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Old 11 January 2012, 14:47   #21
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I have never heard of an air cooled marine engine of that size, hp, and heat production. Not having any cooling water I'm guessing you'll have dry exhaust too? That would be a bit odd on a trailered boat around here.
My intention is to have a conventional water cooled system as used in a car with the cooling for the radiator, intercooler and oil coolers supplied by electric and hydraulic fans, rather than a separate heat exchanger and pumping sea water round via a heat exchanger to cool the engines coolant.
The exhaust will be short and dry with lagging around the turbo and pipe to contain the heat. The engine box will be well ventilated with double blind air ducts, so plenty of air will be passing through with any water splash dealt with by the blinds. I dont believe the heat is going to be a problem.
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Old 11 January 2012, 16:13   #22
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I dont believe the heat is going to be a problem.
Hmm, I think your engine box will be toasty.
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Old 11 January 2012, 17:47   #23
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Quote:
Originally Posted by Rokraider

My intention is to have a conventional water cooled system as used in a car with the cooling for the radiator, intercooler and oil coolers supplied by electric and hydraulic fans...I dont believe the heat is going to be a problem.
At full chat - and I'm assuming that having taken the trouble and expense to uprate the engine to 275hp you intend to use it - then you'll be looking to dissipate something like 200kw heat to coolant through a coolant to air radiator and 200kw heat down the exhaust.

I suspect the cooling is going to need careful thought to avoid thermal runaway. Electric and hydraulic fans may well do a good low speed, low heat job as they do in a car...but 200kw heat to coolant to air at boat speeds using ram air only? That's a very big ask.
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Old 11 January 2012, 18:13   #24
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Its gonna be noisey too, if you do get enough circulation to cool the engine then you'll end up with pretty big vents too.
The turbos gonna throw out a shed load of heat, if its on load for any period of time its prob gonna end up glowing red.
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Old 11 January 2012, 19:27   #25
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Agree with Leapy and Chewy here.

You have a big heat dissipation problem and in opening up the engine compartment to create the air flow while using dry exhaust you are creating a big noise problem.

One of the huge benefits of wet exhaust in the massive reduction in volume you get via cooling the gas. That volume reduction with water alone muffles sound quite well compared to a dry muffler.

I would look again at a water-water heat exchanger and wet exhaust. There's a reason 99+% of inboard RIBs have gone the wet exhaust route. As far as air cooling with a radiator, I don't think its feasible unless you have a essentially open engine like a car - and a big radiator. There are no low work downhills at sea.
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Old 12 January 2012, 12:55   #26
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All good points to consider. Nothing is set in stone at this point. One of my biggest headaches is there is a lot of surface weed where I intend to spend a lot of my time we have had several boats cook their engines due to weed blockage in the seawater circuit. I am interested in exploring alternatives. The mud pluggers I have built in the past with radiotors in the back and fans have worked fine even when under heavy loads with no airflow to help.

More to think about on the subject..
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Old 12 January 2012, 14:21   #27
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With the right kind of strainer, a good filter basket and an exhaust overheat alarm I think I'd be going down the raw water cooled route.
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Old 12 January 2012, 15:46   #28
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With the right kind of strainer, a good filter basket and an exhaust overheat alarm I think I'd be going down the raw water cooled route.
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.
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Old 12 January 2012, 17:19   #29
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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.
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Old 12 January 2012, 17:29   #30
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I'd scrap the particle filter straight away, having it mapped and leaving the DPF is a backward step.
Does the jetdrive have neutral?
A guard around the keel cooler would sort the ground problem.
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