Rather than a big hole, I prefer to think of sea chests (if properly engineered) as part of the hull which happens to poke inwards, like an armpit, rather than outwards, like a breast.
They poke in far enough to have an
inspection port above the water line, but there are other
ports through the hull above the waterline, and in the case of a centrally situated sea chest, there's no prospect of that port going underwater due to heel.
They may create longer pipe runs on luxury yachts with stuff everywhere, but I like the fact that there's a
single place to go to, to turn seacocks on and off, and to check on, if water's coming in.
If you're going to be away from civilisation for extended periods and still feel queasy about the whole
concept of intake failures, i guess you could contrive a seachest with a sufficiently large inspection port into which you could fit, from the inside, a blanking plate the size of the opening.
I was thinking you'd have to arrange some way of levering it closed against the inflow, but you could surely stem the inflow with tapered softwood plugs or some approximation thereof...
The main reason I had the idea for such a blanking plate would be for a boat planning to either
winter over without hauling out, or which might get snookered into an involuntary layover, in icy latitudes.
Even if the seachest is made with
draft (tapered like a casting pattern or the compartments of an ice cube tray) so the block of ice can self extrude, you don't want it keying into the inlets and thwarting the cunning plan ... but I'm not convinced a blanking plate is the best way.
I think a better, easier way would be either precutting a flat
fender to fit slab(s) inside the chest and fill up enough of the space so the residual ice had no structural strength, or to carry a full sized
fender tucked away to be cut up for that purpose if needed.
The blanking plate idea would need to be equipped with a cunning seal which was preattached around the plate, and the opening of the chest would need to be provided with a small inwards flange to prevent the blanking plate falling right out. Failing the seal (possibly as well as that) you'd need to have some quick setting underwater
sealant to make the seal good enough, having pumped out the chest. All seems too hard, to me.
The inwards flange is worth thinking about retaining though, so you could have a mesh grille removable from the inside (which would incidentally help retain the foam ice-defeaters). An inwards flange (effectively just a smaller cutout in the hull then the
interior dimensions of the chest) would be easier to make and stronger than a streamlined opening, on a metal hull in particular, but also in solid FRP retrofitted with a seachest.
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The idea of situating such an 'armpit' under the keel (per the idea Noelex just posted) is novel and through provoking.
I can't use it myself as my planned keel swings into the hull, but I'm thinking of having a dedicated entry point for cooling water from the keelcase, which is effectively a big seachest, (mine will have a big enough lid to enable lifting the keel out) and which can never clog.
One caution about standpipes: I reckon they need to be strongly braced back to the hull in all directions, unless they're very short, which they usually are not.
A piece of
gear might break free in a knockdown or pitchpole, and if it's heavy (a
battery, a spare storm
anchor, a big
fuel canister, or perhaps a heavy
stove, like a Dickinson) it might smash through joinerwork to get at a standpipe which on the face of it is protected from any possibility of such insult.