ultra heavyweight horizontal pivot

[WFair]

I am working on a design for a show that has a large ship. Overall the ship will be about 25 feet long, about 2 feet deep and will have a couple of lightweight masts sticking up above it (attached to the back). There will be several actors standing on the "deck" (the 2' wide portion...safely held in place by rails in front and behind). I am trying to come up with a creative way to have the whole ship pitch in the rough sea. It will only move a few feet up/down, but I want it all to move in tandem as a single unit. I know I can manipulate the weight fairly easily with a long lever arm, but want to place the pivot point of the ship near the middle. I have done MUCH lighter applications before by nesting two steel pipes inside each other and greasing the inside pipe to pivot easily. That said, the total weight of this unit will be around 1500lbs fully loaded, and I am unsure that my pipes approach is the best at this scale. Has anyone successfully placed a horizontal pivot of some sort in a scenic element of this weight and size? Any ideas? Thanks!

 

[BillConnerFASTC]

I'm not quite clear, but basically a teeter-totter? In that case, since it just "rolls" back and forth, a pipe or even rounded wood beam on rails or even just the deck would seem effective and simple.

 

[RonHebbard]

If I'm understanding the OP correctly, what he's worried about is his 'pipe in a pipe' pivot's ability to resist bending / collapsing when supported from only one end, the up stage end that's hidden behind the ship and out of the audience's site.
I could easily be wrong but that's how I'm interpreting this.
Toodleoo!
Ron Hebbard

 

[SHCP]

How high must the unit be off the ground in order to make the kind of rocking you want? I have built something similar by framing my deck with 2x6 construction and sitting it on a center pivot made of 2x10. I used some heavy duty hinges to attach the unit to the center pivot, and then had tires cut in half on either end as shock absorbers. Here is a quick sketchup because I am bad at explaining things.

 

[bobgaggle]

I'm picturing the stereotypical ship in a play you see in cartoons. There are two cutouts of waves that slide back parallel to plaster line to simulate the roiling waves. Is it something like this? Really what I'm asking is, is there a ground row in front of the ship? Or is the entire hull visible to the audience? If there's a ground row you can go an easier route and mount the ship on a half circle that just rolls on the deck. Make sure your deck can support the load on such a small point.

If we see the whole ship and you need to use some sort of shaft as a pivot point inside the ship I'd go with solid shaft rather than pipe. I'm not going to recommend a diameter or material, but if you position the load on the shaft close to the bearings you're dealing with the shear strength of the material and negating any bending moment...

 

[WFair]

The teeter totter approach is good. I think rather than a single point, I can do a pair of semi-circles from several layers of plywood at the DS and US edges of the deck. The deck of the ship is about 8' in the air...so I have plenty of space below to build good support structure and to distribute the load out a bit. Thanks @SHCP for the idea about using tires as shock absorbers...good one. I will poke at the design a bit more and let you all know how it turns out. Thanks!

 

[BillConnerFASTC]

Ship 8' in air changes things a little for my suggestion. You don't want the long lever arm from ship to pivot on floor - too hard to control I believe and too easy to tip over. Consider an A frame support with just a horizontal bar or pipe or rounded 4X4 or similar, and plywood inverted "U" that just sits on this horizontal piece - like a teeter-totter (at least the ones in my school playground 60+ years ago.) Actually the whole A frame could be pipe using rota-locks or speed rail fittings. Just be sure that high that you have a "leg" or solid stopper. I suppose you could build a whole platform that was nearly as long as boat and legged to sit just under it so the platform stopped it - so boat would work by itself at floor level, or work safely atop an 8' platform.

8' up, do consider the performer safety and fall hazard - as I know you are already. You seem to have it down for when they are "on board" but boarding and de-boarding is tricky too.

 

[WFair]

No...the pivot would be at the (roughly) 8' in the air...but most of the mass of the ship will be below the pivot point reaching just about to the floor. The lever can still push from the ground...no issues there. The whole ship will also be set to lock in the horizontal position from the outer edges (for boarding, moving, etc)...so the height is not really a big part of my issue. There are exit stairs built in. The main technical challenge to this is locating the approximate center of mass (taking into account the ship and the actor positions) so that it is not too far off balance during the rocking scene, and then the need to somewhat spread out the load of a 25' ship, concentrated on a relatively small point...and then redistributed back out to the bearing points on the floor.

 

[BillConnerFASTC]

Lots of challenges..... Especially if on a tight budget.

 

[bobgaggle]

No...the pivot would be at the (roughly) 8' in the air...but most of the mass of the ship will be below the pivot point reaching just about to the floor.

So you're building one of these?


That may change people's suggestions...