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Old 22-03-2013, 20:45   #541
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Re: Nauticat 52 Refit

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OT
We had snow this morning. Not a lot, but in South Whidbey one of my customers had 8 inches !

It's all gone now.

Steve

Yep, here too. Happens almost every year at the beginning of spring it seems. The high winds the other day were more of a bother, I had a spider web of heavy lines from my shed roof to strategically placed one ton cement blocks. It was a bad one, shattered several 2x4 in my framing. No real damage though, just scrambling for a few.
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Old 24-03-2013, 08:50   #542
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Re: Nauticat 52 Refit

This is a Sandy boat that was sent over here. Hull just repaired and refinished. It was washed off the stands in the yard. Hull stove in, lead wing keel severely bent.
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Old 24-03-2013, 08:53   #543
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Re: Nauticat 52 Refit

Check out the bending rig used to bend the wing back straight. That's an 1800 lb cement block. It's still floating 1/4" off the block here.
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Old 24-03-2013, 08:56   #544
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Re: Nauticat 52 Refit

Still got a little way to go. Need to move the block outboard a bit. Don't try this at home, it's easy to lift the boat right off its stands and knock it over-again! Careful blocking and wedging required....
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Old 25-03-2013, 04:35   #545
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Re: Nauticat 52 Refit

Interesting method. My question, why are you using the block on a lever? Wouldn't bottle jacks work better to control the jacking? Maybe apply some heat to the wing to facilitate bending. That begats another question; where on the wing is the bending moment?

I imagine the force involved would be measured in the tens of thousands of pounds (equal to the boat weight dropped from a height) Perhaps that answers my questions. Weight x Arm = Moment. What size jack would be required? Would it be of such a required size that it wouldn't fit under the wing? Tricky thing you're doing there.

Still, I am wondering how you control the bending moment.
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Old 25-03-2013, 07:19   #546
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Re: Nauticat 52 Refit

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Interesting method. My question, why are you using the block on a lever? Wouldn't bottle jacks work better to control the jacking? Maybe apply some heat to the wing to facilitate bending. That begats another question; where on the wing is the bending moment?

I imagine the force involved would be measured in the tens of thousands of pounds (equal to the boat weight dropped from a height) Perhaps that answers my questions. Weight x Arm = Moment. What size jack would be required? Would it be of such a required size that it wouldn't fit under the wing? Tricky thing you're doing there.

Still, I am wondering how you control the bending moment.

We played around with several methods here, this is just what worked. Since the wing was bent up,the only way to jack it is with a jack between the wing and the hull. It would definitely punch through the hull before bending the wing. The forces involved are massive, look at the bend on that box beam. Where the wing meets the keel it's about 4" thick. Heat doesn't really help, because a huge lump of lead like this is a serious heat sink. You can't just heat the area in question, the heat gets instantly dissipated throughout the whole keel. So you'd have to heat the whole thing up, which is bad for a number of reasons. The malleability of lead doesn't change a great deal with a bit of heat either. We control the bending moment by positioning the block on the lever arm, in or out, and slowly lowering it from a forklift. As I said, in these pics it's just floating there just off the wood blocks. Needs to be moved outboard a foot or so. The problem is that I think the box beam will noodle out on us and the outboard edge will hit the ground before bending the keel far enough. We may have to insert a bunch of steel bar edgewise into the box beam to make it stiff enough. Sometimes improvisation is the name of the game.
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Old 25-03-2013, 07:25   #547
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Re: Nauticat 52 Refit

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Interesting method. My question, why are you using the block on a lever? Wouldn't bottle jacks work better to control the jacking? Maybe apply some heat to the wing to facilitate bending. That begats another question; where on the wing is the bending moment?

I imagine the force involved would be measured in the tens of thousands of pounds (equal to the boat weight dropped from a height) Perhaps that answers my questions. Weight x Arm = Moment. What size jack would be required? Would it be of such a required size that it wouldn't fit under the wing? Tricky thing you're doing there.

Still, I am wondering how you control the bending moment.


Ah, I see now. You think we are bending the wing up! No, it was bent up from falling over, and we are bending it back down. There is a large steel plate fitted to the underside of the wing to spread load. This was the welded to the box beam, and the whole contraption is thru bolted through the wing. Look closely at the pics, you can see the plate underneath and the bolts sticking out the top. See in the last pic how she's not bent down far enough yet?
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Old 25-03-2013, 13:05   #548
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Re: Nauticat 52 Refit

Minaret

Verra interesting: thanks a bunch!

