Would venture to say as Knot-Right has it rigged it is near spot on, seems he could, only compensate by rising the tail shaft upwards which would possibly correct the angle of attack (propeller angle to the surface) any thoughts? You have the Green and White Fountain with the Arneson's correct?

Great question
what is a concern is the prop shaft here is
trimmed all up it is about negative two degrees
when measured with a angle finder in relation
to the last foot of running surface.
so what im trying to say is the the entire propshaft is not able to trim positive to the running surface.
ex if the boat is level on trailer and u put a
marble on the shaft it would still roll towards propeller nut. I cannot without raising the box
trim cyl get positive trim.

Two angles of the running surface is shown here One is shown with the string which exstends forward To the first running step about 15 feet then runs aft And just touches the keel. Second is a straight edge alum angle iron running against the last 4 feet of running surface This is max up trim.

should you have lowered the whole assembly closer to the bottom of the boat?arneson wanted us to be 3/4" from the bottom when we did the conversion on the 47 excaliber?

What will turning in vs out do with the props. Won't one give you bow lift which sounds like what you are concerned about?


Chris

The only reason I asked was in my set-up my boat reaches maximum speed at right around neutral or slightly negative trim but my boat is a v bottom and my thrust tubes are a lot shorter than those .

bpms
4.5 degrees
prop shaft nut to transom 65 inches
propshaft center (measured at ball and socket to running surface) 5.120 inches
bottom of ball and socket to running surface .75 inch
bottom of wedge in between bpm and transom to running surface measured at transom 2.250 inches high.

Drysump sixes 48 inches from prop nut to transom 3.5 inches above running surface Best overall position neutral to slightly positive trimm

I don't know much about surface drives, just what I have picked up on the v6 twin turbo ASD6 project I am involved in.
I believe, and may be wrong, but the trimming up of the surface drive is mostly to reduce drag and optimize the prop position in the water at a given speed, and will have very little effect on bow lift due to lack of leverage. Center of mass of the boat is critically important.
We set our baseline trim at center of prop shaft level with the running surface at the center of the trim stroke, its a much shorter thrust tube and slower top speed.
All I said may be incorrect, but that's the way I understand it at this point.
BTW - I am seriously impressed by the work you do yourself with the turbines, and the rigging is absolutely beautiful. You have set the bar very high!
Thank you for the inspiration!

.
I do know that in my boat that if I even try to trim beyond neutral at max speed the drives will push the boat out of water in such a way that the boat becomes unable to be driven .

From all my info and testing with arneson type drives , V-bottom boats get there bow lift from high rake props and cats get there bow lift from the hull so they don't need high rake props and you want to get the drives as close to neutral as possible to achieve maximum thrust in a straight line to drive the boat out out of the water .