Let's talk about thru hulls for drains,bilge pumps and gray water.

ben2go · Jul 21, 2014

I frequent a few boaty forums.One complaint I have seen is the level of thru hulls for bilge pumps,a/c drains,grey water,and gensets.Main complaint I read about is the noise of them expelling water overboard.I was on a larger run about/ski boat that had one of the thru hulls almost at the top of the hull on the side of the boat.It was quite annoying listening to it at idle.Not sure what it was for but it consistently dropped water about two feet to the lake.

1)So how do you feel about your thru hulls?

2)Where are they in relation to the hull water line?

3)Since my boat hasn't been built yet,where would the best location be to keep them quite and trouble free?

4)I know I will have three gray water lines,galley sink,head,sink,shower.Can these be plumbed to one through hull?There will be a diverter valve to send everything to a gray water tank when the need arises.

5)Water are the pitfalls with having the thru hulls just above water line?I know I will need anti siphoning valves.

If there's any other advice about thru hulls,I am all ears.

healhustler · Jul 21, 2014

I also have one thru-hull about 2 ft. above the waterline for the A/C raw-water cooling dump. The rest are near or below waterline and I'd love to eliminate the majority of them using a sea-chest. A marvelous example of a sea-chest system is in the Great Harbour GH and N-series engine rooms. The extra plumbing can be an issue for low profile engine rooms and limited space. This is a photo of the starboard half of the N-37 engine room (no kidding). The other half looks the same except with a higher ceiling. The sea chest sits between the twin Yanmars as shown by red arrow.

Russell Clifton · Jul 21, 2014

Are you sure that's a engine room on a boat? Looks like it could be a generator room for a hospital.:lol

ben2go · Jul 21, 2014

healhustler said:
I also have one thru-hull about 2 ft. above the waterline for the A/C raw-water cooling dump. The rest are near or below waterline and I'd love to eliminate the majority of them using a sea-chest. A marvelous example of a sea-chest system is in the Great Harbour GH and N-series engine rooms. The extra plumbing can be an issue for low profile engine rooms and limited space. This is a photo of the starboard half of the N-37 engine room (no kidding). The other half looks the same except with a higher ceiling. The sea chest sits between the twin Yanmars as shown by red arrow.

Oh yeah.I forgot about those.That engine room is HUGE.I will have an I/O with an engine cover.I don't thing there will be room for one or maybe I can reverse engineer something like it that will work.It would be nice to have one thru hull with all drains leading to it.Good thing is,all my thru hull drains will be on the same side.

ben2go · Jul 21, 2014

Russell Clifton said:
Are you sure that's a engine room on a boat? Looks like it could be a generator room for a hospital.:lol

Capt.Bill11 · Jul 21, 2014

People on boats or near the water complaining about splashing noises baffle me. If you live on or near the water and don't like the noises water makes, maybe it's time to move to the desert.

Other wise a stand pipe discharge Christmas tree is the best way to eliminate water discharge noise.

psneeld · Jul 21, 2014

Some of the Sea Rays I worked on back in the early 2000's had a 6" or so diameter PVC pipe glassed to the hull in the engineroom/lazarette....all the discharges and sumps went to this pipe and it drained out the transom or into the underwater engine exhaust...I forget now but a single drain for many different systems is definitely possible and sounds like a good idea.

ben2go · Jul 21, 2014

I am slowly working out ideas in my head.My hull draft will only be 8 to 10 inches.I had thought about one for the water intake side, but my build wouldn't have enough draft, IMHO.From research I have done so far,most boats with intake stand pipes, or sea chests, are displacement vessels with drafts around,or deeper,that 3 feet.Not real sure how well one would work on a planning hull.

HopCar · Jul 22, 2014

My air conditioner discharge is very close to my head when I sleep. I kind of like listening to it. I guess it's like one of those white noise generators. The discharge is only about a foot above the waterline so it doesn't make a lot of noise.

You mentioned a grey water tank. I've never run into an area where you couldn't discharge grey water. You might want to do some research about the areas where you'll cruise before you install the tank.

BruceK · Jul 22, 2014

My IG runs the shower, vanity basin, sink, to a large shower sump like box, which pumps out, it has a bilge pump switch and pump. No grey holding tank, I don`t believe they are required. Yet.

Aquabelle · Jul 22, 2014

If I were building new, I'd go the sea chest route

twistedtree · Jul 22, 2014

Interesting idea to use a sea chest as a common discharge. Normally they are used as a common intake.

Sea chests can have some benefits, but maybe not as much as might appear on the surface. Thru hull failures are typically at the connecting hoses, or degradation and collapse of the valve/thruhull metal. Non of that goes away on a sea chest, and it is all exposed to the same sea water as with individual thruhulls. The picture posed earlier is a good illustration. I count 5 thruhulls, 5 valves, and 5 hose connection points. All are exposed to the open water just like if they were run right through the hull rather than the sea chest. Plus, you introduce the sea chest itself as a new potential failure point.

