Heating and ventilation in a small cruiser
The only problem I see is that the “mass” part of the “mass heater” isn’t particularly proa friendly.
I imagine that in a small confined space like a 30 foot proa, the rocket stove could be scaled down to a bucket-size with a weight of about 10 kg. A rocket stove/mass heater the “mass” part could be a 60 mm pipe surrounded by 3 - 10 cm sand.
The weight should end up at around 50 kg. Maybe a water-tank that can be filled with seawater and heated by the rocket-stove when one needs to keep warm through a cold night?
Cheers,
Johannes
I like the idea about using seawater as the mass, it could work very well in a small proa. Keep the tank empty while you’re sailing, then fill it up when you stop for the night, build a nice big fire to cook your dinner, leave it burning for an hour or two and stay warm all through the night, then just drain the tank when you’re ready to set sail the next morning.
300 liter ballast will calm down the hull, so there is less movement when at anchor.
I really like this idea. I hope I can use something similar in my large proa (if it ever get built…)
The rocket stove and mass heater are great ideas. I have to try one. I am looking for some small steel plates to build one. I want to build a really small rocket stove. One that fits in the palm of my hand.
Cheers,
Johannes
300 liter ballast will calm down the hull, so there is less movement when at anchor.
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The rocket stove and mass heater are great ideas. I have to try one. I am looking for some small steel plates to build one. I want to build a really small rocket stove. One that fits in the palm of my hand.
300kg seems a bit excessive for heater mass in a small-ish boat. If you were transferring, say, ~25%-40% of the energy released by the burning wood into the water, you’d need to burn 2 or 3 kg of wood per 10˚C of increased temp. You might be better off with a smaller mass that heats up more quickly and then all the ballast you want out in the bows and the ama, where it will do the most good.
For small pieces of steel, try calling around to some local metal working shops. They’ll have plenty of scrap pieces that may be just what you’re looking for, and if you ask nicely they’ll probably sell you what you want for peanuts.
A wonderful technical solution, but surely complete overkill!
Looking at your data (good spreadsheet, might borrow that, never knew how to allow for ventilation), is 20deg inside a bit generous, we always have problems getting our old house above 15deg! Outside temperature of 0deg, is pretty cold for most during the average winter day, well at least here in Scotland. So on average here could be half the heat loss, which is actually very little.
This would easily be catered for by a more simple, and yes, less efficient system. The question is what that is. As you say, there is a high risk with fuel burning, (are there more sailors killed with carbon monoxide or blown up with gas than drown? perhaps.) Definitely a chimney to outside. Ideally a fully sealed system, with ducted air supply to the combustion and then flue back out. A double skinned chimney where the air is drawn in in the outer part, exchanging heat from the flue gas, very good. And it gives a balanced flue, that is the supply and exhaust coming from close by outside, so there is no pressure difference, blowing out the flame. This could work with kerosene / paraffin, or gas with a simple off the shelf burner.
With wood, the Rocket stove principle is worth looking at. This works by combustion temperature being boosted to give high efficiency. The flue gases pass back and downwards outside the combustion chamber ,so it gets very hot, (it has to be a clay - ceramic chamber.) Not sure that the simple rocket stove has all this going on - look at the Rocket mass stove. A small version for a boat would be well worth a go, not as much for its efficiency, but to reduce the amount of timber fuel to be carried.
My only heater so far: a large clay plant pot, upside down, placed over the stove, with a flue of 22mm copper water pipe from the hole in the bottom (now top) leading through the hatch. Simple pretty effective, v cheap, v quick to make. Ok it was very crude, but a plant pot does make a good combustion chamber. now added
cheers
Mark
@ Manic: I hope it is ok if I spam your thread with one more post about rocket stoves?!
I built a very small rocket stove out of three food cans and some thin wire.
It burns really hot and there is very little smoke. I think it is to short, as there is to much flame outside the stove. I built it out what I had laying around.
It is still to hot too touch 15 minutes after I removed all the wood and put out the fire inside it. Impressive for souch a small stove. It is filled with sand.
This is a very fun test that I encourage everyone interested in simple heating systems to try. It took me about half and hour to build it with a pair of pliers, a knife and a metal shears.
Cheers,
Johannes.
