Blocks: why is recommended maximum diameter rope, so slender?

Well I use 14mm and huge genoa cars/blocks, stupidly oversized..
( try outlets that might stock end of line/used/bankrupt stock and no I am not going to help exactly where but if you go to enough winter boat jumbles that is one source)
Bigger rope and surface area -for a cruising boat- = more contact area , less wear. Easy innit. easier on the hands too when tired. wet. etc.
 
Blueboatman said:
Well I use 14mm and huge genoa cars/blocks, stupidly oversized..
( try outlets that might stock end of line/used/bankrupt stock and no I am not going to help exactly where but if you go to enough winter boat jumbles that is one source)
Bigger rope and surface area -for a cruising boat- = more contact area , less wear. Easy innit. easier on the hands too when tired. wet. etc.
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Exactly right - but we are not talking about a substantial cruising boat, but if I understand the OP correctly he is using 14mm for the main sheet on a Topper and complaining about the size and cost of the blocks that go with it!
 
Blueboatman said:
Bigger rope and surface area -for a cruising boat- = more contact area , less wear. Easy innit. easier on the hands too when tired. wet. etc.
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Blueboatman, Searush, Seajet: you relieve my mind...the mature, intelligent choice, in favour of a more comfortable option.

I seem to remember a cross-country run at school, on which the route could be slightly cut-short, if one went through a particularly verdant patch of nettles. I, and a handful of other young dumbwads, really thought we were tough, coming back stung all over. :rolleyes:

Tranona said:
Exactly right - but we are not talking about a substantial cruising boat, but if I understand the OP correctly he is using 14mm for the main sheet on a Topper and complaining about the size and cost of the blocks that go with it!
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Sorry, Mr T; you misunderstood. I was (ages ago!) quite happy with my much-thicker-than-standard Topper main, which could easily be threaded through the boat's standard blocks...

...I was now only curious why the option of further increasing the comfort, by upping the rope diameter on more powerful boats in more testing winds, seems to be obstructed by the manufacturers' restrictive recommendation of rope diameter, for any given size of block...

...but I'm persuaded there's no good reason at small-boat level, not to use as thick a line as can fit round the sheave. :)
 
dancrane said:
Blueboatman, Searush, Seajet: you relieve my mind...the mature, intelligent choice, in favour of a more comfortable option.

I seem to remember a cross-country run at school, on which the route could be slightly cut-short, if one went through a particularly verdant patch of nettles. I, and a handful of other young dumbwads, really thought we were tough, coming back stung all over. :rolleyes:



Sorry, Mr T; you misunderstood. I was (ages ago!) quite happy with my much-thicker-than-standard Topper main, which could easily be threaded through the boat's standard blocks...

...I was now only curious why the option of further increasing the comfort, by upping the rope diameter on more powerful boats in more testing winds, seems to be obstructed by the manufacturers' restrictive recommendation of rope diameter, for any given size of block...

...but I'm persuaded there's no good reason at small-boat level, not to use as thick a line as can fit round the sheave. :)
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I can understand your desire to have thicker bits of string for comfort - but you can't get away from the fact that to run smoothly you need to use the sheave size designed for the cordage size. If it were not the case you might wonder why all those smart people in the rigging business go to all the trouble to ensure that the correct kit is available to make the best use of the properties of the cordage.
 
Tranona said:
I can understand your desire to have thicker bits of string for comfort - but you can't get away from the fact that to run smoothly you need to use the sheave size designed for the cordage size. If it were not the case you might wonder why all those smart people in the rigging business go to all the trouble to ensure that the correct kit is available to make the best use of the properties of the cordage.
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I'm inferring that you mean, "don't expect thick diameter sheets to run happily round very small diameter sheaves"?

I'm thinking if the sheets concerned are never likely to encounter even 10% of their breaking strain, the loadings they'll suffer, passing round, eg. a 60mm dia sheave, won't see their useful life shortened much.

I can certainly see that the exaggerated curve of a thick line round a tiny sheave, wouldn't do the rope any good.

But I doubt that'll be a problem. I was concerned that it might be an issue regarding the line's clearance through the top of the block. I couldn't see why 22mm of space, wouldn't allow a line thicker than 14mm!

Barton size 7 looks like ample curve and clearance for a luxurious sheet that'll pamper my tender ungloved hands. :rolleyes:
 
Mr Tranona does know a thing or two about these things ( wots this, mutual forums day?):)

The thing with tackles is that the friction increases vs the increasing factor of theoretical advantage ( the number of sheaves). Bending a thick rope around a thin diameter is unhelpful. Its tedious when the boom ( for example) refuses to ease out in a gentle breeze because of the augmented frictions...
Have we saved you some dosh yet then?:)
 
Blueboatman said:
Mr Tranona does know a thing or two about these things ( wots this, mutual forums day?):)

The thing with tackles is that the friction increases vs the increasing factor of theoretical advantage ( the number of sheaves). Bending a thick rope around a thin diameter is unhelpful. Its tedious when the boom ( for example) refuses to ease out in a gentle breeze because of the augmented frictions...
Have we saved you some dosh yet then?:)
Click to expand...

Is a mischievous humorous streak slipping in here?

I'm very much open to experts' advice on specific kit. That's why I asked the question in the first place. So...you tell me...

...a couple of Barton size 7 blocks, threaded with 20mm Marlowbraid, for use as a mini-cruiser mainsheet...

...technically, the rope is oversize, so technically the cordage might suffer from the sheave being only 70mm across...

...but, hard to imagine the loading ever exceeding a tiny fraction of the blocks' or rope's breaking loads. So, no problem?

