converting from fresh water cooling to keel cooling

We are in the process of rebuilding a 40' steel boat.
It has a Perkins 4-236 diesel engine that is currently
fresh water cooled which we want to convert to keel-cooling.
Can anyone help us with A- Calculating the size and lengths
of pipe we would we would need to effectively cool our engine,
and B - would anyone be able to supply us with instructions or
photos to change over the existing fresh water plumbing system.
We are also going to convert to Dry-stack Exhaust.
Our boat is going to be operated mostly on the North-Channel
of the Great Lakes, but we are planning to do The Great Loop in
about four years.

Thank-you in advance for your assistance
B.H.B.

 

Buck,

Your title is misleading, I think, but the idea is good. If I understood your post correctly, you want to eliminate the raw water loop. Your steel hull is a good choice for adding a keel cooler. You can weld fairing blocks to reduce drag, or cut and weld a recess so the cooler is fully protected. If you dry stack, you can eliminate one pump; your existing fresh water pump might have enough capacity to circulate coolant through the keel cooler and engine; worst case, just install a slightly larger pump. Apart from sizing, the most important issues to be considered, of course, are protection of the external cooler from impact damage, drag elimination, corrosion protection, and loss of efficiency from fouling. I'd size for the warm waters you might encounter on a trip south and regulate temp with the right thermostat. The information you want is readily available; these links should be a good start:

http://www.passagemaker.com/discus/messages/3/3026.html?1157974963

http://powerandmotoryacht.com/columns/maintenanceqa/0504qa/

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=53239

http://www.flagshipmarine.com/keelcool.html

 

Hi Charlie

Thank-you for the quick response.

Very interesting & informative.

That formula was a great help

Buck

 

Keel cooling size caculations

I went through this exact keel cooling situation with a detroit 3-53 80 hp. About the same as a Perkins 236 at about 80 hp also.

So, the comercial bolt on keel cool system available was two meters of four swirlled tubes of about 1" each. That is four wide, but two going foward then two returning. So to be clear that would be about 24 feet of length.

But this is not the same for pipe as the walls are thicker and don't have the "swirls" that are built into comercial units. Back then a new bolt on keel cooler cost about a grand. The pipe I welded up cost about twenty bucks at the scrap yard.

Now I ended up finding boiler tubeing that was thick walled so we decided to bouble the underwater length adding drag but saving dollars. This turned out to be way too much and we probably could have easly gotten away with 30-35 feet of pipe length.

We also made a cute little welded in through hull that was both the in and the out. This worked well but really was not needed and we would have been better leading hull pipes right to the engine ports.

I have a book out called Metal Boat Repair and Maintenance that covers lots of sections of refitting a steel yacht, but it does not cover the keel cooler so I'll give a bit more detail.

You might also have to deal with the gearbox cooling. We did that with a tube to tube cooler on the return from the keel cooler and before the engine. This worked very well.

If you want to get rid of the salt water pump and all the extra complications then exhaust manifold and exhaust cooling have to be thought about.

The exhaust manifold should be water cooled to prevent the fire hazard of an injection line cracking and the whole engine room bursting into flames. I have an easy design if you need to build one.

The water cooled exhaust we delt with by resorting to a dry stack and thus we also got rid of the salt water pump.

I think that was about it. After ten years I would only go through all the trouble for a huge cost savings. Getting rid of the salt water pump saved lifetime of maintenance costs.

We had bought a used military surpluss detroit 3-53 for 500 bucks and had it installed completly for another 500. That's a big savings all in all. The complete instalation has been pretty trouble free since. I think we have about 5000 hrs on the system now.

The two photos should show both ends. Not very slippery for underwater shape, but it has been trouble free.

Good luck with it.

Scott

 

A recent article in Pro Boat Building by Dave Gerr has all the info and math you will need to work the problem.Exhaust tricks are in the same article.

With keel cooling some luxury options are quite inexpensive.

Leading coolant through the FW tank for free heat is OTS , but a similar loop with an added circ pump can feed baseboard heat at little extra cost ,or complexity. They will feed box heaters too, but they need an extra fan to deliver cabin heat adding to the batt load after shutdown ,the baseboards just radiate engine stored heat for free.

For boats used in warm climes , a valve or two will allow the same circ pump to "power cool" the engine by dumping the engine heat through the keel cooler when stopped.. This can make the evening engine / boat cool down much more rapid, and pleasant.

Our work boat has a 6-71 with (2) 21 ft pieces of 1 1/2 pipe and has worked from Maine to the Keys.And we enjoy free heat in Maine and lower on board temps in the Gulf.


FF

 

hi...... beta marine. give skin tank specs for engine size www.betamarine.co.uk

 

simple and very cheap to use a pressed up channel , one each side of boat 2 inches deep, and 4 wide as long as you can make it Done this many times on work barges with high duty cycle
if I repeated anyone sorry, use proper anti corrosive and or antifreeze

 

Inside cooling tanks and channel cooling

Chanel is great and strong. In fact I would have loved to use it just for the extra strength.

The question was about refits. It's difficult to tear out the interior of a long yacht to weld and treat the keel cooler. That is what we were faced with. I wanted an interior tank built into the keel, but refit did not allow this either.

That is why we eneded up with exterior pipe. We only attached to the hull with small tabs and on each end where we could reach the inside hull.

I have to say the keel cooling has been pretty trouble free.

Lots of money is spent on the salt water loop in engine systems. Keel cooling saves on thoes costs. It's the simple solution to self marinization.


Cheers

Scott

 

Lots of money is spent on the salt water loop in engine systems. Keel cooling saves on thoes costs. It's the simple solution to self marinization.

All true , but one of the biggest virtues is the boat can be used daily , in sub freezing weather , with out winterizing daily.

Saves big time on labor and freezing risk!

FF

 

Lots of these systems on steel work-boats , usually channel welded to the inside of the bottom plate, sometimes equal angle. You have to allow for the thermal conductivity of a thick paint film inside or out and they work very reliably.

I have seen a few larger steel yachts that used part of the box keel as a retro-fit cooling tank. The insides of one ( aft end of a long keel) I looked at had been in service for over 20 years, it was pristine inside but it had been epoxied.

There is also a good publication put out by John Deere on marine cooling "Engine application guidlines" Publication AG-24. You can get this faxed from your John Deere agent. I don't think they have it in an email format.

You will also need your engine specifications particualrly 'Engine heat rejection' if you want to calculate the areas closely.

Cheers