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Old 07-22-2014, 02:31 PM   #21
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Most, if not all, Marlow's have sea chests. And most Marlow's can plane off.
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Old 07-22-2014, 06:20 PM   #22
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Well I don't have any thru-holes on the side of my boat! On each side I have these pipes that run to the back of the boat. All my grey water, bilde, A/C water, etc are plumbed to these pipes and it all runs out the back.....
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Old 07-22-2014, 06:27 PM   #23
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Well I don't have any thru-holes on the side of my boat! On each side I have these pipes that run to the back of the boat. All my grey water, bilde, A/C water, etc are plumbed to these pipes and it all runs out the back.....
I had thought about that but I don't want to cut holes thru my structural frames.A small reenforced hole maybe ok but I wouldn't like it.
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Old 07-22-2014, 09:30 PM   #24
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Interesting idea to use a sea chest as a common discharge. Normally they are used as a common intake.
... and as noted and shown in the Great Harbor pics and comments, those are intakes. Two engines, a generator and the AC... all below the waterline. Defever was another big user of these. A lot to like if done right.

You see some boats with a variety of outflows running through a manifold or semi-"sea chest" exiting above the water line . Yes you reduce the number of holes in the boat, but it the single hole must be of the proper size to allow all possible flows out. Another trade off is the need to run some longer hoses than may otherwise be necessary, involving some installation, maintenance and potential pump priming issues. Everything's a compromise!

One thing nice about discharges closer to the waterline is less staining of the hull in tannic or dirty waters. Yeah modestly less noise too, but I have never felt that was an issue nor really have heard it brought up as in issue before.
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Old 07-25-2014, 06:59 AM   #25
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Quietest is installed in the painted water line.

Downside is a genuine sea cock will be required for each , and an anti syphon loop on many.

Upside is the WL is easy to repaint when thru hulls are pulled for inspection.
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Old 07-25-2014, 07:55 AM   #26
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Twisted Tree. As past Sales Manager for Great Harbour Trawlers, I will tell you that our sea chests have been a complete, unqualified success. While you are indeed correct that there are the same number of raw water inflow "holes", the sea chest itself is most definitely NOT a failure site. The chest is a pultruded fiberglass piece which is actually bonded into the structure of the hull - and the hull is over 3/4" thick at that point!

So, here are the actual benefits of a sea chest system like this: First, even if one of the seacocks fails, as long as you have SOMETHING to plug the hole, you can simply reach into the sea chest (that clear lid on top removes with four thumb screws) and stick a plug, or a rag, or whatever into the hole and stop the leak. Second, you can actually plumb a new seacock (to add another AC unit, or a watermaker, or whatever) into your boat WITHOUT HAULING IT. We've done it. Get's maybe a quart of water into the boat. So, obviously, it goes without saying that it is also VERY easy to replace an old or damaged seacock, by yourself, with the boat in the water.

Third, it eliminates the need for sea strainers. There is literally NO suction discernable outside the hull. We use a 70% stainless mesh to keep fish from swimming into it, but, it NEVER sucks up plastic bags, or weeds, or sand, or jellyfish. All of the suction is inside the sea chest. Here's why: Let's say your boat has five seacocks (two engines, one genset, and two AC pumps) Each seacock is a 1" hole (about .8 square inches). Multiplying that by five gives us a total area of about 4 square inches for all that suction - all pulling sand, weeds, baggies, jellyfish, etc. from under your boat. The sea chest has an 8" x 8" screen at the bottom, so you have an area of almost 45 square inches (64 sq. in. x 70% mesh) spreading all that suction out!

Fourth, it's very easy to clean out. Most of our owners have one of those electric pressure washers in the engine room. Pop the top off the sea chest, hook the pressure washer to the engine room fresh water outlet, stick the wand into the sea chest and blow any marine growth right off the walls and off the mesh. Do that monthly, and you never have a problem.

Lastly, all of your seacocks are in the same place and very accessible. You can always check them by eye and, of course very easy to periodically test for proper operation.

Sorry for the long essay, but on a displacement trawler, if you have the room, a sea chest is ALWAYS going to be a better option than a bunch of random through-hulls!

ERIC

And, for your further enjoyment, here's an N47 engine room (7' headroom.)
That's a great summary of other advantages to a sea chest.

When you talk about replacing or installing a new sea cock, how do you bed it while it's submerged, even if only in the sea chest? How do you clean off the old bedding compound, apply new, and get it all to seal properly? I've never tried it, but it doesn't sound very viable in actual practice. Perhaps on a sea chest with a main intake shutoff where the chest can be drained, but on a sea chest open to the water all the time?

All sea cocks in one place is indeed nice when it comes to inspection, but that also goes hand in hand with longer hose runs and more chafe points.

Again, I don't dispute that there are benefits to a sea chest, but just encourage anyone considering one to carefully think through the pros AND the cons.
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Old 07-25-2014, 12:04 PM   #27
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When you talk about replacing or installing a new sea cock, how do you bed it while it's submerged, even if only in the sea chest? How do you clean off the old bedding compound, apply new, and get it all to seal properly? I've never tried it, but it doesn't sound very viable in actual practice.
It's no big deal to scrape away the old sealant. And to reseal you just use a moisture activated sealant like 4200. No different than putting in a new transducer or thru hull with a boat in the water.

What ever minor cons a properly designed seachest may have, they are far out weighed by the pros. Once you run a boat with a proper seachest you'll never want to go back to multiple strainers scattered around an engine space.

Throw in multi discharge stand pipes and you have perhaps the perfect raw water system.
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