Which screw to choose?

[Colvic Watson]

I need to replace the rigging screws and saw these http://stores.ebay.co.uk/Boat-Chandlery-Stainless-Marine_CHAIN---RIGGING-SCREWS_W0QQLHQ5fSellerWithStoreZ1QQLHQ5fTitleDescZ1QQ_fsubZ13QQ_sasiZ1QQ_sidZ37652391QQ_trksidZp4634Q2ec0Q2em322

Which size would you choose for a 19 foot day sailer, masthead rig 4mm wire stays?

Thanks!

 

[Salty John]

For 4mm wire diameter you need M8 thread diameter.

 

[Colvic Watson]

Thanks - would you recommend open or closed body?

 

[Seajet]

Open body are supposed to be the 'in thing', but I must say I'm not at all keen on the split pins all over the place, very easy to shred sails or ankles ( if it's SWBO's ankle, take cover ! ) - careful bending & lots of protective tape required.

I think I may go back to closed body next time I change; I prefer lock-nuts too...

 

[Colvic Watson]

I agree except I wondered if open body more readily showed corrosion? But unless I hear of a reason not to I'll go closed - they look neater!

 

[ProDave]

I have closed on my boat, and there's one thing I don't like. You can't see how much thread is left engaged.

So say you were slackening your forestay for example, you could without waring unscrew it all the way. Whoops.

With an open screw you can see how much thread is left and know when to stop.

 

[VicS]

4mm wire is generous for a 19ft day sailer
It has breaking strain of 12KN (equivalent to approx 1200kg)

There are no specs given for the rigging screws in the link but 6mm would probably match that while 8mm will exceed it by a comfortable margin.

What size is fitted at present?

Before you commit your self check the lengths. If you go up a diameter on the original you will also be increasing the length. If you buy them too long you have a problem.

I'd have said 6mm was adequate for the size of boat.

 

[Colvic Watson]

Sorry Vic you're right I've just checked and it's 3mm wire - does that mean 6mm screws are OK?

 

[sailorman]

I need to replace the rigging screws and saw these http://stores.ebay.co.uk/Boat-Chandlery-Stainless-Marine_CHAIN---RIGGING-SCREWS_W0QQLHQ5fSellerWithStoreZ1QQLHQ5fTitleDescZ1QQ_fsubZ13QQ_sasiZ1QQ_sidZ37652391QQ_trksidZp4634Q2ec0Q2em322

Which size would you choose for a 19 foot day sailer, masthead rig 4mm wire stays?

Thanks!

rigging screws same size as the wire.
no point in larger its all down to the min breaking strain of the component parts

http://cgi.ebay.co.uk/2-x-BRAND-NEW...tEquipment_Accessories_SM&hash=item20b78cab62

 

[Salty John]

I prefer open body because you can see what's going on, but no strong feeling one way or the other.

4mm might seem a little heavy. However, if you go to 3mm wire and M6 thread rigging screws the wire breaking load nearly halves from 1340kg to 765 kgs. There is no 3.5mm wire. So, with such a big jump between the two It would be important to go with whatever the designer selected.

For information, an M8 rigging screw is typically between 240mm open and 160mm closed in length, pin to pin.

Whatever you do make sure you put the appropriate toggles on those fixed forks to give full articulation.

 

[VicS]

Sorry Vic you're right I've just checked and it's 3mm wire - does that mean 6mm screws are OK?

The figure I have for the breaking strain of 3m wire is 7kN

The figure I have for M6 riggings screws is 13kN These should be plenty heavy enough to go with 3mm wire.
Even M5 at 800kN exceed the strength of the wire! If necessary you can come down to these.

 

[Fantasie 19]

I have closed on my boat, and there's one thing I don't like. You can't see how much thread is left engaged.

So say you were slackening your forestay for example, you could without waring unscrew it all the way. Whoops.

With an open screw you can see how much thread is left and know when to stop.

I couldn't agree more. and I believe the closed versions may have contributed to my dis-masting last year simply because I couldn't see that the thread wasn't engaged as much as it should have been.. go for open body every time, and split pins, and to solve Seajet's valid issue, get some covers to shield the pins from passing ankles...