I've been tuning my boat based on information from the previous owner and an old tuning guide from North sails.

I have set my rig tension considerably tighter than the North guide recommended.  I have my uppers set at about 1200 lbs and my lowers set a about 900 lbs as a starting base.    If it is windy, I put another turn on my lowers to control mast bend. 

I measured my jib hoist by attaching the jib halyard to a tape measure and measuring to the point at which the jib attaches.  North was suggesting this should be about 981 cm.  My measurement came out around 12 centimeters short of this, suggesting that my mast may not be as raked as it should be. 

Are there any base measurements for mast rake and shroud tension that anyone could share with me?  I wondering how close I am to the boats actively sailing one-design. 

Dave,

I'll try to give you some feedback on the way we set up Convictus. Just one small problem, I can only remember the Loos Gauge settings and not the values they represent.

Starting with the rake, we have found the following to be the most consistent and repeatable method to measure;

Measure from the center of the forestay pin on the bow casting to the center of the forestay pin on the mast braket.

There are too many variables to measure any other way. To do this you will access to shear legs, but once it's done you can mark a spot on the turnbuckle and then measure from there down to the bow casting and add your known distance to the mark.

On Convictus, using this method, we use a forestay length between 32' 6 3/8" and 32' 7".

As for shroud tension, measured at eye level from the upper deck, we have 32 on the Uppers and between 30 and 32 on the Lowers. Anything more than 32 is simply too much tension. We never change the upper shroud tension.

You'll notice the lowers are about even with the uppers. As we have the original spar and this is boat number 114, later boats might use somewhat lower tension on the lowers but not less than 28.

You might find these to be good starting parameters for your boat. If you sail in mostly lighter winds, do the following;

• Mast rake should be closer to 32' 7"
• Lower shroud tension should be closer to 28

If you sail in mostly heavier winds, do the following;

• Mast rake should be closer to 32' 6 3/8"
• Lower shroud tension should be 30 to 32

Convictus has had a fair amount of success in one design sailing and I can tell you that we do not make constant changes to the rig. We find one mid point setting we like and the boat stays that way for the season or until the sails are changed.

Off the cuff, I would say your shroud tensions are about right (perhaps a hair tight on the uppers) and you're doing the right thing in a breeze by tightening the lowers, if you are inclined to tune for the prevailing conditions. I think the key for you is to figure out where you stand on the rake...this has a huge effect on the sail plan.

Hope this helps Dave...

I have used a North tuning guide for base setup on my rig as well. I found that the original numbers give a relatively straight mast (2-3 inches of pre-bend). This was probably great when the main was new, but I have gone to tighter outers and much looser lowers than the specs. This has given more pre-bend to compensate for my baggier 4 yr old main and keeps my forestay tighter when it blows. In very light airs I have also eased off the forestay about 2-3 turns to increase rake and slightly increase weather helm.

Just the observations of a rookie (first season with the boat).

Rigging Question,

I followed the suggestions above for the Loos guidelines but I notice that in wind above 10 knots my lowers will be slack on the leeward side. Traditionally on my other boats I would take a turn or two to snug up the slack, however per comments above it is stated that you want to keep the lowers slack to allow the mast to bend properly. I don’t want to jeopardize the mast, so how much slack is acceptable?