Re: Where to mount thru hull for cooling water intake?
Food for thought!
The Merc A drive requires that the lower unit sea water pump (and path) remain active for upper unit cooling...., even while doing a direct thru-hull pick up system. As the sea water passes through the upper housing, it removes an amount of heat.
I don't know about the B drives, but you may want to consider this prior to completely circumventing this sea water path.
Or add a shower.
As for cutting a hole for a thru-hull fitting...... have no fears.
Many of us have thru-hulls...... seacocks for head water, generator cooling, wash down pumps, True "Thru-Hull" transducers, etc.
Do as the pros do, secure it and seal it well, and you should have no problems.
Rick ... aka Ricardo
28' SDN F/B w/ twin Volvo Penta 5.7L DP's