capturing heat from an outboard

[the_gr8t_waldo]

has any one come up with a practical way of recapturing the heat from an outboard motor? in my own case i'm hopping to used it to heat a smallish cutty cabin?. lately i've been facinated with boats that are effecent users of low powered outboards. and i've tenativly picked out a few designs that would serve as a next project. but on my "must have" list , heat for off season use is rather high. i know that a propane cabin heater would do the trick, but i'm worried about adding weight.and devoteing space to a heating plant.

[L.W. Baxter]

Great Waldo, have you heard of the "hot sink" modification for outboard motors? Basically, a hole is drilled in the thermostat housing and a hose run to a tap for hot water. Nice for hand washing here in the cold, damp months. Here's a link to a discussion about the process, even some pictures from guys who've done it: hot sink (http://ifish.net/board/showthread.php?t=190030)

I suppose one could run the hot water through a heater core and get forced air heat out of it, though I haven't heard of that being done.

[Thorne]

Try a small single-mantle propane lantern. Century makes one, can be turned down to quite dim, heats a small cabin nicely.

[the_gr8t_waldo]

thanks l.w., that looks like what i had in mind-although i'm starting to think that the hot sink approch delivers a bit too little heat for what i had in mind.still i was glad to see that link, and incorporate it into the new boat. probably as and experiment to see if it would work. fall back use would be as a place to rinse off hands after fishing.i'm a bit skidish about having fumes inside a cabin. so a heating plant of some sort is probably in my future. thanks to all for the helpful replys

[Rob Stokes, N. Vancouver]

Hot sink concept in conjunction with an old truck heater may give you what you need.. Better yet, hot sink concept to a small heat exchanger mounted near the engine, and a closed loop water (glycol if you live where it freezes out) system to an old truck heater...that way you can run in salt and not have to worry about putting salt through your heater....

[doyle007]

I use a center console into January here in NJ for striper fishing, so I have no mechanical heating of any kind. Lots of layers of clothes, topped off with a water and wind proof layer.

One of the things that I have found as being very helpful are the 8-hour back heat pads that are supposed to help relieve aching backs. You can stick one of those one your back, and you feel a good deal of heat in your core. It has really helped me. Not exactly what you are looking for, but it's cheap and effective.

[Bruce Hooke]

Seems to me that when the motor is running you shouldn't be in the cabin (because you should be steering the boat!) and when you are in the cabin the motor won't be running and so won't be kicking out any heat. That combined with the relative modest amount of heat I'd think you'd be able to extract from a small outboard makes me think it would be a lot of work for not all that much benefit...

[JimConlin]

Seems to me that before worrying about the plumbing, a calculation of the BTU's available in waste heat would be a good first step.
Has someone got the data to do this?
How large an engine and at what level of output?
My gut feel is that there isn't enough heat to make the scheme worthwhile.

[the_gr8t_waldo]

yes jim, that is my own gut feeling. transfering heat represents no great challange, but without enough heat to do the required task, it would be pointless. except as an experiment. i'm thinking that a fan blowing over a small radiator or heater core. would deliver the heat. and placed on the common bulkhead between the sterring station, and the cuddy cabin. with a "diverter"that could be inserted to shuffle warm air to either the steering station ( glass windscreen w/ canvas cover and walls) or the cabin.

[jonboy]

Also think that any heat scavenged from the outboard's cooling system via pipes and exchangers and radiators is going to cause the outboard to run too cold....inefficient , lumpy, too much gas used...how about a low watt 12v caravan or camping heater run off the battery charged by the outboard... no propane or nasty heavier than air gases to go ka-boom...

[JimConlin]

Also think that any heat scavenged from the outboard's cooling system via pipes and exchangers and radiators is going to cause the outboard to run too cold....inefficient , lumpy, too much gas used...how about a low watt 12v caravan or camping heater run off the battery charged by the outboard... no propane or nasty heavier than air gases to go ka-boom...
Better ask the output of the outboard's alternator. As a reference point, small resistance heaters consume at least 1KW.

[George Ray]

Think it is a marvelous idea in theory as the only thing internal combustion engines do really well is produce waste heat. There is likely a demon in the details such as the previously mentioned issue of insuring the engine maintains proper operating temp. A thermostat is what is usually used but not so much on small engines. One way around that would be to use an air cooled engine and duct the warm air to the cabin and hope there is no oily smell. I love my little 2hp Honda air cooled OB.

I hope you do it and tell me how ....!

[Woxbox]

What size outboard do you have? The cooling water in the small 4-10 hp motors I've used never gets hot enough to actually heat anything.

I've also found that heavy long underwear & socks is the best investment for cold weather boating. If your only comfortable in a heated cabin, you'll find yourself cooped up in there all the time. If you're dressed to be outdoors, then you'll be comfortable everywhere on the boat.