My SuperCat Stove blows out. Defective windscreen?
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Delmar O'Donnell
(Bolster)

Locale: Between Jacinto & Gorgonio
My SuperCat Stove blows out. Defective windscreen? on 10/03/2013 22:56:10 MDT Print View

I have a traditional self-made aluminum flashing windscreen for my SuperCat stove, and on a recent windy morning I could not keep the stove lit due to wind. My alum flashing windscreen has relatively small 1/4" holes along the base of the screen, about 5/16 from bottom edge to center of the 37 vent holes...in other words, relatively small holes that are pretty close to the base of the windscreen. I'm thinking that should be reasonably effective in breaking up direct wind, and errs on the side of holes that are too small for a SuperCat, if anything. (SuperCats need loads of air.) The screen is 2-1/4" tall so it nests inside a Grease Pot.

I've been pondering my windscreen problem.

I was reading some of Zelph's old posts. One in particular, where he noticed how screen door mesh really cut down on a brisk wind. Has anyone tried just plain mesh for a windscreen...if so, what happens? I imagine you'd lose a lot of the reflective nature of the windscreen with all mesh, but does an all-mesh windscreen tame the wind, with its much much smaller holes?

I've also considered somehow affixing a strip of screen just around the holes of my alum flash windscreen, to baffle the air even further.

I've also considered making a plain, short (1" high), unperforated inner ring of flashing, sitting perhaps a quarter inch inside my existing windscreen, whose job it is to simply break up any direct wind coming through the 1/4" holes.

Another fix, which I don't want to contemplate, is making a taller windscreen that doesn't nest.

Ideas? Are my descriptions clear, do I need to post photos?

Edited by Bolster on 10/03/2013 23:09:44 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: My SuperCat Stove blows out. Defective windscreen? on 10/03/2013 23:13:43 MDT Print View

Can you estimate the distance from the top lip of the cook pot to the windscreen?

--B.G.--

Delmar O'Donnell
(Bolster)

Locale: Between Jacinto & Gorgonio
Two on 10/03/2013 23:17:51 MDT Print View

When pot on SuperCat, there's 2" of pot visible above the top of the screen. If I make a taller screen, no more nesting. :-(

Are you thinking wind coming in over the top of the screen, and blowing down, was the problem? That would indicate cinching up the windscreen more tightly around the stove. SuperCats are "big breathers" so you don't get the option of cinching it up too tight, but typically I have 1/4" between the screen and the pot, all the way around. Not good?

windscreen

Edited by Bolster on 10/03/2013 23:20:33 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Two on 10/03/2013 23:31:34 MDT Print View

I was a little surprised to see this.

Some people use a short windscreen like this, and it keeps the wind off the flame area and that's all.

I always use a tall windscreen, and it comes up to the height of the cook pot on the burner. That keeps the wind off the flame area, and it also keeps the wind off the cook pot. That seems to be much more efficient, heat-wise. It holds more exhaust heat around the cook pot.

The space between the top of the cook pot and the top of the tall windscreen varies, but it is generally equal to the size of my index finger or maybe one centimeter.

--B.G.--

Delmar O'Donnell
(Bolster)

Locale: Between Jacinto & Gorgonio
Simmer, maybe on 10/04/2013 00:00:46 MDT Print View

I'm certain you're correct, Bob, a taller screen would add efficiency. I cut it as you see it so it would nest inside the pot, under the pot's strainer. It's maximum height under that constraint. As is, I'm not complaining about efficiency, the 30 hole SuperCat is giving me 4-min boils for two cups of water on 3/4 oz alcohol, with flameout at 6 min. Part of the reason is the Grease Pot's wide circumference...the flame must dwell along the bottom of the pot a long time before going up the sides.* Other stoves can do better, efficiency wise, but I'm not complaining. I AM complaining about flame stability in wind, and keeping it lit.

One other possibility I'm considering is making myself a "SimmerCat," same stove with only one (top) row of holes. Such a stove would need less air, allowing a tighter windscreen around the circumference. Also the vertical distance between the holes of the windscreen and the holes of the stove would be greater. And, on top of that, I've been reading that slower stoves are generally more efficient. So maybe I need to make myself a new cat stove to get a more stable and dependable flame.

