boiler insulation / wood staves

[lighthousekeeper]

Hi well I hade my first launch yesterday june 8th pretty exciting day and stressful many technical issues on my mind , from how the trailer wood work, position of boiler and engine, is the prop selection good, what kind of speed would I achieve, wood the insulation around boiler work, would I be able to maintain steam pressure. Anyway most things worked out fine my biggest problem was a onboard fire with my insulation and cedar staves surrounding the boiler, would the heat shield work under boiler. Plus adding to everything I was by myself !

I bought industrial insulation called duck wrap for pipe and tanks good for 750 degrees F my fire box gets up to 550 F the insulation burnt thru and started the cedar staves on fire no big deal to put out.

So my question is this what type of insulation are u guys using? and second what type of wood do you have around your boilers?

here is a link to my launch https://youtu.be/gY1x6lbtZ14

[Edward]

Dear lighthousekeeper ,

On my boat's boiler the insulation is 1 1/2" mineral wool loft insulation which is fairly compressed by the teak staves . Nevertheless it is quite effective enough .
BUT the boiler has a wet firebox/waterleg ; so at 200psi the insulation only has to cope with 200C degrees . Loft insulation is cheap but wouldn't begin to cope with the temperature around your firebox .
I'm sure you'll get all the right answers as to what insulation material to surround the firebox to deal with the 750F degrees you quote but it might be worthwhile (cheaper) to use the expensive stuff around the firebox and loft insulation around the upper part of the boiler .

Regards Edward.

[fredrosse]

What kind of boiler do you have? A wet furnace will not exceed water/steam temperature, and a layer of fiberglass insulation with wood over that will be OK. If you have a dry furnace wrapper, then temperatures will be high, you need good high temp insulation, and, if you want wood over that, then there must be a "thermal break" between the insulation and the wood. This is best accomplished with an air gap of about 1/2 to 1 inch all around, with provision for air circulation between the wood and insulation.

From a previous post on this forum: Having very good insulation between hot boiler parts, and a wood boat structure is problematic UNLESS there is an "thermal break" or "Thermal barrier" between the insulation and the wood. An air gap of about 1/2 to 1 inch between the insulation and the wood is one solution, and a moderate air circulation will keep high temperature away from the wood. If the insulation is in contact with the wood, then the wood temperature can rise considerably.

Search "Insulation" on the forum, there have been plenty of reasonable ideas posted there.

[DetroiTug]

Congrats on your first outing.

The insulation typically used for that is unifrax or fiberfrax, I think they are the same thing. If it's getting that hot, I'd go with 2" thick. Some Ebay sellers have it. Also, I've purchased by the square foot on line but I cannot remember where. Seems to me it was in Grand Rapids, Michigan at a heating and cooling place - can't remember the name.

Found it, here it is:

http://www.infraredheaters.com/insulati.html

-Ron

[lighthousekeeper]

Well just got back from town bought a product by johns Manville called minWool 1200 pipe and tank wrap high temp insulation according to their specs it good to 1200 degrees F or 650 degree C it is 1 1/2 inchs thick.

Now I have a new problem should I leave a air space between insulation and wood staves which I think I will go with a hard wood local black ash.

Oh and yes my fire box is dry I got temp of 550 degrees F

jamie

[fredrosse]

If you have the published thermal conductivity for your new insulation I can calculate the interface temperature between wood and insulation. I think you will need an air gap.

[Lopez Mike]

I have 2" glass wool blanket with no air gap between it and the wood staves. The only discoloring of the wood is right around the boiler penetrations. I wasn't smart enough to leave enough room there. Also, there is no or little blanket at those points.

This is on a water tube upright boiler.

I have a wood ring around the top of the staves made up of eight segments (arcs?). Their cross section is about 2" by 1/2". I glued the ends of the segments with biscuits and yellow/white carpenter's glue. Mistake. I will need to re-bond them with something better. Perhaps epoxy.

[steamdon-jr]

I myself and many other steamers I know with a water lef on their boiler hve no insulation, I am in my third year of operation with mahogany staving and no insulation and it has been absolutely fine. I believe all or most of Rappahanock boatworks builds have direct wood over boiler as well

[Lopez Mike]

Seems like you would be wasting a lot of fuel by not insulating you boiler with more than a layer of wood.

[steamdon-jr]

I can hold my hand on it for more than 10 seconds so not too much heat loss