Anyone seen this type of sea-chest before?

Left side of the picture, stainless.

Questions:

1. Can you take the top off normally, in other words just unbolt it and reach in and clean out gunk? I assume the waterline is below it (I'll verify of course)
2. Is there or should there be a strainer in there? If there isn't when I crack it, is that a problem (I'd think so, although I see a strainer inline in places.
3. Confirm that the plastic elbow at the bottom is a bad idea. I think it is, no valve and could break easily.
4. Is it OEM? Add on?
5. Is it a plus for the boat, or a liability?
6. I probably forgot a question, general opining encouraged.

Don’t know if it is OEM or not. There may be an external strainer on the bottom, need to check. If it was properly built you should be able to remove the top with the boat in the water. I do not like the plastic elbow at all. I would get a shutoff valve and get rid of the plastic.

It’s not OEM and the top is below the water level. I’m not sure there’s a strainer. There looks to be a strainer to the right of it with the ball valve between the two.

Why would the top be below the water level? That seems nuts.

I'm not sure it is, the perspective in that picture is off, but until I get back and measure I can't say either way.

Another question, assuming a cored bottom - was the hole properly bedded and filled with epoxy for the required standoff distance?

sunchaser said:

Another question, assuming a cored bottom - was the hole properly bedded and filled with epoxy for the required standoff distance?

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Great question, how could you tell without disassembling it. I wouldn't bet either way on this boat.

For fun, a pic of the sea-chest from the bottom.

At least they put on an external strainer. I would still like to have a fine mesh strainer on each system coming off the sea chest. You might be able to tap around the external strainer to see if it sounds solid or hollow to see if the filled the core with epoxy. May work or may not tell you anything. Otherwise you will probably have to pull the sea chest to look inside. If you have any doubt you probably better look and see if it is done correctly. If it isn’t and you leave it you could take on water into your core and then hang on...

Take the top off strainer; Pull out basket; Open ball valve. A LOT of water should pour out. Close ball valve. Turn on bilge pump.

I wouldn't bother to change plastic elbow until you're on the hard. It's not going to disintegrate. Have a set of foam or wooden plugs close by just in case.

I would not trust the plastic elbow. I would make sure the bilge pumps work and then put a sheet of plastic under the hull where the intake strainer is and change out the plastic.

bridaus said:

Great question, how could you tell without disassembling it. I wouldn't bet either way on this boat.

For fun, a pic of the sea-chest from the bottom.

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That's not a strainer, this is a proper strainer.



Ted

If that seachest is made of Stainless Steel, I hope it has a big pencil anode.

Ted

It looks like stainless. I didn't see an anode, but I didn't look hard either.

Yeah I like that strainer better.

In ships and big boats a vertical sea chest is common. Usually with a valve at the bottom and an air fitting near the top. Air pressure pushes the water out, you close the valve and the whole sea chest is dry. Some are made to accommodate a strainer basket. This one doesn't look like it. You need to inspect sea chests routinely for marine buildup. Usually there's a round scraper on a handle for cleaning the sea chest.

Some have 2 sea chests. One on each side of the keel. One is for intake and the other for outflow.

Bigsfish said:

I would not trust the plastic elbow. I would make sure the bilge pumps work and then put a sheet of plastic under the hull where the intake strainer is and change out the plastic.

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I would be equally concerned about the lack of a shutoff valve on the plastic elbow coming out of the sea chest. It appears as though the line to the strainer has a nipple and a ball valve attached to the sea chest. It's unsupported. I would redo both lines with appropriately supported valves. Until then, plugs provide an adequate safety backup.

The grey pvc plastic elbow is a strong thick schedule 80 one. You can find them at Lowes. I use some also after thru hulls valves, they have never been a problem in more than 10 years. I also have some polypropylene black plastic elbows, they are real nice as they cant crack.

https://www.amazon.com/Banjo-SL125-90-Polypropylene-Fitting-Schedule/dp/B0079JTCF4

After valves is fine. This has no valve. It's getting replaced next time she's on hard.

How do you support a valve in this setup? I've seen lots of installations where I'd call the valve "unsupported". Perhaps doesn't make it right, but I've seen so many.

bridaus said:

Why would the top be below the water level? That seems nuts.

I'm not sure it is, the perspective in that picture is off, but until I get back and measure I can't say either way.

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I agree. I measured the water line to the ceiling in our engine room, ~8”. You could be good.

Bridaus, You can try loosening the top flange bolts slowly and see if the water level is below the flange it’s under very little water pressure, If it is take the flange off, plug the outlet on the inside of the sea chest with the plastic elbow and do your replacement. The pvc elbow maybe a better use than having two dis-similar metals since the sea chest is stainless. The pvc elbow dosen’t look like it’s in a area easy to step on and break.
You should also be able also to clean the sea chest strainer with a brush, scraper, or water jet.
The whole point of having a sea chest is being able to work the water supplies to thier strainers and internal cleaning of the sea chest while afloat.

bridaus said:

How do you support a valve in this setup? I've seen lots of installations where I'd call the valve "unsupported". Perhaps doesn't make it right, but I've seen so many.