I see what you mean: it's hard (and expensive) to arrange a structure to act as an "inverted piece of ground", situated up off the ground, to push downwards against with a hydraulic jack.

And even pulling down with a pull ram, you'd require unrealistically strong ground anchor.

It strikes me that another advantage of lowering a heavy weight onto the end of a lever is that it's easy to rig so that it shares an advantage with hydraulics, being that you can easily avoid overstraightening due to 'runaway' when you reach yield point in the item you're trying to straighten (in other words, the force applied drops off very quickly with displacement)

In your case, you've got a packer under it to bear the weight as soon as deflection exceeds the amount you require. Simple and effective ...

I guess a similar result could be achieved with more ease of adjustability in a workshop where overhead gantry cranes were available to suspend the block, or stropping a chainblock from a sufficiently strong roof structure (perhaps not quite so good using mobile cranes, which are not so stiff). Not so easy outdoors!
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Old 25-03-2013, 13:37   #549
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Re: Nauticat 52 Refit

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Minaret

Verra interesting: thanks a bunch!

I see what you mean: it's hard (and expensive) to arrange a structure to act as an "inverted piece of ground", situated up off the ground, to push downwards against with a hydraulic jack.

And even pulling down with a pull ram, you'd require unrealistically strong ground anchor.

It strikes me that another advantage of lowering a heavy weight onto the end of a lever is that it's easy to rig so that it shares an advantage with hydraulics, being that you can easily avoid overstraightening due to 'runaway' when you reach yield point in the item you're trying to straighten (in other words, the force applied drops off very quickly with displacement)

In your case, you've got a packer under it to bear the weight as soon as deflection exceeds the amount you require. Simple and effective ...

I guess a similar result could be achieved with more ease of adjustability in a workshop where overhead gantry cranes were available to suspend the block, or stropping a chainblock from a sufficiently strong roof structure (perhaps not quite so good using mobile cranes, which are not so stiff). Not so easy outdoors!

Yep, it was a puzzler. Many thought this wasn't possible. Springback is pretty substantial too, gotta overbend it a bit. Should have seen what happened when a less substantial beam was tried early on...
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Old 25-03-2013, 21:30   #550
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Re: Nauticat 52 Refit

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Check out the bending rig used to bend the wing back straight. That's an 1800 lb cement block. It's still floating 1/4" off the block here.
Ohhhhhhhhh, ok now I see. I thought the two wood blocks lying next to the plywood were fulcrums. Now it all makes sense.
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Old 25-03-2013, 22:12   #551
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Re: Nauticat 52 Refit

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Ohhhhhhhhh, ok now I see. I thought the two wood blocks lying next to the plywood were fulcrums. Now it all makes sense.


I can see how it would be easy to think that at a glance. I'm not a great photo documentarian...
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Old 25-03-2013, 22:19   #552
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Re: Nauticat 52 Refit

Perhaps that makes it a bit clearer. This one pic per post thing is killing me.
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Old 26-03-2013, 06:37   #553
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About the only way I see that might improve this process if there is a next time is to run the beam all the way through to the other side. the keel then becomes the fulcrum. you could have put the weight on one side and a jack on the the other then your adjustments would have been controlled with the jack pushing up on the lever arm assisted by the weight bearing down on the other side by the block. probably need a good sized steel I beam for that, I can t imagine the torque loading that would take!
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Old 26-03-2013, 07:30   #554
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Re: Nauticat 52 Refit

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About the only way I see that might improve this process if there is a next time is to run the beam all the way through to the other side. the keel then becomes the fulcrum. you could have put the weight on one side and a jack on the the other then your adjustments would have been controlled with the jack pushing up on the lever arm assisted by the weight bearing down on the other side by the block. probably need a good sized steel I beam for that, I can t imagine the torque loading that would take!

Couple of problems with that. First, the weight of the boat is resting on that big block under the keel. You could saw a big notch for the beam into a block, or use two blocks fore and aft, but this would be a pretty iffy method of blocking for a wing keeled boat. Especially when you are applying astronomical forces like this. Second, both wings actually angle down a bit. Therefore the beam would hit the wing on the other side before the necessary angle of bend is reached, especially with springback. I'm guessing this method would end with the boat on its side, we had to get very creative with blocks and wedges as is. Scary stuff, we've got well over 30,000 haul outs with an accident free record, don't want to ruin it now....
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Old 26-03-2013, 10:59   #555
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Re: Nauticat 52 Refit

It's not flexing the hull before bending the lead alloy? surprising and interesting....
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