Which screw to choose?

Seajet

...
Joined
23 Sep 2010
Messages
29,177
Location
West Sussex / Hants
Visit site
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

Well-known member
Joined
23 Nov 2004
Messages
10,862
Location
Norfolk
Visit site
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

Well-known member
Joined
5 Sep 2010
Messages
15,262
Location
Alness / Black Isle Northern Scottish Highlands.
Visit site
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

Well-known member
Joined
13 Jul 2002
Messages
48,324
Visit site
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.
 

sailorman

Well-known member
Joined
21 May 2003
Messages
78,864
Location
Here or thertemp ashore
Visit site
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
 
Last edited:

Salty John

Active member
Joined
6 Sep 2004
Messages
4,563
Location
UK
www.saltyjohn.co.uk
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

Well-known member
Joined
13 Jul 2002
Messages
48,324
Visit site
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

Well-known member
Joined
23 Mar 2009
Messages
4,459
Location
Chichester, West Sussex
Visit site
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... ;)
 
Top