Shared Thru-hull fitting

[tfoster]

I am contemplating adding air conditioning to my 1990 Hunter 30g. To avoid the expense of a haul-out which is about a grand at our local marina, I would like to share the seawater line for the engine with the seawater line for the A/C. Since the A/C is only run on shore power, I would not be running the engine when the A/C was operating.

My concern is whether the suction of the seawater pump on the engine would have any adverse effect on the seawater pump on the A/C installation.

I would apprecaite your thoughts.

 

[Rich Stidger]

The engine pump is a positive-flow rubber impeller pump that will suck all the water out of the A/C unless you have a check valve that will close positively tight. If the check valve leaks and you do pull all the water out of the A/C you will then pull air into the engine seawater pump and you could burn up the impeller and overheat the engine.

Yes, this is a worst case scenario, but how lucky are you really?

The other choice is to insert a hand valve into the A/C line that you will open and close for A/C use. But, if you forget to to close the valve it's back to the worst-case scenario.....

Can you tap into another thruhull until you next haul the boat and put in a dedicated inlet?

 

[Bill Roosa]

yes there will be suckage

The raw water pump will no doubt suck air through the AC cooling plumbing when the engine is running. This is just a matter of putting an additional ball valve to isolate the AC plumbing from the engine cooling though.

Why put AC on a boat anyway? If you are going to stay at the dock just stay home and enjoy digital TV, a real reefer, flush toilets...... all the comforts of home. It is not like you can use the thing at anchor.
I have noticed that, at least on my boat, there is a really large body of water right behind it. Your boat may be different though. Even in the heat of summer it is quite refreshing to just sit on the stern with my feet in the water or even better take a dip (avoiding the jellies of course) and let yourself air dry. 12 volt fans are handy for sleeping and can be used while at anchor.
the reason I ask is I have an AC unit on the boat. PO had it installed or it was factory. I have only use the thing once and I was pretty disapointed with the result. You had to stay in the cabin to stay cool. I suspect that is true of all AC units BTW. the view from here is pretty limited so unless you like looking at teak furnature...... Perhaps I bought my SAIL boat for a different reason than others.

 

[Steve Dion]

There was a posting like this a couple of months ago where someone had an issue with this.

If you insist on doing it this way, I suggest you have it setup so you can bypass either the engine or the AC, so there is no chance that you will have any issues.

 

[tfoster]

Another alternative is the water intake for the head. My concern there was sucking less than clean water out of the flush pump on the head by the A/C pump. Again this could be resolved with a check valve or better yet a hand-closed valve, but the same issues are present if one forgets....

 

[Steve Dion]

I would suggest the engine intake. It has a strainer (which may or may not be an issue). You could use a 3 way valve to control the direction of the water flow.

 

[Steve Dion]

An Apollo 3 way bronze valve can be purchased for about $40. This will give you a positive flow to either the engine or AC or all off.

 

[Ken13559]

Another alternative is the water intake for the head. My concern there was sucking less than clean water out of the flush pump on the head by the A/C pump. Again this could be resolved with a check valve or better yet a hand-closed valve, but the same issues are present if one forgets....

I did just that for my aircon. Sharing thru-hull with head water intake. No problem whatsoever. Both function at same time. No check valves or addition isolation valve.:dance:

 

[Calaloo]

I have a shared intake for the engine and A/C for over five years now and never had a problem. I used a two way valve from WM which acts like a Y valve. What is great about this is that when is turned to engine, the A/C side closes off and will maintain the prime while sailing. You have to find a way to install the valve on a fixed place because it will need a little force to turn it and the hose alone will not hold it from turning. The fewer thru halls the better.
Calaloo

 

[Sailgunner]

I used the same intake for the head and A/C on my old 30T. However, since I was on a lake I convereted the head overboard discharge to the intake for the head and A/C. I then used the old head intake for the A/C discharge. It worked great.