Building an Aligator

[f350ca]

Guarantee with the crew building this thing the bottle would be empty before it ever had a chance to swing.

[Good Mann]

And...
Why waste a good bottle of Dom Perignon?
Hum, not that the ship isn't worth the gesture.
How about an expensive Perrier or Canada Dry?

[f350ca]

Aligator wrestling today.
Flipped it over so its right side up. Came up with an elaborate system of slings that worked amazingly well. The first part was easy, wrapped heavy slings around it then stood it up on its side with a second tractor tied off as an anchor in case it went over.


Laying it down from its side was a little more tricky. Had to get the slings arranged to transfer the weight as it came over the balance point. With the second tractor as an anchor we pulled it over then caught the weight with the loader. Have to say it was smooth, not one jerk or bang. Tom took a video, will post it if he gets it to me.



Now the fun mechanical part starts.

[vtsteam]

I see I'm a week late to the event -- but good to see the hul rolled over and painted!


If experience with building my houseboat was typical, it should rain continuously now that it's turned over! I call it the Noah effect. You find yoursel drilling holes in an otherwise sound hull to let the water out.

[f350ca]

Yep, raining today as a matter of fact.

[vtsteam]

(04-27-2015, 01:40 PM)f350ca Wrote: Need to do some actual engineering design work now, and would like some input on paddle size.
My thought is paddle size would be based on the boat sitting stationary and applying steam pressure to the engine to get it moving. Too much paddle area and you won't move the paddle through the water, too small and you won't get enough thrust to move the boat at a reasonable acceleration.
The dia of the paddles will be 8 feet. That gets the shaft at deck level and the bottom of the paddles even with the bottom of the boat.
Rotational speed would be set to give hull speed plus a certain amount for slip.      How much slip?
Once the speed is determined I can calculate the torque available at the paddle shaft based on the bore and stoke of the steam engine and boiler pressure.
So for a given torque and a 4 foot arm how do I determine how much area on the blades can be moved through still water at startup?

Any thoughts would be appreciated, there's not much in the way of engineering formulas out there on the net for paddle wheelers, wonder why?

Greg, I've thought about this problem and wanted to answer, but I can't in all honesty. Apologies..... so much depends on the particulars of this hull, displacement, the engine, etc.

What I can tell you is that this part "Too much paddle area and you won't move the paddle through the water." isn't true. The paddle will always move through the water if the boat is statiionary, unless the engine stalls.

How much thrust that is generating for the hull is variable, depending on area, depth, "slip", cavitation (if too fast), etc. But it will move. If you're tied up to the dock and the motor runs you'll get 100% slip, and cavitation too, likely. But the blade will move, unless something breaks or the engine stalls. Same for any boat tied up and running.

But abstract theory isn't really what you want (and I can't provide). Ballpark, is what you want, and for that, I'd shoot for the blades to be running at about twice hull speed at the engine top speed. So go by your engine spec, then calculate no slip on a 4 foot radius to yield 2 times hul speed. That will give you your reduction needed (if you are going to have reduction.) Double hull speed is, by reversal, what ballpark was for radial turbines, and this is basically the same thing if you think upside down, which I generally do.

If you don't have sufficient power to run the blades at double hull speed while actually moving at hull speed, your top speed will be less than hull speed. It will settle at whatever available effective horsepower you have at the wheel.

Also if you don't have a reduction to give twice hull speed, the boat will still move, but the efficiency will be reduced, so top speed will be less than it could be. Unless of course you have so much power in whatever engine she'll have below decks, that efficiency doesn't matter -- which is the modern trend in small craft.

My guess is no, you don't. Which is good!

Keep in mind this is a piece of free advice -- per your sig. and you know what to do with it.

Good luck!

--Steve

[f350ca]

Thanks Steve. Your gems of wisdom are pretty much what I've come up with too, so it must be true wisdom, or at least a good shot in the dark.
The guys Im building this with have a LOT more experience with steam than I do. They figured about 200 rpm would be a good speed for the engine at cruise. We'll have 20 feet at the water line so hull speed should be 6 knots or 607 ft/min. I somewhere ran across a 20% slip factor for paddles, not sure if that number is good your double speed probably is closer. Anyway at 20% figured 29 rpm on the paddles. We found an old gear set out of some farm equipment with a 32 inch dia bull gear with 94 teeth and an 11 tooth pinion. About 8 1/2 to 1 so 250 rpm at hull speed. If the slip number is low then it will just run faster and use more steam so more wood to fire, All seams to balance out.
Came to the same conclusion about too much paddle area, except you can't really stall a steam engine in the same sense as you would a gas engine. It will develop full torque at no rpm if the piston is at mid stroke. The engine is 5 inch bore and 5 inch stroke. We plan to keep the pressure down at 80 psi, (its an old boiler) still gives 327 foot pounds of torque at mid stroke. With the 8.5:1 reduction we'll have 2800 foot pounds torque at the paddle shaft or 700 thrust at the blades.
So think getting it moving won't be a problem, using the tried and true seat of the pants thats sounds about right theory.
So used that same philosophy and determined the most efficient paddle size. Think the boat will draw a little over a foot of water so decided the paddles should be 12 inches deep. The hulls 8 feet wide, we can get a permit to move 12 feet so clearance to the hull and the skirt around the paddles gave an exact paddle width of 16.000 inches. Decision made order the material.
Actually thanks Steve, your thoughts seam to be pretty much along with what I've come up with so as they say brilliant minds think alike or was that fools seldom differ.

[dallen]

not sure if it will help, but here's a link to a page that has a bunch of photos of alligators on it

http://www.mcelroy.ca/notes/alligators_algonquin.html

[vtsteam]

Great Dallen! Wonderful photos.

Okay check the gearing and wheel diameter estimate for reduction ratio. It's possible that the slide gear was either for reversing or for overland travel. Reversing in steam engines was often just changing the timing with reversing valve gear, so I'm going to guess the gear change was for land drive. Anyway, if your steam engine is similar, ballpark, you gear reduction nd wheel size can be worked out. I'm thinking it will roughly bear out what I mentioned and you were thinking Greg.

steve

[vtsteam]

By overland travel I mean the winch drive.