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Oct 19, 2015, 11:32 AM
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Build Log

Steam Plant for a Tug Boat

Its time to start documenting my journey, The first pictures are of a complete steam power plant that I purchased already assembled but never fired up. As you can see the previous owner had painted it with black paint which I believe is Tremclad (never dries).
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Oct 19, 2015, 11:35 AM
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This next picture shows some of the bits and pieces after disassembly.
Oct 19, 2015, 11:38 AM
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Here are some pictures of the boiler and fuel tank after preliminary buffing.
Oct 19, 2015, 11:43 AM
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Here are some pictures of my fathers old blow torch, which I have actually used as a kid/teen in the late fifties early sixties. I had started to restore it several years ago and knowing that I was going to be polishing this boiler set-up I decided to use this as my practice piece.

Quite pleased with the results, its is now prominently displayed on my desk beside my monitor.

Oct 19, 2015, 12:10 PM
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And now to the heart of the matter, I will be finish polishing the boiler, fuel tank, and condensate tank shortly and ready for sub assembly. Which brings up a couple of questions.

1) What to insulate it with. I have read several posts and it appears that the common methods are Felt, Cork, or Fiberglass. I have thought of an alternative, remembering my days of racing go-karts I am thinking of using header wrap. It is highly heat resistant, very flexible and is available in strips 1 inch wide by 1/16 inch thick for about $1 a foot. I am thinking of two layers spiral wrapped in opposite directions. On the go-kart headers we just wrapped it with black mechanics wire tied tightly.

2) What to glue any insulation with, obviously it would have to be something that was heat tolerant. I don't know how CA glue would react to the heat.

3) I am thinking that the copper stack supplied with the boiler, which will probably end up passing thru a plastic, or fiberglass kit stack should also be insulated.

4) What to clad the boiler with, I know most are using mahogany but I have Oak or Maple available to me and don't think it should matter much, but I don't know.

5) As received the condensate tank was clad with wood strips, my first thought was NO it should not be insulated you want the heat to dissipate for the steam to condense. Then I thought clad it to protect your little fingers. I really don't know what to do here.

Oct 19, 2015, 04:08 PM
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The condensing should not take place in the condensate receiver, but before that...
You want the condensate receiver to be as warm as possible, safes fuel, or better said, raises the steam capacitiy of the boiler: heat of evaporation of water equals the heat needed for a temperature rise of 20 deg C (36 F).
Oct 20, 2015, 11:36 AM
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Brooks's Avatar
If you are going to mechanically hold the insulation to the boiler, you won't need glue. I'd avoid glue anyway: as the boiler expands with heat, the insulation needs to let the metal slide. Otherwise, say if it's glued, the expansion of the boiler will try to shred the insulation.

Copper stacks are heavy, and put the weight up high, reducing a boat's righting moment. You might consider replacing the copper with thin brass tubing, or even aluminum. For my launch, I replaced the copper pipe stack supplied with a rolled piece of aluminum cut from a pop can. Painted flat black (bbq paint) it looks good and weighs almost nothing.

The wood cladding of boiler can be anything you want :-).

I disagree with Brutus1967 - a cool condenser (i.e. no cladding) will help generate more power (by reducing back pressure on the exhaust side of the engine; Watt's original engine developed power exclusively by condensation, for example. Watt's innovation was to condense the steam outside the piston chamber, not within the cylinder as previously done). But at model scales this will probably not mean much. So, do whatever you wish with the condenser.
Oct 28, 2015, 08:25 AM
Submarine or Target?
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I agree with Brooks concerning the condenser. It IS called the "condenser" after all. Condensing the steam there creates a pressure differential across the piston. That is what causes the steam pressure to be converted into kinetic energy (moving the piston). Anything that can be done to get the condenser as cool as possible and lowers the pressure inside it as much as possible should improve power and efficiency. I have even wondered if increasing the size of the condenser outlet piping would be helpful to minimize condenser pressure.

