Engine Heat Exchanger And Strainer.Adding a wash down pump.

Would there be any issues plumbing a wash down pump off the water strainer feeding the engine heat exchanger?I know it's not recommended.I just don't want to put more holes in my hull than necessary.The wash down would be used on the anchor and rear deck.

Are there any other through-hulls that you might be able to T into for the washdown pump line. eg feed to head?? We have our deckwash T'd into the watermaker feed line just after the through-hull. Since we do not make drinking water while washing the anchor/deck, no problem. If the engine feed is your only option, I would be careful the first few times you run the deckwash while operating the main engine to make sure that the deckwash pump is not starving the engine feed. I assume you will need to run the engine while washing down the anchor. FWIW if your main impeller is in decent shape, I would guess it is more likely the engine will starve the deckwash.

I would think you could do it....but you will want to install a valve in line from the T and before the pump to prevent any air leaking back into the engine intake line...and I would not be inclined to run that pump while the engine is running....

Chrisjs said:

Are there any other through-hulls that you might be able to T into for the washdown pump line. eg feed to head?? We have our deckwash T'd into the watermaker feed line just after the through-hull. Since we do not make drinking water while washing the anchor/deck, no problem. If the engine feed is your only option, I would be careful the first few times you run the deckwash while operating the main engine to make sure that the deckwash pump is not starving the engine feed. I assume you will need to run the engine while washing down the anchor. FWIW if your main impeller is in decent shape, I would guess it is more likely the engine will starve the deckwash.

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This is going to be for a build I am planning for spring 2013.

JAT said:

I would think you could do it....but you will want to install a valve in line from the T and before the pump to prevent any air leaking back into the engine intake line...and I would not be inclined to run that pump while the engine is running....

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I'd use a valve because of the possibility of a leak and for the reasons you mentioned.


The engine would probably be idling while pulling the anchor and washing it down.Depends on wind and current,if any.Washing down the rear deck,I will probably be anchored with the engine off.I'm sure both will not be used at the same time.

I ran my washdown off my genny strainer. No problems using the washdown while the genny is running. I just had to size the thru hull and strainer up so the washdown would have water available.

You could have a single thru hull and seacock feeding a manifold from which you would supply water to all systems if you really feel it is necessary. Just make sure it is large enough to supply everything at once.

My washdown pump shares a thruhull and seacock with my raw water head. The original owner had installed it with a valve to feed one or the other, but I determined that that was not necessary and was cumbersom to use so I replaced the valve with a "T". It works just fine.

the only thing that will be on the thru hull would be the engine heat exchanger and the wash down pumps.Without doing the math,I think a 1.5 inch thru hull would be more than enough to feed them,since the wash down pump wouldn't be run much with the engine running.This will be something I keep researching until I know as much as possible.

ben2go said:

the only thing that will be on the thru hull would be the engine heat exchanger and the wash down pumps.Without doing the math,I think a 1.5 inch thru hull would be more than enough to feed them,since the wash down pump wouldn't be run much with the engine running.This will be something I keep researching until I know as much as possible.

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It's not a good idea to make an assumption about when the washdown would be used because you, a crew member, or a future owner might forget or not know about your assumption.

Since you are apparently building this boat from the keel up, it's just as easy to use larger plumbing and not risk a problem.

But how about this - give the engine its own dedicated water supply and let the washdown system, air conditioning, genset, and whatever else share another intake.

ben2go said:

the only thing that will be on the thru hull would be the engine heat exchanger and the wash down pumps.Without doing the math,I think a 1.5 inch thru hull would be more than enough to feed them,since the wash down pump wouldn't be run much with the engine running.This will be something I keep researching until I know as much as possible.

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why not just go with a true sea chest.....that way everyvalves happy

I tend to agree w psneeld. Other than the sea chest I've been halving many of the same thoughts. If I can't maintain my through hull for the head and holding tank in Washington state I'll use that through hull. But if I can I'll be considering the discharge side of the sea water pump hose near the pump. My 40hp engine may not have enough volume to feed a wash down pump so I may need to use the wash down w the engine at 1800rpm and placard the switch. Also I would feel more comfortable w a flow sensor in the pump to heat exchanger hose. But whenever I think about it I tend to think a dedicated extra through hull for the wash down water may to probably will be the better way to supply the wash down pump. A well installed and maintained through hull in a good fiberglass hull is quite safe, dependable and even durable. I think I'll probably go w the extra through hull.
Speaking of the sea chest I wonder if they are often higher than the water level. That is regarding the inner chamber and then would the water tight integrity of a well made chest insure that the chest would remain completely flooded at all times? If not then the sea chest would be useable only on fairly deep draft vessels. That may be a consideration for Ben2go.

This is what Groco has to say on the subject. They include a nice size chart.

Good info and thanks for the guidance.I only have raw water supply for two items,the heat exchanger for the engine and the wash down pump.I really don't want to put two thru hulls into my fresh wood hull.Since engine cooling is critical,it looks like it may be safer and simpler to install two thru hulls.I'm searching thru manuals trying to find the info on how much a 3.0L Mercruiser sterndrive will pump through the heat exchanger.I can't seem to find the info so I can do the math for total flow.

ben2go said:

Good info and thanks for the guidance.I only have raw water supply for two items,the heat exchanger for the engine and the wash down pump.I really don't want to put two thru hulls into my fresh wood hull.Since engine cooling is critical,it looks like it may be safer and simpler to install two thru hulls.I'm searching thru manuals trying to find the info on how much a 3.0L Mercruiser sterndrive will pump through the heat exchanger.I can't seem to find the info so I can do the math for total flow.

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If you're using a sterndrive, I wouldn't even consider trying to tap off the raw water intake.

As far as holes in the hull, properly done, these holes don't seem to be a problem. It's more likely that a torn or failed bellows will let water into your boat than a failed seacock.

Your boat won't have air conditioning? A genset?

rwidman said:

If you're using a sterndrive, I wouldn't even consider trying to tap off the raw water intake.

As far as holes in the hull, properly done, these holes don't seem to be a problem. It's more likely that a torn or failed bellows will let water into your boat than a failed seacock.

Your boat won't have air conditioning? A genset?

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When I do the loop,I will add A/C.I think I will use an on deck small portable Honda genny.I will keep my options open but I don't have plans for much running on AC power.

ben2go said:

When I do the loop,I will add A/C.I think I will use an on deck small portable Honda genny.I will keep my options open but I don't have plans for much running on AC power.

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You will need cooling water for an air conditioner unless you use a household window unit or RV rooftop unit.

While my wife and I do quite well without AC on the hook, it is nice to pull into a marina and have AC with shorepower.

There are a lot of safety issues with using a gasoline powered portable generator on a boat. It's not something I would do although I have friends who do it.

rwidman said:

You could have a single thru hull and seacock feeding a manifold from which you would supply water to all systems if you really feel it is necessary. Just make sure it is large enough to supply everything at once.

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If I had a genset or raw-water washdown system, I'd run them off my large-capacity strainer's manifold.