Rules of thumb for rigging size?

[Kelpie]

I've always suspected that our boat may be a little bit under-specced in terms of the standing rig. I recently got in touch with another owner, whose boat has 8mm rigging where ours is only 6!
Short of employing a rigger to look over the whole boat (I don't even know where my nearest one would be), is anyone aware of a ready reckoner or table that would give an approximation of what size rigging wire I ought to have?

 

[savageseadog]

Suggest you contact Allspars in Plymouth

 

[lw395]

You could get yourself a yacht design book and work out what's needed.
At a guess, it's more likely the other boat is over-rigged.

 

[Salty John]

There are a couple of rules of thumb but you'd be best advised to consult a rigging expert if you are concerned you might be under rigged.
One rule says double the weight of your ballast in lbs and that should be the breaking strain of your wire.
Ian Nicolson's Boat Data Book has a chart which shows that 6mm wire is OK for up to 10 tons displacement on shrouds and 6 tons displacement on the forestay.

 

[Tranona]

Sounds fine to me. Some people think that oversize rigging is a "good thing". Rarely do cruising boats generate loads anywhere near the maximum of the wire. Rig failures are almost always fittings or physical failure of wire due to damage or corrosion.

 

[Kelpie]

Thanks for the replies.
We are about 5.5t design displacement on a keel stepped masthead rig with single spreaders.
She's not got a huge sail area or particularly tall mast, and being a centreboarder the ballast weight is not as low down as it would otherwise be- so I presume this makes her more tender and thus places a bit less strain on the rig?

However 6mm seems kind of light, just gut feeling. My previous boat, a Vega, had 6mm on the forestay and 5mm elsewhere- and that is a boat of only 2.3t design displacement.

I would try contacting the builders and/or designers but this has not been very helpful in the past.

 

[knuterikt]

Thanks for the replies.
We are about 5.5t design displacement on a keel stepped masthead rig with single spreaders.
She's not got a huge sail area or particularly tall mast, and being a centreboarder the ballast weight is not as low down as it would otherwise be- so I presume this makes her more tender and thus places a bit less strain on the rig?

However 6mm seems kind of light, just gut feeling. My previous boat, a Vega, had 6mm on the forestay and 5mm elsewhere- and that is a boat of only 2.3t design displacement.

I would try contacting the builders and/or designers but this has not been very helpful in the past.

can recommend this book https://www.amazon.com/Complete-Riggers-Apprentice-Techniques-Traditional/dp/0070648409

 

[Tranona]

Thanks for the replies.
We are about 5.5t design displacement on a keel stepped masthead rig with single spreaders.
She's not got a huge sail area or particularly tall mast, and being a centreboarder the ballast weight is not as low down as it would otherwise be- so I presume this makes her more tender and thus places a bit less strain on the rig?

However 6mm seems kind of light, just gut feeling. My previous boat, a Vega, had 6mm on the forestay and 5mm elsewhere- and that is a boat of only 2.3t design displacement.

I would try contacting the builders and/or designers but this has not been very helpful in the past.

My Bavaria 33 with similar displacement and a fractional rig which relies far more on rig tension to keep the mast up also has 6mm. Why do you think yours is inadequate? Your boat comes from a top rate designer and respected builder so guess they will have done their sums right!

 

[savageseadog]

Thanks for the replies.
We are about 5.5t design displacement on a keel stepped masthead rig with single spreaders.
She's not got a huge sail area or particularly tall mast, and being a centreboarder the ballast weight is not as low down as it would otherwise be- so I presume this makes her more tender and thus places a bit less strain on the rig?

However 6mm seems kind of light, just gut feeling. My previous boat, a Vega, had 6mm on the forestay and 5mm elsewhere- and that is a boat of only 2.3t design displacement.

I would try contacting the builders and/or designers but this has not been very helpful in the past.

6mm could be about right. The OP could consider 7mm for the forestay and using Dyform as replacement when it comes to it as it's stronger.

 

[macd]

My Rival 32, widely regarded as tougher than a brick outhouse, had 6mm, which it took to the Antilles and back. Doubt you have a problem.

 

[Kelpie]

Thanks, all very encouraging! I may well consider upgrading the forestay, although to be honest we only fly a self tacking blade on it, which is considerably smaller than the as-designed headsail. We also have a 5mm removable inner forestay which we use for the big lightwind/downwind genoa, and the (not yet used) storm jib.

 

[savageseadog]

A general point would be that rather than dwelling on wire sizes, focus on the fittings, bottle screws, articulation and fixing pins. Make sure the ends are properly made off, the correct size of pins are used compatible with hole sizes, forestay properly articulated, fittings on mast are in good order etc etc.