*Off topic, one "problem" of the grease pot, IMO, is that it's too tall, with too much capacity for solo. It's 4-1/2 cups. It would be nice to be able to re-roll the lip of a grease pot about an inch lower, to get a squat, wide pot. Can't beat the weight, though. These grease pots are lighter (and more conductive) than Ti. (Not to mention, $7 at Kmart).

Edited by Bolster on 10/04/2013 00:08:53 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Simmer, maybe on 10/04/2013 00:08:50 MDT Print View

"These grease pots are lighter (and more conductive) than Ti."

So far, that hasn't gotten you very far.

--B.G.--

Delmar O'Donnell
(Bolster)

Locale: Between Jacinto & Gorgonio
Say what? on 10/04/2013 00:10:06 MDT Print View

What do you mean, Bob? The pot (and stove and screen) have functioned excellently for many dozens of meals. I'm complaining about one windy morning I couldn't keep it lit, which I attribute to the windscreen and stove (and perhaps my technique), rather than the pot. I'd say the pot's gotten me pretty durn far. But the pot is a side issue; I'm trying to fix my flameout problem, with an eye toward more windy days in the future. But let's not go so far as to assume abject failure, here.

(I should add, I DID get my breakfast that windy morning. I used my CCF sitpad as a windbreak, and all was well.)

Edited by Bolster on 10/04/2013 00:18:38 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Say what? on 10/04/2013 00:19:43 MDT Print View

I use a 1.8 ounce titanium bowl that holds 20 fluid ounces. It is thin enough that thermal conductivity is not a problem, but I use it primarily over an Esbit burner. I have four or five alcohol burners as well, but they don't hold much advantage for me. The 12-10 alcohol burner seems the best of the bunch.

If your windscreen is aluminum flashing metal, then there is a break in the circle. Try opening up the break so that there is a gap to let in more air. Either that will make it better or make it worse. That will tell you if it is an input air problem.

--B.G.--

Mole J
(MoleJ) - F

Locale: UK
taller screen on 10/04/2013 01:18:00 MDT Print View

If a taller screen is needed (probably the case), then a nesting one can still be made. Just make it in 2 pieces - i.e. add an extension top half which you can sit on the existing screen. Join them by cutting matching slots/castellations in each piece. Sounds like you will only need the top piece occasionally.

J R
(JRinGeorgia) - F
why is taller the only answer? on 10/04/2013 06:13:26 MDT Print View

I'm not sure about the singular focus on the height of your windscreen as the source of the problem. Maybe, but what about the simple possibility that the intake holes facing the wind are letting too much in? I'd suggest trying the windscreen upside down, with the side facing the wind flat to the ground and using some small twigs or pebbles to prop open the bottom around the sides and back. Or, just use a bit of aluminum foil to block the holes facing the wind. If that works then you can investigate a way to block some of the holes more permanently.

Dan Yeruski
(zelph) - MLife

Locale: www.bplite.com
not the norm on 10/04/2013 06:42:18 MDT Print View

I would guess it was more windy than normal. Just one of those things that happen when out in the field. Use your pack and your body to block the wind on those exceptionally windy days.

Delmar O'Donnell
(Bolster)

Locale: Between Jacinto & Gorgonio
Fine mesh screen? on 10/04/2013 09:35:32 MDT Print View

Hi Dan! Thanks for weighing in, hoped you would...what's the scoop on simply using a fine mesh screen as a windscreen?

PS: Recently ordered my first Zelph stove, a SimmerLyte (or whatever you are calling it), very excited. Thanks for the special BPL offer on those.

Edited by Bolster on 10/04/2013 09:36:10 MDT.

James Klein
(jnklein21) - M

Locale: Southeast
Re: My SuperCat Stove blows out. Defective windscreen? on 10/04/2013 10:29:55 MDT Print View

I bet is isn't the height of the windscreen.

I use a cone type windscreen. With the first one I made, I could blow out the stove inside the cone. The next iteration used paper-hole-punch sized holes and is much more difficult to blow out.

You could try to attach a strip of screen around your windscreen with a paper clip or maybe a run of shock cord/large rubberband.

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Use your pack and your body to block the wind on 10/04/2013 10:43:05 MDT Print View

Dan also made a video showing how raising the bottom of the windscreen 1/2 to 3/4 of an inch off of the "ground" aided in flame stability. This would also allow for more air flow to feed the stove's flame.