No I don’t mind at all. 😉 This thread is called “Heating and ventilation in a small cruiser”, and that’s what we’re talking about here. Personally I still much prefer my very controlled heating ventilation scheme for it’s good controllability high safety, and autonomous operation (you can just leave the kerosene burner running 24/7 and never have to add firewood or remove ash), but the rocket stove is pretty cool (and I love the tin-can version!)
Rocket stoves weren’t really anything new for me though, I think Dr. Winiarski pretty much reinvented the wheel there: the finnish army uses a stove of very similar construction (though with the army stoves you put firewood in through the lid at the top, see picture!), to heat their tents in the winter. Those themselves are mechanically simplified versions fo traditional sauna stoves which work exactly the same way, but have a drawer to remove ash at the bottom, and a side-mounted door to put in firewood. The army ones have a chimney which goes through the top of the tent (you can see some of the pipe sections lying on the ground in the picture, for transport you just put the chimney pipe pieces into the stove itself). Inside that big metal can there is a grill on which the firewood sits, meaning the airflow from the lower duct (which is adjustable) flows into the combustion area from below, while the upper air inlet (also adjustable) feeds air in to the bottom-side of the combustion area. Those things are simple, cheap, and have been used for ages.
That definitely brings back some fond memories! -32C, outside all day alternating between sweating while skiing / running around in a meter of snow in all our winter combat gear, and then stopping for a break and freeeezing in our sweaty gear like nothing I’ve ever felt before or since. Then at the end of that, right before we start the next day with the same thing all over again, they give us 2 hours to sleep in a tent which is actually warm. It’s crowded, you’re exhausted, hungry, feel like shit, you’ve literally got ice on the tips of your eyebrows and on the outside of your clothing from frozen perspiration, but in that moment you don’t care; a 50°C temperature difference, just by being on the other side of a cloth tent flap = absolute bliss! 😊 I loved those stoves.
Back on topic though… The convection on those things is very strong, on both the army and sauna stoves you can really hear the airflow streaming in through the vents, and I can testify to their relatively smokeless and high temperature combustion. You can easily get the steel to glow with an orange color if you add enough firewood and put the vents into their open position. I personally would recommend something more like the Finnish army stove for a boat, as opposed to the rocket stove, because you’re likely to have less trouble with waves if you have a lid at the top of the stove to insert firewood, instead of a hatch or whatever on the side of the oven, which would need a fastener of some sort. With the lid, you just take a piece of wood to move the lid to the side a little (it’s hot), drop some pieces of dry firewood in, put the lid back on, and it stays there.
Marco
I really like those army stoves, especially the vertical wood feed. I agree that vertical feed would be more seaworthy than horizontal feed and in addition to that, vertically loaded firewood would be self tending; put a nice long stick in the feed tube and as the lit end burns away, gravity pulls fresh wood into the flames and the fire keeps on burning with no need for anyone to fuss with it. A horizontal feed stove seems to me like it would need someone to occasionally push the firewood further into the stove (disclaimer, I have no experience with wood burning stoves, I’m just guessing).
I think the rocket/finnish stove could incorporate some ideas from the kerosene stove concept, that would make it seriously efficient, without making it too much more complicated. The first is bringing in the combustion air directly from outside because, as Marco mentioned, these stoves will generate significant airflow. If you pull that airflow from the cabin, you are in turn pulling an equally significant volume of freezing cold air into the cabin which is totally counter productive. By using a “closed” loop for the combustion gasses, you can minimize the cabin/outside air exchange which will minimize the heat loss and by extension minimize the firewood consumption of the boat. The second is the double walled flue heat exchanger. Since the wood stove is super low tech and simple, forced air is out of the question (IMO) so instead of using the heat exchanger to preheat the cabin inlet air, it could be used to preheat the combustion air. By taking waste heat from the flue and putting it back into the combustion chamber, we increase the combustion temperatures and by extension increase the heat transfer from the heat riser into the mass and cabin without using any extra wood. The cabin itself could be ventilated by natural convection, with an (insulated) inlet near the floor behind the stove and an overhead outlet on the far end of the cabin and an adjustable grate on the outlet to allow just enough air exchange to prevent condensation.
A few more thoughts;
- Drawing supply air form the cabin does have the advantage of giving air change, especially if the incoming air passes over the chimney. Not as safe as a closed system though.
