Looking for a simple start.

[hartleymartin]

Thanks for your advice. Perhaps I've looked at it too much from the perspective of the model-builder who would normally make a very small copper/brass boiler.

If experience suggests that steel is a better way to go, then I'll listen to the voice of experience. The afore-mentioned M-boiler might be the way to go because of it's small size.

[Lopez Mike]

I can't comment in any useful way about that boiler. The link is interesting but gives no numbers like heating area. And I don't know much about water tube boilers.

I thought you wanted a VFT?

[hartleymartin]

I didn't know what type of boiler the M boiler was, although judging by the shape I thought it might be a water-tube type.

I would like a vertical fire-tube boiler, but hopefully something not too difficult to build.

Type C in this diagram was along the lines I was thinking, but I need to figure out some dimensions for it.

[Lopez Mike]

Yes, diagram C is your basic VFT. As I mentioned before, go and look at the Beckman Boat Shop web site. Their ratings for each size they sell are not that far off of the mark. You could copy their dimensions without fear of making a big mistake of some sort.

http://www.steamboating.net/page7.html

[hartleymartin]

Unfortunately that website is blocked for some reason.

[hartleymartin]

Well, here just goes to show that a steam launch doesn't need to be very big to have fun with it:

http://www.steamboat.com.au/Alba.htm 10'0" LOA, 3'6" Beam.

[Lopez Mike]

It works for me. Maybe just type in Beckman Boat Shop in your search engine.

[fredrosse]

A few comments on Mike's Advice, which is an excellent perspective on this issue:

I would not bother with any boiler material but steel. Silver soldering a complex structure like this is a nightmare. I have done it once and will never do it again. The heat transfer advantages of copper alloys are illusive at best. And the differential expansion of ferrous v.s. non ferrous materials is significant. (This is all true and correct, also note that most silver solders having even small amounts of Phosphorus in the alloy can be seriously degraded by any coal containing Sulfur. I would not recommend building a copper boiler beyond perhaps 5 square feet heat transfer surface area.)

Make it out of steel. Have the welding done by an experienced welder. Roll the tubes in. Perhaps a TIG sealing weld on the ends. A rolled tube is easy to replace. A licensed pipeline welder can handle it if you can't find an experienced boiler welder. The welds on pipelines are done with a TIG root weld and 7018 filler. Nothing else is being done on pipelines. They operate at pressures far, far beyond anything you will ever see. (All true. Note however the 7-1/2 inch railroad community often uses welded steel boiler shells, with rolled-in copper firetubes, the Stanley steam car used small rolled-in Copper firetubes also with good success.)

Have a discussion with the prospective welder before you cut any steel. If he does not specify certain clearances and shapes for a full penetration weld and does not seem aware of such things as the tube sheet and mud ring being recessed, smile and find another welder. (Good advice, but a good welder is not necessarily a good boiler designer, best if you use some good drawings that specify the welding requirements rather than having them decided by someone who, while qualified to do good welding, may or may not understand the design of welds, sizing, clearances, etc.)

Build it with a water leg. Much simpler than a bunch of refractory. This was beaten to death over a hundred years ago. (A water leg VFT is a better design, but a simple VFT without one also works, similar to a Stanley boiler, and would cost much much less to build. The more simple VFT with gas firing or oil firing can work well, look up the Margaret S. boiler, 20 square feet, ASME Code design, free plans if you like.)

Save yourself a lot of effort, expense and grief and build a very ordinary boiler. Copy a Beckman VFT. They work. I have one and I have zero complaints. (All true, a boiler that has given good service, although not meeting ASME requirements)

I know less than zero about water tube boilers. Others here can illuminate the subject for you. They work fine too. Just a different set of design and welding skills. (In a pinch you can use a monotube boiler, and buy the coils ready-made, but in my view the more relaxed operating requirements favor a firetube boiler.)

Sorry to sound so rigid and dogmatic but we see this here again and again. A new person trying to invent the wheel. It is a significant project to complete a launch. And equally as much work to design some unusual power power plant with illusive advantages. Most of us enjoy complicated and unusual machinery but usually on someone else's boat. (All true, best to follow the experience of proven equipment, and as much input from those of us who have experienced various options first-hand.)

[Lopez Mike]

More good input.

I see that Beckman does sell ASME versions of their VFT's. I have no idea if they are much different in design or whether it is a way to amortize the cost of getting the license.

[hartleymartin]

So it seems that I've managed to settle most decisions when it comes to a very simple-to-build (relatively speaking) steam launch.

Essentials:
1.) Simply shallow V-bottom hull in plywood
2.) Single-cylinder engine - I can start with a slip eccentric or go without a reverse gear and later upgrade to stephenson link.
3.) Vertical Fire-Tube boiler, preferably a wet-back firebox

Other equipment: (to be added in due course)
4.) Hand-pump and a motor-driven water pump.
5.) Steam Condenser with oil trap
6.) Removable roof/shelter - can be over just the aft end of the boat