Cave Plate Depth?

[Kris Flynn]

Hey All,

i wanted to know where the best place to line the cave plate on the leg on the outboard up with? on my current tunnel, it is level with the roof of the tunnel (tunnel depth is about 21mm), but on the new one i am designing it will end up about 13mm above the tunnel roof, when the center of the prop shaft is 1/4" above the inside sponson edge (tunnel depth will be around 14-15mm)

would this affect performance? because i heard somewhere that you should line the cave plate up with the tunnel roof, so water can flow out of the tunnel and got straight under it or something...any help would be appreciated

1 more thing i have to clear up...if the angle between the transom and the sponson inner edge isnt 90 degrees (say its 89), do i follow the angle of the inside sponson edge back to the drive dog (black line in pic) or do i come out 90 degrees from transom (purple line) to the drive dog then measure the height? hopefully the pics will expalin what im trying to find out

Again, ANY help will be GREATLY appreciated

Kris

 

[Kris Flynn]

here is the pic i forgot to attch in the other post

 

[Jerry Dunlap]

Kris,

It's my belief the depth of the cavitation plate isn't as important as the depth of the prop in relation to the bottom running surface of the sponson. It's easier for me to determine the depth of the prop by using a setup board.

Most of my 3.5 tunnels run with the c/l of the prop 1/4"-5/16"(sorry, we Yanks don't do metric) above the bottom of the sponsons.

The only way to find the "sweet spot" is to run the boat and make adjustments to prop height, thrust angle, and balance point.

Jerry Dunlap

 

[Kris Flynn]

Hey Jerry

thanks for the help, i just wanted to make sure the cave plate didnt have to sit a a certain hieght..now its all good

i understand about getting out there and running it to find the "sweet spot" just though i might have been able to do something in the design stage to improve performance as much as possible

Kris

 

[Rob Duck]

I use a piece of glass which just happens to be the top of my workbench (1/2" thick, I build control-line stunt aircraft) and place the boat on the glass and set the engine propshaft bottom above the running surface of the hull. Set it parrallel with the running surface of the sponsons and your off. You can adjust the running attitude at the pond either negative or positive by the engine mount angle but ultimately weight added or the proper balance of the boat with an angle of 0 degrees will give the best speed. Negative or positive trim angles just take forward speed away.

 

[Kris Flynn]

Hey Rob,

thanks for the input...i will find a glass surface somewhere and line it up using that

Thanks Again

Kris

 

[Ron Olson]

If you have an expandable dining room table, pull it apart slightly and slip the skeg through that, wives love it when you do that! ;D I use an old door panel with a slot cut in it.