Boiler Installation

[csnco]

What are the proven means of shielding the hull area below the ash pan from fire box heat? All thoughts will be appreciated.

[Edward]

Dear csnco ,

The best system is to have a wet ashpan . In other words an ashpan with an inch or so of water in it .
With this the hottest it can get under it is 100 C . In practice it will be much less .

Additional advantages are that it reduces the amount of fine ash that escapes to form a good grinding paste in the engine bearings . If you're burning coal the water vapour drawn through the bed of the fire will produce some extra oxygen and hydrogen , I've heard it claimed that this can offer a substantive reduction in fuel consumption . It is also claimed by reliable people that the life of the firebars is extended .

If your oil-burning then the above advantages are obviously lessened , but for a penalty of perhaps increasing the height of the boiler in the boat by three or four inches I believe it is well worth having one .

Regards Edward .

[dhic001]

A wet ashpan is all very nice in theory, but some of us go to sea where there are proper waves. A wet ashpan would stay wet for only a few seconds in a good sea!

Zeltic has a dry ashpan by neccesity. The bottom of the firebox has about an inch of castable refractory protecting the steel from the ash itself. The firebox is mounted in a steel frame in the hull, which has a stainless liner in it. There is a gap of 1 inch between the floors in the bottom of the hull and the stainless liner. There is an inch thick layer of Kaowool between the floors and the stainless liner.

The original firebox (dry), which lasted 12 years didn't have a castable refractory base, it just had a steel floor in the base of the box that was raised off the stainless liner by one inch, and that gap was filled with Kaowool too.

After 12 years use, and thousands of miles of steaming, and weeks in steam continually, there was no heat damage to the hull at all. i'm expecting at least the same with the new firebox.

Daniel

[SL Ethel]

The Ethel has a dry firebox for her wood fired boiler as well, and it has never been a problem, even though I have less insulation than Zeltic. The 1/8" mild steel bottom of my firebox is protected by two 1/4" thick layers of high temp boiler/furnace insulation. Not sure what the correct name for it is, but it looks and feels like a very thick piece of felt. Over that 1/2" of soft insulation I have about an inch (maybe a bit less) of castable refractory. While I don't have a lot of hours on my plant yet, the times when I have had it under steam all day produced no problems with heat damage to the surrounding paint.

Cheers,
Scott

[fredrosse]

The Margaret S. has its VFT Boiler mounted on a 1/4 inch thick, 24 inch x 24 inch steel plate. Two inch thick firebrick is used between the firepot (which glows a dull red when continuously underway), followed by a 1/2 inch thick layer of kaowool on top of the steel. The steel plate did get very warm, but not hot enough to damage the wood/epoxy frames in the boat.

I had made provisions to put cooling water on the steel plate (see four pipes, welded to the bottom of the steel plate) if it got too hot, but found this cooling system to be unnecessary. Allowing air circulation around the bottom of the steel plate provides enough cooling such that the firebrick & kaowool layers provide enough insulation. If good insulation was to be used under the steel, then the temperature of the steel plate would rise considerably, possibly damaging the wood frames.

[fredrosse]

From another reply here: "Additional advantages are that it (wet ashpan) reduces the amount of fine ash that escapes to form a good grinding paste in the engine bearings . If you're burning coal the water vapour drawn through the bed of the fire will produce some extra oxygen and hydrogen , I've heard it claimed that this can offer a substantive reduction in fuel consumption . It is also claimed by reliable people that the life of the firebars is extended."

Catching fine ash, true, and this is an advantage.

Producing Hydrogen and Oxygen as water vapor passes thru the fire bed, also true, but certianly no reduction in fuel consumption. The coal combustion energy used to break the water (H2O) into its consiuent parts (Hydrogen & Oxygen) results in no net gain in heat available from the process.

Increased life of firebars, also true, as the firebars are exposed to a rather cool water surface (212F/100C or less) under the firebars. However, the radiant energy from the fire in this area is lost in evaporating water from the wet ashpan, and that evaporation keeps the ashpan at or below 212F/100C. Fire energy used to evaporate water in the ashpan is energy that is not available to evaporate water within the boiler proper.

This is not to say that a wet ashpan is necessarily a bad system, just that it reduces the heat available from the fuel. But then, fuel economy is a secondary consideration for most of us, and possibly burning a hull frame is a rather important consideration.

[preaton]

I have my makeup water tank below my boiler (made of SS). No worries about the hull.

Cheers

Paul

[JonRiley56]

All,

Reading these posts I am starting to have misgivings about how I am setting my boiler up. I have a water tube with a pretty deep ash pan under the grate. I have set it in place with about 1 inch of air space between the metal floor of the ash pan and the boat floor. Hopefully you can see that in the attached pictures.

am I asking for trouble ?

jon

[JonRiley56]

sorry about the picture orientation....................................

[fredrosse]

Wood ash is actually a very good insulator, and an inch or so of the stuff in the ash pan would significantly cut down any heating of the floor. For your setup, it is recommended that you put a wet pan, the size of your ashpan, in the space under the ashpan. This wet pan should be about 1/2 inch deep, and some old cotton toweling is set into the pan. Water is then added, the cotton will keep it from splashing out when underway.

Pay attention to the temperature of this pan, and how often you have to add water to the pan, keeping all the cotton wet. The water in the pan will positively keep this area at or below 212F/100C. If the supply of water is too much for conveinent operation, then some modifications would be required, however the setup recommended here will let you know if there are problems, and will protect your floor from excessive temperatures.