensate( versus big time left before) Its getting closer... just now in fine tuning it

you guys have been huge wealth of information getting this dialed in.

 

Keep going avi8r, Many are interested and appreciate your posts & updates.

In giving, only "tokens allowed - herewith ::::: ::::: ::::: ::::: use with pleasure infront of "D" to make smilies

 

CHARMC siad what I was thinking. The rudder looked huge. The photo angle wasnt dead-square from the side or level with the keel, so it was hard to tell.

If you sharpen the rudder, make sure to plane the whole face down so you don't have any angle changes. I'd only remove a 1/2" at a time from the bottom, too. It would sure suck to have too small a rudder, and have to start over. I think you have the right idea for the bottom edge, just too much angle in your drawing. You'd want to have the bottom edge running level at top speed, maybe even a degree or two down in back, but I might be wrong about that. I think there'll be more drag from water spilling of the bottom edge at an angle than from it spilling straight off the back edge.

Your steering drag will lessen as you remove material from your rudder, too. Hopefully it will steer correctly at the same point it runs fast enough.

How'd you do your water pick-up?

Looking forward to your next update.

Lance.

 

Yeah it is huge.. I knew it would be, but wanted to try it before cuttin anything to establish a baseline. So far I have removed 6 lbs from it and its getting better. Right now i have 8 degrees on the bottom.

I installed a spacer and raised my rudder 1 in above its mount. That way I can take 1 in off at a time and if I take too much off, I can drop it back down on mount (remove spacer ) and fine tune from there

My speed is coming up as I make the rudder smaller and sharper. Great tip on offsetting it to the left, it has virtually eliminated my torque problem.

after done trimming off the bottom, do you think i should sharpen bottom like leading edge to further decrease it pushing nose down?


and I think its now the worlds fastest PWC ( at least I dont know of anyone faster) I really appreciate everyones continued help getting it dialed in.


btw, I tried a 13 in yamaha drag prop with 17 pitch this weekend... it bit the water so hard that it wouldnt even idle or come on plane. I had a friend pull me on plane and once running, it was great, but ofcourse its not practical since it wont get on plane by itself.... I will have to stay with small prop to allow it to idle ( the slippage)

 

CONGRATULATIONS to avi8r, well done, I hope it is recognised, for all the effort and risk you deserve it.....

 

That's awesome!

Glad to hear you've done so well.

Still curious to see how fast it will really go when all the little adjustments are made.

Congrats on all your work.

Here's the big question...How is this going to affect the rest of the PWC industry? A heretic with a prop setting a PWC record. They're gonna hate you, David. I wonder how many will try to copy you and take it to the extreme. I still think a 150mph PWC is possible with a longshaft, steerable surface drive.

When do you contact Guiness?

Lance.

 

The guys who have been following the build from beginning are really supportive, but I am really surprised by the reception its recieving.. really not much negative on it, but I try to keep it humble and not push any buttons until its in the books

shhhhhhhh dont tell anyone, but this is the pwc I will be using for guiness record Hopefully will have 2, one with jetpump and one with propeller and reset it with both forms of propulsion. I Having a low center of gravity will make it much safer as speeds get higher

 

Does a three-point hydro qualify as a PWC?

You still have the world's fastest PWC.

Keep us posted.

Lance.

 

I doubt it qualifies.. but it does look really cool.... I am talking to the guy about it... would love to see a pwc version of this 3pt hydro I would prefer exhaust on inside ( not outside) taller seat and handlebars but I can see it happening

thanks for words of encouragement its a great deal of fun. When I get it sorted out, you should fly down and take it for a spin
David

 

Like a "gold bug" I guess a "speed bug" must be equally addictive....Best wishes in your ventures...

 

this is what it looks like in building... it has tunnel design like a stv boat.

I wont highjack my own thread, and when I get the hull will create a new one if you guys want to follow the build.. I am sure I will be asking questions on it

just have to finish current prop conversion now

 

Man Dvaid,

It's awfully nice of you to offer a ride, but I just wanted to build one, I never said I wanted to ride it. I have a speed freak buddy willing to do the test runs if I ever build one. I have a wife and two kids, and by the time the kids are grown, I'll probably be too old to do it anyway.

I'm reminded of the foolish things I did from age 13-17 every time the weather turns cold. (shoulder and knees) I'm not ready to start that again.

Thanks again for the offer, and if you ever find yourself near Lubbock, Texas, give me a shout and I'd be happy to take you stalking wild hogs or pheasants or whatever is appropriate for the time of year. Or just take the wives to dinner.

Lance.