Pumping shower water overboard

My shower water runs into the bilge. The yardmaster says the shower-sump pump doesn't have the power to push water through the thru-hull which is a couple inches below waterline. (The sump-box isn't watertight.) He's suggesting creating an above-water-line thru-hull to correct the problem. What are your thoughts?

markpierce said:

My shower water runs into the bilge. The yardmaster says the shower-sump pump doesn't have the power to push water through the thru-hull which is a couple inches below waterline. (The sump-box isn't watertight.) He's suggesting creating an above-water-line thru-hull to correct the problem. What are your thoughts?

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Mark - Figure a way out of this buddy. Get a marine sanitation expert aboard if needed. You should not have shower water entering into your bilge. Ewwww - think about it!

Mark I don't see why the discharge being below the waterline would make it harder to pump. I assume the sump is higher than the waterline or water would flow in.
Has it worked in the past?
Is there a blockage in the line?
Most shower sumps use little bilge pumps. A common failure mode for these is that the impeller starts slipping on the shaft. The pump runs, it just won't move water. It can drive you crazy trying to figure out what's wrong.

Is your sump below the waterline but the discharge hose goes up to a vented loop?

I`ve only ever seen these outlets about/above the waterline. If that was intended, could the Coot be sitting a little lower than usual. Does it mean seawater can flow down into the shower sump? The unsealed shower sump draining to the bilge! Refueled and watered lately? Bilge pumps in good order?
Cutting a new exit thru hull and closing the existing one seems an excessive solution. Is this a new problem or has it always been like this? How about trying a more powerful pump?

The Coot is always "sitting" normal. The sump/pump is a foot or so below waterline. Used the shower less than a handful of times, always without successfully pumping water overboard. Definitely need a more powerful pump (hate the idea of another hole in the hull), but the yard says a larger pump won't fit in the box and that discharge below waterline is a design flaw. But then, why not a larger box? (The sump pump works OK when the boat is out of the water.)

Get rid of the sump and plumb it directly into a diaphragm pump through a vented loop then overboard. Works on my boat, just turn on the pump when you want the water out. Diaphragm pump eats everything. Closed system, no spooge in the bilge.

In my opinion, the complexity and failure rate of shower sumps isn't worth the trade off to just eliminate a manual switch.

Mark-like Bruce, I have never seen a drain below the waterline (except for the black water discharge). We have 5 gray water through hulls and all are above the water line. The design specs call for the at least 3" above the DWL. Our shower sump is just below the waterline so that line has a loop that rises about 10" above the waterline. So the sump pump is lifting the water about 18-20 inches. No problems with it in about 4 years. I would explore the option of moving the through hull above the WL.

markpierce said:

The Coot is always "sitting" normal. The sump/pump is a foot or so below waterline. Used the shower less than a handful of times, always without successfully pumping water overboard. Definitely need a more powerful pump (hate the idea of another hole in the hull), but the yard says a larger pump won't fit in the box and that discharge below waterline is a design flaw. But then, why not a larger box? (The sump pump works OK when the boat is out of the water.)

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Your yard guy is wrong.

Moving the thru-hull above the waterline will NOT make it easier to pump. The hydrostatic pressure on the pump discharge will be HIGHER if you do this.

Think about it. The total height of the water column from the pump discharge to the outside water level (as it is now) is lower than the water column required to pump above the water line.

It sounds like you need a different pump. Not necessarily bigger, just one that has a higher output pressure.


Moving the thru-hull is a separate issue. Either way, you'll need to sort out the pump issue.

How about an inline pump? Large as you like, but needs to have run dry ability if you use it manually. Or trigger the inline pump off the existing switch in the sump.
Even the bigger shower sump you suggested, accommodating a bigger pump, beats welding a patch and cutting into the hull again,make that the last resort.
(Odd set up on my IG, everything grey leads to one sump, which has a seriously big and original looking pump, with flipper switch.)

Mark-- On our boat the shower has a collection pan under the teak grate and a hose from the drain in the pan goes to a pump in the engine room which pumps the water from the pan out a through-hull about a foot above the waterline.

Presumably your boat has a bilge pump or two that discharges above the waterline. Perhaps the pump for the shower sump could be plumbed to the same through-hull used by a bilge pump with a T or Y fitting. Then you wouldn't need to have another hole cut in your hull. I would think the plumbing could be arranged so the shower water wouldn't run back down the bilge pump hose into the bilge.

Our galley sink drain is like that. The hose from the bilge pump ties into the vertical sink drain line at a downward angle. So the water from both goes out the above-the-waterline through-hull, but since water can't run uphill the the water from the sink can't get into the bilge pump hose.

"I don't see why the discharge being below the waterline would make it harder to pump. I assume the sump is higher than the waterline or water would flow in."

On ships the bilge pump outlet is below the WL so no lifting is required.Vastly more efficient.

A pump is not a seacock , so some sort of valve will be required.