So, they can have advantages, but reducing the number of water intrusion points isn't one of them.

Shoalwaters · Jul 22, 2014

psneeld said:
Some of the Sea Rays I worked on back in the early 2000's had a 6" or so diameter PVC pipe glassed to the hull in the engineroom/lazarette....all the discharges and sumps went to this pipe and it drained out the transom or into the underwater engine exhaust...I forget now but a single drain for many different systems is definitely possible and sounds like a good idea.

Some of the larger Bertrams had the same arrangement: simple, effective and reduced the number of thru-hulls. They even had screw caps at the inboard end and on a centrally located "Y" for cleanout if required. I would definitely consider such a system on a new build.

Ben: As an alternative to anti-syphone valves, you might consider looping the discharge hoses up under the side deck and then down to the thru-hulls. Less things to go wrong.

I agree with you about a sea-chest probably not working too well in a planing hull. I suspect that most intakes would have problems in a planing hull with an 8"/10" draft - lots of air being ingested along with the water. Self-priming pumps with rubber impellers don't mind this too much, but the type used for a/c raw water pumps tend to fill with air and loose prime. I think Ski in NC had some good info on this.

Granted that fittings mounted on a sea-chest are subject to many of the same problems as when mounted direct to the hull. The advantage is that they are easy to see, so inspection and maintenance tend to be better.

Discharging grey water into a sea-chest would likely have a couple of drawbacks:

1) Two sea-chests would be required: one for inlet and one for discharge; otherwise your heat exchangers and a/c units would be running on a diet of potato peelings, coffee grounds and hair.

2) Some of the stuff in grey water is buoyant and would form a floating (eventually stinking) layer in the sea-chest.

healhustler · Jul 22, 2014

Ben: Looking through the archives, I remembered seeing this application of a sea-chest arrangement on a Volvo inboard. I always thought that if and when I ever did eliminate the thru-hulls, this is how I would do it. It's a stainless steel unit with one major feed from a single thru-hull, and the various devices are plumbed to it. Given that you've got a planing hull, putting the unit's thru-hull deep and centered in the hull would probably do it. More than that would be that a properly positioned, size-able sea-chest would tend to keep its water supply while underway, preventing loss of prime for those temperamental pumps like A/C.

kraftee · Jul 22, 2014

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.)

healhustler · Jul 22, 2014

Eric: Please stop torturing us with those GH engine room spec's!

I still dream of such an ER.

Your points are well taken about a sea-chest installation on an FD trawler, but can you comment on your Mirage planing hull designs. The original poster has a planing hull and might benefit from your input.

ben2go · Jul 22, 2014

HopCar said:
My air conditioner discharge is very close to my head when I sleep. I kind of like listening to it. I guess it's like one of those white noise generators. The discharge is only about a foot above the waterline so it doesn't make a lot of noise.

You mentioned a grey water tank. I've never run into an area where you couldn't discharge grey water. You might want to do some research about the areas where you'll cruise before you install the tank.

I haven't decided on the type of A/C yet.I'm real tempted to go roof top, because I can get them real cheap around here from wrecked travel trailers.The one noisy thru hull made a spitting sound.Thinking about it more,it sounded like a bilge pump was spitting the last little bit of water out, that it could suck up.

The grey water tank is for the inland lakes I will be in.Most of them do not allow grey water discharge.

BruceK said:
My IG runs the shower, vanity basin, sink, to a large shower sump like box, which pumps out, it has a bilge pump switch and pump. No grey holding tank, I don`t believe they are required. Yet.

Only required on inland lakes.Plus,we may have to make an emergency potty stop while hauling the boat overland.

Aquabelle said:
If I were building new, I'd go the sea chest route

twistedtree said:
Interesting idea to use a sea chest as a common discharge. Normally they are used as a common intake.

Sea chests can have some benefits, but maybe not as much as might appear on the surface. Thru hull failures are typically at the connecting hoses, or degradation and collapse of the valve/thruhull metal. Non of that goes away on a sea chest, and it is all exposed to the same sea water as with individual thruhulls. The picture posed earlier is a good illustration. I count 5 thruhulls, 5 valves, and 5 hose connection points. All are exposed to the open water just like if they were run right through the hull rather than the sea chest. Plus, you introduce the sea chest itself as a new potential failure point.

So, they can have advantages, but reducing the number of water intrusion points isn't one of them.

My thought is they will all be in one location,close to the engine,and can easily be inspected.If they're spread out through the boat and under things like the settee or galley,I may not check on them as much as I should.Outta sight outta mind.My boat will be a trailer trawler.

Oh yeah,no thru hulls on the outside of the hull would make for an interesting conversation.

Shoalwaters said:
Some of the larger Bertrams had the same arrangement: simple, effective and reduced the number of thru-hulls. They even had screw caps at the inboard end and on a centrally located "Y" for cleanout if required. I would definitely consider such a system on a new build.