Is it at all possible that your stove was being starved for air despite the windy conditions?

Party On,

Newton ;-)

Dale Wambaugh
(dwambaugh) - MLife

Locale: Pacific Northwest
Re: My SuperCat Stove blows out. Defective windscreen? on 10/04/2013 12:37:02 MDT Print View

I would build another screen with no holes on one side and experiment with holes on the other. That way you can orient it to suit the wind direction. Or just add foil tape to yours.

The physics of alcohol stoves and pot size, air gaps, and air holes is a mystery to me. It seems like a lot of trial and error is needed.

+1 on using your pack, foam pad, etc as wind blocks.

Steven McAllister
(brooklynkayak) - MLife

Locale: Atlantic North East
Re: My SuperCat Stove blows out. Defective windscreen? on 10/05/2013 04:14:08 MDT Print View

Screen does reduce wind gusts, but still allows good air flow.

It is common to use pantyhose/nylons stretched over a wire frame around microphones to reduce wind noise for outdoor recording.

Aluminum screen would work, specially double with a space in between, but at what weight?

I have used my sleeping pad formed into a big wind block tube during extreme wind.

Christopher *
(cfrey.0) - M

Locale: US East Coast
Re: My SuperCat Stove blows out. Defective windscreen? on 10/05/2013 15:09:22 MDT Print View

My first blush response would be to agree that the problem is not enough air.

Wind rushing past those small evenly spaced holes in your screen may be setting up something akin to a venturi siphon, sucking the air out of your system. Add in the fact that the lingering combustion gases across the bottom of your wide pot are looking for an exit and ... well who knows. I'm just spitballing. I don't think a taller screen is the answer though. I think it was Tony Beasley (here or on BPLITE) who showed that as combustion gases rise and cool, if you entrap them too long they can actually steal heat from the sides of your pot. I'm just repeating (poorly) what he said though, with no proof one way or the other.

You might want to play with varying the hole size and height of your vents relative to one another. Good Luck. I'd be interested in hearing how you make out.

Edited by cfrey.0 on 10/05/2013 15:16:49 MDT.

Delmar O'Donnell
(Bolster)

Locale: Between Jacinto & Gorgonio
Insights on 10/05/2013 18:26:01 MDT Print View

Thanks for the interesting leads, folks. I had not considered "air starvation" on a windy day as a possible cause.

I tried to repeat the effect in my home kitchen by setting up an 18" Patton fan (no small fan) and set the fan on medium (no small wind) and placed it 7 feet from my stove. This gave me a blustery test area. Turned off the overhead lights so I could see the flame. Used the same windscreen as before, but set it a little tighter, maybe 1/4" space all around. (I believe I had set it at maybe 1/2" all around when I got my failure.) The flame danced about plenty, but did not extinguish. So, puzzled, still. In previous testing, the SuperCat has been very sensitive to "screen too close" so my impulse is to leave the windscreen relatively loose around.

I'm curious about the comment on the even spacing of the holes. That makes a difference?? Is it better to have holes randomly spaced? Oval?

What about even more, even smaller holes? In effect, making my own screen?

Regards the idea of holes in one side of the windscreen and none on the other: that occurred to me too, and I made a screen like that. It was a failure; the flame would burn brightly only on one side of the stove (the side with the screen's holes), and I got an anemic weak flame on the side of the windscreen with no holes. A severely asymmetrical flame. Clearly this SuperCat wants to breathe, and breathe heavily.

John Donewar
(Newton) - MLife

Locale: Southeastern Louisiana
Re: Insights on 10/06/2013 06:50:20 MDT Print View

Here is the link to the video that Dan / Zelph made that shows and explains the idea of raising the windscreen much better than I could.

http://www.youtube.com/watch?v=a7mb-DU2sWY

FWIW here is a picture of my version of a MYOG aluminum flashing windscreen in which I incorporated Dan's idea of a raised windscreen.

"Raised" windscreen with Foster's pot test burn

A windscreen like this will allow air to feed the stove flame but you may still need to use your pack and or foam pad as a wind blocker on those blustery days on the trail.

Party On,

Newton ;-)

Alpine Dad
(AlpineDad)
Elevated windscreen on 10/07/2013 06:44:46 MDT Print View

Thanks for posting that video link John. I am going to have to redesign my windscreen now.

Cheers