Metacentric Height and Stability

[tandemcompound]

now that I am building a boiler for a 20 foot boat I am wondering if putting 1000 lbs of boiler and water 2 feet above the keel is stable. Other boats seem to do it. Generally I will be steaming in inland waters which has occasional blows to 2 foot waves. The weight of the boiler loads the boat down so it tends to be more stable under way. Dunno just a few late night thoughts at 2 am.

[barts]

What sort of hull do you have?

- Bart

[tandemcompound]

I do not have a hull yet. I was planning for a 26 foot standard lifeboat. nice and long and beamy and able to take the weight. tho some say 5 nhp is not enuf power to run it.

[barts]

I do not have a hull yet. I was planning for a 26 foot standard lifeboat. nice and long and beamy and able to take the weight. tho some say 5 nhp is not enuf power to run it.

I've seen plenty of 22' steel lifeboat hulls. They were rated at 22 to 30 persons - likely @150 lbs apiece. Your boiler will not cause any problems in this hull. They are quite slow, of course, with a 8' beam, but they're a great platform for learning about steamboats. Lots of space... can take several people w/o an problems. You can carry lots of wood, too. Be careful about getting the propeller down into the water w/o needing to add ballast.

We had such a hull years ago; it was in poor shape and we finally scrapped it.

I've not see 26' hulls, but I'm sure they're bigger and more burdensome yet.

Our Rainbow is a 26' ex-Navy wooden whaleboat hull, completely rebuilt by a local craftsman. Also not fast, but feels wonderfully secure 5 miles from land in a stiff breeze. She has a Scotch boiler and a 5-7 hp compound. Boat weighs something like 5000 lbs.

IMG_20170717_174449.jpg (190.5 KiB) Viewed 13275 times

- Bart

[tandemcompound]

Hmm. thanks for insights. Mind presently occupied by trying to figure how to drill 1.5 inch holes in 2 foot dia gas pipe. A big drill bit and a portable magnetic drill press.

This looks surprisingly like Deception Pass, Whidbey Island, WA state.
what design is your engine? My other steamer has a Scotch boiler. great unit.

[DetroiTug]

"how to drill 1.5 inch holes in 2 foot dia gas pipe. A big drill bit and a portable magnetic drill press.''

With the torque required, If the bit hangs, very dangerous.

This is large machine work, at the very least a Bridgeport type mill, preferably a radial arm drill where the work can be secured for the drilling and the reaming and step into it. I've made 18" upper/lower sheets with 1.25" holes drilled and reamed in a CNC Bridgeport and they were not easy. Lots of manual quill work with no power feed like that of a radial drill.

I've ran jobs drilling 1.5 and 1.75 inch holes in steel jigplate in a CNC mill about the size of a small school bus. Peck drilling .15" it would shake the bus stop sign out front on the street. Big holes are big jobs.

Some of these hole saws for metal nowadays do very well, something to consider.

Ron

[barts]

Hmm. thanks for insights. Mind presently occupied by trying to figure how to drill 1.5 inch holes in 2 foot dia gas pipe. A big drill bit and a portable magnetic drill press.

This looks surprisingly like Deception Pass, Whidbey Island, WA state.
what design is your engine? My other steamer has a Scotch boiler. great unit.

This is Swifts Bay on Lopez Island, a few miles from Deception Pass.

Rainbow's engine is a Burleigh compound, 3x5x4; there's a 1:1.5 step up drive so the original 18"x26" prop could be used.

I would definitely try an annular cutter for drilling 1.5" holes in 2' gas pipe. Your mag drill is likely already set up for these.

- Bart

[fredrosse]

"annular cutter for drilling 1.5" holes"

As Barts recommends, a good bi-metal annular cutter works ok for large holes in mild steel. Keep plenty of lubrication on the cut to avoid heat buildup. This method is good for holes that will have threaded connections welded to the shell of a boiler. Full penetration welds are required, and the thread-o-let should be held about 1/8 inch from the shell before welding proceeds.

Tubesheets I have had made by e-machine shop, $485 for two 15 inch diameter x 3/8 thick tubesheets, 48 holes 1-1/4 diameter. They wanted much more money with my material specification, so I arranged to send the boiler plate to the machinist, and got the great price of $485 for two tubesheets. They were perfect, all dimensions well under a half thou. of an inch, but that was 11 years ago.

I recently had tubesheets made in 3/8 boiler plate by plasma cutting, 85 holes, one inch diameter in 15 inch diameter tubesheets. The cost here was very low, however in the future I will use waterjet cutting, as plasma cutting leaves hardened steel, which required cobalt or carbide cutting tools to finish the holes for rolled-in tubes.

You mention using "gas pipe" for the boiler shell. Is that an acceptable material for a boiler?? Even if you are not building an ASME Code boiler, you should use materials acceptable by the Code. I use SA-106 seamless pipe, SA 53 seamless is also acceptable.

[Mike Rometer]

I'd go with a hole saw for that one, preferably a 'Starrett'. I've got some up to 6" dia. Well lubed they just seem to keep on going. Just make sure everything is well tied down, and put on your 'patient' hat.

[RNoe]

Here's a picture of how I drilled the smokestack hole in a 9" diameter steel smokebox, using my drill press.
This was before I acquired a good milling machine, which would have made the job much easier.
Keys to success:
- Securely clamping the tubing to the drill press base;
- Slow rpm on the "hole saw" cutter;
- Generous use of lubricant;
- Patience.

It worked as desired.
RussN