A/C raw water pick up

This make me wonder if it isn’t a good time for you to install a “closed system”. One pump with one scoop, one sea strainer, one seacock, etc to a heat exchanger and one pump to circulate a closed system to the a/c units.

My boat has four a/c units (2x 12kBTU + 2x 8kBTU). One cooling water pump. I have an oversized strainer, which is for me a major benefit .

Two feet the temp is about the same, 7' and the temp is cooler.

I can't run my ac under way as it picks up air like you said and the pump loses prime

What good is that? Have you tried a clam shell on it to direct water up there?

One thru-hull located at optimum place, one large strainer, one oversized pump. I find it reliable because is much simpler to inspect and perform routine checks.

Pascal, my boat has four a/c units cooled through a raw water pump. I mentioned the closed loop because it seems to be getting momentum in the industry.

The benefits I see from a closed system are:
- always clean pipes and clean a/c units
- less risk of sinking due to seawater intrusion because seawater circuit would be short and simple, possibly 100% visible in the engine room.

The ideal configuration would be a centerline pick-up / mini-sea chest with a manifold to direct raw water to your users, sized for the necessary flow of water. Vee - hulls with pick-ups 2 feet inboard are less than ideal as you have found out and Bertram or the installer took the easy way out on this one.

I ran a closed system for about 6 years. My boat is a 70' aluminum motoryacht. Pascal will remember my boat as he did the delivery (rodeo!) when I bought her. She had an interesting keel cooled closed loop system, which was excellent in theory. The problem is in the Florida Keys (bayside) the water is constantly 90 degrees during the summer months, much warmer than the 60 or 70 degree cool great lakes. The amount of surface area the current closed system had was too low and loop temperatures would often approach 115 degrees causing the system to be inefficient.

So, trying to keep the benefits of a closed loop system, I added a Sen-Dure 180,000BTU heat exchanger and decommissioned the keel cooler. The heat exchanger was designed by Flagship Marine https://www.flagshipmarine.com/heatexchanger.html One pump pushing seawater through the heat exchanger in the engine room and another pump circulating fresh water through the loop. This was more efficient, but I was still dealing with 105+ degree loop temperatures.

I'm unsure if it was due to constant use 24 hours a day 365 days a year (live aboard and air conditioning running is pretty much all year for us) or an undetected bonding issue (you'd think my aluminum hull would take the brunt of it... not the CuNi core), but the heat exhangers proved to be less than durable. I dealt with the manufacturer and had a mechanic check for a stray current, but everything was fine. Leaks would develop at the end cap of the core bundles on the raw water side. I would check the zincs monthly and they always were in tact and no more than 50% done. I went through 3 heat exchangers in 3 years. At $2,800 each I just decided to decommission the heat exhanger and pump raw water through the boat to my 7 stand alone systems.

I should have done this a long time ago! My air con is much more efficient and I'm consuming less electricity. A closed system is a great idea if you are sitting on sea water that is 70 degrees or cooler, but in the tropics it is inefficient. You are still pumping seawater into your boat, but it is nice to have it isolated to one area. I could have chased down the issue with the heat exchanger getting chewed up, but it just made more sense to keep it simple.

Yeah Flagship makes quality stuff. Sen-dure actually made the heat exchangers. They make quality stuff too. The reason for repeated failure remains a mystery, but I'm over it when it comes to a fresh water loop system.