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Two years ago we bumped the wood pilings of a fishing dock and the anchor (which hit first) twisted sideways and bent the stainless steel flange holding the bow roller. [I don't know why we didn't just anchor then bleed the fuel line
and dock under power instead of trying to dock under sail.]

I'd like to bend it back. Anyone have suggestions on how to do this while its on the boat?
 

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pictures would help . hard to advice without them. but I do know it takes more force to straighten then it did to bend it. if it is stainless the bend will work harden and will not want to bend back as easy as the rest of the part. most times they need to be removed to be straightened properly.
 

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Your fasteners and mounting system have already taken a huge amount of abuse. Dismount it, get it straightened properly and remount it with new fasteners.

I know that the lack of access inside usually makes it a rotten job to get the nuts off but that's why God made small people! ;)

You may find hidden damage you are unaware of when it is off as well.
 

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Now after you heard all the cautious advice, here mine:

Assuming the flange is flat metal: You take an adjustable pipe wrench, or a large adjustable wrench, and grip the stainless with it. Use some thin hard plastic or hardwood to prevent deep scratches.

If needed, you can put a pipe over the handle of the wrench for more purchase.
Also, you can use two wrenches, one holding, one bending, to avoid putting excessive load on the fasteners.

If it was bent a lot, it might crack when you bend it back. But then, if that happens, the part was pretty much done already anyways. :)
This is the classic BFFI approach and is sure to eventually cost ten times the other methods described above.
Plus you will surely hurt yourself when you try it.
John
 

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This is the classic BFFI approach and is sure to eventually cost ten times the other methods described above.
Plus you will surely hurt yourself when you try it.
John
It's hard to make this assessment without seeing it. It all depends on how badly it's bent and the access to it, and whether you can do it without risking further damage as SJB warns. I have had fairly good luck straightening things as long as there hasn't too much distortion in the material. The key is to try to exactly duplicate the incident that bent it, only in reverse, and in a slow and controlled manner. That means the stationary end should be held steady to take the pressure off the mounting bolts if you're able to leave it on the boat or bolt it down down to something solid if you have to take it off. Then slowly apply the force in exactly the opposite direction that bent it from the same point that hit the dock. Stop several times in the process to make sure that flanges are straightening instead of kinking. I have found crescent (adjustable) wrenches highly useful in the process of slowly helping flanges back into shape. Sometimes the hardest part of straightening something in place is having the room to over bend the piece because you almost always have to bend it past its original shape so it can spring back into shape. I would discourage using heat if at all possible because it will lead to more distortion, besides being downright dangerous if you're able to leave it on the boat.
 

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After seeing many such bent bow rollers made out of 1/4 inch stainless, I started building them out of half inch stainless plate.
You can put a length of pipe on your pipe wrench for more leverage .
 

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Two years ago we bumped the wood pilings of a fishing dock and the anchor (which hit first) twisted sideways and bent the stainless steel flange holding the bow roller. [I don't know why we didn't just anchor then bleed the fuel line
and dock under power instead of trying to dock under sail.]

I'd like to bend it back. Anyone have suggestions on how to do this while its on the boat?
Extremo--

A few years ago we had exactly the same experience when docking on a windy day at the St. Pete YC. One of the harbor master's assistants could have reached out and fended our bow pulpit, as I expected, but instead he simply stood there and watched the fluke of our port anchor catch the corner of a fender piling and bend the heck out of the side-plate on the bow roller before a chunk of the piling was ripped off.

I went through many of the exercises described here by others during the subsequent weekend to ensure we had a usable roller when we continued our trip the following Monday. The rebent roller "kind'a" worked, well enough that we didn't need to interrupt our trip, but, in the end, to really get a usable roller that functioned properly, we had to replace the damaged one. We ended up with a unit made by Kingston that was designed for our CQR that was relatively inexpensive although a terrific pain in the neck--literally and figuratively--to mount, but it was the only real solution. If one is going to do something one might as well do it right the first time, no?

FWIW...
 

