Converting a 430hp 6CTA-8.3 Cummins to keel cooling

I am re-powering an Alaska gillnetter with a Cummins 6CTA-8.3 rated at 430hp. The 430hp model of this engine is only available in a sea water after cooled configuration, and for my application, a keel cooled engine would be better.

The stock cooling system pumps seawater (via 1-1/4" Jabsco, positive displacement pump) into the after cooler, and then into a heat exchanger (which cools the jacket water), and then overboard.

I was planing to use two keel coolers, one for the jacket water, and one for the after cooler, on separate circuits. I have been told that there are commercial boats "all over Alaska" that are configured for keel cooling, with the 430 hp model of the 6CTA-8.3. I haven't seen one, so if anyone knows of such a setup, I would be grateful if someone could give me some details.

I have the jacket water circuit figured out, but I am uncertain about the after cooler circuit. Neither the local cummins dealer, nor the vender that sold be the engine has been able to provide me with the necessary information.

I have consulted Walters Keel Coolers, through a Hamilton Jet dealer in seattle. They recommended a 6 tube, 8ft cooler, operating off of the stock sea water pump. I already have a 4 tube 12ft cooler, so to save money, I would like to use that instead of buying a new cooler.

I have only been operating my vessel for two seasons, so I have very little experience in these things. From what I have heard, Walters Keel Coolers is a requitable company, but I can't see how a keel cooler would provide as much cooling as a direct seawater system, without more water flow. Maybe the system The Walters Keel Coolers recommended, (even though it dose not provide as much cooling as the stock system) will be enough, but I can't afford to blow up the new engine, so I want to be sure it will work.

If anyone can help me with this I would be grateful.

I have attached a page with the specs

 

A cooling system is usually sized to drop the engine Out water 20-25deg F.before it is returned.

Walters Keel Coolers is a good old company,and in AK waters cooling should not EVER be a problem.

IN The Carib , towing at 3K with 85F water and some fouling on the cooler is a different problem.

Most coolers are designed for worst case , no speed and warm water.

Over cooling is possible under most circumstances and there are by pass thermostats that will return the water at a correct temperature.

 

In order to compare the 6-tube cooler with your 4-tube unit, we must know the pipe diameter of the respective tubes, and the flow path. Primarily it is the wetted surface that counts, but the flow resistance and the resulting water velocity will determine the final cooling efficiency.

A rule of thumb is that the aftercooler needs about the same surface as the engine (including oil cooling).

 

Thanks for your input.

Both the 6 tube cooler that Walters suggested, and the 4 tube cooler sitting in the basement are single stem coolers, with 1in ID tubes. According to the specs, the output of the seawater pump is 63gal/min, (238 liters/min).

The cooler for the jacket water circuit is a single stem, 4 tube cooler with 10ft tubes.
The output of the jacket water pump is 85gal/min, (322 liters/min).

The expected speed of the vessel WOT is 15kts, without any fish onboard.

I think the sea water temperature of Bristol bay is rarely above 60 deg F.

 

Hello MLC,

I am also looking to install 2 keel coolers in my Bristol Bay gillnetter with a Cummins 6CTA 8.3 motor. The boat is Daniels/ Nordic fiberglass boat which is comparable your roberts. I am going to install one cooler for the aftercooler and one for the engine jacket circuit.

-Could you tell me which keel coolers you ended up installing and how they ended up working out for you?
-How did you end up plumbing them? Did you use your engine water pump for the engine jacket circuit and your jabsco raw water pump for the aftercooler circuit?
- Are you using your engine jacket cooler to cool your gear box as well?
-How are you cooling your hydraulic oil Case drain/ return lines?
-What size prop did you end up going with? I currently have a 26x20 4 blade and was curious if that would do the trick.
-How do you like your new motor re-power? What kind of speed/performance are you getting?

 

I bought 20' x 3/4" k copper pipe for a 30hp diesel which is slightly more than manufacturers recommendation of 5/8" which were made for North Sea waters. Others formulas have said even more cooling is needed so picked in the middle.

Using Sabb numbers for 30hp 15sf of copper is needed, for 430hp 215sf. Find what area under the boat to put pipes than you can figure what size pipes and the length required to get 215sf. Use the pipe OD multiplied by length.

 

This is two 10' with a 180 degree turn. Had put silicon bronze bolts embedded in what i thought was epoxy anchoring glue bought from HD so i could take off nuts in the future. There are about 8 clips around the pipe fastening it to the hull, after the third clip had found it odd that glue was gritty and reread packaging to find out it was not epoxy.

Now there was a mess on my hands and had to get epoxy into holes for bolts. Decided to JB weld the rest and tightly pack it around all the bolt and nut fastenings which ended up in my eyes being good since now there were no more protrusions of the bolt heads to pick up debris, everything is streamlined, its attached and sealed very well.

A side note to read packaging on JB weld and use the one rated at 550 degree

 

Pics should be showing horizontal. At the time had no antifouling and had to use primer, hence the cracking, which is only the primer. When available I always apply antifouling to new epoxy wet on wet.

As you can see the JB weld formed nicely it was about 45 degree maybe in warmer weather a lil aerosil might b needed

 

I can't comment on the Cummins specifically but I have a keel cooled Ford that was converted from having "regular" cooling.

I have two circuits. One for the jackets and engine oil cooler by the engine circulation pump. The other circuit takes care of the transmission and after cooler and the pump is the old raw water pump.

If you decide to run the transmission on the same circuit as the jackets, check with the manufacturer what the max operating temperature is. In my case, and this is a fault in the design, the two circuits share expansion tank so in effect the engine circuit warms the transmission circuit which leads to my transmission running at 70 degrees C (max is 80). It's been like this for some 6500 hrs so not a problem for me but it could be for you.

 

Those numbers for square footage area are incorrect since I was multiplying square inches of pipe diameter by foot length.

5/8" Copper pipe is 3/4" OD which is .0625SF multiplied by 20' makes 1.25SF of total cooling area, yours would need 18.0SF.

I have seen box type keel coolers which could be sloped fwd for less turbulence and deflection of underwater objects, also less total area than a maze of pipes. Maybe copper is available in square tube or channel in various gauges like steel.

 

If the aftercooler is converted to JWAC, and consequently runs hotter than before, you could duct in some of that nice cool Alaska air straight to the intake to make up the loss.
A few degree hotter at the aftercooler are not likely to have much affect, except possibly at high throttle settings.
I would run this question by Tony at sbmar.com, he is the absolute Guru, especially re specialty mods as required by commercial applications.

 

I doubt you will get away with cooling the aftercooler from the keel - well, it will function but it won't "cool" anything. It seems to me you won't need anywhere near all that HP, so I'd ditch the aftercooler and retune for zero smoke.

 

Steve, many aftercooler use jacket water (coolant) to cool their air, and it is thermostatically controlled, so how is that different than keel cooled coolant?
The coolant that flows through the aftercooler is taken from the front of the motor, the cool side of the loop.
Certainly the aftercooler could be removed, and the intake fed with cool outside air, as opposed to warm engine room air commonly used.