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Quick release hook

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Sam Longley 114/11/2018 13:27:52
722 forum posts
26 photos

Without going in to the long convoluted reasons our local mooring holders have a problem laying their mooring sinkers.

We have to place 40 concrete weights weighing up to 3 tonnes in the River Blackwater. To do this we are going to place the weight ( complete with the chain & buoy attached) at the low water mark. We will attach a flotation bag to the weight & as the tide rises (5 metres) it will lift the weight off the sea bed.

We will then tow the weight to its position using a work boat & drop the sinker with chain etc thus placing a mooring.

The bottom of the flotation bag will be approx 1.5 metres below the water level and we have to release it from the sinker.This means we have to make a quick release hook. The hook must not come undone accidentally as it is waiting for the tide coming in due to wave motion & it must never come undone in the wrong place as we cannot move an incorrectly placed mooring which would be a disaster

So what I want to know -- can anyone come up with an idea for a simple release hook that can be operated from a workboat at water level safely under 3 tonnes of load. We have to be able to make it ourselves. I have milling & welding capabilities etc I want to be able to make it as economically as pos & it to be fairly basic idiot proof.

Please do not suggest other mooring methods- there are countless reasons why we have to do this. 50 mooring owners have applied their minds to this & this is the direction we must go

I am hoping someone may have seen something in a factory somewhere that we can adapt. Or, being engineers, they may have an idea

Thanks,

Edited By Sam Longley 1 on 14/11/2018 13:29:43

Neil Greenaway14/11/2018 13:47:57
70 forum posts
3 photos

Could you use a chain shortener clutch hook of a suitable size which could be attached to a chain link and possible release itself using gravity - these are normally sized for standard lifting chain. The pin end could be fitted with a loose lift chain.

Neil.

Martin Kyte14/11/2018 13:56:46
1488 forum posts
24 photos

Have a google for quick release mooring hooks. The basic idea is the hook section pivots between two side cheeks and is controlled by a latch on the tail of the hook. When the tail is released the hook flicks outwards towards the load and the loop in the load line slips off. The action is like a hand holding the handle of a bag and then releasing by straightening the fingers and opening the hand. Sea going salvage tugs use a large version.

Here is one version and a video

**LINK**

regards Martin

Neil Wyatt14/11/2018 14:06:06
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Moderator
16570 forum posts
687 photos
75 articles

You probably want something like a bomb release mechanism, designed for reliability under shock loads and carrying lots of weight.

A look at patents suggests something like a car boot/bonnet catch.

Perhaps a car boot catch operated by a wire would work?

Neil

Michael Gilligan14/11/2018 14:17:48
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14014 forum posts
608 photos
Posted by Martin Kyte on 14/11/2018 13:56:46:

Here is one version and a video

**LINK**

.

That's very decent of them

... Couldn't really ask for a better demonstration of the mechanism

MichaelG.

Edited By Michael Gilligan on 14/11/2018 14:19:25

Nick Hughes14/11/2018 14:38:44
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201 forum posts
130 photos

A couple of simple ones to copy (HK3 or HK6 ?) here:-

**LINK**

Nick.

Martin King 214/11/2018 16:18:45
608 forum posts
223 photos

Hi All,

Having done many underwater lifts using lift bags between 100kg and 4 x 5 tonne bags (16 tonne propeller.) I would advise extreme caution with the method you are proposing.

Are you contemplating using fixed bouyancy bags or standard 'parachute' lift bags with dump valves?

Take the scenario where you are in the middle of the river about to position your mooring; at the correct moment you hit your quick release mechanism. What will happen then is that the lift bag, strops and most of all the heavy shackles will explode out of the water flailing in all directions The potential for serious injury is enormous.

What you are in fact proposing is what happens when a lift goes wrong for whatever reason, strop failiure for instance. You really do not want to be anyhere near it trust me.

IMHO the correct way to do this is to use a qualified diver to actuate the dump valve under careful control; this also allows for easy repositionong if needed by adding a little air from a SEPARATE cylinder tied to the bag.

