the roof on my boat is a little crumpled and I’m trying to straighten it back out. I’m trying to use these clamps in reverse but WOW are they not super strong for this.
Any ideas?
If I’m interpreting that photo correctly, the clamps are being used as spreaders, right? If that’s the case, maybe cut out a wedge in the correct shape and drive it into the gap between the top and bottom beams?
In my (admittedly limited) experience, once Al crumples it will never be as strong as it used to be, so it might need permanent support from that wedge.
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exactly. I’m not sure how a wedge like that could be made, though. I guess it would have to be steel?
My immediate thought on hearing of metal crumpling is that you need to replace that metal.
If you want to try to bend it back, I would start with a better clamp. Try using a pipe clamp, the way you are currently trying. Heat would also be tour friend, but not sure if that works with the roof material.
I would use some kind of angle iron or square pipe to brace the bottom and spread the load while trying to unbend the the top surface.
My immediate thought on hearing of metal crumpling is that you need to replace that metal.
Well, one thing is that this doesn’t really need to support any weight other than a little thin sheet metal and, like, rain. 
At least this part doesn’t. A section of the roof aft of this will be supporting solar panels, but all that weight is transferred through parts that have nothing to do with the crumpled section.
I would start with a better clamp.
I would love to, but I can’t find anything that fits the bill.
square pipe to brace the bottom and spread the load
Way ahead of you, already have exactly that underneath the bottom beam.
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I feel like the kind of “clamp” I would need would be something with gears and a clutch that would let me ratchet the ends further and further apart. I don’t know what something like that would even be called, though.
a little bottle jack? hydraulic spreader?
A thing you may want to consider is the strength of the metal after deformation. It’s going under a LOT of stress in the original damage. Strightening it will compound those stresses and it will weaken. I’d recommend cutting it out and sisteringer the piece inserted with new metal and bolting the whole thing bacvk together.
Clumsy looking? Yes. Strength maybe 80% of original.
Bottle jacks are too wide - the center of pressure can’t reach the spot where the push needs to happen (unless I want to cut out the sheet metal front facing, which I… don’t really wanna do :-/
Yes, but as previously mentioned, this really doesn’t have to be that strong, it’s not supporting very much at all. This is a cosmetic fix.
If it’s not really structural, you might be able to get away with a plywood wedge to straighten and support the damaged area. Something like 3/4" plywood would be very strong. I suppose it would first have to be well-sealed with epoxy to stand up to the water.
My guess is that the aluminum beam is hollow, so I’d be a little concerned that jamming a wedge in could make the already damaged beam collapse inward. It could even do the same to the bottom beam 
what about a body spreader?
You’re right – all of them are hollow, although judging by how well it’s resisted the force of both those clamps at once so far, I suspect the walls are fairly thick.
Presumably this connects to… something? Which does the actual pushing against the beams?
Yes, this is the ram
the rest of the parts are bits and bobs that fit on either end of the ram to push different shapes different distances
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aha! thank you!
I have a hydraulic spreader/ pincher that Jon mentioned above if you want to borrow?
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Dang the price for the tool has come down quite a bit.