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
, 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
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.