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Boating Forum Q on Overheating

The answer on overheating engines was particularly interesting to me, as I had hoped to avoid these problems by choosing a reputable builder (Evans) and a reputable engine (Beta).
In considering the Alde heat exchanger solution I need to ask if a pump is needed as I assume that my Eberspacher has an integral pump which pushes the water round the system when the heater is on. If a pump is needed, any advice on what and where to fit it would be helpful.
When increasing ventilation, does it have to be outside the boat, or would adding vents inside the boat into the engine room be effective?
Finally, my worst overheating incident occurred when trying to keep up with other boats on leaving Limehouse Lock. Why is it necessary to speed up so much if the passage up the tidal Thames has been properly timed to go up with the rising tide?

Asked by: John Rich  | 9.01am, Thursday 15 August


WW says:

Thank you for your response to the boating forum questions- we are always glad to know that they are useful!
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It must be said that fitting skin tanks is not a fine art- it is a fairly inefficient way of cooling an engine and can be subject to quite a few aspects which can make them even worse at disipating heat. Alas, even very experienced boatbuilders do not always size the skin tank effectively or construct it in a suitable fashion- and even when they do, it can, for a number of reasons, not perform as expected!
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Slab skin tanks on the swim (or worse, on the baseplate) are almost unique to UK inland canal boats. Other boats, at sea or rivers that use skin cooling do so with proper keel coolers- which at its simplest is an external pipe running around the hull- or on large vessels, grid coolers integrated into the hull or just on the outside. Even some very big displacement cruisers, like the seagoing Nordhavn range, with large (300hp+) engines use keel cooling grids- and never overheat! This is because the heat transfer rates are properly calculated, rather than the "suck-it-and-see" approach of most UK boatbuilders alas.
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The Alde heat exchanger route can work well (and give free central heating as a bonus) but to work, it needs to be carefully positioned. There are two sets of connections- 22mm for the central heating system and 5/16" for connection to the engine circuit (most often on narrowboats, the calorifier return pipe). Ideally the connections should be fitted so they run counter-current, to maximise heat transfer. The heat exchanger must be fitted so that water flowing out runs into the heater feed, if possible. This would stop the diesel heater, if switched on, from heating the water up (and so reducing energy transfer).
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A second pump is needed, which can be fitted anywhere in the system, though an accessible place near the heat exchanger (ideally on the return pipe to the exchanger- which will be colder) is probably a good idea.
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You can fit a simple switch to control the pump- and a general central 12V heating circulation pump would work well (Jabsco make one which is common on boats). Magnetic drive pumps work well and give a sensible flow of water. Often there is a relay in a diesel heater control for running a second pump- in fact, Eberspacher (and others) would recommend a second pump in some systems- so this could then have a second control from the diesel heater, so when it runs, it uses its inbuilt pump and the separate pump.
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You also need as much heating area (radiators, towel rails and convectors) as possible in the boat- a blow-air matrix unit can shift quite a lot of heat, and eliminate cold spots at floor level. You can only distribute as much heat as you have space to convect it- so if your radiators only will distribute 2kW, then that is all the thermal load you can continuously remove from the engine. Fan matrix units can help increase that, and are useful when running hard!
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A completely different alternative would be to fit a car-type heater into the calorifier return, and simply vent the hot air out of the boat! I have seen boats that have fitted small radiator systems (from dumper trucks, and the like) into the engine room, vented externally, with the fan manually switched to enable excess heat removal. This could work very well, if you have insufficient radiator space inside a boat. They wouyld probably need plumbing into the main coolant pipes (on the retrun from the skin tank) rather than the calorifier feed though.
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as for ventilation, ideally it should be from outside the boat, as this will be cooler. As hot air is less dense and rises, having vents which allow the air to escape from the highest points of the compartment are really useful- especially above exhausts (such as often using the throttle control column on some boats).
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If you take air from the cabin, you run the risk of fumes entering the cabin (which could include carbon monoxide, if the exhaust system leaks)but more likely, the smell of oil and diesel can permeate the cabin. One tried and tested ventilation route that does work, is to take air from under the cabin floor (with a corresponding air inlet under the floor at the very forward part of the saloon) and duct this (via a loop, which can help reduce hot fumes returning to the cabin) and bringing the duct into the engine bay near the alternator- this has the advantages of supplying air, cooled by the baseplate, to give additional cooling air for the alternator- very useful if you have a large domestic alternator. However, you still need air vents higher (or have ducts that, say, go from the engine room, to vents on the cabin roof) to allow hot air out.
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Finally, if you don't go fast enough travelling with the tide (or with any current) it can become hard to steer accurately- and you might run the risk of missing the turn of a tide and so having to punch tide flowing in the opposite direction. However, if you plan it well, as you say, you shouldn't need to go like the clappers!
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As a slight postcript, freshwater cooled engines still have a lot of advantages- though some drawbacks- but for river based boats, they can make far more sense than keel cooled boats. I certainly know that my next narrowboat will be freshwater cooled, with a wet exhaust- to avoid running hot- as well as a cooler engine room and quieter exhaust!
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If I can be of any more help, please feel free to contact me directly on mark.langley@waterwaysworld.com
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I hope that has been helpful!
Mark

Mark Langley  | 11.20AM, Thursday 15 August

I could also add that you can use mechanical ventilation, to help remove excess hot air from the engine room. An inline extractor fan, to take air from the highest point of the engine compartment (and preferably as far from air inlets as possible) can be switched to run when the engine is running hot, or with an thermostat, at a predetermined temperature. As an engine emits 10% or so of its rated power through radiated heat (plus the inside of the skin tank surfaces, exhaust, gearbox, etc.) giving the engine cool air can help general cooling substantially. It also prolongs the life of components, such as batteries, alternators and diesel heating systems!

Mark Langley  | 3.54PM, Thursday 15 August

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