For all things to do with underwater lifts go look at JW AUTOMARINE in Holt Norfolk, they make the finest bags in the world.

Just my 10 peenorth..

Cheers, Martin

Martin King 214/11/2018 17:35:28
608 forum posts
223 photos

Cannot remember the figures but concrete as a mooring weight medium is less than ideal, weighs so much less in water, you may need to take that into your calculations?

Mooring systems these days tend towards hydraulically driven galvanised screws, driven in vertically with extra sections bolted on until they ground out. Ones I ihelped install in the BVI years ago have just withstood Hurricane Maria with sustained 150 knots for 14 hours. 60 foot boats all survived except 2 where the cleats ripped out of the hulls!

Martin

Sam Longley 114/11/2018 17:46:14
722 forum posts
26 photos
Posted by Martin King 2 on 14/11/2018 17:35:28:

Cannot remember the figures but concrete as a mooring weight medium is less than ideal, weighs so much less in water, you may need to take that into your calculations?

Mooring systems these days tend towards hydraulically driven galvanised screws, driven in vertically with extra sections bolted on until they ground out. Ones I ihelped install in the BVI years ago have just withstood Hurricane Maria with sustained 150 knots for 14 hours. 60 foot boats all survived except 2 where the cleats ripped out of the hulls!

Martin

Sorry- do not wish to be blunt but I want to avoid thread drift- I said in my first post that we are NOT interested in alternatives. We know all about specific gravity, screws, anchors, concrete (145lbs / ft3) marinas etc & have been using sinkers as best option for 30 years. We still believe that there is no economic, viable alternative having fully investigated them over the years. Even to the point of engaging outside marine consultants.(waste of time of course!!) Diving is a no-no simply because of visibility. Lots of divers have told us so, otherwise we would just reconnect new chains to the existing sinkers on the seabed without raising them. (we are not using bags to raise them)

I will take your first post ( & i thank you for that ) & go back to the air bag supplier who suggested it & has offered a bag for trial prior to purchase. However, there will only be a linking hook between sinker & bag so the situation is not quite as you suggest. We are dropping, not raising which is different.

 

Edited By Sam Longley 1 on 14/11/2018 18:18:05

SillyOldDuffer14/11/2018 21:44:45
4713 forum posts
1010 photos

Aren't quick release hooks a standard maritime item? You can get small ones on Amazon up to giant ones for un-mooring ships. Perhaps a Ship Chandler would have what you want. The working principle of this Amazon example is fairly obvious if you wanted to make one.

Re Martin's point about the floatation bag rocketing to the surface on release, I don't think there's much difference between raising and lowering. To lift a 3 ton concrete block you would need about 1.35 tons of buoyancy. To lower the same block, slightly less. Say the bag is about 10 feet deep. The amount of energy released when the bag rises through water is the same order as a 1.35 ton weight dropped from a height of 10 feet. Easy enough to get a feel for the forces involved with a football and an oil drum full of water.

I think the method of moving the blocks is basically sound, but it would be dangerous to operate the quick release before the buoyancy of the bag was much reduced by releasing most of the air. On something like this I'd do a risk assessment and plan suitable mitigations. I suspect professionals wouldn't mess with bags for this - they'd use a barge fitted with a 5 ton crane to lower the blocks straight into the water, making it a standard lifting job.

Dave

Nathan Sharpe14/11/2018 22:00:48
131 forum posts

Sounds to me as if Sam is describing a surface flotation system, not a fully submerged bag. In that case the bag is sized so that it is oversized for the lift and will not "explode out of the water with strops etc flailing in all directions" and if the bag manufacturer/supplier are involved should be perfectly safe. Neither manufacturer or supplier would wish to involved in a dangerous scheme as they would be liable if it went wrong. If correctly specified the bag should do no more than bounce on the surface . Nathan.

Edit because I quoted the gist not the actual wording.

