Load on unsupported hull

[Sir Percy]

...and by 'unsupported', I mean when the boat is being craned out of the water. I was moving some old paving slabs out of the way for new ballast, and tucked a lot of it (about six layers) away under the foredeck. That's a fair old lump of weight. I was just wondering if anyone has a similar load in an extreme point of the boat (Aga? Extra large water tank?) and whether this is a concern when lifting out?

[Ex Brummie]

The crane driver will be able to ascertain any imbalance of his load as he starts lifting, but heavy weight at either extremity is not a good idea if being craned out.

[Parahandy]

12 hours ago, Sir Percy said:

...and by 'unsupported', I mean when the boat is being craned out of the water. I was moving some old paving slabs out of the way for new ballast, and tucked a lot of it (about six layers) away under the foredeck. That's a fair old lump of weight. I was just wondering if anyone has a similar load in an extreme point of the boat (Aga? Extra large water tank?) and whether this is a concern when lifting out?

What I always worry about where Craning is concerned is the stresses placed on the hull especially when its an old Boat , I would have removed the ballast prior to craning . Similar loads at the extremities of Boats are relatively commonplace .

[MtB]

A weight of that amount is no concern at all. Probably no heavier than the engine in the other end.

 

Steel is immensely strong. People worry far too much.

 

 

[rusty69]

1 hour ago, Parahandy said:

What I always worry about where Craning is concerned is the stresses placed on the hull especially when its an old Boat , I would have removed the ballast prior to craning . Similar loads at the extremities of Boats are relatively commonplace .

Yep. Had our older boat craned a few years back.....never before,and certainly never again.I am sure things moved that shouldn't have done, though I am far from certain the lifting slings were sufficiently far apart. I have some photos somewhere, but am loathed to look at them again.

[Parahandy]

2 hours ago, rusty69 said:

Yep. Had our older boat craned a few years back.....never before,and certainly never again.I am sure things moved that shouldn't have done, though I am far from certain the lifting slings were sufficiently far apart. I have some photos somewhere, but am loathed to look at them again.

There is a Boat Yard South of Milton Keynes which displays a sign which says Boat Owners must be Insured for any lifts so clearly the risk is with the Boater . I choose a Dry Dock every time .

[rusty69]

Just now, Parahandy said:

I choose a Dry Dock every time

I will never use a crane again,well, certainly not the one we used last time

[NB Esk]

 

Lifted this some time ago, an elderly 70 footer.  Weight is broadly off the slings in the photo but when hanging free there did appear to be some downward deflection at either end.  Was a relief when it landed without any drama.  It's not unknown for a crane operator to decline to lift a boat if its other than steel and with questionable internal bracing.

If the OPs boat is steel hulled, I doubt he'll have anything to worry about.

 

 

 

 

[rusty69]

12 minutes ago, NB Esk said:

 

Lifted this some time ago, an elderly 70 footer.  Weight is broadly off the slings in the photo but when hanging free there did appear to be some downward deflection at either end.  Was a relief when it landed without any drama.  It's not unknown for a crane operator to decline to lift a boat if its other than steel and with questionable internal bracing.

If the OPs boat is steel hulled, I doubt he'll have anything to worry about.

 

 

 

 

Yep, very similar to when our 70 footer was lifted.The spreader bars didn't look far enough apart to my untrained eye, but perhaps that is the norm? I think if ours didn't have a huge great keelson, it would have ended up banana shaped.

[Clodi]

My boat has recently been craned in and out with a heritage stove midships and 6 Trojan 105's on the port side at the stern with no problems at all

[rusty69]

3 minutes ago, Clodi said:

My boat has recently been craned in and out with a heritage stove midships and 6 Trojan 105's on the port side at the stern with no problems at all

Our boat was craned a couple of years ago. I had to move ALL Mrs Rusty's hand bags to one end of the boat to balance out ALL her shoes at the other end.

[ditchcrawler]

All boats will flex when out of the water, even the bostocks of a dry dock dont support the weight the same as a boat floating in water. That is why even on large ships they align the drive while its afloat, not on land.

[NB Esk]

2 hours ago, rusty69 said:

Yep, very similar to when our 70 footer was lifted.The spreader bars didn't look far enough apart to my untrained eye, but perhaps that is the norm? I think if ours didn't have a huge great keelson, it would have ended up banana shaped.

 

It can be seen from the side view that we had the straps about as far apart as practical.  There is a limit as to how far you can spread the bottoms in relation to the tops.  If your lift looked anything like this it probably wasn't too bad.

The real horror stories are two chains coming straight from the hook block and ending up about four feet apart at the baseplate.

 

 

[rusty69]

19 minutes ago, NB Esk said:

 

It can be seen from the side view that we had the straps about as far apart as practical.  There is a limit as to how far you can spread the bottoms in relation to the tops.  If your lift looked anything like this it probably wasn't too bad.

The real horror stories are two chains coming straight from the hook block and ending up about four feet apart at the baseplate.

 

 

Nope,ours were parallel. I won't post a picture (I can't look at them)?.

Edited October 7, 2019 by rusty69

[David Mack]

3 hours ago, NB Esk said:

 

Lifted this some time ago, an elderly 70 footer.  Weight is broadly off the slings in the photo but when hanging free there did appear to be some downward deflection at either end.  Was a relief when it landed without any drama.  It's not unknown for a crane operator to decline to lift a boat if its other than steel and with questionable internal bracing.

If the OPs boat is steel hulled, I doubt he'll have anything to worry about.

 

 

 

 

If thats a fully welded steel hull and cabin it will be tremendously strong.  I would be a little more concerned about an open hull or one with a wooden cabin.

[Murflynn]

you will never get the slab sides of a narrowboat to bend in the vertical direction.  They will buckle first, and that should never happen if the boat is properly designed and built, and fully welded including the cabin.  In effect the hull is an enormous I-beam with the bottom of the boat forming the bottom flange, and the 2 sides forming the web.

 

the crane driver should adjust the slings if needed to ensure it lifts off the supports at both ends simultaneously.

[Boater Sam]

From experience its the point load where the slings or chains crush the edges rather than the hull bending longitudinally that is most likely.

Older thin and rusty hulls can get badly distorted on the edge of the base plate and the side above where the sling is. I saw an old Springer crushed to the point where it leaked.

Very few use spreader bars under the hull because of the difficulty of getting  them under the boat.

Edited October 7, 2019 by Boater Sam

[David Mack]

Acidents do happen when craning boats. In this case it was apparently due to a rivetted seam in the hull unzipping.

Corrected link for the first post in the above thread:

https://www.expressandstar.com/picture-galleries/2008/05/29/drama-on-canal-as-boat-falls/

 

Edited October 7, 2019 by David Mack

[Ex Brummie]

The last 4 blackings I've had have been craned out and placed on cradles. No problems were encountered in the boat. One dry docking made the bathroom door difficult to open, as did one slipway  docking, when chocks were added after drawing out. Once back in the water, everything was back to normal. I've seen a boat that was fitted out on hardstanding that needed remedial work after launching.

Having just looked at David Mack's link, my last 4 lifts have been at Stretton !!!! I don't think that will stop me using them again.

Edited October 8, 2019 by Ex Brummie
After looking at the previous post.

[Sir Percy]

I was really just wondering about the hull strength the ability to withstand uneven forces. My particular boat does have a steel hull and a keelson, and is only 40' in length so I do think it would withstand a fair load. No plans to destruction test it, though!