- A closed system, with mechanical heat recovery air change is all very good, but as the cabin has to be well sealed, it would be a hazard if the fan stopped working! I would always want an open vent.
- Taking heat off a flue is a risk. The VW beetle / camper van had heat exchanger on the exhaust. I think mine must have leaked a bit, always arrived a bit light headed (& nearly beaten up in a Welsh country & western pub, when we all started giggling, but I stray…)
- Could the rocket stove principle be used with a paraffin wick stove, thus increasing its efficiency to that of a Primus type pressure stove, without all the hassle of blocked jets etc.?
Like the Swedish tent stove, could you do a sketch to show how it works inside? Love the tin can one even more.
Also just picked up on were this thread started. I would think 25mm foam enough for a small boat, try it on the spread sheet, it will not make that much difference. The better insulating foams are structurally no good. I would only use Stryfoam. I have a Styrofoam / epoxy windsurfing board, now 30 years old, just about surviving, though not much used recently.
cheers
Mark
Regarding foam and insulation. Sven Yrvind http://www.yrvind.com uses a very clever and easy (and expensive) way to get good insulation, good structural strength and stiffness and an unsinkable hull, by using a very thick divinycell core. He uses 40 - 50 mm, but one could use much thicker foam than that. With a 4 inch = 100 mm foam core one could get a very clean smooth interior without all the stringers and only a few bulkheads. A very good insulation and an enormous structural stiffness.
With an inner layer of 3 inch foam with carbonfiber on each side and an outer layer of “sacrificial” foam with a very flexible layer of polyester weave and epoxy as an outermost layer, one gets a very good global stiffness and strength and a very good local impact energy distribution and absorption.
By laminating several layers of foam, it is easy to use different densities in different areas.
With enough foam one would probably not need any additional heat source to keep warm throughout October here in Sweden (or Finland).
Cheers,
Johannes
Like the Swedish tent stove, could you do a sketch to show how it works inside?
I could be wrong but, from the looks/description, I’d guess it works like this:
When doing my military service we spent two weeks in a cold hell-hole in norther part of Dalarna here in Sweden. It was really cold, especially the nights. One night our stove did not work. We got a fire going for 10 minutes and than it died. We tried and tried and we were all freezing.
I got really pissed off, so finaly i poured one liter of gasoline into the tent-stove. One second later all the hair in my face was burned off and the stove was burning like mad. The flames shoot 3 meters out of the flue. It really roared.
They were very effective when working properly.
Cheers,
Johannes
Here’s a sketch of the finnish army tent stove. It really is very simple, but works great. There is definitely a downside to using it on the boat though, and that’s the problem of ash, though a rocket stove will have that problem as well. If you use well-dried firewood in these stoves you do get very little ash, but there is some, which means you have to get it out sooner or later. With the army stove you just take it, upend the thing and the ash comes falling out. Not particularly elegant, but it works fine.
For a stove which is permanently installed, that would be a problem though. With the rocket stove I think you have a similar issue, since getting the ash out the side somehow is not particularly practical either. The best solution I can think of is to just do it like they do for sauna stoves, which is to have a drawer in the lower compartment, which the ash simply falls into. Then you can take out the whole drawer, pour the ash out, and put it back in. The drawer, left open a little, can also serve as the lower air vent.
What’s the deal with its swedish couterpart? How is it designed?
I bet the finnish one is better! 😊—Or at the very least, a lot cruder. xD
Marco
P.S. - I’m still for the closed loop kerosene heater. The burner doesn’t need a fan, so no issues there, and a cabin fan failure wouldn’t be a particularly serious issue. If you set it up like gregs sketch, where the fan is the last component before the air is vented into the cabin, it’s easily replaceable, and you can see if the fan is running or not. If the fan fails, then your heating and ventilation is out (you’re not drawing air into the cabin through the heat exchanger after all), but there’s still no danger of combustion gases getting into the cabin. Personally I’d just take a spare fan along, but provided you have warm sleeping bags onboard, which is a must anyway in my opinion, I’d consider the heating going out be more of an inconvenience anyway, as opposed to a serious danger, at least for a short leg. So all in all, the fan-failure problem is non-critical to safety, is easy to detect, and easy to fix provided you have a spare, so I’d be quite content with that setup.