Sea Chests ???

The idea of having your seacocks all in one spot on a sea chest seems to make a lot of sense from a safety perspective. My question is why don't more builders do this? The only designs I know of that do it are Great Harbour and Defever. Surely there must be others?

... and while I am asking random questions, why is it that Great Harbour and Defever designs are also the ones with big (as in stand up big) engine rooms, in boats under 50 feet? Does anybody else do big ERs under 50' ?

There are others that do it. One of the downsides is that it requires all your hoses to run to that location which may not be as easy to plumb. Salt water flush heads are one that come to mind. They're often at the far ends of the boat.

Ted

Tollycraft also uses sea chests in some models.

Diesel Duck and Seahorse Marine have sea chests too.

CPseudonym said:

Diesel Duck and Seahorse Marine have sea chests too.

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They also have a stand up engine room.

I have one in mine. The pic is shown looking down on top of it, 2 thru hulls, one to engine, one to head. There's also a spare that is plugged off.
Mike

Hatteras used sea chests on many of their earlier boats, then went to individual through hulls.

Non-Diesel Duck Seahorses are not stand up engine rooms but they have a sea chest.
North Pacific has sea chests also.

Yeah. Tell me about it.

I think a twin engine applications might be more favorable for a sea-chest, as it can be mounted low in the hull and at center. Full center keels might not prohibit them, but it would require mounting them on one side or the other. I considered doing one on my own boat when it was time to change-out some thru-hulls, but with the full keel and only 3'2" draft at the bottom of the keel, it would be drawing from maybe 2.5 ft. below the waterline. When she's rolling, with multiple sources drawing water at the same time, she'd be sucking in whatever crud, grass, suds or plastic that was near the surface.

Great Harbour's have a great setup, even with only 2'10'' draft.
The sea-chest is mounted dead center at the deepest part of the hull between the engines.

IIRC Nordhavn uses them on larger models, and there's a good technical article on the Nordhavn site discussing them.

David Rive said:

The idea of having your seacocks all in one spot on a sea chest seems to make a lot of sense from a safety perspective. My question is why don't more builders do this?

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Money?

I am guessing that the builders know that if a buyer really is savvy enough, and particular enough to want a sea chest, they will be willing to spend more money on a boat. A production builder who is likely aiming at a different market won't bother to spend the money to do it because they can't recoup the cost from their customers.

Again, just a guess from an old sailor.

I agree though, it would be very nice to have.

Pumps like AC's don't prevent reverse flow. Get a little restriction on the hull screen, and AC's cycle off, and your main engines/gennie will suck air. Not good.

Lots of plusses, but needs to be done carefully. Best for deep draw boats where there is plenty of positive head.

O C Diver said:

There are others that do it. One of the downsides is that it requires all your hoses to run to that location which may not be as easy to plumb. Salt water flush heads are one that come to mind. They're often at the far ends of the boat.

Ted

Click to expand...

This is not an issue on DeFevers. Salt water heads - can't say as I've seen one lately on DeFevers.

Have three take-offs from my sea chest. One goes to the engine and the other two to nowhere. Suppose one of the unused would go to a nonexistent genset and the other for a seawater deck washdown (but the boat is plumbed for a freshwater washdown).

David Rive said:

The idea of having your seacocks all in one spot on a sea chest seems to make a lot of sense from a safety perspective.

Click to expand...

OK. I'll bite. Why does it seem to make more sense?

"Does anybody else do big ERs under 50' ?"

Todays diesel require little besides PM and oil changes.

The room to stand to observe the engine is taken from the volume of the vessel

Like a huge toilet space , are you willing to give up that much internal volume for 15 min a day.

To my mind a better design would allow an engine R&R with just minor pulling of a hatch in the cabin sole , and a similar hatch in the overhead.

FF said:

To my mind a better design would allow an engine R&R with just minor pulling of a hatch in the cabin sole , and a similar hatch in the overhead.

