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Old 21-08-2012, 09:30   #1
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Sea of Cortes H20 temp & Skeg Cooled Engine Concern

I plan to take my 42 ft steel sailboat built for Canadian water (8-12 degrees C) to the Sea of Cortes this winter. The skeg circulation works great in cool water but I've had occasional overheating issues in the warmest bits of BC summers and wonder how the 25-28 degree C Mexican sea water temp will affect the engine operation. Does anyone have experience/advice?
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Old 22-08-2012, 17:12   #2
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Re: Sea of Cortes H20 temp & skeg cooled engine concern

You are right to query whether the the engine will tolerate a 20 degree C increase in cooling water temp in light of intermittant overheating in the cooler BC waters you have already experienced.

You are almost bound to have issues with overheating with this level of increase so need to sort out the the reason why now.

You should start with the easy checks and eliminate problems or not to spec issues as you find them one at a time.

First check the engine cooling requirement from the manual. Lets say 20 litres/min at 2000 rpm. Then check the actual flow through the engine by measuring with a bucket and stop watch at the exhaust outlet with the boat at the dock/berth, in forward drive and with the engine at its saturated running temperature and stable.

With a known sea water temp, a known running temp and a known engine throughput in litres /min this will tell you whether the engine will handle the 20 deg C increase you expect to see. Your engine temp should be less than 80 deg C at normal running temperature.

While the engine thermostat should handle the temp change, if you already see intermittant overheating it suggests that the cooling water throughput is probably less than it should be now.

Good luck
Acushla
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Old 22-08-2012, 17:25   #3
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Re: Sea of Cortes H20 temp & skeg cooled engine concern

How much coolant does the skeg hold? What is the circulation of coolant in the skeg? By that I mean does the input pull from the bottom of the skeg and the outlet from the engine dump coolant into the top of the skeg or do you have many feet of pipes running through the skeg and coolant flowing through the pipes in a closed loop system?

Half pipe closed loop systems work well in steel boats but they have many feet of pipe directly in contact with the steel hull on one side and the water on the other. This forms a very efficient heat transfer system. If you are just dumping hot coolant into a small reservoir and drawing coolant from that same reservoir you may not have enough surface area to dissipate the heat.

You will have to measure the volume of the reservoir, input and output temps, external water temps. and surface area in order to determine if you have a large enough reservoir.
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Old 22-08-2012, 17:29   #4
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Re: Sea of Cortes H20 temp & skeg cooled engine concern

You be lucky to find 25 deg. water in SOC in winter,it gets pretty cold by December.It usually hovers in the low 20's,but warmer south of Puerto Vallarta.My friend has a keel cooler on his steel motorsailer and has no problems down there.
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Old 22-08-2012, 21:02   #5
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Re: Sea of Cortes H20 temp & skeg cooled engine concern

Thanks everyone who has weighed in on my post. the engine is an Issuzu 40-hp, the skeg cooling system utilizes a dipper tube to draw intake coolant from the bottom of the skeg and engine return to the top of the skeg. there's a header tank in the system. engine is a dry exhaust configuration. sadly didn't measure volume of coolant(h20/antifreeze) in the system...
thanks again for the advice....
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Old 22-08-2012, 21:09   #6
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Re: Sea of Cortes H20 temp & skeg cooled engine concern

You may be able to add an internal tank utilizing the hull as the outer skin to supplement the skeg. Of course it will require a lot of grinding and welding and repainting. However without knowing the volume of coolant in the system you would be just guessing at the size of tank needed. I guess if you were going to do all that work it might be better to go with the 1/2 pipe on the outside of the hull.

Check with the guys on the "Metal Boat Forum". They may have some other ideas.
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