SPORT 20 HELP !!!!!!!

[TOM MOORE]

Hey Guys,

Please help me, I tested a new sport 20 today dumas with a few mods to sponsons nova rossi eng x442 prop, the problem is in the turns the right sponson would rise up a good inch. the turn fin has the 10 degree bends in it and i think its riding up on the turn fin. it even rose up in the straights a couple of times. any help on what kind of turn fin, and the depth well h$$l any help would be appreiciated.

Thanks Tom

 

[shoboat]

Tom,

I would check the turnfin mounting position first. Is it running parallel to

the bottom of the boat? Is the outside edge of the fin sharpened only?

If it was my boat I would try a curled turnfin similar to a Roadrunner

turnfin. You can also make one with a 1" pipe and bend the fin around

it. Another thing to check would be different propeller setups. A 1640

pitched up I here works well on that boat. Different propellers are

going to change the angle of attack on the boat also. How much did

you change the sponsons? Do you have access to a digital level? This

is a tool that you should really consider purchasing if you are going to

build boats and play with setups. The level would give some great info.

on the sponson angles,then I could help you more.

Tom, Try a 215 Prather while your at it.

Thanks,

Mark Sholund

 

[MikeP]

My Dumas Pay-N-Pack lifts in the corners, I tried several different fins with little improvement. I was told it was caused by the narrow hull.

Mike

 

[TOM MOORE]

The turn fin i was using was off a 40 hydro i cut it down a little it had the 2 10 degree bends in it. all i did to the sponson is take the rocker out of them. Im planning on running a straght fin first to see if that helps i will try the 1640 prop iLL let you know what happens Thanks for the imfo.

Tom.

 

[PHIL THOMAS]

Tom,

May be you can try running the boat with out the turn fin to see how it handles. the fin on a sport 20 should be as small as possible. Sounds like the fin is lifting the sponson. Usually motor and prop torqe will lift the left sponson..

Check the front to back alignment of the fin with a straight edge held on the inside of the fin, this should be parrallel to the running pads edges. Try to find a fin that is thin too, like .040 stainless. The rudder must be straight also, not cocked to one side.

 

[GTR]

Hi guys

One of the things I have wondered about is how (say for the DUMAS P&P) the running attitude of the hull is effecting the handling. Why I say this is the 'original' design called for the strut to run with downtrim - lifting the back of the boat, & with a lifting rather than X series prop. What I'm leading to is the hull is possibly struggling to run with the transom high enough and this would cause the sponsons to run at a much high angle of attack increasing the lift in the front of the hulls tunnel. All this would lead towards an unstable hull in a straight line - forget about the corners. Just a thought floating through empty space (eg. my head)

GT :blink: