Rocket stove to heat a 30' sailboat

Hi everyone!

I have a fellow mariner that suggested a rocket stove for heating our Catalina 30' liveaboard sailboat. He is hardcore into optimal energies and I know he is heating his family well this winter. Their 45' boat is toasty like a sauna (his words)  as winter arrives. The challenge is... he is very tight with details on how I might do it. He wants us to cross the Salish Sea to come for a visit but we don't really want to go to Vancouver during the pandemic. We'd rather hang out in tranquil bays.
We use a propane bulkhead heater as a maintenance heater and a kerosene floor heater to warm things up quickly in the mornings but it's annoying to source fuels while cruising, and expensive.
My thought is to put in a wood heater where the bulkhead propane heater is. It's a small space.
I'm very new to the idea of rocket stoves and to heating mass for lingering radiant heat. We are in small communities with hardware stores and are quite proficient scavengers.

Any ideas and wisdom on something that I could build that could tap into the existing 3" pipe in the space where the bulkhead heater currently sits would be greatly appreciated by me and my wee family as winter fast approaches in the Pacific Northwest.

Hi Mike;
3" is to small but you might do 4"
Here is a rather long post that might interest you.
https://permies.com/t/43809/Masonry-stove-diy-build-feasible
Check it out and see what you think.
Oh and no rmh secrets here... we will share freely.

In my pre homesteader days I was briefly into sailing.  I went to a school for sailing in Florida in 1972.  There are wood stoves designed for tiny houses that may work for you.  As Thomas has said, you will probably need a 4 inch flue. I am not so sure about a rocket stove.

Hi Mike,

Here is a link where a fellow rocketeer is building a rmh on a boat. Could be something in there that may be of help to you.

Radiators-rocket-mass

I just don't see how a rmh, as pictured in the video, would fit on a 30 ft boat.  Even at 1/4 the size there would be serious issues regarding both weight and volume.  I am curious to see if there might be another approach.  I guess I am wondering  about a rocket heater.... that is a rmh without the mass.  I still dont see how it would work, but I am far from an expert on rmh or sailboats, although I have encountered both.

If you limit your expectations to having some warmth lasting between the last fire in late evening and the first fire in the morning, or equivalent stretches of time during the day, it might be possible. I think you couldn't make anything worthwhile less than about 16" wide x say 24" deep x 3' tall. It would need to be built inside a metal shell to keep structural integrity as the boat moves, and would need to be as low and as centered as possible in the boat's footprint so as not to unbalance the boat.

A few observations on this possibility:

1) yes, 3" vent is too small.  RMH world generally holds that a 4" diameter system is the minimum size.
2) I briefly looked for but didn't find a capacity number for the C30.  Its not considered a heeay boat, probably a medium displacement design.  A heavy displacement boat just wouldn't care about an extra 1000 lbs of mass, but you might want to consider what that much mass would do, and what you could shift to maintain balance.
3) To get academic, you either need a highly insulated and sealed space, or a constant source of heat.  A rocket heater can pack into a mass which then slowly releases that heat as your constant source.  Given the limits of boats, moisture, etc. you're not going to insulate and seal your way to warmth.  So the rocket & mass can be a substitute for a classic boat heater.  An apt comparison is the TeePee at Wheaton Labs (Montana) which works well in the winter with a large bench as mass.
4) Small space, filled with stuff.  That stuff is mass.  If you can heat that interior mass with radiant heat from a stove you may not need a classic bench mass.
5) yeah, I worry about flexing.  I'd not want to count on a brick design and slip ... either a cast core or a fibreboard design to reduce joints.
6) I really wish there was a way to use water as a mass - after all, you've got plenty!  I've tried to imagine a tank that could be filled with seawater when you want the mass... heat it up, yay.  Want to sail somewhere and lighten the boat? pump that water out.  But getting the intense heat of a rocket into water is tricky, and adding salt to the equation doesn't improve it the design.
7) fuel storage.  liquid fuel is sure easy to store, transport and has tremendous energy density.  A 30' boat has very limited storage for wood.  Granted, a rocket can be tremendously efficient but you still need something like one to two cubic feet of wood per day (other readers may have better numbers there...).
8) driftwood - seems like it could be an ideal find BUT I'd like to know what hot aerosolized salt will do to ceramics since its probably like acid on metals.
9) done well, the rocket is extremely clean and will not stink up the anchorage as much.

There are a lot of variables in play here so its hard to give a definitive answer.  If you can process some of what we're throwing at you and help us reduce the problem a little ... like how much space you can devote to the heater itself, how much storage you can give, how much weight you can add and then we can probably provide more direction.