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Looks like a long lever connected to the sea chest via a thin nipple. Putting excessive force on a stuck valve may just snap the nipple. You might hit it when crawling over the strainer to service the battery. You can glass in a bracket or supporting structure and fasten the valves to it with plumbers strapping.

Vibration may also be an issue. You have two dissimilar metals connected in a constant salt water bath so the strength of the nipple would be suspect.

(Any PO who went to HD to buy a plastic elbow probably bought a brass nipple.)

I have not dealt with Sea Chests in over 30 years, but I would think on a boat the upper portion would/should be above the waterline? A large ship, no.

I guess it doesn’t matter in this case, because he will find out soon enough.

I have the same type of seachest as shown in the op. Also the same fear when I first opened it. The top of mine is above the water line and has a tubular strainer which lifts out for cleaning. Two lines come out of mine, one to engine raw water pump and one for flushing the head. Also have a spare that’s not being used. Before you unbolt it make sure to mark the top and side so the top goes back where it came from. Also, take it easy prying the top off so no damage to the gasket. My guess is yours is above the waterline.

You can find the water level relative to the strainer height easily by closing the raw-water valve, removing the hose from the seawater strainer and holding the hose up at different levels while slowly opening the raw-water valve. You may have to add a bit of hose on to the end you have removed from the strainer as the existing length may not be high enough. But it will be very low pressure. This will give you some comfort level to know exactly where the water level is before opening Pandoras box.

We have a sea chest on MOJO and the top is several inches above the waterline. I suspect yours is the same. One thing you may want to watch for - bubbles running along the hull from the bow can find their way into the sea chest and displace the water. Over time the sea chest can fill up with air such that unless the lines coming off the chest are very near the bottom, you will end up sucking air rather than water. The solution is to install a very small fitting (1/8", 3/32", etc.) in the top of the sea chest to act as a vent and run a line up well above the water line and leave it open to the atmosphere. You can put a valve in it to close it off if your want, but it's really not needed as long as the vent line is secured well above the waterline. This will allow any air that enters the sea chest to escape out the top.

Regarding the plastic fitting, It's probably fine, but I'd change it out to either Marelon or stainless steel at the next haul out. You can find stainless fittings at agricultural supply stores and places where food processing equipment is sold.

MOJO said:

We have a sea chest on MOJO and the top is several inches above the waterline. I suspect yours is the same. One thing you may want to watch for - bubbles running along the hull from the bow can find their way into the sea chest and displace the water. Over time the sea chest can fill up with air such that unless the lines coming off the chest are very near the bottom, you will end up sucking air rather than water. The solution is to install a very small fitting (1/8", 3/32", etc.) in the top of the sea chest to act as a vent and run a line up well above the water line and leave it open to the atmosphere. You can put a valve in it to close it off if your want, but it's really not needed as long as the vent line is secured well above the waterline. This will allow any air that enters the sea chest to escape out the top..

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You have described the sea chest on our DF (and most DFs) perfectly. There is a 1/2" valved line coming off the top for air release.

sunchaser said:

You have described the sea chest on our DF (and most DFs) perfectly. There is a 1/2" valved line coming off the top for air release.

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[emoji106]What Sunchaser said[emoji651]️..... I leave the sea chest vent valve open on our DF44, and the static and running water level is normally about 10-12" below top.

Our DeFever sea chests are about 10"SQ ID, as seen forward of stbd engine in picture. Which brought a question to mind when looking at the OP's picture.... My raw water requirements obviously greatly exceed that of the OP's boat, and 4" standpipe would starve my systems.

Salty's sea chest feeds twin JD mains, 12KW generator, A/C R/W pump, and an anchor washdown pump. Not uncommon for all systems to occasionally be in use at the same time.

Actually to me the ugliest thing in that picture is the battery switch etc, in the bilge in the background. WTH is that all about?

bridaus said:

Why would the top be below the water level? That seems nuts.

I'm not sure it is, the perspective in that picture is off, but until I get back and measure I can't say either way.

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My Bruce Roberts had one with the cap below the waterline. I was always afraid to sail into Mexico because I was afraid some idiot drug search team would insist that I remove the top. It was an 8" pipe to the bottom of the keel and at one time contained a forward looking sonar. Previous owner had scraped the sonar head off on a reef. It was scary to have it there!!!!

caltexflanc said:

Actually to me the ugliest thing in that picture is the battery switch etc, in the bilge in the background. WTH is that all about?

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looks like a batt switch feeding an emergency start jumper solenoid. The issue being?? There could be some exposed +12V, however.

I have 3, one for each engine and one for the fire pump.
They are below waterline but on top of the seacocks.
They all contain filters but are easy to remove and clean.
Never have to worry about anything getting into the raw water pumps.