I have never heard of a valid reason to not drain shower water into the bilge.

The soapy water can help keep the bilge sweet We have done it for decades with no problem or issues..

If a dedicated thru hull , past any heeled water line is not to your liking . perhaps feeding it into the sink could be done.

On one occasion we had a used lube oil spill into the bilge , and by pumping it into the sink, that had a bunch of oil absorbing pads , were able to collect the oil with out a vi$it from the Sheen Police.

I am in the BS camp that the pump wouldn't just start, fill the line, create a siphon and it would drain as Parks mentioned...otherwise the reverse would happen.

My relatively new shower sump by Rule had a badly designed check valve right at the pump exit of the sump. The pump couldn't push past it. Got rid of it and now the pump cycles a few more times with drains back...but at least it pumps overboard.

FF said:

I have never heard of a valid reason to not drain shower water into the bilge.

The soapy water can help keep the bilge sweet We have done it for decades with no problem or issues..

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General washed off grime, hairs, dead skin, and other body "items/juices" have never been a bother? Reason it is called gray water is because of the detergents and human "things" included in the mix. Doesn't the bilge become coated... especially in the area where the draining originates? Inside a home shower's pipes can get layered with washed off body junk.

We have straight-line independent bilge pump with switch at each shower that can be activated at will when water begins to build in shower pan (low flow shower heads with thoughtfully limited shower duration). Pump is just below pan level. Both showers discharge above water. I do not like shower sumps... too many problems.

BTW - When needed (not too often as we swim a lot) our shower time and water usage is minimal with bio-degradable soap.

Happy Shower Daze! - Art

Mine has no sump. The drain line passes to the pump remote mounted in the ER which pumps the shower water overboard via an above waterline thru hull.

I don't seed the harm in having a dedicated above wl thru hull.

FlyWright said:

Mine has no sump. The drain line passes to the pump remote mounted in the ER which pumps the shower water overboard via an above waterline thru hull.

I don't seed the harm in having a dedicated above wl thru hull.

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No harm / No foul... (build-up/smell that is)!

Soimething doesn't make sense. If the thru hull is a couple inches below the water line and the sump pump is a foot or so below the water line, what is keeping water from draining back into the sump through the pump from the thru hull?

It sounds to me like the pump is fighting the water pressure from the thru hull and sump being located below the water line. Or you have a inline check valve and the pump can't force it open against the water pressure on the other side of it.

Either way it should not have been plumbed that way. Now you could still use that below water line thru hull for the drain if you can set it up like a stand pipe and run the pump discharge hose first up above the water line then down to the thru hull. Stand pipe above the water line "Christmas trees" multi hose discharges fitted to below the water line outlets are common in larger boats.

Otherwise just cap it off and put in another thru hull just above the water for the pump to discharge to.

There is nothing complicated to any of this. But you damn sure don't your shower sump discharging all that soap, body scum and hair into your bilge.

Unless of course FF is going to volunteer to fly in and clean your bilge after ever time you take a shower.

sump

I don't care for using the bilge as sump because of possibility of human waste from a guest possibly fouling up the bilge. In my humble opinion any through hull below the waterline line needs a valve. Why not make life simpler and installed a new through hull above the water line and a new shower sump with a automatic submersable bilge pump. That's my set up using a 8d battery box and lid. Its bullet prove.

It is utterly disgusting to pump shower water overboard in areas others may use that water....for swimming and such...as fecal matter does go into the shower sump more than occasionally.

For gosh sakes...it is way less sanitary than elcectroscan waste water.

I suggest leaving it in your own boat and having a pump out dispose of it.

I think there's some confusion here about the way the gray water plumbing usually works. In my experience most sinks are above the waterline and so water can drain from them to a thru-hull below the waterline with no need for a pump. Most shower and tub drains are below the waterline and so cannot drain to any through hull - a sump pump is needed. If the thru-hull is below the waterline there needs to be a way to ensure water doesn't flow into the boat through the pump. A common way to do this is via a loop that goes up from the thru-hull to a point above the waterline and then u-turns back down to the sump pump. At the top is an anti-siphon valve. This means that the sump pump has to be able to lift the water to the top of the loop which may be a few feet above the pump itself. This loop/anti-siphon arrangement is frequently used on above water-line through hulls too (it is on my boat) since they may be below the waterline when the boat heels.

So in Mark's situation he will need some kind of pump that can push the water above the waterline - wherever the thru-hull is located. Perhaps the yard was thinking that there would be no need for the loop with an above waterline thru-hull and so a lower power pump could work since the actual height pumped would be less.

Mark - do you have a loop as described? I would be looking at fixing your pump situation rather than drilling another hole in your hull. There's no guarantee that your pump will work even after this is done.