Thank you all for the amazing thoughts. Is there such thing as a micro rocket? Is there a way to do it without the mass or with minimal mass for more realtime heat?

The space available is very small. 9"W×(12"-18"H)×12"L
I would like to put something where the existing propane bulkhead heater currently resides. (see photo in my original post). There is an existing 3" pipe. Ideally I'd like to keep 3" so if want to reinstall the propane heater when we sell the boat I can.

1) yes, 3" vent is too small.  RMH world generally holds that a 4" diameter system is the minimum size.
2) I briefly looked for but didn't find a capacity number for the C30.  Its not considered a heeay boat, probably a medium displacement design.  A heavy displacement boat just wouldn't care about an extra 1000 lbs of mass, but you might want to consider what that much mass would do, and what you could shift to maintain balance.
3) To get academic, you either need a highly insulated and sealed space, or a constant source of heat.  A rocket heater can pack into a mass which then slowly releases that heat as your constant source.  Given the limits of boats, moisture, etc. you're not going to insulate and seal your way to warmth.  So the rocket & mass can be a substitute for a classic boat heater.  An apt comparison is the TeePee at Wheaton Labs (Montana) which works well in the winter with a large bench as mass.
4) Small space, filled with stuff.  That stuff is mass.  If you can heat that interior mass with radiant heat from a stove you may not need a classic bench mass.
5) yeah, I worry about flexing.  I'd not want to count on a brick design and slip ... either a cast core or a fibreboard design to reduce joints.
6) I really wish there was a way to use water as a mass - after all, you've got plenty!  I've tried to imagine a tank that could be filled with seawater when you want the mass... heat it up, yay.  Want to sail somewhere and lighten the boat? pump that water out.  But getting the intense heat of a rocket into water is tricky, and adding salt to the equation doesn't improve it the design.
7) fuel storage.  liquid fuel is sure easy to store, transport and has tremendous energy density.  A 30' boat has very limited storage for wood.  Granted, a rocket can be tremendously efficient but you still need something like one to two cubic feet of wood per day (other readers may have better numbers there...).
8) driftwood - seems like it could be an ideal find BUT I'd like to know what hot aerosolized salt will do to ceramics since its probably like acid on metals.
9) done well, the rocket is extremely clean and will not stink up the anchorage as much.

There are a lot of variables in play here so its hard to give a definitive answer.  If you can process some of what we're throwing at you and help us reduce the problem a little ... like how much space you can devote to the heater itself, how much storage you can give, how much weight you can add and then we can probably provide more direction.

Mike:

For posterity and internet search engines I'm going to say that an RMH in a boat could work... it would be awesome to build some mass below one of the berths or the settee.  But in your case ... this is tough.  

Consider this 4" core : http://www.dragonheaters.com/4-dragon-burner-rocket-heater-core/  This ALMOST fits your space (just a little long ... maybe if it were mounted higher up?).  This style of construction makes sense in your situation, but this is of course just one of the components.  To burn cleanly and provide a radiant surface you need a "bell" - often a repurposed steel drum.  This core recommends a 30 gallon drum ... which is roughly 20" in diameter and 28" tall.  For your mounting spot I don't see how to integrate a 20" barrel ... but maybe the barrel could be cut in half, stacked and a back welded on ... making a semi-circular tunnel, 10" in radius and up to 28" tall.  

HMM ... the geometry of the pieces is important.  Not sure if it matters, and I'd have to dig around to find the answer, but that semi-barrel might be too tall for the riser.  Maybe a kind and more knowledgeable person will read this and chime in.

Anyway... hat would give you a nice radiating surface - but no mass. Generally the mass is charged by running the exhaust through it (largely a conductive process), but I don't see how to easily add a mass in this case - best option might be just radiating off a boat load (hah!) of heat and trying to get everything warm that way.  Alternately, a panel of just plain firebrick between the bulkhead and the half-drum would provide some mass.  Hmmm... a thin sheet of metal with air gap mounted on the builkhead, a frame holding bricks against that, and then the barrel.  Could work...

Uncle Mud has a "Cottage Rocket " (https://permies.com/t/150536/Uncle-Mud-CottageRocket-Paper) design that packs all of the normal features of an RMH into a single 55 gallon drum, sacrificing both mass and radiative surface for compactness.  I think the exhaust is probably hotter than in a classic heavy-bench system (but it might not be hotter than what your current stove puts out).  Anyway, the point is that his design is for small spaces so I think there is something to learn from his work for this application.

BUT - and this is a big one - while everything above is a "might work - let's see" there is no way this will work if you stay with the 3" exhaust.  You'll get smoke in the cabin, temperatures will be too low, you might get creosote in the exhaust (and risk a chimney fire).  So if you can't/won't enlarge that through-deck fitting, consider if there is a window you could modify.

