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Old 02-15-2019, 04:09 PM   #81
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I think adding a sendure (I think thatís the name) heat exchanger would be really straight forward, and substantially easier than converting to keel cooling. You just need so engineering (not guessing) on the exchanger size and the required raw water flow. And be sure the calcs allow for coolant cooling of the manifold in case you want to do that now or later. The rest is simple plumbing and mounting brackets.
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Old 02-15-2019, 06:33 PM   #82
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Thanks to all for the interesting info. Out of business due to toe surgery a while ago. I'll do my best to reply to all tomorrow! Nurse is pissed off she will take phone away!
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Old 02-15-2019, 07:55 PM   #83
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Quote:
Originally Posted by neurodoc View Post
Thanks to all for the interesting info. Out of business due to toe surgery a while ago. I'll do my best to reply to all tomorrow! Nurse is pissed off she will take phone away!
You definitely do not want to piss your nurse off!!

Ski, twistedtree, djmarchand and psneeld all have very good suggestions, information and advice. (Along with many others in this thread) I am simply trying to help you with some of the info I have learned in doing a redesign of my keel cooled boat that has heating problems. What I do know is that it takes a lot of cooling to keep a 120 HP engine happy at WOT. And as has been stated that when you are using the same coolant flow to remove exhaust manifold heat you need at least 50% more capacity and water flow. Information is very scarce out there and those that know seem to be quite tight lipped about it, maybe fearing for their exclusive knowledge and their jobs. I also know that some of the people that should know this info are not giving correct info. Just trying to share what I believe to be correct and not trying to convince you that a keel cooler is the only solution.

Another important part of cooling is the flow of liquid coolant. This is usually stated as BTU. One BTU is the amount of heat required to raise the temperature of one pound of water one degree F over one hour. So the flow of water required to carry away the heat the engine water jacket produces is calculated with the formula Gallons per minute = BTU divided by 500(water and 450 for anti freeze) times Delta T (difference in temp of water leaving engine compared to return) The water pump on my 120 HP Mitsubishi is rated at 58 gpm. I have checked that on a new and a rebuilt pump on my own test bench and find the pumps will do at least that flow at 8 psi. This may be helpful in determining if your sea water flow is adequate. Your raw water flow at 1" sounds low to me as well. I keep coming back to the same conclusion, that at low pressure of 2 to 8 psi out put of the engine water pump you need a 2" flow to get to 58 gpm. If you have a higher pressure raw water pump it is possible to get enough flow at 1" though.
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Old 02-15-2019, 08:13 PM   #84
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You are getting some good information. I can add, based upon HXer design experience on both very big industrial and small HXers like on our boats, that a safety factor needs to be added. Generally add to the "paper" design something around an additional 20 to 30% which will cover the gradual scaling up as time passes.

Also, if not mentioned, raw water and coolant flow rates on most of our vessels increase as RPM increases. So calculate the size of the unit for the higher flows to insure no inordinate rise in friction head within the HXer itself.
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