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Author Topic: A quesstion for you tuggies.  (Read 2886 times)

boatmadman

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A quesstion for you tuggies.
« on: December 16, 2007, 04:00:28 PM »

Why is the tow point on a tug always attached at about the centre point for/aft?

When a gog eye or winch is used, the effective tow point for anything other than straight for and aft moves away from the tow hook, so why not put the hook further aft, so that sideways forces wont try and capsize the boat and do away with the gog?

Probably an obvious reason, but I dont know it.

Ian

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ddraigmor

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Re: A quesstion for you tuggies.
« Reply #1 on: December 16, 2007, 04:37:37 PM »

What a question!

Gog's first: The reason for the gog aft is to give better control to the tugmaster and also prevent to rope from going foul of the beam. It also allows for more control of any 'side slipping'. Hard bowsed down great for straight line towing but eased off for any manouvering!

The tow hook centre line is a bit more dificult to answer! Firstly, most tugs have a righting arm which pivots on the centre of the vessel but allows a swing through arcs either side of centre.

Why centre or midships? Best point of towing which allows for a combination of weight and power to be exetrted in full but also allows the hook to pivot on a horizontal plane.  In this way the heeling moment (when she dips over to one side or the other) is greatly reduced as is also the danger to the tug itself. Most tow hooks swivel in the horizontal and are usually resticted to half the beam of the tug itself. Please note that all tow hooks are fitted with a 'tripping' or 'quick release' mechanism so that if there is any danger of girting, the tow rope is let go. On one tug I was on we also had a man standing by with a heavy axe....in case!

Not all tugs have towing hooks. Some will have centreline bollards (large H bitts) whilst oters will have bollards and a hook

The winch, as used by many tugs, is based on the same principle but many will be fitted with 'Auto Loading' so that, at a given tonnage of exrtion, the winch will ease off automatically. This also halts heeling. As the winc wire slackens, then the winch again 'takes up' the weight.

Hope that helps?

Jonty
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tobyker

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Re: A quesstion for you tuggies.
« Reply #2 on: December 16, 2007, 07:41:33 PM »

I thought the hook was midships so the tug could steer - if it's too far back the tow will always pull the tug in line with the rope/hawser. But then again I'm not a tuggie, so my opinion counts for nowt here.
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ddraigmor

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Re: A quesstion for you tuggies.
« Reply #3 on: December 16, 2007, 09:09:37 PM »

The hook is midships - it is the gog rope that is aft!

On the deep sea tugs I was on, you had a metal sleeve - actually mangalese alloy - which was called a saddle. That went over the tow wire and was controlled by a capstan. Put the weight on when going in a straight line (so as to keep it over the stern for better traction and control - but ease it out either side when turning.

Nowadays you have a huge metal eye which does the same job, I think - never worked them.

Jonty
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BobF

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Re: A quesstion for you tuggies.
« Reply #4 on: December 16, 2007, 09:36:35 PM »

Hi all,

I made the mistake on my full size sailing cruiser of tying some mooring pontoons that had broken away (on a flooded river), tight to the stern against two tyres to avoid damage.
The result, as mentioned by tobyker, was a 90 foot barge that would not respond to the rudder.
I had to let go one of the lines, so I could get the whole thing back under controll. Because I was then towing from one side the tyres dropped away and the broken bracket on the pontoon took a large piece of gel coat out of the transom. Since then, any thing I rescued was either tied along side, or on a long rope.

Bob
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catengineman

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Re: A quesstion for you tuggies.
« Reply #5 on: December 17, 2007, 10:20:24 AM »

Large tow eye gogs are normally found on harbour tugs that are not useually employed at deep sea towage work, The eye is used to erduce the stress put on the winch spooler gear which (when fitted) is normally smaller than that on a ocean/sea going towage tug.

