Why through-hulls?

[Caracal]

Originally Posted by Bash

I'm surprised no one has waxed poetic about the merits of a sea chest at this point. Sea chests are common on ships, and eliminate the need for thu-hulls.

Drag?

[ElGatoGordo]

My current boat (which I designed and planned this way) has only one through hull, and its above the waterline. I like it that way. But...

In my previous boat, an Irwin 28, I had 5. To me that was pretty ridiculous. Both sinks had their own for a drain. The head had 2 of course. And the engine intake. If I were equipping that boat for long range cruising, that would have been reduced a lot, probably down to 2. But no, it wouldn't be practical to eliminate them on a boat not designed that way from the start.

[Cheechako]

I eliminated some throgh hulls on one of my boats. In the end I felt I would never do it again. I ended up with more connections , joints, tees, nipples and long hose runs... it was a mess... and any one of those joints could sink the boat. I'll take short hoses with thru hulls nearby any day. JMHO.

[David M]

Originally Posted by Cheechako

I eliminated some throgh hulls on one of my boats. In the end I felt I would never do it again. I ended up with more connections , joints, tees, nipples and long hose runs... it was a mess... and any one of those joints could sink the boat. I'll take short hoses with thru hulls nearby any day. JMHO.

Sounds like the counterargument to a sea chest....long complex hose runs. I do understand why ships have them.

[ElGatoGordo]

Originally Posted by Cheechako

I eliminated some throgh hulls on one of my boats. In the end I felt I would never do it again. I ended up with more connections , joints, tees, nipples and long hose runs... it was a mess... and any one of those joints could sink the boat. I'll take short hoses with thru hulls nearby any day. JMHO.

A good observation

[Pyrate]

Sea chests are nice if you have one good area for it (often they are relatively large because of the number of systems sucking water off of them). They have their benefits and problems. It's one larger through hull fitting instead of a number of small ones. You're banking everything that it doesn't get plugged. You still should have cutoff valves for each hose exiting the sea chest (ideally you don't want to shut off all of your water to replace one hose), as well as one for the through hull. Furthermore, you still would need through hulls for waste, as you don't want your head or sink to empty into your engine coolant water. Diesels can smell enough without that added risk! Drainage can be done above the waterline in most cases, but it's still a through hull and should still have a shutoff valve in case you're riding lower in the water than normal or heeling over or in large seas, etc. You also would have hoses running from every salt water system in your boat to this one area. That could be a lot of hose running inside your boat that would need to be inspected regularly and have potential for failing. The extra hoses also create additional drag along the line, resulting in less pressure and extra work for any pumps. All that being said, there is a reason that many larger vessels do use sea chests to consolidate their through hull fittings (or at least some of them). On a smaller boat though, I think they loose their efficiency fast, take up valuable room and actually increase the complexity of salt-water run systems.

All of that being said, I'll echo what others have mentioned here. Reducing through hull fittings is not a bad goal. Just be sure that the goal isn't just to reduce the through hulls for that sake alone, but to actually improve the system design. Don't let it over-complicate things just to reduce a through hull fitting, a safe technology that is used often for good reason.

[s/v Jedi]

I would love to have a keel cooler! Not just for the engine, but a second circuit (in the same cooler) for the genset. That leaves one to deal with a hot exhaust, or keep pumping water for injecting it into the exhaust. If you want to eliminate the thru-hull, then it's a hot exhaust.
For now, I think I'll keep those thru-hull fittings.

But...

Let's start eliminating thru-hulls. I know a bit about it because my 64' boat came with only one single thru-hull...

All discharges are to be done using standpipes. Indeed easy to do with metal boats but also simple for plastic fantastic. You can buy fiberglass pipe from Centek (for exhausts) which needs to be laminated into the hull. Make very sure where the waterline is on the inside at the location. The pipe should be an inch or two above that at minimum.

On the outside, drill a hole that the pipe fits through. Then the grinder to grind a 12:1 beveled edge around it. Make it pretty
Now sand the pipe and stick it in (perfectly vertical!), an inch or so too far out. Use a little 5-minute epoxy to "tack weld" it in place. Cut a round piece of fiberglass cloth a little bigger than the outside perimeter. Cut hole in the center that just fits around the pipe. Brush some epoxy on the pipe and beveled edge and wet out the cloth. Bring it in place so that there's just a little bit alongside the pipe wall upwards into the deepest point of the beveled edge and then spread out all around. Use a brush to work all the air bubbles out, let the edge come onto the outer hull surface a bit. Now repeat this with ever smaller diameter until it is filled up. With cored hulls you can put some fine woven roving in the center of the stack to hurry it up. When done it's back to grinding and fairing, barrier-coating (for this small patch just use same epoxy) and anti-fouling.

Now the inside... the pipe needs some support here. You could start with a couple of rings (2-3) of 1/2" G10 stock stacked up (sand it well), reducing diameter by twice the thickness so 1" for each disc, using high density filler in the epoxy to glue them in place while filling the voids. Fair the "steps" created with the rings with the same thick mixture and before it gells, drop a wet out piece of cloth over it just like done on the outside. Work that with the brush to make it pretty again and fair and/or put extra cloth over if desired. After cure, sand and paint with Bilgekote.

