Okay, let me write about the point of view of Dashew when he designs boats like our Sundeer:
The most likely points of water ingress are:
- prop shaft (like when you loose it, friends lost
their boat that way)
lower seal/bearing (damage after hitting bottom)
- thru-hull fittings
on or near the bow
- engine raw water
- holed at the turn of the bilge
, rocks etc.)
He next took several counter measures to deal with these risks:
- make prop shaft so that it can't go overboard
(can be as simple as a shaft-zinc on the inside; we have PSS seal and thrust bearing)
- design rudder
with a weak spot so that the lower 1/3rd will break off in a grounding. This relieves pressure while keeping some steering
- minimize thru-hull fittings. Jedi had one (1). For discharge, there are standpipes, schedule 80 PVC pipes laminated into the hull and raised well above water line.
- a forward water tight bulkhead, separating the forward 14' of the hull. When I pull the depth
transducer here and let water come in, it will stop at 1 foot high and only when you know the water is in there you can see the bow a bit down (an inch or so)
- an aft water tight bulkhead, separating the aft 16' of the hull. This is where thru-hull fitting, rudder, prop shaft, engine, genset etc. is. When this compartment get flooded it will lead to water damage on the engine and systems, but hull maintains maneuverability.
- an additional 3/8" fiberglass
reinforcement in the turn of the keel
. This was a customer option but every buyer opted for it at, I believe $5k extra cost.
- integral water tanks
along 3/4 of the hull mid section between the water tight bulkheads. used as ballast tanks too.
While most of this needs to be addressed at design time, some can be done any time like the prop shaft issue. If you're designing/building your own boat, the above points are better than insurance!
There are some points to consider:
the standpipes mean that anything that gets discharged must be pumped out. The solution is to gravity feed all but toilets to a central, small gray water tank. Just like in a home. We have the tank in the keel sump and use float switch and Whale gulper 220 to pump it out the the closest standpipe. Toilets have no problem as they already have the pump needed.
thru-hull wasn't enough for us, spoiled as we are. We have 4 now; the three added are for genset, water maker and one shared between deck-wash and air conditioning
unit. The original one is just for the engine now. We have eliminated feeds to toilets by switching to fresh water flush. That also eliminated two raw water
circuits in the (vulnerable) mid section of the boat. We added a new raw water circuit to air conditioner which is now the only one. It could be eliminated with a more expensive split unit.
The trick to this is that there are still no thru-hull fittings in the mid section. All are in the end sections with the bulkheads providing safety
When you build metal boats, you can (should) add 2-4" of foam insulation
sprayed against the hull. This provides insulation
for temperature and sound, solves condensation
drips and provides (questionable, how much volume is this etc.) flotation support.