Nope. Not so far. I've replaced one, but the engine had 2500 hours on it, so not a shock.
My oversize alternator required a TIGHT belt, which undoubtedly hastened the failure. I've installed Balmar
regulators which ramp
up the start charge, so I don't have to tighten as much.
BTW, regarding the raw water
A new M19 belt from Yanmar
is TOO TIGHT even at loosest setting when new.
I've just burned through two of the stock pumps again (I've got two engines), so I said the heck with all that and plumbed in two ELECTRIC
pumps which are relay controlled by the oil
They work ok, but will steam at high RPM
after a while.
But they sure as heck DON'T LEAK!!!