As I suspected initially, it's like the expiry date on tinned foods...not to be taken too pedantically seriously. If the sheet and blocks were used to hoist the boat vertically from the water, maybe...but in moderate conditions on a small boat, not worth worrying over. Cheers. :)
 
Dan

14mm sheets on ANY dinghy is ludicrous. Do you open your walnuts on xmas day with a sledgehammer? ;)

Big chunky ropes do not bend as easily as light ones. They also weigh a truckload more. Fine if it's windy, but on a light day your main will refuse to square off on a run, and all your sails will be pinned in/clews weighted down by the miles of unnecessary yacht rigging you are dragging round with you.

The mainsheet on my 49er is 6mm and it works beautifully. And bear in mind that's skiff style sheeting, straight from the ratchet block on the boom to your hand. And that is also a big beasty of a sail. I wear gloves, £3 Showa builders gloves, and it's fine. Compare that to a hobie I borrowed on holiday, with a 65:1 mainsheet or similar, chunky 10mm plus rope, and it tore my fingers to shreds. No gloves, but it's friction and movement that wrecks hands, not line diameter.

I think we only had 10mm tapered on the 18' skiff kite, however it was run through opposing ratchet blocks. Mind you, I was usually at the other end of the boat on the which way stick...

It's thin for a reason, and no, I would never wear gloves on a big boat as protection...only to keep the cold out, and I'd never sail a dinghy without gloves unless it was seriously light. (or I'd not thought to pack them on holiday!)
 
dancrane said:
Is a mischievous humorous streak slipping in here?

I'm very much open to experts' advice on specific kit. That's why I asked the question in the first place. So...you tell me...

...a couple of Barton size 7 blocks, threaded with 20mm Marlowbraid, for use as a mini-cruiser mainsheet...

...technically, the rope is oversize, so technically the cordage might suffer from the sheave being only 70mm across...

...but, hard to imagine the loading ever exceeding a tiny fraction of the blocks' or rope's breaking loads. So, no problem?

As I suspected initially, it's like the expiry date on tinned foods...not to be taken too pedantically seriously. If the sheet and blocks were used to hoist the boat vertically from the water, maybe...but in moderate conditions on a small boat, not worth worrying over. Cheers. :)
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I'm using 20mm mainsheets on an 840 square feet fully battened mainsail running via multiple blocks that are certainly less than 100mm (cannot remember the exact size and I'm not onboard) going back to a Lewmar 65 hydraulic winch - we have no line wear issues at our loads so trust me, you will have no wear issues! But, as said, you may have to push the boom out! :D
 
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Blueboatman said:
Mr Tranona does know a thing or two about these things ( wots this, mutual forums day?):)

The thing with tackles is that the friction increases vs the increasing factor of theoretical advantage ( the number of sheaves). Bending a thick rope around a thin diameter is unhelpful. Its tedious when the boom ( for example) refuses to ease out in a gentle breeze because of the augmented frictions...
Have we saved you some dosh yet then?:)
Click to expand...

I endorse this. An example which I may have mentioned before: I too use 14 mm jib sheets for handling comfort but they only turn through a small angle at the car then go round the winch. The main sheet, on the other hand, is a very different kettle of fish. It's a 3/6:1 tackle and 10mm line was originally used. At 6:1 it was a real effort to get it as tight as I wanted and at 3:1 it needed overhauled to run out. I replaced it with 8mm and it was transformed: single handed tensioning and it runs out freely at 6:1.

It's the most cost effective change I've made to the boat and, because of the hugely reduced friction, the 8mm line is much more comfortable to handle than its 10mm predecessor.
 
Thanks for recent posts...good points, about friction from oversize sheets. Perhaps I'll also have a secondary, 1:1, 4mm Dyneema mainsheet, to substitute during force-ones. :rolleyes:

Iain C said:
14mm sheets on ANY dinghy is ludicrous...the mainsheet on my 49er is 6mm and it works beautifully.
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Iain, I thank you seriously for your convincing reasoning, but I reckon those sentences show you're made of sterner stuff than I!
 
I am very surprised no one mentioned the load applied on a block, if the rope is used at its maximum strength.
Of course, the manufacturer of the block knows the max. load his block will hold, thus he specifies the corresponding rope to be used.
Modern ropes have an enormous strength :
from the Marlow web site, "cruising / racing" Dynema
8 mm. : breaking load : 3450 kg.,
10 mm.: breaking load : 5350 kg.,
12 mm.: breaking load : 6900 kg,
etc.

According to this, a single block must have a breaking load at least double the rope's breaking load:
8 mm. : above 7'000 kg.
12 mm.: over 14'000 kg.

Of course, you never experience such a load on your dinghy, but the manufacturer has to guaranty his block for such loads.
How can he know how the block will be used?

This is an explanation why the big blocks are so expensive.

It's up to you, knowing how you shall use a block to choose the most convenient for you.

Just my 2 pennies.
 
Mr D Crane, No mischievousness intended nor implied:)

And as you can see, lots of broadly concurring advice/caveats


No one has mentioned 'end for ending'-or even buying overlong-sheets then cutting back and resplicing every season or few, to move the wear spots away from the sheeves.
 
Blueboatman said:
Mr D Crane, No mischievousness intended nor implied:)
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No problem! :) Good idea, of yours - buying a longer line, then moving it up annually, refreshing any areas that are most subject to wear. Although in ten years on the Topper, my very abrasive-seeming ratchet block never wore any thin fluffy patches in the 14mm line I used.

I loved that 14mm line. :rolleyes: After the nasty coarse bit of coloured string the Topper came with, it felt like a different boat.
 
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