Edited By Nathan Sharpe on 14/11/2018 22:03:46

Sam Longley 114/11/2018 22:16:28
722 forum posts
26 photos
Posted by SillyOldDuffer on 14/11/2018 21:44:45:

Aren't quick release hooks a standard maritime item? You can get small ones on Amazon up to giant ones for un-mooring ships. Perhaps a Ship Chandler would have what you want. The working principle of this Amazon example is fairly obvious if you wanted to make one.

Re Martin's point about the floatation bag rocketing to the surface on release, I don't think there's much difference between raising and lowering. To lift a 3 ton concrete block you would need about 1.35 tons of buoyancy. To lower the same block, slightly less. Say the bag is about 10 feet deep. The amount of energy released when the bag rises through water is the same order as a 1.35 ton weight dropped from a height of 10 feet. Easy enough to get a feel for the forces involved with a football and an oil drum full of water.

I think the method of moving the blocks is basically sound, but it would be dangerous to operate the quick release before the buoyancy of the bag was much reduced by releasing most of the air. On something like this I'd do a risk assessment and plan suitable mitigations. I suspect professionals wouldn't mess with bags for this - they'd use a barge fitted with a 5 ton crane to lower the blocks straight into the water, making it a standard lifting job.

Dave

 

You need 1.7 tons ( imperial) but there are other bits like weight of the mooring chain & the bag etc plus the effect of being towed through the water so the bag will probably be between 4 -5 ton capacity which( I think) is less that a 6 ft cube. there is a difference between raising and lowering as to raise one needs to pull the bag under the water to force the weight upwards. This needs attendant gear to do it. To lower it one hooks it tight to the weight & waits for the tide to come in & lift it, so there are no extra strops etc other than those on the bag. The bag will only sink about 3 feet so will not actually "shoot up" as suggested

If one released some of the air (assuming one could do a controlled release) the bag would sink & if for some reason the hook did not release then we could not return it to shore to sort the problem because the weight would drag on the seabed, leaving a dangerous object partially sunk in the water. Believe me, we have thought those situations through.

We just need a good simple quick release hook operable from the surface

The hook you kindly suggest is difficult to release under load very successfully & has to be pulled from the correct direction. Believe me I have released a few off a rolling yacht at sea with a billowing spinnaker trying to throw me overboard. Ships hooks tend to be designed for horizontal use as in warps and anchor chains through the hawse pipes so the designs do not really work for us.

Edited By Sam Longley 1 on 14/11/2018 22:17:54

Pete Rimmer14/11/2018 22:16:29
424 forum posts
18 photos
Diving is a no-no simply because of visibility. Lots of divers have told us so, otherwise we would just reconnect new chains to the existing sinkers on the seabed without raising them. (we are not using bags to raise them)

Find better divers. I had guys working at 24 metres down rigging up a concrete cutting setup in zero viz by touch alone. If I told them that it was impossible to attach a chain in zero viz they would fall over backwards laughing.

https://www.dropbox.com/s/fjvd2154o6cg4lo/divers.jpg

Edited By Pete Rimmer on 14/11/2018 22:17:28

Edited By Pete Rimmer on 14/11/2018 22:18:46

SillyOldDuffer14/11/2018 22:24:09
4713 forum posts
1010 photos
Posted by Nathan Sharpe on 14/11/2018 22:00:48:

Sounds to me as if Sam is describing a surface flotation system, not a fully submerged bag...

Good point! But Sam did say 'The bottom of the flotation bag will be approx 1.5 metres below the water level'. That means it will pack a punch. A bigger bag floating on the surface would reduce the shooting up problem, but then you have to worry a stiff breeze might make the job uncontrollable. I'm sure it's all do-able though, just needs a bit of thinking through.

Dave

Brian Sweeting14/11/2018 22:48:13
379 forum posts
1 photos

Plastimo do a 9000kg, swl5200kg, snap shackle, is this your idea?

