I am looking for the
boat which is as close to perfect
for my purpose I can find.
I quote some info I found online below:
Though it's time-consuming to correctly align the
gearbox and propshaft, shaftdrives have the distinct advantage that the
stainless steel propshaft and
bronze prop allow the use of slow-leaching copper antifoulings. These paints last much longer than the non-copper paints needed for aluminium
saildrive legs, and if your
boat is
steel,
stainless steel and
bronze are less susceptible to
electrolysis than an aluminium leg.
Although to my knowledge very few (if any) saildrive diaphragms leak, if your boat is left afloat unused for long periods, there's more
security in having a small stern gland than relying on rubber diaphragms.
When I interviewed
bareboat charter operators in the Whitsundays about their drive system preferences, their main gripe was the fine
coral particles from
reefs in the area. They said that these particles blocked saildrive cooling-water intakes with monotonous regularity. Once the unscreened intakes of a saildrive leg had clogged, the
hull had to be slipped and the drive leg removed to clear the blockage, unlike the separate cooling-water intakes of shaftdrive motors, which could be cleaned by simply
diving over the side and removing the grit with a screwdriver.
Saildrives generally have only one
gear ratio choice and the ratio is the same ahead and astern to facilitate counter-rotation. But even with small shaftdrive
Yanmar diesels such as the
1GM10, three different ratios are offered and the two taller ratios have a higher ratio ahead than astern. This allows the
engine to reach its torque band faster and reduces overloading when going astern to stop the yacht or when using the
engine to back off a sandbar.
To reduce overall size and weight, most saildrive gearboxes have dog clutches whereas shaftdrive boxes have cone clutches that allow for a more progressive take-up of ahead or astern
gear and have a longer lifespan. Shaftdrive
maintenance is also lower than saildrives because only the shaft and prop are exposed to seawater and the
gearbox may be serviced from within the
hull.
CHOICE DEPENDS ON APPLICATION
As most new fibreglass yachts come standard with saildrives your drive system choice is severely limited.
If you're fitting-out from scratch a fibreglass yacht with a separate
keel and
rudder for harbour
racing, the ability to concentrate engine and drive system weight amidships makes a saildrive very attractive.
But if you're fitting-out a cruising yacht, especially a heavy
displacement hull designed for passagemaking that won't be frequently slipped, then I'd recommend staying with a shaftdrive.