Thoughts on how to straighten a bent strut?

[bsurvey]

the only way it can be straighten in place is to heat it up before you try to make it straight otherwise if you try cold straightening it will break.
if you heat it too much it will melt the FRP. you may want to try a heat gun verses a rose bud fitting on a torch
you should also ink dye penetrate test it for cracks especially around the hub


20 degrees is a lot so it may be fractured so it would have to come out to be brazed or replaced. it should be just encapsulated in sacrificial FRP

[Terra Nova]

Originally Posted by Tetepare

You're going to have to remove the shaft and strut...

Originally Posted by Squanderbucks

Remove and fix/replace...

At least some are using their heads. Remove, repair/replace.

Anything seems possible when you don't know what you're doing.

[TheThunderbird]

l'd cut it in 2 pieces.

Replace the bent portion with SS new part, and bolt it on the 'pedestal'

[teneicm]

Quick update- Keith from Turn Wright Machine Works was very helpful in suggesting that it may be possible to bend the strut back using the shaft as the attachment point of a come-a-long. He reasoned that the SS shaft is lot stronger than the bronze strut, and the leverage exerted on the shaft itself will be nominal, whereas the spreading of the load across the strut would be beneficial. He stressed not to heat the marine bronze as it will weaken it. He also reasoned that if the hull had endured the shock load of the initial impact, it should be able to take the re-bend.


On the matter of alignments being measured in thousandths of mm's, that's the alignment of the engine/ tranny to the shaft connection. I know we'll need to realign the engine, but I'm certain that the boat builder in the initial layup wasn't able to achieve those sort of tolerances as he glassed the strut in. As long as we can get it straight and running cleanly through the middle of the shaft tube, we should be able to adjust the engine to match.


We'll probably give this a try (albeit may use a bending tool rather than a come-a-long) and I'll report back on how it went. Still interested in hearing new ideas though!


Cheers- Matt

[leftbrainstuff]

Lots of leverage.

[Pete7]

Originally Posted by svHyLyte

Christopher on a Crutch. We're talking about bending a 7"-8" long, 1/4" thick bronze plate all of about 20º. Speaking as a registered structural engineer for 40+ years, such a limited cold bend most assuredly isn't going to "work harden" the plate,

Does Bronze ever work harden?

Originally Posted by TheThunderbird

l'd cut it in 2 pieces. Replace the bent portion with SS new part, and bolt it on the 'pedestal'

How were you thinking of joining the stainless steel to bronze?

Pete

[fatherchronica]

That sounds correct to me. I think you should try to attach whatever you use to apply pressure right next to the strut so the strut cannot become a fulcrum to bend the shaft. In fact if you could find a way to attach it to the shaft on both sides of the shaft to apply roughlt equal pressure would probably be ideal. I once replaced engine mounts at the slip and after lowering the engine back I thought I would try to get the shaft close and then hire somebody more experienced to fine tune the alignment. I began with a tape measure then when it seemed perfect to the 1/32 of an inch I eyeballed and cut little measuring shims to see how much I was moving everything. When there was no vibration I motored to a boatyard and their guy looked, listened and touched around and said there was nothing for him to do. Dumb luck maybe, but doable with a little bit of time. Good luck

[hellosailor]

Indonesia? No problem, harness up an elephant to the shaft, walk it out.

Straightening a shaft properly requires big ass rollers that have been lathed perfectly round, and other equipment you are unlikely to improvise if you REALLY want that shaft balanced and straight again. Elevator and printing press repair shops do this all the time. Prop shaft repair shops will have similar equipment. A navy yard might be bribed, or know where the equipment is.

But I think any YouTube Kludges will just destroy part of your boat.

It is not just a matter of "bend it back", metals distort when bent and the distortion isn't easily undone. Let a pro do it.

Yes, it may be cheaper to have a replacement shaft shipped to you, or to go to a place that has a proper repair facility.

I firmly believe in DIY and repairing, but this one requires more than throwing a come-along around a big tree. Even if the gunsmiths in the Khyber Pass probably COULD do the job...I don't think any other bunch of artisans has the rep for doing this kind of thing. Kludge something, yes. Make it 100% right? No.

[Cheechako]

My guess is this is a very gradual bend, no sharp bend, almost nil work hardening. Anything rotating, like a shaft is very hard to straighten well for sure. (V blocks or roller blocks, dial indicators and an arbor press.) But the strut only has to get the cutlass bearing back in alignment with the stuffing box/rear coupling. In either case over bending is required to get it back in place. May have a chance. We'll see!

[stone beach]

I had one side strut bent last year.

In my case the strut was too substantial to bend it back cold and imo it is not possible to heat it sufficiently in place, heat travels upwards through the strut, impossible to arrange a decent heat sink to stop the heat damaging the surrounding glass resin.

Start by splitting the coupling, then you will see how far the shaft springs out of line.
If you can, then remove the coupling and pull the shaft.

In my case the shaft still rotated (just) but after the coupling was split it sprang until pressed hard against the side of the shaft log and was difficult to move fore & aft. At that point I actually cut through the bent strut and committed to renewing it. In my case the strut was bolted through the hull.

In my case the shaft was not bent.

The strut may well be bent in two planes, you are unlikely to be able to straighten it adequately in the hull.

Digging it out, pressing it straight (with heat), refitting and realigning using the shaft straightened as required is all feasible, it isn't any different to the initial instal procedure.