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Old 06-08-2012, 20:14   #1
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Please No More Holes in the Boat !

When I bought the boat I found a 1" thru-hull that used to service the POs generator. The genset had been removed and the sea cock was closed. I installed a second A/C unit and used this thru-hull for the cooling water pump. Three years later I installed a Northern Lights 6kw and thought to share the thru-hull with the air conditioner. It worked fine for a year and then the genset began to suck water out of the A/C pump. Both strainers are below the waterline as well as the A/C pump and the genset raw water pump. There seems to be plenty of water available to both devices when I remove either hose, but the genset wins the battle and the A/C gets no cooling water. I considered installing some sort of reservoir or manifold before the strainers, but after thinking that through, I don't believe it would improve things. Is my only hope to haul the boat and install another thru-hull for the genset? I really don't want to do that. Any ideas?

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Old 06-08-2012, 20:29   #2
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Re: Please no more holes in the boat!

Install a flowback preventer to avoid water being sucked out of the AC but you still have the issue of insufficient water for both devices.
BTW, I would install a flowback preventer on both lines, just to be safe.
As far as water flow is concerned, either the through hull isn't big enough (or it's obstructed somehow) or the pump that circulates the AC cooling water isn't strong enough to overcome a presumably small negative pressure resulting from the generator sucking in cooling water (is the pump defective maybe ?).

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Old 06-08-2012, 21:37   #3
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Re: Please no more holes in the boat!

Originally Posted by F51 View Post
It worked fine for a year and then the genset began to suck water out of the A/C pump.
So what changed? Maybe your thru-hull is plugged. Did you check that?
Wherever we want to go, we go. That's what a ship is you know - it's not just a keel and a hull and a deck and sails, that's what a ship needs. But what a ship is...really is, is freedom. ~Johnny Depp as Capt. Jack Sparrow
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Old 08-08-2012, 20:51   #4
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Re: Please no more holes in the boat!

You need to know two important values.
1. the pump capacity of the A/C unit
2. the pump capacity of the gen set
Having established this you need a thru-hull large enough for the combined flow. Then install a "tee" or "Y" with the inlet the size of the thru-hull and each branch the size of the capacity of each unit. This well better control how much water each recieves. The other way is to install a restrictor valve on the one sucking up all the water. You may need to install flow meters on each line to make sure they get enough water.
wow ... my heat transfer and fluid flow course I took 40 years ago finally did pay off. ... lol

The other, and actually more practical solution would be to install an additional large capacity pump right off the thru-hull, then split to each unit.
Lowell - s/v Chasing Summer - Spencer 42/hull 17 ... happy sailing
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