For my main engine cooling I've decided to use a keel cooling system. Engine cooling seems to be one area of operating a boat that tends to give boat operators a large percentage of their problems and it is for this reason I've decided upon using the keel cooling method.
With a more conventional cooling system one sees on production trawlers, the engine sucks water in to the cooling system from outside the boat, cools the engine, then pumps the water overboard. The problem with this is that screens get plugged, impellers go bad, engine's overheat ( this can kill an engine in a moment), and maintenance for sure increases. Overall, the reliability of such a system is not very high and detracts from the boat as a whole in my opinion. The last thing I want to be dealing with on a night time passage is an overheating engine due to a Walmart baggie being sucked into the engine intake screen, or worse, loosing an engine due to a baggie that costs 1/10 of one penny.
My main engine cooler consists of 60' of 5" channel welded to the hull. The water basically goes in one end of the channel cooler, runs its route through the channel, then returns back to the engine out the other end of the channel as cooled water. I've seen other builders use split pipe on the hull, but for me the channel was easier to work with and I'm pleased with it's form. A young guy from our neighborhood was an engineering student at Utah State University ( Justine Gastrich), and needed a project during his senior year as a requirement for graduation. He calculated and designed the requirements for cooling my engine by using the 5" channel as a cooler. His report was very thorough and it was kind of neat seeing the boat build put to that use. The report that Justin developed was very much in line with all the rule of thumb designs other builders used, so I went with what Justin recommended.
I had to alter the engine a little to make the keel cooler work better but this was not a big deal. Because of the large volume of coolant I needed an expansion tank to give the coolant a place to go as things up to operating temperature. I also will use this expansion tank as the fill point to add coolant and a way to get the air out of the system. My engine modification was basically removing the fill cap from the engine heat exchanger and moving it to the expansion tank, then connecting the expansion tank back to the engine heat exchanger. The expansion tank is at a slightly higher elevation than the engines heat exchanger so getting the air out should be easier. I'm using extended life coolant that is premixed using distilled water and coolant. I'm also thinking of adding coolant filters as part of my system. Coolant filters need to be compatible with ones coolant ( either organic or non organic).
I've had the engine running since I've finished the keel cooler and all seems to be OK. I only had the engine running at a high idle but it did get up to operating temperature and stayed that way for the times I ran her. One good thing about the keel cooler is the ability to run the engine while on the hard.
I also decide to keel cool my air conditioners that I'll have on board. I'm going to have two air conditioners ( one for the lower forward cabins, and one for the Salon and Wheelhouse). I think the lower AC unit will be around 12,000 btu, and the upper AC unit will be around 18,000 btu. I know of quite a few boats in our harbor that are always having problems with maintenance regarding their air conditioner from junk getting sucked up into the units. Keel cooling these air conditioners, while much more expensive, will eliminate most problems associated with a marine type air conditioner. While traveling down and aroun various harbors, I'm amazed at the number of boaters that leave their air condtioners running while away from their boats for extended periods of time. I know of one boat that has been sunk due to the marine air conditioning unit failing and pumping water into the boat. While I don't think I'll leave the air conditioners runnig while I'm not on the boat, with keel cooling I will have the ability to leave boat and not have to worry about the air conditioners. For the air conditoner coolers I used 2" sch. 40 pipe split in half and welded to the keel. Becuase the air conditioners will be used while the boat is sitting still I wanted to get the coolers as low in the water as I could. There is a cooler on each side of the hull for each air conditioner. The cooler for the forward cabins enters and leaves the hull amid ship, and the cooler for the upper areas of the boat enter and leave the hull more aft.
Again, the hardest part of building these coolers was air testing my welds. I air tested all the coolers to 10 psi. Tacking the coolers to the hull went relatively quickly with me having only a few hours in the fitting and tacking. Air testing on the other hand found me spending at least a full day fixing leaks for each cooler.
While these types of coolers might seem a little labor intensive in some folks eyes, the robust nature of the cooling systems adds to the boat as a whole in regards to function and safety. That robustness will also translate into lower operating costs in the future witch, in my opinion, will easily off set the cost of my labor to build these devices.