MapisM
Well-Known Member
Mmm... While it's true that in principle a shallow shaft angle is more efficient AOTBE, the effect of that (and of tunnels) on stern lift is actually the opposite.
The same hull, with the same engines placement, would have more stern lift with no tunnels and a consequently higher shafts angle.
As always, it's a matter of compromising between the pros and cons...
As an aside, Rob, your drawings reminded me what you said in another thread re. your interest in being able to dry out the boat.
Considering the deep keel you've got, which leaves the props above its bottom, you might consider enclosing each shaft in a steel skeg, with steel bars going under the props and working as rudders shoes.
It's a solution widely used in trawlers/workboats, and such setup would surely be far safer with regard to drying out.
Though of course, purely in terms of efficiency you might loose half a knot max speed or whatever, and burn a bit more fuel, particularly at higher speed....
...horses for courses springs to mind.
Just a thought, anyway. It would have been a nightmare to make such change on a GRP moulded hull, but with a steel vessel at least you've got the choice!
