Is it possible to lift a boat up by her chainplates ?

[Boo2]

Hi,

Q.a.t. : are a normal yachts' chainplates strong enough to lift her up by ? (I do know that it's normal to use straps, I'm just asking ).

Thanks,

Boo2

 

[davidej]

I must admit in have never tried but I would have thought so.

If you think that a 360 bdegree roll or a capsize is caused by the pull on one sides chainplates which must roughly equal half the boats weight, then QED both sides will carry the full weight

 

[Thistle]

I must admit in have never tried but I would have thought so.

If you think that a 360 bdegree roll or a capsize is caused by the pull on one sides chainplates which must roughly equal half the boats weight, then QED both sides will carry the full weight

I neither follow not trust this logic. I regularly roll dinghies over onto their sides to work on the mastheads. It just requires a very gentle pull on the rigging, nothing like 50% of the weight of the boat.

Chainplates are solidly fixed to the hull and are designed to take considerable loads - think of the tension in the shrouds when beating - but I don't think I'd like my boat to be lifted by them.

 

[Alfie168]

It sounds highly ill advised to me. The chain plate secures and tensions the mast and rigging to the deck. Its not designed to suspend the boat from. Just think about the forces involved.

If it was OK everybody would do it and I've never seen it done. apart from anything else strops under the hull support the hull and help stop it distorting.

If I found anyone suspending my boat from the chainplates blood would flow.


Tim

 

[Channel Ribs]

I'm just asking )

Hypothetically. Probably, but you would not want to do it in anything other than a last ditch effort though.

The balance would also be an issue, so you would at least one strop further back. (Edit: you could use the backstay plate??)

Either way it is hard to see it working without at least moderate damage.

What is it that Crocodile Dundee says about eating snake?

 

[john_morris_uk]

I must admit in have never tried but I would have thought so.

If you think that a 360 bdegree roll or a capsize is caused by the pull on one sides chainplates which must roughly equal half the boats weight, then QED both sides will carry the full weight

This is not true. A 360 roll cannot be caused by the chainplate pulling the boat over. There is always the dynamic action of the sea involved. Furthermore the maximum load on the chainplate is the sum of the static and dynamic loads. The static load can be calculated easily from the hull shape and ballast centre of effort and righting moments. The dynamic loads need to be estimated, but can be allowed for in the design.

The maximum load on the chainplate is connected to, but NOT directly related to the total mass of the boat.

The real answer to the question is that 'some boats might be lifted by their chainplates, but not all boats can be lifted in this way...

 

[VicS]

The load imposed by the pre-tensioning if the standing rigging (to 15% of the UTS) will be equivalent to a substantial proportion of the boats weight if distributed evenly between all the chain plates. ( about 2/3 to 3/4 probably)
Once the angle of heel exceeds 20° the loads imposed will rapidly increase above the pretension load.

On that basis yes the chain plates if all equally strong will support the weight of the boat evenly distributed between them.

 

[allangray3]

think about it gents

If the chainplates could take the wieght of the boat why dont we just put a lifting eye on the mast top, The breaking strain of the rigging does not match the wieght of the boat so the chainplates are not designed to take the lifting load. It would probably result in 4 pieces of stainless hanging from a crane whith a large slash below.

 

[Boo2]

I suppose I should explain where I'm coming from :

One of the books I've been reading (think it's the Nichollson one on boatbuilding but it's not to hand right now) shows a kind of goalpost arrangement across a boat with the crossbar attached to the chainplates (kind of an exo-cradle). In the picture in the book, all the weight is taken by the keel, the goalpost just keeps the boat upright.

That made me think it would be a good design of support to use when anti-fouling, which in turn led to the thought that if you put a couple of tackles between the chainplates and the crossbar you could lift the whole boat enough to antifoul the bottom of the keel.

Which led to my question here

Thanks for all the replies,

Boo2

 

[whipper_snapper]

I have seen a big steel boat lifted by its 'chainplates'. Although they were not really chainplates, just damn big eyes that take the rig. I would not want to try it on a GRP boat with conventional chainplates.

