Jib Halyard block failure

[tolhurstorganic]

I have a jib set flying from a furler on a bowsprit traveller. it is hauled to top of mast on a single block positioned on front of topmast. The halyard is 12mm braid on braid. The sail is 16 sq metres (160 sq feet). The jib is left up most of the time and furled away. To maintain luff tension I use a small winch mounted on side of mast and running (Dyneema) backstays. I have had two failed blocks so far in 3 seasons sailing. The first one was probably way to light it was a tufnol one rated at working load of 600kg, it broke at the swivel. The last one was rated to 1.6 tons break load and cost a small fortune. It is now past its guarantee period.
Two questions: Can anybody say what the actual working load would be on this block?
Does anybody know where I may get a suitable single block with swivel for 12mm halyard?
Looking around it seems difficult to find a block to suit 12mm line I have found blocks rated to 1.8 tonnes but only for 16mm line. Not fussed about the material its made from but it needs to be strong. A rigger friend suggested that I need 2 tonne working load, this seems very excessive for the size sail?

 

[FWB]

Try Classic Marine. They are very helpful. 01394 380390

 

[Woodlouse]

Where did the second block break? It sounds like it was probably flawed since the SWL is always very conservative and if the 12mm double braid is not dyneema then I'd expect that to break before a block of that size.

 

[tolhurstorganic]

The cheeks drifted apart and halyard jambed between cheek and pulley, I suspect that the lead was not quite in line!

 

[knuterikt]

The cheeks drifted apart and halyard jambed between cheek and pulley, I suspect that the lead was not quite in line!

You have to find out and fix the reason for this misaligned load on the block, I don't think you will find a block that is designed for that type of load...

have you considered going for a 1:2 halyard?

 

[charles_reed]

In a 35 mph wind, your sail would be exerting a load of c 500lbs.(assuming you don't try sailing in more than bF7).

Using as the LCD, the Barton loadings the following block should be adequate for your needs.

http://www.bartonmarine.com/products-size-2-blocks.asp

If your broken block is smaller than this it was probably underspecified. If not, look for unfair loads on the block.

 

[chal]

I have a jib set flying from a furler on a bowsprit traveller.

I have the same arrangement but, as someone else has suggested, on a double ended halyard: the halyard goes over a block offset to left side of mast, through another block connected to the top swivel of the furler, and over another block offset to right side of mast. None of the blocks is particularly immense but none has ever failed, and I suspect this is partly because there is a bit of play in the system and everything takes up a "comfortable" attitude.

I also have a bobstay tensioner so the load is taken on a block there too, which should be as likely to fail as the one at the top of the mast. If your arrangement is similar, the fact that it's always the higher block that fails suggests that it is more the misalignment than the actual load that is causing the damage.

None of my blocks have swivels incidentally.

 

[heard28]

Is the swivel free to rotate? If it's a bit stiff to turn, then that might make the alignment problem worse. I've had problems with 2-part halyards twisting around themselves and making the jib difficult to drop before I discovered this contributory factor. However, if there is sufficient distance between mast and top block, I would have expected the block to align by itself - is that also part of the problem?

 

[knuterikt]

I have a jib set flying from a furler on a bowsprit traveller. it is hauled to top of mast on a single block positioned on front of topmast. The halyard is 12mm braid on braid. The sail is 16 sq metres (160 sq feet). The jib is left up most of the time and furled away. To maintain luff tension I use a small winch mounted on side of mast and running (Dyneema) backstays. I have had two failed blocks so far in 3 seasons sailing. The first one was probably way to light it was a tufnol one rated at working load of 600kg, it broke at the swivel. The last one was rated to 1.6 tons break load and cost a small fortune. It is now past its guarantee period.
Two questions: Can anybody say what the actual working load would be on this block?
Does anybody know where I may get a suitable single block with swivel for 12mm halyard?
Looking around it seems difficult to find a block to suit 12mm line I have found blocks rated to 1.8 tonnes but only for 16mm line. Not fussed about the material its made from but it needs to be strong. A rigger friend suggested that I need 2 tonne working load, this seems very excessive for the size sail?

I read this post one more time and noticed.
working load 600kg
breaking load 1600kg = working load 800-1000 kg (the safety margin used differs)

If this isn't a typo the increase in working load is not that big.

What kind of block was the second one?
You don't need a fancy block with high tech bearings for this application, blocks with plain bearing is good enough for this type of static load.

Regarding expected load
I looked up the sizing guidelines for a staysail here http://www.facnor.com/uk/products/g...us_line/description_and_technical/default.asp
30 m2 = safe working load 2500 kg
50 m2 = safe working load 4500 kg