I saw those during my research.Some guys install large air fittings,shut the intake valves and blow out the thru hull grate.It is a consideration.

Ben: As an alternative to anti-syphone valves, you might consider looping the discharge hoses up under the side deck and then down to the thru-hulls. Less things to go wrong.

I read about doing this in another thread.It would be better than dealing with those pesky anti-siphoning valves.

I agree with you about a sea-chest probably not working too well in a planing hull. I suspect that most intakes would have problems in a planing hull with an 8"/10" draft - lots of air being ingested along with the water. Self-priming pumps with rubber impellers don't mind this too much, but the type used for a/c raw water pumps tend to fill with air and loose prime. I think Ski in NC had some good info on this.

I saw where guys that have fishing boats are locating there thru hull section in the aft center on the hull or off to one side if the boat has a keel.This forces water into the stand pipe or sea chest.Venting the top to a vent under the gunnel prevents air lock.

Granted that fittings mounted on a sea-chest are subject to many of the same problems as when mounted direct to the hull. The advantage is that they are easy to see, so inspection and maintenance tend to be better.

Discharging grey water into a sea-chest would likely have a couple of drawbacks:

1) Two sea-chests would be required: one for inlet and one for discharge; otherwise your heat exchangers and a/c units would be running on a diet of potato peelings, coffee grounds and hair.

:lol: I agree.All of my discharge line will be on one side of the boat,so the discharge can be on one side and intake in the center or on the opposite side.

2) Some of the stuff in grey water is buoyant and would form a floating (eventually stinking) layer in the sea-chest.

I had though of this while doing research.I saw one boat had an downward angled discharge at waterline and there was a box made to the inside of the hull to hold everything as it flowed out.

healhustler said:
Ben: Looking through the archives, I remembered seeing this application of a sea-chest arrangement on a Volvo inboard. I always thought that if and when I ever did eliminate the thru-hulls, this is how I would do it. It's a stainless steel unit with one major feed from a single thru-hull, and the various devices are plumbed to it. Given that you've got a planing hull, putting the unit's thru-hull deep and centered in the hull would probably do it. More than that would be that a properly positioned, size-able sea-chest would tend to keep its water supply while underway, preventing loss of prime for those temperamental pumps like A/C.

I saw a lot of those during my research.Most went to a fiberglass box mounted to the keel or stringer with a clear lexan top.They were running one huge thru hull to feed a large standard thru hull valve and a short run of pip to the sea chest.

These are all good points.I'm getting my game plan together to talk to Jeff Spira about my build plans for his 30' Sitka.I have a feeling he may suggest another boat to build, and I would be ok with that.

ben2go · Jul 22, 2014

kraftee said:
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.)

Great info.I was typing my last post as you were posting.

That's a beautiful engine room.

Capt.Bill11 · Jul 22, 2014

twistedtree said:
Interesting idea to use a sea chest as a common discharge. Normally they are used as a common intake.

Just to be clear, on a discharge stand pipe, the section of pipe the discharge lines connect to is above the water line. So if the hose or connection of one of the discharge lines fails no water can back flow into the boat.

kraftee · Jul 22, 2014

Larry,

Sorry for the torture! We have never put a sea chest on our planning hulls. So I really couldn't speak to that. There are two main reasons for that. First, all of our planning hulls have been sterndrive or outboard (with an IPS boat under construction.) So, they are drawing their own water through the "foot" of the drive. Second, my big concern would not be so much getting water into the chest at speed. It would be the fact that as a planning hull comes up on plane, there is (as one poster pointed out) very little draft to the bottom of the hull. The way a sea chest functions, the waterline inside the sea chest is the waterline of the boat. So even if you could somehow get the water into the chest with a scoop or whatever, I am not sure you would have enough depth in the box to draw bubble-free water through! It would work fine at anchor though!

On the subject of grey water sea chests, we also put those on many of the trawlers. However, they are generally mounted on the starboard hull side and much (depending on the boat) of the grey water, bilge pump, and AC outflow is piped into them. Makes for only one hole instead of four or five. You can see it in the top right corner of this N37 engine room pic. It has a can of orange soda sitting on top of it (ignore the OTHER can of orange soda sitting on the top of the main fuel tank!)

ERIC

Capt.Bill11 · Jul 22, 2014

Most, if not all, Marlow's have sea chests. And most Marlow's can plane off.

Alaskan Sea-Duction · Jul 22, 2014

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.....

ben2go · Jul 22, 2014

Alaskan Sea-Duction said:
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.

caltexflanc · Jul 22, 2014

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.

FF · Jul 25, 2014

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.

twistedtree · Jul 25, 2014

kraftee said:
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.

Capt.Bill11 · Jul 25, 2014

twistedtree said:
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.

Let's talk about thru hulls for drains,bilge pumps and gray water.

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