keel coolers

Discussion in 'Boat Design' started by rick gray, Sep 24, 2014.

  1. rick gray
    Joined: Dec 2012
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    Location: port coquitlam B.C.

    rick gray Junior Member

    i tried to hijack an existing site, but here is my keel cooler design ideas, with hope of suggestions. on my amphibious vehicle project I intend on a separate systems to cool exhaust and engine> i hope to run a radiator on engine water ,belted fan & electric, the trans and transfercase oil will be cooled at radiator,like a car.I can install a 3" diameter s/steel tube keel cooler by 7ft or so long, faired in outside lower chine port or ?and star, or built in to aluminium hull at lower chine, with vented expansion tank to cool exhaust manifolds and short length of exhaust pipe outleted as close to engine as possible,(double wall) and recirculate with 12 volt pump.the engine water maybe also heat exchanged on demand, with raw water shut off( but recirculated?)hope to get enough cooling ai ducted to engine compartment.

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    FAST FRED Senior Member

    Build one cooling system , radiator and fans like a car or stationary gen set , and dont bother with the rest.

    Either it works or it doesnt , if it works, why guild the Lilly?
  3. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    Cooling System

    Fast Fred is correct, an amphibious vehicle needs a cooling system, almost the same for land based or water based operation, so an air cooled radiator system, sized properly, can do all that is needed.

    There is however the issue of cooling load from the engine and cooled transmission/transfer case. In automotive service, the average load on these components is only a fraction of the equipment power ratings, while driving the boat on the water generally involves much higher, and continuous, power output of the engine and transmission system.

    For example, my automobile engine, operating in the car, gives 20MPG while cruising at 60MPH, that translates to burning 3 gallons per hour in fuel. The same engine in my boat gives 2MPG when cruising at 24MPH, and thus burns 12 gallons of fuel per hour. In marine service, the engine is burning 4X the amount of fuel that is typical for automotive service. The cooling load is roughly proportional to the fuel burn rate, so, in theory at least, marine service demands significantly more cooling capacity.

    In addition to that, the engine and transfer case gets some cooling from ambient air flow around these components when the automobile is cruising down the highway, but very little of this extra cooling from ambient air when enclosed into a boat's engine space.

    The extra cooling load associated with marine service can be accommodated by simply installing an air cooled radiator of larger capacity, perhaps a truck sized radiator or something similar.

    Another option is to put a sea water cooled heat exchanger in series with the air cooled radiator, so that it takes up the extra cooling load when working in the water. Of course the added heat exchanger can be inboard, or a "Keel Cooler" integrated directly into the hull below the waterline, or consisting of cooling pipes mounted just outside the hull.

    For the case of an amphibious vehicle, I would think the pipe type keel cooler would be in danger of damage when operating tween land and sea, so my vote would be for an inboard sea cooled heat exchanger, with no sea water pump, just scoop cooling. Scoop cooling, as in Naval practice, can work well because the air cooled radiator can handle all the cooling load while maneuvering, and will get ample sea water flow when underway with higher engine load.
  4. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    Since he is working with aluminum, is a seawater/freshwater heat exchanger even necessary? Aluminum is a great conducter of heat - what if he just had water pipes built into the aluminum hull, engine water pumped through those pipes would be cooled by conductance to the cooler seawater exterior to the hull (especially if he intends to operate in the northern latitude of BC).

    The real engineering question would be the flow rate needed through the pipes to achieve proper temperatures at various speeds/conditions. One may need an integrated network of smaller pipes with multiple thermostats to provide varying flows to maintain proper temps.

    Too little flow through the circuit and the engine will overheat. Too much flow through the circuit and the water will not have time to cool down (via conductance), and the engine will overheat.

  5. dinoa
    Joined: Oct 2007
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    dinoa Senior Member

    Too much flow should never be a problem. Heat transfer rate would be greater even at small coolant-sea temperature differentials because the mass of coolant being circulated would more than offset the lower temperature differentials. The existing engine thermostat would take care of overcooling.

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