First of all, even if you rebuild
the sea chest, you should have the fill go through a big strainer. Much easier to monitor
clogging and avoid problems. That is how I set up my sea chest.
Most people say that the engine should always have its own thru hull
That is a knee-jerk position, but it is conservative and safe. Even if you know the flow rate needed by your engine, the efficiency of the raw water pump
is going to be affected by the height of the intake over the waterline, pump wear, etc. and this entails a sophisticated calculation.
It is reasonable to believe that if you engine raw water
pump inlet is 1.5 " in diameter, that a thru hull
that size would be adequate for the engine alone.
If the genset has a 1" inlet on its pump, the air conditioner has a 5/8" inlet, etc. then the required through hull
for a sea chest serving all three can be calculated based on the formula . Area of a circle is pi times radius squared.
1.77 square inches area for the engine inlet, .78 for the genset and .31 for the air conditioning
Total is 2.85 square inches of inlet for all three.
Or 1.9 " diameter inlet. So if you had a 2" thru hull
for the sea chest/manifold, you could service
As long as the manifold does not get clogged ( you could inspect it easily) why wouldn't it work? You would want it to be substantial. How about an 8" diameter aluminum