boiler mounting

[dwkoski]

I have just completed installation of the bedding in my Paul Gartside designed hull under constuction. I have done the bedding in white oak rather than fir (mainly because heavy white oak planks were free.) I am unsure as to how I should mount the boiler base (from Jeff Lund) on the planks. I was thinking of covering the bedding with a sheet of Dura-rock and setting a shalloow stainless steel pan on top of that to place a small amount of water in. The Lund boiler has the steel fire box as it's floor. As I am new to this hobby and this boat is my first effort, I could use a bit of advice. All suggestions gratefully accepted...Dave

[gondolier88]

You will need an air gap of at least 1" below the ash pan for a start off. If you can get a sheet of what's known generically as Asbestolux over here in UK this can be cut to shape, filed or sanded to give the best fit possible. You don't want rockwool blocking up your limber holes or you will have problems.

Greg

[dwkoski]

Would I be better off to use stand-offs between the bottom of the ashpan and the bedding planks or a solid sheet of insulation? Asbestos based materials are basically unavailable here. Synthetic insulations are available but the only thing I have seen that might stand up to the considerable weight of a boiler would be a product like Durarock which is a concrete based furnace and stove insulating board. I can understand the disadvantage of no air circulation under the ash pan but cannot see how 600 Ibs of boiler weight could be adequately supported by a few bolts if supported on stand-offs. More info, please....Dave

[fredrosse]

There is a previous thread that addresses this subject, "Boiler Installation" have a look at this.

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.

Another method is to put a water cooled metal plate between the insulation and the wood, much more troublesome.

My boiler weighs about 500 pounds, and is mounted with four "stand off" studs of only 3/8 inch diameter. Considering the effective bolt cross sectional area reduction due to threads of the studs, any one of these studs can easily hold more than twice the weight of the boiler.

[dwkoski]

Thank you, that was the thread I was looking for and couldn't find. I think my plan will be be to build a pan to fit directly on and over the boiler mounting hanger bolts and put 1" metal spacers in the pan to set the ash pan off the bottom. I'll then use the wet towel suggested to keep water in the pan. Just for overkill, I'll use synthetic kiln insulation under the pan and cast an inch of refractory in the bottom of the ash pan.

[barts]

Instead of that inch of refractory in the ash pan, consider an inch of kiln insulation, covered with some stainless steel sheet. The weight will be a tiny fraction, and it will do a far better job of preventing heat transfer. Alternatively, slice some _lightweight_ insulating firebrick ( I used an old bandsaw blade) into the appropriate sizes and line the ash pan w/ that. It's not very strong, but a few cracks won't hurt when it's lying down anyway.

- Bart

[gondolier88]

Asbestos based materials are basically unavailable here. Synthetic insulations are available but the only thing I have seen that might stand up to the considerable weight of a boiler would be a product like Durarock which is a concrete based furnace and stove insulating board. I can understand the disadvantage of no air circulation under the ash pan but cannot see how 600 Ibs of boiler weight could be adequately supported by a few bolts if supported on stand-offs. More info, please....Dave

Asbestos is illegal in just about every country now I think, but I think we are describing the same product- it replace the old asbestos impregnated board used for fireproofing.

The boiler itself should be on steel bearers, if the bearers can be box section, and bolt to the boiler beds a few inches from the boiler then there should be little fire risk.

Greg

[dwkoski]

I think I have it now. I found an aluminum pan used for protecting floors from water heater leaks. It is just the right size to sit beneath the boiler. i intend to set it on top ot the bedding planks with stainless hanger bolts protruding through it. I will then set 1x2x2 heavy steel square tubing spacers on the hanger bolts. I will use separate stainless bolts to connect the ash pan to the top of the square tubing. I picked up some refractory cement and I will caot the bottom of the ash pan with this. Finally, I'll keep some wet cotton towelling between the drip pan and the underside of the ash pan. I also found some synthetic sheet insulation meant for kilns which I will glue between the bedding planks to provide a little extra protection for the hull but I will leave a significant air gap and provision for air circulation....Dave