Some might say none of it is relevant, but I think it all is.
The overall point is that a poorly designed exhaust system can cause a catastrophic failure; in Hunterdog's case (from the information we can see) it appears that (maybe) an improperly fastened rod bolt fell off, an oversized exhaust system (thus not developing sufficient exhaust velocity/volume), with no riser (see post #120), allowed water to enter the ex manifold and subsequently the forward cylinder when the boat
surfed down a large wave, destroying the engine. (others disagree)
Impossible to say if a riser or a properly dimensioned exhaust diameter or a better overall exhaust system design would have prevented the Beneteau
fiasco, but for your application, given the control you have over the design, I can't imagine an installation
where seawater could conceivably have unimpeded access to the exhaust valves, which, without a riser and with a below-the-waterline exhaust manifold outlet, it at some point will certainly have.
In an excess of caution on my boat that never goes offshore
, I have a siphon break in the raw water line between the r/w pump
outlet and the heat ex inlet, a ten inch exhaust riser, and an exhaust riser where the exhaust exits the hull
. But perhaps I've seen too many boats sunk or almost sunk by poor design, maintenance
and neglect...or just unfortunate concatenations.