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Agreed. I have hatches in the cabin sole, so good access and headroom, but no hatch in the roof.

Something I read a while back that does a pretty good job of arguing that multiple seacocks are not really the problem that a lot of people imagine...

Photo Essay – August 2015 | Steve D'Antonio Marine Consulting

Not saying that I necessarily agree with him completely, but it is food for thought.

Northern Spy said:

OK. I'll bite. Why does it seem to make more sense?

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On my current boat I have seven (count 'em, seven) through hulls. I do not close them when leaving the boat due to the hassle, except if I know I am not going to be using her for a long period. (I just replaced all hoses and clamps this year).

With a sea chest with one through hull - it will be shut every time. A no brainer. In fact insurance companies should offer a discount for a sea chest.

On top of that, to change out a through hull you need to haul in many cases. Apart from the one through hull the Sea chest switch out can be done with the boat afloat.

Pretty sure there is not a singular large bore isolation valve on the sea chests we're talking about on this thread. A steel hull like Mark's boat would be easily done, however. Most of them are a true sea chest and not an isolable manifold as you are describing.

Being ignorant once again....

Do most sea chests go high enough inside the boat to be above the waterline so they can be open on the top? (or at last don't have to be sealed to withstand pressure)

Imagine how nice it would be to be able to change a through hull being able to work both "inside" and outside at the same time.

dhays said:

Do most sea chests go high enough inside the boat to be above the waterline so they can be open on the top? (or at last don't have to be sealed to withstand pressure)

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Mine does.

FF said:

...
To my mind a better design would allow an engine R&R with just minor pulling of a hatch in the cabin sole , and a similar hatch in the overhead.

Click to expand...

Works for me except no overhead hatch (but I expect the engine to outlive me), leastwise no crawling.

Maybe I'm missing something here(nothing new there). To change out a through hull, you need to have it "dry" on the intake side. So you would have to have the water level in the sea chest be below the intake. How do you accomplish this without taking the boat out of the water? Do those with sea chests have one big huge valve for the whole thing? I've never noticed such a thing but can't say I've really looked for it on boats I've toured.

To me the attraction of sea chests is one easy to access location and one hole in the boat.The downside is all the extra hose and hose routing. Plus the "single point of failure" issue though I perceive that to be slight.

caltexflanc said:

Maybe I'm missing something here(nothing new there). To change out a through hull, you need to have it "dry" on the intake side. So you would have to have the water level in the sea chest be below the intake. How do you accomplish this without taking the boat out of the water? Do those with sea chests have one big huge valve for the whole thing? I've never noticed such a thing but can't say I've really looked for it on boats I've toured.

To me the attraction of sea chests is one easy to access location and one hole in the boat.The downside is all the extra hose and hose routing. Plus the "single point of failure" issue though I perceive that to be slight.

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I don't think you are missing anything. In fact, you pretty much nailed it.

Sea chests (that I am familiar with) have a removable cover above the water line allowing you to reach in and plug whatever outlet you want to work on downstream. Most only have 2-3 different pipe sizes and plugs to fit are normally hanging right next to the sea chest for use (might have even come with the new Defever I am familiar with...I will have to ask the owner)

My post #7 shows the top of the sea chest. It is a 1/4" aluminum plate w/ 6 bolts and a rubber gasket that can be removed, it's above the waterline. Inside the chest is a 2' long perforated tube/strainer that can be removed for cleaning, which I do at lease once a year. It gets fouled up w/ algae and whatnot, not so bad that water flow is restricted.

dimer2 said:

Sea chests (that I am familiar with) have a removable cover above the water line allowing you to reach in and plug whatever outlet you want to work on downstream. Most only have 2-3 different pipe sizes and plugs to fit are normally hanging right next to the sea chest for use (might have even come with the new Defever I am familiar with...I will have to ask the owner)

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Ah ha, that makes sense for something like replacing a sea cock on the other side. But if for some reason you were replacing or adding an entire through hull, then it sounds like you still need to get the boat out of the water.