Keel cooling

[forkliftking]

About how many feet of 1 1/2" aluminum tubing with a 1/4" wall thickness, would it take to keel cool a Kubota, model 1505, 4 cylinder diesel engine. Estimated HP is 25. We are installing this in a 34' pontoon houseboat.

[hartley]

hi forkliftking....firstly i would not be using alu tubing ,many issues there .
however for copper ,which is the usual material for the job ,the following applies.for a diesel engine you need 12 sq inches of exposed area per hp the equivalent length of 3/4 copper tube is 0.43ft per hp ,also you need to increase these figures by 25 per cent if the exhaust manifold is water cooled
all this is only a guide ,the best way is to fit as much pipe as practical ,and to fit a thermostat to keep the water outlet temp to around 175 degrees, your engine already has a thermostat i suppose. also you have to make sure your pump has the capacity to pump this water around .hope this helps
cheers hartley

[forkliftking]

Thanks for the reply. The reason for the aluminum tubing is that we were going to weld it along the pontoon. It will be in fresh water and using anti-freeze year round.

[mark775]

Aluminum is used all of the time. I know a 1963 Marco gillnetter with original aluminum keel cooling. Skin cooling is even better. Find out from the manufacturer what the cooling requirements are. If no satisfaction, ask "Ski" on boatdiesel.com. Don't get copper near that thing.

[MikeJohns]

Hows your physics?

looking up the engine specs I find 1650 BTU per minute as the heat rejection running at full power. Then you need to know the warmest the water gets in the lake and the flow rate of the water pump/labyrinth combo.

There is a good publication put out by John Deere on marine cooling "Engine application guidlines" Publication AG-24. You can get this from A John Deere agent. It will lead you through the calculation.

[FAST FRED]

One thing you might want to locate is an external thermostat .

On a vehicle the cooling system is designed to lower the coolant temp about 20deg with each pass thru the radiator.

The vessel cooling system will be designed for a "worst case" 105F water and full throttle for hours and growth on the cooler surface ..

This will surely result in over cooling during the usual operation, which can be very hard on the engine.

180F out 160F return ,just right,

180F out 100F return will shock the engine and cause inefficiency .

A by pass thermostat will allow the coolant to leave the engine , and the return water to be at the proper temp.

FF

[forkliftking]

Thanks Fred. That sounds like a good idea.

[baeckmo]

We have built some alu-workboats with this type of cooling. Generally, with Scandinavian conditions; sea water at max abt 20 centigrades and vessel speeds 10 to 20 knots, the low-speed surface (mostly inside) is taken as 1 m2 per 100 hp. For a closer calc you need to know the performance curve of the circulation pump, but if you increase surface by 20 % you should be quite safe, provided you keep painting layers at a minimum. Overdue length will ultimately increase pipe resistance so that throughflow is reduced, so there is a balance to be found.

Then check the internal thermostat, in modern engines you have a 3-way shunting thermostat, dividing the flow from shortcut circulation to cooler. If this is the case with your engine, you don´t need an external. Also make shure that the exhaust cooling (if applied) is bypassed through a bleeding hole during warm-up.

AND STAY AWAY FROM COPPER IN YOUR ALU BOAT!!!!

[forkliftking]

I've been gone for a week. Thanks for the advice.