What SWL for a spinnaker halyard?

[Kelpie]

Hoping to rig my boat (Albin Vega, 27ft) with a spinnaker this year and will need to mount a halyard for it. What would the panel suggest would be a good SWL for the halyard block given the likely forces on a spinnaker?
TIA

 

[Norman_E]

Personally I would rig the spinnaker halyard with the same strength rope and blocks as the genoa halyard, essentially you then have an emergency genoa halyard, albeit routed a bit differently, and a spare halyard strong enough to use for the bosuns chair.

 

[VicS]

Jimmy Green's Sheets and Halyards guide

 

[Kelpie]

Thanks for the replies, but it's not the size of the halyard itself I am looking for, it's the strength of the block that carries it. I can't just make it the same as the other halyards because they use built in sheaves at the mast-head.
So whilst I know I will probably be fine to use a 10mm halyard, should I be looking at e.g. a Barton size 3 block (swl 385kg) or size 4 (swl 630kg). The difference being I already have some size 3 blocks lying about, but of course failure of this block could be pretty catasophic!

 

[boaterbaz]

Go for the largest diameter sheave you can. Small diam equals more friction/resistance whatever you call it. Plus the sharper you bend a rope the more you reduce its breaking strain.

 

[Quandary]

I would be impressed if you could manage a broach that would burst the blocks you already have, even if you race are you likely to keep the kite up much above force 5?

 

[PetiteFleur]

The breaking load of the Barton blocks is twice the SWL, so bear this in mind. My mast is down at the moment for inspection etc and my barton swivel block is about a No2 or 3 - not sure of the exact size but seems OK for me, 33' Moody & 10Ø halliard. It does seem rather light though as it only has a strip shackle fixing it to the masthead so I'm going to root around in my spares box to see if I have a larger block.
I did burst a No 2 Barton block on my kicking strap last year but it was seriously overloaded with my cascade system!

 

[Quandary]

Back again, on the subject of shock loads on spinnakers. A bit of elasticity in the halyard is useful on both spinnakers and gennakers, you are often adjusting the head position anyway and it reduces the stress on everything, particularly the stitching of the panels when a collapsed sail refills with a bang. I have never used dyneema or composite halyards for kites, though it is different when you get to about 50' or so.

 

[Kelpie]

Thanks again for the input.
Now that I think about it, my genoa sheets and my main halyard are all running through no.3 bartons at some point... so I guess I can trust them. And for the immediate future, as I have no desire to chase SWMBO off the boat forever, I will probably not fly a kite if someone so much as farts, let alone F5!

 

[Norman_E]

Take a look at these http://www.seldenmast.com/products/?itemID=29&modelID=26 the sheave is 5mm bigger than the Barton No3 but the safe load is nearly double. I have bought this make of block and am very pleased with the quality.

 

[PetiteFleur]

You could get this - sounds good at the price with 2000kg breaking load http://cgi.ebay.co.uk/low-price-sel...UK_Sporting_Goods_Sailing&hash=item1e60e513fb I'm tempted myself.....

 

[Searush]

TBH, I would expect the weak point to be the fastening of the block to the mast rather than the block itself. Rivets & screws can work loose & pull out over time.