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After seeing many such bent bow rollers made out of 1/4 inch stainless, I started building them out of half inch stainless plate.
You can put a length of pipe on your pipe wrench for more leverage .
What size boats are you putting such thick plate on? I am building a roller for my 30' boat and I had thought 1/4" would be more than enough, but I only want to do this once so any experience would be greatly appreciated.

Thanks
 

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Actually no, that totally depends on how the thing is bent.
If the position of the bend lends itself to proper counter-holding with a second wrench, it can be done cleanly, and as good as by taking the whole thing off.
IF that is the case we could only tell with pictures, not speculations.
I leave that to the owner of the bow roller to judge.

If one would hurt himself trying, or break stuff, depends mainly on how dumb he is; you told what you think would happen to you; others might have different experiences.

:laugher
Okay, I'm trying to visualize how you are going to do this. Boats in the slip, bow in. You are on the dock? On the bow? Getting two wrenches, with cheater bar? Applying force at just the right angle to straighten a "U" shapped piece of stainless steel? Maybe a better approach is to have at a piling in exactly the opposite direction at a moderately sustained just right force? And still you've not looked for latent damage to the deck, deck core and fastenings; setting yourself up for water intrusion into the deck core and all the wonderful things that leads to.
The two wrench approach will only result in stress risers and work hardened metal within piece. The bow roller will be significanly weakened and will bend much more easily on the next event. Using a mandrel and roller press is probably the only way to get this bow roller back into nearly new functionality.
And for what it is worth, I would not injur myself because I would not try to straighten a bow roller in place no matter the degree of distortion.
John
No grins.
 

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Okay, I'm trying to visualize how you are going to do this. Boats in the slip, bow in. You are on the dock? On the bow? Getting two wrenches, with cheater bar? Applying force at just the right angle to straighten a "U" shapped piece of stainless steel? Maybe a better approach is to have at a piling in exactly the opposite direction at a moderately sustained just right force? And still you've not looked for latent damage to the deck, deck core and fastenings; setting yourself up for water intrusion into the deck core and all the wonderful things that leads to.
The two wrench approach will only result in stress risers and work hardened metal within piece. The bow roller will be significanly weakened and will bend much more easily on the next event. Using a mandrel and roller press is probably the only way to get this bow roller back into nearly new functionality.
And for what it is worth, I would not injur myself because I would not try to straighten a bow roller in place no matter the degree of distortion.
John
No grins.
All valid points, but the OP didn't state, 1. Whether the boat was now in the water or on the hard and, 2. How badly or in what fashion it was bent. We know nothing about the roller's relative robustness with respect to its mount. It is impossible to assess whether the roller has to come off or not without more information.
 

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What size boats are you putting such thick plate on? I am building a roller for my 30' boat and I had thought 1/4" would be more than enough, but I only want to do this once so any experience would be greatly appreciated. Thanks
He's putting (probably welding) them on steel boats of his own design.
 

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Discussion Starter #13 (Edited)
OK I created an album "bent anchor roller" with two photos.
The boat is a Voyager 35, its in the water and still in clear shrinkwrap from the winter. This should be one of them:

"
"
I think the bent stainless plate is 1/4 and the center plate is 3/8 but I didn't measure them. The roller functions but the L shaped lock bar obviously doesn't go into the matching hole in the center plate anymore.
 

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If the only piece you're trying to straighten is that one 1/4 inch side plate, then I sure think the tool of choice would be my 18 or 20 inch crescent wrench. Or as big as you've got. Like Chris says, the jaws should reach the bend or even a little farther. Go slow and easy, straightening it a little at time, moving the wrench back and forth along the bend, always keeping the jaws as snug as possible. I really think it should straighten without much problem that way, but another method would be to use a heavy duty C-clamp to either draw the bent plate over to the heavier center plate or, with the sheave removed, press the plate straight, sandwiched between two heavier plates. A little trickier to set up, but that would put no strain on the mount or your dock lines, etc. I would sure try the wrench first. And, of course, you should visually inspect the roller and mount (under the deck too) for possible damage from the collision.
 
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