Crane lift-out, are spreader bars necessary

[Barry777]

My boat was lifted recently by crane at the boatyard where I berth my boat - which is just under 12 metres and weighs in at 18,000 lbs. In previous years they have used a slipway where they haul up the boats on a cradle using a fixed winch.

The lift out is done using 2 slings under the boat that go via chains to a conventional single jib. The backstay is released to allow the crane jib access to the slings. I don't know the height of the extended jib but the mast is around 48 feet from the deck so it is at least clear of that.

My concern is over the pressure exerted on the hull sides, particularly around the point where the hull joins the deck - there is a metal toe-rail fitted. The "squeeze" that the slings apppear to exert as they go to a single point at the jib looks quite eye watering. I have asked the yard manager why they do not use spreader bars which would allow the slings to be more "vertical" and similar to the lift using a travel hoist. However, I was told that it was not necessary. I'm not convinced by his comments and it would seem to me that it is far easier for the yard to crane lift this way rather then using the more difficult and time consuming slip.

I know that the yard has had problems in the past lifting a certain make of yacht where the hull has flexed and caused cracks around the toe rail. They will not crane this make any more - and will only use the slip.

Am I being neurotic or am I right to be concerned? Are there any reference points where I can read up on this? The lift out has taken place but I would like to be sure that I won't discover any damage when the boat is re-launched. What is the view of insurance companies to such method of lifting just using a single jib lift point?

Any advice or comments will be welcome.

 

[sailorman]

spreaders are essential to stop the squeeze

 

[jamesjermain]

At our club's lift in/lift out each year the mobile crane transfers 15 or more boats from land to water and back with a single point hoist (no spreaders). The group is composed largely of small boats - up to 30ft - but it does include one catamaran (not mine!). As far as I know there has never been a problem.

 

[Phoenix of Hamble]

It sounds very suspect to me.... I'd never let my boat be lifted like that.

I'd personally ask them to confirm in writing that this will not damage the boat.... putting things in writing does focus the mind somewhat!

 

[saltwater_gypsy]

Spreaders are best but the slings should also be positioned on strong internal bulkheads.

 

[Sailfree]

Its a question of angles!

If the strop is 100' long there is not much horizontal force but lets say its shorter and the angle is 45 deg. Then say 18000lb divided by 2 strops = 9000lb or4500lb each vertical strop.

At 45 deg the vertical load in the strop will equal the horizontal force of that strop but there is also the opposite horz force the other side therefore total horzontal = 9000lb spread over ALL the contact points but obviously a major part on the more vertical sides of the hull (4500lb pushing from both sides for each strop).

Usually strops are more like say 70 deg so the amount is far less.

A spreader beam resists all this horizontal force and lift is just a vertical force.

 

[johnalison]

It certainly sounds very unsatisfactory and I would make a close inspection now and again after launching, both before and after the rigging has been tightened. If there is any evidence of damage, or the rigging needing more turns to tighten, I think a call to the insurers and a survey would be necessary.

My own boat, being an HR is probably as strong as most, and they insist that it should only be lifted with a spreader.

 

[Refueler]

Later CAD built boats with lighter construction - I would be wary of hoisting without spreaders. But older heavy boats - there is no problem at all.

My tub gets lifted this way nearly every time except once when yacht club guy supervised.

but normally ...

.....

 

[Skents]

I had an interesting conversation with a very experienced offshore sailor and boatyard manager who has lifted my boat several times regarding spreader bars.

His view was that a boat that wasn't up to the stresses of being lifted without spreader bars wasn't a boat you'd want to take offshore.

I know the stresses of being lifted and those experienced in a big sea and a bit of a blow are probably a bit different but I think he had a point.

As a shipwright, I think it is important to make sure the strops are placed at appropriate points but a lack of spreader bars doesn't bother me at all when lifting a well built boat.

 

[Bodach na mara]

It all depends (as has been said) on the angle between the sling and the vertical. The original post suggests that the slings meet at a point at least 48 feet above the deck, thus the angle should be no more than that of a line from masthead to deck edge. Assuming a beam in the region of 12 feet, the angle will be about 7 degrees and the inward force on eact of the four slings will be about 4% of displacement. Not too much I would think.

 

[Rowana]

I would agree with you here, James.

All our boats are lifted out and in each year without spreaders. Provided the slings are long enough, the inward pressure is not too much. My boat weighs about 3.5 tons, and I've never had a problem so far.

Going back in in a couple of weeks.

 

[grafozz]

I have had my cat lifted out every year for 11 years now and not once with spreader bars . the beam is 6 metres and no problems .the strops have always been doubled to give extra length . the jib hook usually sits around 2nd set of spreaders , resulting in a shallow lifting angle .I agree with Skents post with the yard managers opinion about the strength of a boat .

 

[VicS]

No spreader bars are not normally necessary with a robustly built boat if long slings and chains are used. With cats perhaps unless as said extra long slings are used.

Small selection of photos:



Same crane owner/operator being doing our craning for almost as long as I can remember. One boat owner insisted on having spreader bars, and paid for them,
for a few years until he realised he was paying unnecessarily!

 

[saltwater_gypsy]

Quote " His view was that a boat that wasn't up to the stresses of being lifted without spreader bars wasn't a boat you'd want to take offshore"
INTERESTING TEST PROCEDURE!!!!! /forums/images/graemlins/confused.gif

 

[vyv_cox]

I keep four short lengths of timber wrapped in carpet for use in this situation. Their purpose is not to reduce stresses on the hull, which I believe to be quite strong enough to resist the relatively small forces involved, but to prevent damage to the toerail. These are attached fairly lightly and could easily be pressed off, plus some surface damage is quite likely.

 

[wooslehunter]

Another reply in the same vain as most. We do 35-40 boats of all types up to about 30' in & out every year without spreaders and with no problems. I can see that there may be a problem on some boats around the rails which could easily be solved with the wooden blocks. We've never used them though.

 

[tillergirl]

It's about 'Partners', not 'Spreaders'. Partners are the chains that raise the hook height and thereby minimise the squeeze. Note how little 'squeeze' there is here.

 

[pyrojames]

That's the way I've done it with timber boats. 8 tons and 19 tons each. No problems with the hulls, its just a matter of protecting the toerails.

 

[cliffordpope]

There was an amusing (not for the owner though) clip here recently of a boat slipping out of its slings and doing a nose dive into the water. Surely that is one safeguard in not using spreaders - the squeezing stops the boat sliding along?

I would have thought a boat lifted using spreaders needs strops around each end. If the pivot point is not at the rail, but on the turn of the hull, the whole thing is much more at risk once it starts to oscilate?

Also, what is the greatest force that a sling could exert - the weight of the boat? So does that mean that boats would crush themselves if beached on their beam ends?

 

[Refueler]

[ QUOTE ]
There was an amusing (not for the owner though) clip here recently of a boat slipping out of its slings and doing a nose dive into the water. Surely that is one safeguard in not using spreaders - the squeezing stops the boat sliding along?

I would have thought a boat lifted using spreaders needs strops around each end. If the pivot point is not at the rail, but on the turn of the hull, the whole thing is much more at risk once it starts to oscilate?

Also, what is the greatest force that a sling could exert - the weight of the boat? So does that mean that boats would crush themselves if beached on their beam ends?

[/ QUOTE ]

On beam ends does not have keel weight, ballast, underbody weight to account for.