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Weak link for button fender?


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Having re built and fitted the boat out over the past year, I've just fitted a button fender on the stern and a tapered sausage (is that a tipcat?) on the bow. I've used the small steel "carabiners" but it need to replace with d shackles, less easy to pinch. Bow fender has 2 chains, rear 4 chains. Where do I fit the weak link, what's best to use?

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I don't think.most people put a weak link in the stern fender.

 

There's various ways of doing a weak link. I used some thick cable ties on one side. You can also use a thin bit of rope, or hacksaw most of the way through one side of a link in the chain, so it will easily snap.

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There's various ways of doing a weak link. I used some thick cable ties on one side. You can also use a thin bit of rope, or hacksaw most of the way through one side of a link in the chain, so it will easily snap.

I know from experience that hacksawing part way through one side of a link is insufficient. The damn think did not break, despite the bow fender getting caught under a top gate. You need to saw right through, so that the link only has to bend if put to the test.

 

If you have a fender attached with more than 2 chains I would put a cut link in every chain except one, so that it fails whether you get caught up or under. One chain without a weak link ensures you don't lose the fender altogether.

Edited by David Mack
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I have never really understood the need for a weak link in bow fenders, If you are unsure of your ability to keep the bow of the boat away from the top lock gate, just lift the fender and place it onto the fore deck. Many working boats never used a front fender, and if they did it was put on the foredeck when ascending locks

Edited by David Schweizer
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Having re built and fitted the boat out over the past year, I've just fitted a button fender on the stern and a tapered sausage (is that a tipcat?) on the bow. I've used the small steel "carabiners" but it need to replace with d shackles, less easy to pinch. Bow fender has 2 chains, rear 4 chains. Where do I fit the weak link, what's best to use?

Have you got your bow & stern round the wrong way?

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Have you got your bow & stern round the wrong way?

 

No, they are the way round that I want them to be. The stern fender is a round button, I have an outboard so welded up a hinged bumper bar around the engine, with one of the scrap porthole window steel cut outs to fix the fender to.

 

Thanks for the advice folks, half sawn links it is then.

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Chain link fence tensioners!!! An eye on one end a hook on the other and adjustable to boot!! Make sure you buy the cheapest crappiest ones you can find..you want them to fail under load!! Bought mine from Wilkos years ago..eye end through a d shackle hook end through other end of chain..perfect!!

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I have never really understood the need for a weak link in bow fenders, If you are unsure of your ability to keep the bow of the boat away from the top lock gate, just lift the fender and place it onto the fore deck. Many working boats never used a front fender, and if they did it was put on the foredeck when ascending locks

 

With a boat at almost 71 foot we often intentionally keep the front in contact with the gate, especially when on the K&A where a couple of the locks are only 70 foot long. A weak link is a very good idea.

 

Some locks cause significant surging and with only a foot or two of clearance it just isn't always possible to avoid banging against the gate so a front fender is pretty much essential.

 

...............Dave

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I know from experience that hacksawing part way through one side of a link is insufficient. The damn think did not break, despite the bow fender getting caught under a top gate. You need to saw right through, so that the link only has to bend if put to the test.

 

I'll second this. Even a link fully cut through on my bow fender resulted in the bow of the boat being a good 6" to 8" down when I got it caught in a gate, before the link straightened out and released the boat. Just as non-boaty brother in law drew my attention saying "Does your boat normally look that low in the water?", the link gave way, the bow popped up and a big surge of water back and forth in the lock was set up. Allowing yourself to distracted at locks by chatting is NOT a good idea.

 

I very much doubt it would have given way had one side of the link only been cut part way through.

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My last efforts at cutting through one side of the chain met with signal failure. The idea was the cut through a link of a spare bit of chain, twist the link so that I could separate it from the spare chain, then insert the open link in the fender chain and reclose the gap by twisting the link back.

 

The link could not stand tow lots of twisting and at the third attempt I gave up and used cable ties.

 

Nick

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OK I've been cutting half way through the side of a shackle and it sounds like this might not be the best idea. Which thickness of cable ties are people using please?

