Gun Tackle

[Capt. F. E. Peera]

Can GUN TCKLE be used to discharge/load 10 ton wt with 5 ton SWL derrick. never experienced before.

Capt. Peera

[Ivan Cloherty]

Well Cap'n, I wouldn't try it in Oz, NZ,or UK or other EEC countries, so legally the answer would be no, theoretically it can be done because a 5ton SWL derrick would have had a 15 ton load destruction test, but not to forget also that the derrick head blocks SWL has to be taken into consideration, also the angle of the derrick so that you dont lift the heel.

Is this something you have done, or something you want to do, if the latter it's back to the drawing board with your paralellagram of forces, but it's a good way to end up in jail if anything goes wrong

Has it been done, I've seen it done in India and Pakistan on their own flagged ships and also on Greek ships, but not ships under my control and I wouldn't have sanctioned it, always remember ten tons of feathers weighs the same as ten tons of lead when it's under the hook

No doubt you'll get more technical reasons coming your way

[John Pruden]

yes 1 third of the braking strain is the safe working load{but stay clear}if you can.JP

[Les Woodard]

I think you will find that the the SWL is just the same as a mobile crane's SWL. Say you have a SWL of 10 ton for a crane it will only be achieved when the boom is at its shortest and topped up closest to the crane with the maximum amount of falls in the runner. The devil in the SWL of a derrick is not in the purchase power of the running gear but in the purchase power of the topping lift. I know we used to quite regulary increase the purchase power of the runner by using a block with a hook and tying the runner to the head of the Derrick so as there where two falls of runner. All derricks where not suited to this because of the SWL factor. From memory we would know when to do this when they used to come down the accomodation shouting out doubling up on number two or some other hatch.

[Ivan Cloherty]

I think you will find that the the SWL is just the same as a mobile crane's SWL. Say you have a SWL of 10 ton for a crane it will only be achieved when the boom is at its shortest and topped up closest to the crane with the maximum amount of falls in the runner. .

Sorry Les, but not quite true, having been supplying equipment for cranes over 25 years you will find that the only thing that equates closely to a ship's derrick, is a shorebased fixed sheerleg, as neither a sheerleg or a ship's derrick have to take tipping centres, outriggers or ground bearing loads into consideration, all other non-fixed cranes do and that is their achilles heel. Also a ships derrick is designed to have it's effective SWL available at all angles when used in Union Purchase mode where a pair of 10 ton derricks could lift a maximum of 2.7 tons in single whip.

When doubling up on Union gear to say lift 5 tons with a pair of 10 ton derricks then you would use a gun tackle (Doubling up) on each derrick. The Topping lifts on a 10 ton derrick were usually rigged for a 15/17.5 ton SWL.

If wanting to lift more than 5 tons with a 10 ton derrick you would use a gun tackle or a 2/1 or 2/2 purchase and use the derrick as a swinging derrick, using either the spare winch as a topping lift or as an inboard steam guy, when in this rig you have to be careful of the angle of the derrick, not so much because of the SWL factor but because the heel pin is liable to jump out of its socket, as a lot of derrick heels were only secured with a heavy duty split pin, very few were fitted with locking nuts, as these tended to seize up.


Others may have different experiences

[Tony Wilding]

I am amazed at the complexity of lifting gear, all the different terms used, how were they all learnt, ? some lifts were huge just using ships gear, who decided what method to use for a heavy lift, and work out the stresses, i can see why the topping lift is very important, ,were there many accidents with gear giving way,

[Ivan Cloherty]

I am amazed at the complexity of lifting gear, all the different terms used, how were they all learnt, ? some lifts were huge just using ships gear, who decided what method to use for a heavy lift, and work out the stresses, i can see why the topping lift is very important, ,were there many accidents with gear giving way,

Tony surprisingly few on well run ships, unless of course you really are daft enough to try lifting a 10 ton object with a 5 ton derrick then your chances of not having an accident do increase expotentially.

Heavy lifts are something else again and tipping centres have to be taken into account even on ships.

What I have been trying to do is keep the answers into the context of the original question asked about relatively small lifts, which we came across very often on general cargo ships where a particular piece of cargo just exceeded what was considered the norm for the Union Purchase Rigs on a single whip which were the prevalent rigs when us oldies were at sea. We always erred on the side of safety when it came to derrick work, no quicker way to lose your job (or your life) than having two derricks coming together at a rate of knots and damaging each other and you still have a full hold and a couple of tween decks to discharge at that hatch. Caution and safety were the name of the game and you were always kept on your toes by stevedores trying to break the rules if they were on "Piece Work" and if we were in doubt we had formulaes and our pencil and paper to work out the streses on a particular piece of gear in the rig. Like everything else in life it comes with experience no matter what your calling.

Hope above helps

[Les Woodard]

Ivan do not be sorry mate as you pointed out I stuffed up on the information and stand corrected. That is one of the reasons I switched to rigging when I left the sea because there is always more than one way to rig a load and each way is unique to that load. Might bring up one point though. I was always under the impression that the heel that the toe end of the derrick was always called a goose neck for obvious reasons. Not trying to gain back any brownie points mate as I said we all had different ways of talking about rigs. As for mobile cranes well that was to try to point out that the maximum lift is when the load is closest to the base but should not have mixed up the two systems.

[Ivan Cloherty]

Ivan do not be sorry mate as you pointed out I stuffed up on the information and stand corrected. That is one of the reasons I switched to rigging when I left the sea because there is always more than one way to rig a load and each way is unique to that load. Might bring up one point though. I was always under the impression that the heel that the toe end of the derrick was always called a goose neck for obvious reasons. Not trying to gain back any brownie points mate as I said we all had different ways of talking about rigs. As for mobile cranes well that was to try to point out that the maximum lift is when the load is closest to the base but should not have mixed up the two systems.

Hi Les, you are correct "Gooseneck" was the correct word and it was the word that escaped me whilst I was pontificating. Of course you are correct on mobile cranes the SWL only really applies when the boom is near vertical.

Also another fact about mobile crawler cranes is that a circa SWL 250 tonne crane has only a grabbing capacity duty of circa 15 tonnes (including grab weight). In my business of 25 years of supply equipment to contractors it was incredible how many contractors had based their expense calculations on the basis that a 50 tonne crane could handle a 12/15 tonne grab at any angle and got a bit of a shock when they found they had to finance the purchase or hire of a 150/250 tonne crane, this really affects the profit margin! you would be surprised how many did not do their homework before signing their contracts. Small cranes were ten a penny the bigger ones like hens teeth and then there was the grab, so many types not compatible with the cranes available...a different and interesting world

[Bob Hollis]

Ivan and Les, you are both correct in that there is a heel (immovable) on a derrick which is connected to and supported by the swivel arrangement called the Gooseneck.