Link here

https://www.plastimo.com/en/mousqueton-a-ouverture-sous-charge.html

 

Edited By Brian Sweeting on 14/11/2018 22:48:42

Sam Longley 114/11/2018 22:48:23
722 forum posts
26 photos
Posted by Pete Rimmer on 14/11/2018 22:16:29:
Diving is a no-no simply because of visibility. Lots of divers have told us so, otherwise we would just reconnect new chains to the existing sinkers on the seabed without raising them. (we are not using bags to raise them)

Find better divers. I had guys working at 24 metres down rigging up a concrete cutting setup in zero viz by touch alone. If I told them that it was impossible to attach a chain in zero viz they would fall over backwards laughing.

**LINK**

Edited By Pete Rimmer on 14/11/2018 22:17:28

Edited By Pete Rimmer on 14/11/2018 22:18:46

How much do you pay these divers along with all the attendant support gear?

When you tell me, I will laugh as well.

This is all about economics. A tug to lay the moorings wants several £k's poss £6-8K to be confirmed

A local friendly tug guy used to do them for £ 50-00 each as he was passing, minimum 10 at a time. Just because he was friends with us all. Unfortunately he passed away & his family will no longer hire the tug to us

A Flotation bag costs £1000 & will last several years .We can do the job ourselves using our own group launch at times to suit us. Ie not all in one day. So when someone wants a single mooring we can put 1 in & not pay the minimum fee.So for 40 moorings we would charge £ 40-00 each, we would make a small profit for our fund & have a free flotation bag ready for next time

But all we need is to design a quick release hook

Sam Longley 114/11/2018 22:51:54
722 forum posts
26 photos
Posted by Brian Sweeting on 14/11/2018 22:48:13:

Plastimo do a 9000kg, swl5200kg, snap shackle, is this your idea?

Link here

**LINK**

Edited By Brian Sweeting on 14/11/2018 22:48:42

Thanks I did not realise that pattern went that large . Wichard are notoriously expensive but I will find out the cost

Brian Sweeting14/11/2018 22:58:40
379 forum posts
1 photos
Posted by Sam Longley 1 on 14/11/2018 22:51:54:
Posted by Brian Sweeting on 14/11/2018 22:48:13:

Snip

Thanks I did not realise that pattern went that large . Wichard are notoriously expensive but I will find out the cost

Yes, I was surprised too, then again I dread to think of the load on some sheets carrying big sails in a blow.

Pete Rimmer14/11/2018 23:44:35
424 forum posts
18 photos
Posted by Sam Longley 1 on 14/11/2018 22:48:23:
Posted by Pete Rimmer on 14/11/2018 22:16:29:
Diving is a no-no simply because of visibility. Lots of divers have told us so, otherwise we would just reconnect new chains to the existing sinkers on the seabed without raising them. (we are not using bags to raise them)

Find better divers. I had guys working at 24 metres down rigging up a concrete cutting setup in zero viz by touch alone. If I told them that it was impossible to attach a chain in zero viz they would fall over backwards laughing.

**LINK**

Edited By Pete Rimmer on 14/11/2018 22:17:28

Edited By Pete Rimmer on 14/11/2018 22:18:46

How much do you pay these divers along with all the attendant support gear?

When you tell me, I will laugh as well.

This is all about economics. A tug to lay the moorings wants several £k's poss £6-8K to be confirmed

A local friendly tug guy used to do them for £ 50-00 each as he was passing, minimum 10 at a time. Just because he was friends with us all. Unfortunately he passed away & his family will no longer hire the tug to us

A Flotation bag costs £1000 & will last several years .We can do the job ourselves using our own group launch at times to suit us. Ie not all in one day. So when someone wants a single mooring we can put 1 in & not pay the minimum fee.So for 40 moorings we would charge £ 40-00 each, we would make a small profit for our fund & have a free flotation bag ready for next time

But all we need is to design a quick release hook

I've no idea of your economic situation Sam, you didn't say. When you said you'd asked lots of divers I presumed that they were at least somewhat professional ones. A proper outfit could do it but you're right they are in no way cheap, quite the opposite.

Dave Martin15/11/2018 21:52:59
101 forum posts
11 photos

Sam,

It might be worth looking at the design of the hooks used on the falls for ship's lifeboats, as they are remotely-releasable whilst on-load.

Dave

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