 

...................Dave

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OK I've been cutting half way through the side of a shackle and it sounds like this might not be the best idea. Which thickness of cable ties are people using please?

 

...................Dave

 

2.5mm wide ones have a minimum strength of 18lbs

3.5mm wide ones have a minimum strength of 30lbs

4.8mm wide ones have a minimum strength of 50lbs

7.6mm wide ones have a minimum strength of 120 lbs

12.5mm wide ones have a minimum strength of 250 lbs.

 

These are the minimums to the Mil specifications, the 'actuals' will probably be around 20% higher.

Being manufactured from Nylon (primarily Nylon 6.6) cable ties are hydroscopic (absorb water) with approximately 2% moisture content the above figures will be achieved, higher moisture content makes the ties very flexible and much weaker, 'dryer' ties will be much stronger but very brittle.

 

If you have cable ties that are 'brittle' (rattle when you shake them, or snap when you bend them) boil them in a pan of water for 5 + minutes and they will return to normal.

A bag of cable ties should be resealed after removing the ties you need.

 

2.5mm wide ones have a minimum strength of 18lbs

3.5mm wide ones have a minimum strength of 30lbs

4.8mm wide ones have a minimum strength of 50lbs

7.6mm wide ones have a minimum strength of 120 lbs

12.5mm wide ones have a minimum strength of 250 lbs.

 

These are the minimums to the Mil specifications, the 'actuals' will probably be around 20% higher.

Being manufactured from Nylon (primarily Nylon 6.6) cable ties are hydroscopic (absorb water) with approximately 2% moisture content the above figures will be achieved, higher moisture content makes the ties very flexible and much weaker, 'dryer' ties will be much stronger but very brittle.

 

If you have cable ties that are 'brittle' (rattle when you shake them, or snap when you bend them) boil them in a pan of water for 5 + minutes and they will return to normal.

A bag of cable ties should be resealed after removing the ties you need.

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Has the working boat practice of back in the day gone out of favor? a thin (weak ) piece of rope on 1 side & a thicker (stronger) piece on the other, +you don't get the chain digging chunks out of the counter woodwork or if steel damaging the paintwork worse than rope

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I think whether cutting right or part way through your chain for the weak link depends on your chain. I cut 3/4 the way through my rather cheap chain and had it break with a minor hang up ( good thing).

 

I have also tried cable ties but after a few years the U/V got to them and they failed under the weight of the fender.

 

Top Cat

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2.5mm wide ones have a minimum strength of 18lbs

3.5mm wide ones have a minimum strength of 30lbs

4.8mm wide ones have a minimum strength of 50lbs

7.6mm wide ones have a minimum strength of 120 lbs

12.5mm wide ones have a minimum strength of 250 lbs.

 

These are the minimums to the Mil specifications, the 'actuals' will probably be around 20% higher.

Being manufactured from Nylon (primarily Nylon 6.6) cable ties are hydroscopic (absorb water) with approximately 2% moisture content the above figures will be achieved, higher moisture content makes the ties very flexible and much weaker, 'dryer' ties will be much stronger but very brittle.

 

If you have cable ties that are 'brittle' (rattle when you shake them, or snap when you bend them) boil them in a pan of water for 5 + minutes and they will return to normal.

A bag of cable ties should be resealed after removing the ties you need.

 

Interesting stuff here, thanks. So now I need to estimate the static load on the tie when the boat adopts a unhealthy angle, this should be within my engineering capabilities, or skill set as people like to say these days.

 

Interestingly I did some experiments using paracord as the weak link (550 lbs load) and it did break on several occasions when we nudged the gates a little harder than intended. We hang the button just below the nose rather than on the nose otherwise we are too long for a few locks, so a bump at the front can maybe give a bigger tensile force component along the chain. So maybe finding the balance between the boat getting hung up and general shock loads is not trivial

 

.............Dave

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2.5mm wide ones have a minimum strength of 18lbs

3.5mm wide ones have a minimum strength of 30lbs

4.8mm wide ones have a minimum strength of 50lbs

7.6mm wide ones have a minimum strength of 120 lbs

12.5mm wide ones have a minimum strength of 250 lbs.