 

[RAI]

I would certainly like to think they are strong enough from the weight point of view, but the CG of the boat is likely to be behind them, so taking the boat by forestay, backstay and shroud mountings with the mast off should be no trouble. Common crane hook at mast head height of course.

Regarding legs, the first yacht I sailed had yacht legs that looped over the side and hooked onto the cap shroud eyes. Of course they apply much less stress than the boat's weight as the keel takes nearly all of it dried out

 

[VicS]

The breaking strain of the rigging does not match the wieght of the boat so the chainplates are not designed to take the lifting load

You sure ?

6mm wire has a breaking strain of 27kN. there will be at least 7 wires (although admittedly the forestayy and back stay will be far from vertical) so take 6 (the shrouds) 6 times 27kN is 162 kN I think you will find that any boat weighing more than 162 kN will have much thicker wire than 6mm.

162kN would be equivalent to a displacement of the best part of 16 tonnes.

 

[srm]

I think it was in abook by Uffa Fox that I came across the minimum rigging strength guide line that the shrouds on one side should be able to take the full weight of the boat with chain plates sized to match.

However, this was probably a safe rule in the days of proper sea going boats. A couple of years ago our marina was graced by a piece of modern sculpture mounted on a big French production yacht. Closer inspection showed it was the mast neatly broken in three and held together by internal halyards. The cause was also plainly visible - the deck mounted chain plate along with a ss load carrying structure that presumably is intended to takes the rig load to the hull was lying on the side deck next to a neat hole.

 

[Tranona]

I recall seeing X Boats laid up in a shed, hung from the rafters to the chain plates with blocks under the keel. Supposedly to avoid using props that might distort the hulls.

Also the 12 metre Lionheart was lifted from an eye bolt in the keel accessed through a plug in the deck.

However, if the objective is to AF the bottom of the keel, why not just jack it up in its cradle, put some extra props in and remove the blocks under the keel. Or even simpler, ask the crane or hoist to hold the boat while you do the underneath, doing the bits where the strops go beforehand.

 

[Ardenfour]

Have to agree with srm, I also recall reading somewhere that the chainplates ought to bear the weight of the boat. But the force involved in rolling a boat over has nothing to do with the weight, but the righting moment. Think of a half submerged log - you could roll it over with one hand, nothing to do with the weight

 

[VO5]

I would not even dream of trying such a stunt.

Certainly not with a cruiser, let alone a dinghy.

Here in Gib we have a fleet of Victories. These are classic 23 ft clinker boats, that we traditionally race.

There is another fleet in Portsmouth.

By comparison, they are not very heavy in the general scheme of things.

They are fitted with lifting eyes in the keel. Two strops are fitted fore and aft to lift and two strops athwartships to steady them.

I dread to think of the consequences if they were lifted otherwise.

 

[DownWest]

I watched an Amel being launched this way. It is standard for them to use the chainplates, so presumably they have done a few sums. Also the lugs are not the same ones used for the rig, but are part of the same units.(biggerholes for the shackles)
A

 

[boguing]

We lifted an MG335 by just one of it's chainplates to prove to an owner that the boat was as strong as it should be.

 

[Salty John]

Chainplates are, typically, designed to be stronger than the breaking strrain of the wire they support so that the wire will break before any structural damage occurs.
Typically, and it isn't possible to do other than generalise, a design factor of 2 to 3 times the breaking strain of the wire is used. So, a 6mm wire shroud as used on a 30-ish foot boat would have a breaking strain of 3700 kg and the chainplate to which it is attached would be designed for a load of 7400kg or more. Such a boat might have a total weight somewhat less than that, say 5,000 or 6,000 kg, so could be lifted on port and starboard chainplates with some degree of safety.

 

[[448]]

............. I'm just asking ).


Boo2

Says it all really.
And he's a few days late with his post
Dave