And maybe if I say his name out loud three times we'll get Ernie Wisener involved ... he may be the one person in the world who can tell us how to do a rocket on a boat!

Thanks for this input. The bricks and steel backing were something I have been visualizing. The frame suggestion solves how to hold it in place. I'll have a look at the links. Thank you!

Eliot Mason wrote:Mike:

For posterity and internet search engines I'm going to say that an RMH in a boat could work... it would be awesome to build some mass below one of the berths or the settee.  But in your case ... this is tough.  

Consider this 4" core : http://www.dragonheaters.com/4-dragon-burner-rocket-heater-core/  This ALMOST fits your space (just a little long ... maybe if it were mounted higher up?).  This style of construction makes sense in your situation, but this is of course just one of the components.  To burn cleanly and provide a radiant surface you need a "bell" - often a repurposed steel drum.  This core recommends a 30 gallon drum ... which is roughly 20" in diameter and 28" tall.  For your mounting spot I don't see how to integrate a 20" barrel ... but maybe the barrel could be cut in half, stacked and a back welded on ... making a semi-circular tunnel, 10" in radius and up to 28" tall.  

HMM ... the geometry of the pieces is important.  Not sure if it matters, and I'd have to dig around to find the answer, but that semi-barrel might be too tall for the riser.  Maybe a kind and more knowledgeable person will read this and chime in.

Anyway... hat would give you a nice radiating surface - but no mass. Generally the mass is charged by running the exhaust through it (largely a conductive process), but I don't see how to easily add a mass in this case - best option might be just radiating off a boat load (hah!) of heat and trying to get everything warm that way.  Alternately, a panel of just plain firebrick between the bulkhead and the half-drum would provide some mass.  Hmmm... a thin sheet of metal with air gap mounted on the builkhead, a frame holding bricks against that, and then the barrel.  Could work...

Uncle Mud has a "Cottage Rocket " (https://permies.com/t/150536/Uncle-Mud-CottageRocket-Paper) design that packs all of the normal features of an RMH into a single 55 gallon drum, sacrificing both mass and radiative surface for compactness.  I think the exhaust is probably hotter than in a classic heavy-bench system (but it might not be hotter than what your current stove puts out).  Anyway, the point is that his design is for small spaces so I think there is something to learn from his work for this application.

BUT - and this is a big one - while everything above is a "might work - let's see" there is no way this will work if you stay with the 3" exhaust.  You'll get smoke in the cabin, temperatures will be too low, you might get creosote in the exhaust (and risk a chimney fire).  So if you can't/won't enlarge that through-deck fitting, consider if there is a window you could modify.

And maybe if I say his name out loud three times we'll get Ernie Wisener involved ... he may be the one person in the world who can tell us how to do a rocket on a boat!

Hi folks
I'm considering buying a boat for liveaboard in nordic climate and are facing the same challenges as Mike. I'm looking at boats size 35-40', hence a bit larger than Mikes, and a bit more area to heat. I've never had issues finding wood to make a campfire on islands when I've been boatcamping with the 14' boat, without using driftwood, so I guess that salty firewood will not be an issue.
When it comes to mass, I'm planning to have an inboard engine and hot and cold freshwater tanks. I'm thinking that if there could be a way to circulate the engine coolant through the rocket (mass) heater, the engine mass would heat up and work well as a mass. After all the engine is mounted near the center of boat and far down in all the boats I've been looking at, so it does have the perfect placement for radiating heat. I'm thinking of placing insulation around the engine compartment for slowing down the heat radiation. Not sure how much thermal energy an engine would store but assumed it has 200kg of various materials, I guess it would hold quite a bit.
Water tanks... It seems to be normal for boats of this size to have 4-600liter fresh water, and 40-60 liter of hot water. In the heating season, these tanks could swap, so that there is 4-600liter of hot water and 40-60 liter of cold water. Maybe add another 100liter of cold water. I guess in most cases it's possible to put insulation around the water tank as well.
With this setup, the issue of making a light weight rmh in a boat is no longer the missing mass, but rather to find a way to circulate some liquid through pipework through the heater and trough the water tank and the engine. This should be able to run with a solar powered pump, or maybe a TEG mounted on the rocket. If the pump runs too slow, the heater will heat the living space to 90C before the water tank reaches 30C.

How could a rocket be built so that most of the heat is transferred to the tank/engine?
Could this all be combined in such way that the rocket also could be used for cooking food?

Also, grey water  collection, particularly from the shower, would contribute to preserving heat.