What size shrouds?

[bbdave]

I have a Salterns Sou-wester 18 (gaffer) sail area 255sq ft it has 4 shrouds which are 3mm 1x19 stainless with an approx loading of 500kg each is this enough?.
i was thinking of upgrading to 4 or 5mm. I have not sailed the boat yet and the mast will be going up in the next month or so is it worth upgrading?

Dave

 

[prv]

The classic rule of thumb is that the shrouds on one side of the boat should be capable of lifting it. At 18 foot I assume your "four shrouds" is two per side, so each needs to be able to lift half the weight of the boat. Classic Marine says that 3mm 1x19 stainless has a breaking strain of 720kg, so would be suitable for a boat of 1440kg or just under a tonne and a half.

How heavy is the boat?

Pete

 

[merlin3688]

Most 18' boats would have 4mm rigging but check your chain plates and what size pin/shackle they will take, Sta Lok show a 3mm eye will have a 6.4 (1/4") pin and a 4mm eye will have a 8.1 (5/16") pin. Not sure how you attach your wires but you do not want to have to drill out your chain plates.

 

[prv]

Most 18' boats would have 4mm rigging

Do note that rig loads in a gaffer are lower than for bermudan, because the mast is shorter for the same sail area.

Presumably the person who designed the boat didn't just pick the size of the wire at random, and the mast hasn't fallen down yet.

But it won't hurt much (a little extra windage) to go up a size if you're worried.

Pete

 

[chewi]

Do note that rig loads in a gaffer are lower than for bermudan, because the mast is shorter for the same sail area.

Presumably the person who designed the boat didn't just pick the size of the wire at random, and the mast hasn't fallen down yet.

But it won't hurt much (a little extra windage) to go up a size if you're worried.

Pete

I know what you mean here, but if you read the books and the tools, they advise tensioning to a % of the breaking strain, so if you have upped from 3mm to 5mm for peace of mind, then tensioned it for 5mm you'd be massively increasing the loads on the rig and the hull, so the peace of mind might be misplaced if 3mm was right in the first place.

 

[bbdave]

The boat hasn't been sailed yet it is a home build my father did the rigging it just looks small that's all but the boat weighs approx 1.25tons so i guess the 1440kg will cover it.

They will be tensioned with lanyards so not much strain on the hull

Dave

 

[VicS]

The weight of the boat according to my research is 1¼tons.
According to Jimmy Greens website the breaking strain of 3mm 1x19 stainless wire is 790kg, although other data I have suggests nearer 700kg.

Either way if you apply PRV's rule of thumb 3mm will be adequate.

Personally I'd replace it with 4mm as and when it needs to be replaced.

My Sea Wych ( which is a much lighter boat) has 3mm rigging. I have replaced the forestay with 4mm and I would replace the rest in 4mm if I was re-rigging it but in reality the existing rigging will probably see me out!

Heed the warning above about tensioning the rigging though. If you upgrade the wire do not increase the tension. Tension it as though it is still 3mm.

 

[bbdave]

Thanks chaps i'll probably stick with the 3mm then up it to 4 when i re rig

Dave