Originally Posted by captnjack
In an auto engine? I don't have any data, but having salt in there just gives me the hebie jebies. If I ever get a inboard powered boat again I will be getting a sea chest/raw water strainer with a macerator to chop up any offending weeds.
Keel coolers are nice but never seen one on a planing boat. Being partial to wet exhaust myself the keel cooler seems like excess risk of corrosion or impact when you need to bring water into the boat for exhaust anyway.
I wouldn't run salt water through the engine cooling system. That would just have a sealed system with the usual anti freeze / water mix circulating. The engine coolant would pass through a heat exchanger which is essentially a radiator that uses sea water to cool it, rather than air. The heat is drawn out of the engine coolant and transferred to the sea water via the heat exchanger.
I agree about keel coolers, they would seem very vulnerable, especially as it is likely to spend time in very shallow water with a high risk of going aground. At speed a large area of the hull will not be in the water much of the time.
The castoldi jet unit has a take off pipe that will pump sea water round a circuit when the jet is pumping, but will do nothing when the jet is in neutral, it will still need a second pump to circulate the sea water if the engine is idling with the jet in neutral.
To complicate the exhaust further, I am going to run a particulate filter to clean up the emissions. It is not very pleasant being towed in a dinghy behind a diesel. It would not be possible to allow salt water to pass through the filter, so if it ws to be exited via the exhaust, it would have to be down stream. At the moment, the planned exhaust is only going to be probably 4 feet long from the turbo, with the particulate filter taking up at least 2 feet of that, so the benefit of water cooling the last 2 feet is almost negligible.
My plan is to wrap the entire exhaust including the manifold, turbo and filter using the upper end of the product range:
Thermo-Tec : Latest exhaust insulating and heat protection technology
My theory being that the exhaust is so short with little backpressure, that the gas will pass through quickly and the wrap will contain what does hang around, hopefully limiting much radiation.
In an ideal world it would be good to have a water jacket around the exhaust manifold, but it will be a very high dollar option and difficult to manufacture reliably unless cast.