The easiest way to attach to this standpipe is to get 6" of exhaust hose that fits around it and put it half on the pipe with a T-clamp. Now in the other half, use PVC pipe with an adapter to thread and create a PVC manifold there. No need for a valve, but design it so that anything discharged goes down into the standpipe and not back into another connection.

Keep those standpipes limited to just a couple. We have 1 for all the shower sumps and sinks in the boat. They all gravity feed into a grey water tank which pumps it into a standpipe.

[ArtM]

This question was motivated by a series of posts I've read in recent months:
- One guy who stated flat out that he would never own any boat that was balsa cored below the waterline - PERIOD
- Horror stories about rotted hulls and expensive repair jobs due to poorly fitted or improperly sealed through-hulls FROM THE FACTORY
- Horror stories about through-hull fittings and valves constructed from incorrect materials that dissolve away, leaving the core subject to rot
- Horror stories about boats losing their hull integrity due to hidden core rot and simply falling apart at sea
- Horror stories about risks of sinking, or at least heavy flooding due to broken and leaking fittings

It just seems like there's no need for all this risk in a high-priced luxury yacht.

I should add that I'm thinking specific of expensive luxury cruisers with full electrical and plumbing systems, not pocket sailers with hand-pumped sinks and port-a-potties.

[Cheechako]

I would avoid hulls cored below the water line for sure. However, that doesnt mean I wouldnt buy a boat I liked with a core hull. It would have to have been made by the right yard, and in the right manner before I would take the risk. TPI is one of the yards I would buy from, but still not without an close inspection.

[Pelagic]

Originally Posted by Bash

I'm surprised no one has waxed poetic about the merits of a sea chest at this point. Sea chests are common on ships, and eliminate the need for thu-hulls. I had a buddy with a Gulf Star 50 who eliminated all his thru-hulls, consolidating all the salt-water intakes with a central sea chest. Seemed like a lot of work/expense just to eliminate perfectly functional thu-hulls.

Sea chest - Wikipedia, the free encyclopedia

Don’t understand this logic Bash.
A sea-chest is just one big hole in the bottom (Without the possibility to close from inside) in which thru-hulls (with valves) are attached to distribute sea water.
These distribution thru hulls can still sink the boat if they fail un-noticed.. so there is no real safety advantage.

Primary advantage of Sea chest:
Its over-size creates less suction to bring in debris.
As standpipe is higher than waterline, you can clean out basket strainer while things are still running.
Lends itself to installation of Cathelco system to prevent growth inside pipes. Anti-fouling System: Marine Cathodic Protection solutions,MMO-coated Titanium anodes, Cathelco Systems

Main disadvantage are the longer pipe runs to users further forward

[noelex 77]

Agree with others about the pros and cons of sea chests.

The best design I seen was over the keel, near the trailing edge. The sea chest spanned both sides of the keel with a grating on the port and starboard sides of the keel. Debris like a plastic bag would be very unlikely to block both sides, making the cooling water">engine cooling water reasonably immune from blockage.

The central location also meant hose runs were reasonable.

[thinwater]

Certainly doable, but always compromises.

• No core below the waterline or at least in the through hull area (They can be grouped).
• Engine. With a cat up to 40 feet outboards are a real possibility.
• If you use inboards you also have 2 shaft or saildrives.
• Rudders.
• Drains. On a cat these can be inboard (out of sight) an well above the water line.
• Head. The sea/fresh thing is completely overblown by the adherents of that religion. Funny, really. But certainly if you want to haul water you can. Head discharge can be pump out; discharge above the water line would be mess.
• Bleach in the head is a terrible idea. Won't last too long. Every maker will tell you that. Research heads and holding tanks.

My 27-foot cat had no through hulls.


My 32-foot PDQ has 3 below the water line (head + speed) and they are through a non-cored (most of the boat is cored) section in a bulkheaded compartment. I wouldn't miss the speed fitting; haven't used it in years.


So yes, you can group them and use a non-cored section.

[Andrew Troup]

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.

- - - - -

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.

[Paul Elliott]

Originally Posted by Andrew Troup

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.

True, but you can say the same thing about regular seacocks. Perhaps the lever-arm on the standpipe is longer, but a battery that's come adrift could bash anything loose. I have plugs tied to my seacocks, and I would suggest having plugs and other damage-control stuff ready to patch a broken standpipe. Of course a standpipe is probably larger in diameter than a typical thru-hull, so the resulting hole would be more critical. I'm just thinking aloud...

By the way, has anyone tried the foam plugs made by Forespar?
These look pretty useful.

[Maine Sail]

In a well built boat the thru-hull / seacock will be 100% isolated from the core. This builder seals the edges of the cut outs with solid glass strips then laminates in solid fiberglass sheet with VE resin to the thickness needed. This is for a Forespar Marelon OEM/93 Series seacock.. The hull is also infused...