If anyone is still interested in a heater, I stumbled across this one while looking for steering mechanisms: http://www.faymarine.com/plansite/fire_design.htm
The rest is my rambling on one of my ideas for small scale heating.
Having done some experimenting rocket mass heaters it caught my eye. A RMH would have no place on a boat (unless it was much larger than any I can imagine myself in) but some of the ideas are still of interest.
- Heat the body, not the air.
- Hot surface temperatures are bad
- Storing heat is good
- Burn fast
Radiant heat will feel better than air temperature and transfers heat directly from the heater to the body, but radiation falls off at the inverse square for distance (which means that if you are twice as far from the heater you will get you will get 1/4 the heat not 1/2) so close is important.
Direct heat transfer if even better. Most RMH have a built in heated bench with which to warm one's body directly... may not transfer well to a boat unless one has hot water heating from a running engine, scratch that.
Insulation is like a resister, the warmer the heater is, the better it's heat goes through the walls to heat the outside. So cooler (just shy of being able to damage skin) surface is more effective for the fuel input.
Saving the excess heat in mass is good, except there is not really much room in a boat (particularly a light weight one) for such nice things.
As others have mentioned, burning fast is better for heat extraction and produces less harmful flue gas. So aside from not being as likely to kill you, it uses less fuel. Both of these things are good for a boat... but hotter is not.
Maybe there is somewhere in between. Burning fast has a number of problems besides loosing heat out the flue and through the cabin walls. It requires better shielding, it is easy to get burned and it uses the fuel faster. However, I am thinking of two things (maybe three or four by the time I am done) that could help.
- Phase change heat storage
- A Bell heat exchanger
Space is limited, but I have noticed that whatever the size of the heater, there is not anything mounted above it. It is nice to be able to also cook on it, this is true. And while cooking could be achieved at chest height, most would rather not have something hot way up in the air where an errant motor boat wake might fling it on top of someone. However, placing a second chamber on top would allow capturing a good deal of the "waste" flue heat. This is called a bell (in the masonry heater world).
So this is great being able to get more heat before the flue gas and the heat in it leaves, but this would leave to much heat at once. Phase change is the answer I think. Put a second box around the small stove and fill it with tin which melts at about 230C and absorbs much more heat to melt than it does in just heating (lead would be possible too and might hold more heat for volume). This box would have to be welded shut (as in sealed) so that molten metal didn't get all over things. Now as even 230C is very hot the next thing to do would be to put insulation around the outside of this box. (big grin as I wait for sarcastic remarks about keeping the heat in the heater) The insulation is probably not very thick (welders blanket?) but allows the surface temperature to remain relatively cool... maybe we can get it down around 100C or less.
The idea is that the fire burns for a short while till the tin has melted and then let die. The Stove continues to shed heat for hours as the Tin "freezes". The insulation keeps the cabin from over heating with a fast burning fire and also lets the heat keep radiating longer.
A further idea is that the tin boxes could be detachable and placed under bedding or seating... or for that matter placed under a pot to boil water.
I realize that because a boat has a small inside space, most people are not worried about saving fuel so long as it works and keeps them warm and dry. So maybe the world is not ready for such ideas... gotta make one.