Project 40 - Hull Cooling Experiment

The conventional method of cooling an engine in a marine environment is to have a seacock where salt water can be drawn in and used to cool an internal water circuit connected to the engine. These units require diligent maintenance, especially with sacrificial anodes, or they will corrode very quickly.
There is another alternative with steel boats that makes more sense to us, closed loop keel cooling.

There isn't a whole lot of information or research available on this subject, just examples of other peoples experiences.
There are two possible methods of closed loop cooling:

1-A split pipe along the outside of the hull, around the keel
2-A "box" inside, attached to the hull, which would be new!

Heat dissipation calculations could vary widely depending on the dimensions of the box, square, rectangle, number of baffles etc.
With a split pipe the same thing has occurred, and small baffles really need to be used....but then again, maybe not!

We have decided to go with the box type as this won't effect the outer hull. Originally it was going to be a square, about 15 square feet, on each side. But because of conflicting data we have found, ( ie 1/2 square foot per horsepower to half that again, to almost twice that! ) we are making it length-wise. 16 feet long x 1 foot on each side

For this we have had some 1/8" plate cut into 11" to 13" strips, and bent to a 45º on the sides. Of course this couldn't be used whole ( it would've been nice! ) as it needs to curve around the hull between stringers. ( Photo at the top )
We are going to place baffles every foot or so to keep the water stirred up. This is very important because the flow isn't very fast and without baffles, the hot water would just remain at the highest point, away from the hull where the cooler water is!

I cut out 1 1/2" high slots through 8 frames and then slightly bent each piece so it would slide in easier ( by jumping on it haha !) then marked and cut the ends to get a "curve" in the overall shape.

The reason we went with 45º on the edges was so Gena could easily get good welds to the hull along side the stringers.
Tomorrow we will put in the baffles. This will take some time as the original idea was to accomplish 1" inside depth for 1" flatbar baffles. Unfortunately there must have been a misunderstanding on where the 1" dimension was to be because the depth is only 3/4" ! This means lots of grinding.

The photo right shows how the cooling units will go together once against the hull.
The 1" flatbar is just tacked in as we saw no real reason to weld them in solid. The ends are tacked in now so they will be easy to weld on once in place. We could have just added a piece of flatbar on after, but this way 2 sides can be welded. Why tempt fate? Before installation, the insides will be brushed clean of any loose slag. ( Not something you want flowing through the engines water pump! )

To the right is one of the slots cut out under the web frames. Note that the stringers are not compromised and all of the plate will fit between the stringers in place with enough each side to weld.
The hull plate will be sandblasted ( yuk! ) then the pieces, each four feet in length, will be slid in from aft, where there are frames nearly 4 feet apart. This all works out very well being able to slide longer pieces in, thus less welding.
Placing the holes for circulation was a subject of some debate.

We are confident the approx. 32 square feet of area will give ample cooling, and hope to have to use the bypass valve to an extent! Guess we won't know for sure until she is in the water, with the engine running.

To the left is a little ( cool 3d! ) diagram of the circulation. The take-up or expansion tank will go on the hot side, and a bypass valve.

The diagram shows how the circulation will work. The holes at the ends are also the high points ( except the fill tank ) and the pipe connecting them must have bleeder valves to get trapped air out apon filling.
( I'm taking Gena's word on that one!)

Arrows denote direction of flow, Bleeder valves are to release trapped air. There are 3 drain plugs at the lowest points

Here's the sections going into place. They had to be slid back from the forward frames which aren't full webs so there's more room.

It's a good thing Gena was reading through an article in "Metal Boat Society" magazine (recommended! ) that happened to mention drains in thru-hull cooling. We'd never have thought of it!

Gena is still taking a good amount of time to work on the hull cooling tanks, and making progress!
She has patience I couldn't even come close to. 1 hour at that and I'm ready to hit the bottle!

Many days have passed and still the hull cooling isn't finished. I was ordered ( rather than asked ) to cut the holes in the webs bigger. I expressed concern about weakening the structure but was re-assured the pieces would be welded back in afterwards.

Needless to say, Gena is getting pretty frustrated with the whole thing. If we'd have made them 2" narrower, getting a good weld would be much easier. The problem is, the stringers are in the way, running alongside. Even though the box is a 45º angle, the welds can't be done well.

When pressure tested to 10 psi, the leaks are always under the webs, so the angle of the welding torch there is an issue.

A month more of weekends later....

At long last the hull cooling units are in and no leaks. Gena has been using the time-tested soapy water method for testing for air leaks. No more bubbles! Bravo Gena.

The performance after running the engine one land for an hour, looks promising. Even in air, only 1/4 of the hull area was hot, 1/4 warm, and the other half not noticeably warmer than the rest of the hull.

During sea trials, (shakedown) running up to 4 hours under load, the bypass valve, that is, a valve that controls how much water loops past the cooling system, had to be opened some as there was much too much cooling. The gauge never got above 170º F! In my (inexperienced) opinion, less than half of this system would easily cool any 60 horsepower diesel engine.

Now that we know it works, we can't imagine why anyone with a metal boat would want to use the "old" method of transferring heat to salt water in an exchanger. Just the "forget anode/destroy engine" issue was enough to turn us off it.