Have a look at VS ship handling tugs then look at a few AH tugs to see the difference also AH tugs use kalm forks rather than a 'gog rope'

R,
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boatmadman

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Re: A quesstion for you tuggies.
« Reply #6 on: December 17, 2007, 01:16:37 PM »

Ok,

Great answers, but what the 'eck is a kalm fork?

ian
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catengineman

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Re: A quesstion for you tuggies.
« Reply #7 on: December 17, 2007, 02:11:44 PM »

I know them as kalm forks, they come out of the deck via hydraulics and there are normally 4 in total "two inner" "two outer" on older small tugs they can be called norman pins but these are normally placed in position by hand.

Now I wait to be corrected from a different region! O0
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ddraigmor

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Re: A quesstion for you tuggies.
« Reply #8 on: December 17, 2007, 04:53:17 PM »

They're called Karm forks, made by Karmfork of Norway. Basically, they are two pins that rise hydraulically from the deck. They are not gog type stuff though - they are used to hold wire or chain in place.

The ones you are thinking of are also hydraulic but are called 'Stop' pins and can be raised or lowered and also rotated so they form a sort of fairlead (either closed or open). With it in place, you have a gog that can be moved by hydraulic action whichever way required and without a couple of men on deck to tend to it.

When used in tugs of lesser horsepower in sea and harbour work, they do away with the need for a gog rope. Made by people like Karmfork or Triplex, they are also known as 'shark's jaws' and can take a few variations! They are like forks, with a V out of them for gripping wire or chain. They are often used together so that a gripping device (the Sharks Jaw ) and also used in conjunction with the stop pin.

In my day out in the wild Northsea (when men were men!), we used a wire pennant which was fastened to a Smit Bracket just under the crash barriers. You had to allow the main towing winch to hold the weight on, shackle the pennant to the wire or chain and then ease back on the winch so the weight was transferred to the pennant from the Smit Bracket. With anchors weighing 25 tonnes, and in a force 6 + gale, the word 'hairy' still comes to mind..........!

Jonty
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boatmadman

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Re: A quesstion for you tuggies.
« Reply #9 on: December 17, 2007, 05:02:13 PM »

Great stuff - but what the 'eck is a Smit Bracket?
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ddraigmor

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Re: A quesstion for you tuggies.
« Reply #10 on: December 17, 2007, 06:33:55 PM »


Right! As you can imagine, it was developed by Smits during their deep sea towage days.

They are a very simple and eficient way to connect a tow to a barge / ship etc as it allows for one end of a towline (or chain or wire bridle) to be secured by a large sliding pin, which is then locked off by a good whack with a hammer to bend it into position.

You can find details and a photo here.http://www.anchormarinehouston.com/Towing.html

I bet you never thought there was so much to towing, eh?

Jonty
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farrow

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Re: A quesstion for you tuggies.
« Reply #11 on: December 20, 2007, 11:05:55 PM »

When I worked on harbour tugs, the gog or dogging rope/wire was used when towing of the hook especially when working as the stern tug to stop the tug girting and then capsizing . The wire was put to the aft capstan and weight was put on it to limit the radius oh the tow rope/tow hook, so that if the towed vessel puts strain on the tug when it was in a awkward position it pulled the tug stern round instead of rolling the tug over, that is the main job of it in a screw tug.
The tow hook is position where it is in a screw tug to allow the tug to manoeuvre under strain to alter the directional pull of the towing point in relation to the tow. If it is after the tug would not be able to manoeuvre and be locked in one direction all the time. As a tug must be able to alter its towing position from say ahead to of the beam when pulling a ship in an enclosed area to turn the tow etc, in other words to alter towing position from the towed vessel while maintaining strain on the towing wire.
Tractor tugs such as voith Snider's, aqua master tugs etc, do not use gog/dog ropes, as due to the nature of their towing units, they do not have to alter the angle of the hull through a rudder to alter their towing position to the towed vessel. Their units are multi directional so they thrust sideways  to what ever postion they want to maintain on a towed vessel, in theory they cannot be girted and capsized, except in a indirect tow but that is another subject.
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boatmadman

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Re: A quesstion for you tuggies.
« Reply #12 on: December 21, 2007, 10:26:43 AM »

All becomes clear, great stuff, thanks fella's

Ian
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