Richard

Our boats shower/tub drained into a large fiberglass open top box in the engine room between the stringers when we got the boat, took the drain line out the box, trashed the pump and cleaned..cleaned..cleaned the box. Mounted a Whale Gulper in the tub drain hose and new hose to a thru hull above the waterline with a switch for the pump in the head. Now the water goes directly overboard from the tub, works great and the old sump box is no longer a source of odour.....

markpierce said:

My shower water runs into the bilge. The yardmaster says the shower-sump pump doesn't have the power to push water through the thru-hull which is a couple inches below waterline.

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Others nailed it with a check valve your pump cannot overcome the back pressure of to drain. You stating it works fine hauled confirms the problem is back pressure and nothing else.

markpierce said:

He's suggesting creating an above-water-line thru-hull to correct the problem. What are your thoughts?

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Completely agree with his suggestion. Be sure a loop of hose above the sea cock is present when job is complete.

Now, about this sump box that is not water tight....

psneeld said:

It is utterly disgusting to pump shower water overboard in areas others may use that water....for swimming and such...as fecal matter does go into the shower sump more than occasionally.

For gosh sakes...it is way less sanitary than elcectroscan waste water.

I suggest leaving it in your own boat and having a pump out dispose of it.

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This is not a serious post, right?

CPseudonym said:

Others nailed it with a check valve your pump cannot overcome the back pressure of to drain. You stating it works fine hauled confirms the problem is back pressure and nothing else.




Completely agree with his suggestion. Be sure a loop of hose above the sea cock is present when job is complete.

Now, about this sump box that is not water tight....

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Good suggestions.

It is also possible the the power of the pump cannot exceed the inertia of pumping into water as opposed to pumping into air.

Mark the first thing I would check is the sizes of the drain hose and the through hull. ( what size is the through hull?) It is possible that the pump cannot overcome the head pressure through the hose and fittings (and check valve if present) sufficiently to keep up with the water flow of the shower head. You may solve your problem by just installing larger hoses on the interior of the system which will significantly lower the head pressure and increase flow (GPM). Worst case, you will have to do what the yard suggests. You could also try using a shower head with a lower GPM so the pump can keep up with it. However, it does seem odd that the shower sump is below the water line since its a sump line.

I'm having a hard time with the idea that drilling a hole in the hull is a good solution for an underpowered pump. I don't agree that the current design is unworkable. I don't like the idea of a simple check-valve as opposed to a loop and anti-siphon valve.

There is another alternative. Do you have a sink close by to the sump pump? In my sailboat the sump pump is connected to the drain hose from the head sink (at a point above the waterline). When it pumps, the sump water backs up into the sink which acts as a holding tank while the water drains through the sink's thru-hull. The amount of water is never enough to overfill the sink. A quick rinse of the sink afterwards is all that is needed. The sink acts as the anti-siphon valve. It's crude but effective.

Richard

Mark, do you have a vented loop to keep water from back syphoning into your bilge. It seems that you are dependent upon one check valve that could easily malfunction and sink the Coot. I would cap off the existing thru hull fitting until used for an intake later.

Shower water has hair and human skin cells as well as other organic matter. It should not drain into the bilge. Over time sewer odors would be evident.

bligh said:

Good suggestions.

It is also possible the the pewr of the pump cannot exceed the inertia of pumping into water as opposed to pumping into air.

Mark the first thing I would check is the sizes of the drain hose and the through hull. ( what size is the through hull?) It is possible that the pump cannot overcome the head pressure through the hose and fittings (and check valve if present) sufficiently to keep up with the water flow of the shower head. You may solve your problem by just installing larger hoses on the interior of the system which will significantly lower the head pressure and increase flow (GPM). Worst case, you will have to do what the yard suggests. You could also try using a shower head with a lower GPM so the pump can keep up with it. However, it does seem odd that the shower sump is below the water line since its a sump line.

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How would bigger hoses increase the output of a pump passed it's rated output or change the head pressure it sees?

If it's let's say, trying to pumping up vertically 4 feet with 3/4" hose, how does that rise change if you switch to 1 1/2" hose?

Wouldn't 1 1/2" hose hold more volume of and thus weight of water making it even harder for the pump to over come it?

Moonstruck said:

...It seems that you are dependent upon one check valve that could easily malfunction and sink the Coot...

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My concern too.

Capt.Bill11 said:

Wouldn't 1 1/2" hose hold more volume of and thus weight of water making it even harder for the pump to over come it?

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No - static pressure is only dependent on the "head" of water above the point pressure is being measured, whether that's a 1" hose or the entire ocean. Flow rate is another thing though - and for a pump to increase its flow rate through a narrower hose it has to increase pressure. So a wider hose may help the flow rate but shouldn't make any difference to the ability for the pump to pump. At some point, with a long enough and narrow enough piece of hose that friction in the tube may become a factor. I doubt it's significant in this case.

Richard

Thanks for all the suggestions. I'll discuss them with the yard.

markpierce said:

Thanks for all the suggestions. I'll discuss them with the yard.

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There is something just not to design specifications...that said, my suggestion is to contact the builder. They should know the boat and setup better than anyone. I would email Seahorse before doing anything.