With that being said, I will mention that most of my experience so far is with steam turbines in a nuclear submarine and not at the hobby scale. So I could be mistaken. But the theory should be the same. On the submarine, the condenser was cooled with sea water and a vacuum ejector helped pull a vacuum in it to raise the pressure difference across the turbines. Liquid condensate in a spinning turbine is bad news. But it should be avoided in piston steam engines as well, since water does not compress well. That is why periodic cylinder blow-downs are necessary on many engines.
Oct 28, 2015, 11:03 AM
Registered User
You are certainly correct about turbine engines from what I remember from my qualification days, but I was a forward guy anyway.
In models most are not really running a proper condenser, it is more a condensate trap to catch the oil and water, mostly so the oil does not end up on the model boat or in the water. Leaving an oil slick on the water after running a steam boat will cause most public ponds and such to quickly ban boats being used.
So it is wise to run a condensate trap.
What most are calling a condenser is a small tank with an inlet and outlet and a way to drain or suck the water and oil out after a run. If the trap is insulated it might help to pass more steam so it can be exited out the stack or a pipe near the stack for a smoke like effect, which always looks good.

Former STS1 (SS)
Nov 10, 2015, 09:42 PM
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Progress has been slow, been running back and forth to a sick children's hospital (3 1/2 hour drive) for the last week or so. Got side tracked by the arrival of my chosen tug kit (Assurance from model Slipways).
Have finished most of the buffing, chose to repaint the the boiler ends, used VHT header paint.
Most of the wood cladding is cut and partially sanded.
New twin cylinder marine engine from Graham is awaiting assembly.

Now I am here looking for some help.

1) I am in need of a pop-off valve for 35psi.
2) I need some sort of "throttle" valve for the engine, which is suitable for servo control.
3) While thinking about the pop-off valve I am deciding that it should be mounted remotely as opposed to directly on the boiler as supplied. The thinking is that if it is inside the hull when it opens it would release steam insider, endangering the crew.

thanks in advance
Nov 11, 2015, 10:15 AM
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Brooks's Avatar
Mount the safety valve on the boiler, per usual practice, and provide a pipe to discharge (most of) the steam above decks. That is, the valve would discharge into a circular cone mounted above the safety valve (not attached to the valve or boiler). The cone is attached to the discharge pipe. This ensures that steam discharged is free of obstructions, yet has a path to the open air above deck.

It would not be safe to move the safety valve to a remote location. A) if the remote location pipe got even partially plugged, the safety valve would not see the true boiler pressure and would thus fail to provide safety. B) when a discharge is needed (due to boiler overpressure), it needs to lower the boiler pressure immediately; with a long pipe, that discharge would be hampered by the friction and resistance offered by the pipe.
Nov 12, 2015, 10:39 AM
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Thank you Brooks.
This exactly the info in need to make proper decisions, I will do as suggested by you.

Your previous comments about gluing the insulation has caused me to reevaluate that process. I have had bad experiences with thermal expansion in the past so i have decided that since my chosen insulation is very soft and pliable I will tack it in placer with glue, allowing lots of free material to avoid having it shred. (total expansion of the boiler length, for 350 degree temperature rise is about 1/32 inch)

Last edited by srama; Nov 12, 2015 at 10:49 AM.
Nov 17, 2015, 02:54 PM
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Progress is slow, found a safety pop-off and it is ordered (from UK) cannot progress on boiler until it is in hand. It will require me to drill out existing bushing and silver solder in a new one to suit new adjustable pop-off.
Need to start assembling Graham engine, I would like to paint the bare aluminum pcs but don't know what paint would stick and handle the elevated temperatures, any suggestions.
Nov 17, 2015, 06:42 PM
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steamboatmodel's Avatar
I would try engine paint used for full size cars or BBQ paint.
Nov 18, 2015, 04:09 AM
Often afloat
SailorGreg's Avatar

Steam throttle valve

You asked about a throttle valve suitable for servo operation. I use one from Polly Model Engineering You have to download the catalogue and go to page 44 "steam valves for radio control". It is a small, neat fitting that has a 90 degree swing on the control arm. There is lots of other useful stuff in the catalogue as well. No connection, just a happy customer.


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