 

These are the minimums to the Mil specifications, the 'actuals' will probably be around 20% higher.

Being manufactured from Nylon (primarily Nylon 6.6) cable ties are hydroscopic (absorb water) with approximately 2% moisture content the above figures will be achieved, higher moisture content makes the ties very flexible and much weaker, 'dryer' ties will be much stronger but very brittle.

 

If you have cable ties that are 'brittle' (rattle when you shake them, or snap when you bend them) boil them in a pan of water for 5 + minutes and they will return to normal.

A bag of cable ties should be resealed after removing the ties you need.

What incredible abstruse information you learn on CWDF! Interesting stuff, that.

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I think whether cutting right or part way through your chain for the weak link depends on your chain. I cut 3/4 the way through my rather cheap chain and had it break with a minor hang up ( good thing).

 

I have also tried cable ties but after a few years the U/V got to them and they failed under the weight of the fender.

 

Top Cat

 

Black will give better UV protection than 'natural' (White) but better still is "W-Grade" which has the addition of 2% carbon-Black. these will give double at least) the life of 'natural' ties.

 

Many years ago I was involved in a Tender for a major Australian Cities new (raised) mono-rail system, we lost out on price to a Taiwanese competitor.

 

Come opening day, the mayor and all the local dignitaries took the first 'ride' around the city, the train stopped. all of the cable ties had fallen off and the cables were left hanging. The Fire Brigade had to rescue all of the dignitaries by ladder.

 

We offered the 'correct' grade of cable ties (weather resistant for out door use) and we secured the contract for the retro-fitting.

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  • 4 years later...
On 14/08/2016 at 14:55, dmr said:

 

Interesting stuff here, thanks. So now I need to estimate the static load on the tie when the boat adopts a unhealthy angle, this should be within my engineering capabilities, or skill set as people like to say these days.

 

Interestingly I did some experiments using paracord as the weak link (550 lbs load) and it did break on several occasions when we nudged the gates a little harder than intended. We hang the button just below the nose rather than on the nose otherwise we are too long for a few locks, so a bump at the front can maybe give a bigger tensile force component along the chain. So maybe finding the balance between the boat getting hung up and general shock loads is not trivial

 

.............Dave

Thank you for this bought a bag of ties from toolstation and they were snapping off before fully tightened  I will try the boiling method as desperate and used a few or would have returned them 

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4 minutes ago, Maudesmaster said:

Thank you for this bought a bag of ties from toolstation and they were snapping off before fully tightened  I will try the boiling method as desperate and used a few or would have returned them 

 

This is reviving an old thread 😀.

The force from any small impact, such as nudging the front button against a lock gate, is big, and will likely snap cable ties. I had no success at all with them. Putting a weak link in the chain appears to be the only way to go. This is done by cutting right through a link, probably at the weld. The link then opens up under a dangerous load. This works.

The link will likely open up progressively under normal boating impacts so will need forcing back into shape every few months. I use a small portable vice to do this. Cutting part way through a link or shackle did not work for me.

 

...............Dave

 

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1 hour ago, dmr said:

 

This is reviving an old thread 😀.

The force from any small impact, such as nudging the front button against a lock gate, is big, and will likely snap cable ties. I had no success at all with them. Putting a weak link in the chain appears to be the only way to go. This is done by cutting right through a link, probably at the weld. The link then opens up under a dangerous load. This works.

The link will likely open up progressively under normal boating impacts so will need forcing back into shape every few months. I use a small portable vice to do this. Cutting part way through a link or shackle did not work for me.

 

...............Dave

 

I cut through one side of a link, I have had one open up and snap the link whilst descending in a lock rather than the fender just riding up over the stem post.

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12 minutes ago, Rob-M said:

I cut through one side of a link, I have had one open up and snap the link whilst descending in a lock rather than the fender just riding up over the stem post.

 

Some fender chains are much lighter duty than others, but are you sure the fender was not caught on some little sticky out thing? We've had a couple of experiences in the last week where very small insignificant sticky out things have really caught the front button.

 

...........Dave

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