I was looking at the new boat project that I haven't started I am considering using a reduction pulley and belt to fine tune the propeller to the engine rather than fool around changing props .My thoughts are to use Weston Farmers tables to get it close then alter the speed of the prop to dial it in. My question for the day is-- In an ideal world what would be the preferred angle of the driveshaft to the plane of the boat? Too much angle would tend to bury the bow and to much angle the other way would create a rooster tail. So should the angle be the same as the plane of the boat? So everyone,put on your thinking caps and see how many of us come up with the same answer!! Thanks Den
My experience has been that the propeller lives in flow that, to a large extent, follows the bottom of the boat. So it is almost impossible to get the prop shaft to line up. The flow at that point is never downwards, occasionally horizontal, and most often rising towards the surface.
The thrust to weight ration in our launches is very high, That is, compared to the weight of the boat, the thrust is low. On a powerful boat, the angle of the prop shaft can lift the rear of the boat. That's most of the force lifting the rear of a hydroplane.
To a large degree, the thrust drops off as the flow of the water deviates from being parallel to the shaft. I suspect it approximates a cosine function. What that means in a practical sense is that it probably isn't that critical.
I would mount the shaft for convenience and tip clearance. And go for a quiet reduction drive.
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
In "Propeller Handbook", Dave Gerr recommends a maximum shaft angle of 15 degrees. He suggests that this is because past this the difference in forward velocity of the sides (one side advancing and the other retreating) will cause vibration.
Some other interesting data points: the closer to square the more efficient the propeller... and for our displacement boats, the larger the prop, the more efficient it is.
I am considering using a reduction pulley and belt to fine tune the propeller to the engine rather than fool around changing props .My thoughts are to use Weston Farmers tables to get it close then alter the speed of the prop to dial it in. My question for the day is-- In an ideal world what would be the preferred angle of the driveshaft to the plane of the boat? Too much angle would tend to bury the bow and to much angle the other way would create a rooster tail. So should the angle be the same as the plane of the boat? So everyone,put on your thinking caps and see how many of us come up with the same answer!! 
Thanks Den
