Shroud Tension

[Thistle]

Can anyone tell me, or point me towards (web) resources which would tell me, what range of tensions I should be looking for in my shrouds? 23' boat, deck-mounted mast, 7/8 fractional rig, cap and lower shrouds, swept-back spreaders, roller jib, single backstay with limited adjustment.

TIA

 

[saxonpirate]

I was lucky enough to to know Bunty King of Hood Sails back in the day when I was just starting out and hungry for knowledge. I bought his book Sail Power which proved to be a bible to me when setting up my masthead rigged boats. I've never owned a fractional rig..

One thing I'll always remember him saying to me is this.. tighten your bottle screws as tight as you can by hand and then a turn or two with a spike, put some pre-bend in your mast, then put the boat through every point of sail and adjust until you've no slack rigging on your lee side. Tight is right..

Here's a handy PBO write up anyway, which I'm sure will give you all the relevant information to set you on your way..

How to set up your rig: tension your shrouds on masthead or fractional - Practical Boat Owner

 

[geem]

The selden rigging manual is online. Just Google it.
It will tell you how to tune it and tension it. I have just done mine yesterday

 

[ean_p]

Copy the 'Hints & Advise' pdf from here;

Rigging instructions & sailmakers guide : Seldén Mast AB

bugger.......

 

[Thistle]

Useful pointers. Many thanks, guys.

 

[Concerto]

If you can buy or borrow a rigging guage, you will get a much better and faster rig tension.

How to use Tension Gauges - Loos & Company, Inc. - Cableware Division

 

[William_H]

I am a skeptic of large rig tensions. (yes in the fa bend ce of advice Selden etc.) I have yet to see a boat where lee shrouds do not go slack when hard on wind. The problem is Mr Selden can give date on rigging wire and fittings stretching etc but can not account for the hull stiffness. ie you load up the tension on forestay/ back stay and the hull bends like a banana. You load up the cap shrouds and the hull can squeeze in under pressure. Many people report toilet door won't close or open when rig is tensioned. It is not just the immediate effects of rig tension on hull but long term it can cause permanent distortion of hull. All very small distortions but enough to make it difficult to get an d keep rig tension.
Some boats in my club with rigs just like yours used for racing have a high field lever in forestay which is released after each race to remove standing tension from the rig.
IMHO opinion on OP rig yes tension it up firm. But it is the ratios of tensions that provide the mast shape. So back stay no tension rig the cap shrouds firm giving the desired mast rake (just a little) and vertical from side to side. Use a halyard out to each side. With little tension on intermediate side stays the mast should have a fair bit of bend middle forward. More cap shroud tension or more spreader bend aft to increase mast bend.This is then pulled out to lessen mast bend middle forward while at the ame time balancing tension of 2 intermediat shrouds to get mast straight side to side.
from there in a blow add back stay tension to straighten fore stay. And yes lee shrouds will go slack. ol'will

 

[geem]

If you can buy or borrow a rigging guage, you will get a much better and faster rig tension.

How to use Tension Gauges - Loos & Company, Inc. - Cableware Division

The same thing can be achieved with a 2 metre rule fixed to your rigging wire and some vernier calipers to measure the stretch. 1mm of stretch for every 5% of rigging tension, regardless of 1x19 wire size. It's easy and cheap. For us with 12mm and 1/2" rigging, the cost of a gauge runs in to many hundreds of ££.
The Selden rigging manual explains how to do this and it works very well.

 

[geem]

I am a skeptic of large rig tensions. (yes in the fa bend ce of advice Selden etc.) I have yet to see a boat where lee shrouds do not go slack when hard on wind. The problem is Mr Selden can give date on rigging wire and fittings stretching etc but can not account for the hull stiffness. ie you load up the tension on forestay/ back stay and the hull bends like a banana. You load up the cap shrouds and the hull can squeeze in under pressure. Many people report toilet door won't close or open when rig is tensioned. It is not just the immediate effects of rig tension on hull but long term it can cause permanent distortion of hull. All very small distortions but enough to make it difficult to get an d keep rig tension.
Some boats in my club with rigs just like yours used for racing have a high field lever in forestay which is released after each race to remove standing tension from the rig.
IMHO opinion on OP rig yes tension it up firm. But it is the ratios of tensions that provide the mast shape. So back stay no tension rig the cap shrouds firm giving the desired mast rake (just a little) and vertical from side to side. Use a halyard out to each side. With little tension on intermediate side stays the mast should have a fair bit of bend middle forward. More cap shroud tension or more spreader bend aft to increase mast bend.This is then pulled out to lessen mast bend middle forward while at the ame time balancing tension of 2 intermediat shrouds to get mast straight side to side.
from there in a blow add back stay tension to straighten fore stay. And yes lee shrouds will go slack. ol'will

You are correct that boats hulls vary in stiffness. We replaced our rig recently and yesterday adjusted the tension. We used a 2m rule fixed to the rig using the 1mm of tension per 5% measure. Our hull is stiff. It is an Airex foam core composite hull. Way stiffer than a solid glass hull. The recommendation is for about 15% of wire breaking load as rig tension. We set the aft lowers to 13% and I really didn't want to go with any more load. 1/2" wire and struggling to turn the spanner any more. We set the caps to 10%. Again, adding any more load was a struggle on a large adjustable spanner. We will see how we get on as the wire settles and stretches a little. Loading the wires above what we have done would be new territory for us. One size does not fit all

 

[penfold]

The same thing can be achieved with a 2 metre rule fixed to your rigging wire and some vernier calipers to measure the stretch. 1mm of stretch for every 5% of rigging tension, regardless of 1x19 wire size. It's easy and cheap. For us with 12mm and 1/2" rigging, the cost of a gauge runs in to many hundreds of ££.
The Selden rigging manual explains how to do this and it works very well.

I'd agree, used that and found it satisfactory.