mast tuning on a Hunter 30 (1989 Fractional rig)

[Dave Japikse]

Can anyone tell me a good starting point for mast tuning on a Hunter 30-2 Fractional rig (1989)

How much mast rake, prebend, and upper/lower tensions as a starting point?

It needs new sails too, but I would like to tell the sailmaker how much prebend to start with in the sail design discussion and play with tuning with current sails first.

Thanks.

 

[Dan_Y]

Hunter (Eddie Breeden) told me last year for my '91 30 "The average on the rake is going to be about 8". Seems like the average on the pre-bend was 4". My boat has closer to about 10-12" and maybe 2-3" of pretend. Had the new sails cut for this and she points well. Also had new main to be cut loose footed. Boom is plenty sturdy according to Hunter.
Dan

 

[abinkc]

would like to know the recommended Loos tension on the rigging.

 

[Dan_Y]

abinkc-
Hopeful this is not considered a highjack!

I doubt Loos numbers exist from Hunter. I found that the rigging instructions were using words like "medium tension" which I interpret as half way in the tension range, e.g. if 10 -20% of breaking strength, try 15%. Ultimately, I think my loos numbers won't help anyone (other than ball park) because they are based on the geometry of my rig mast rake, prebend, and mast stiffness, besides potentially uneven chain plate heights. The rigger taught me to spend time sighting up the mast while I pull on the shrouds at the dock to understand what's going on. Then do the same while underway to be sure the stick is straight under load. It can go out under load and come back under no load. Loos won't help that tuning much. Maybe the racers have a technique with Loos though. I have a roller furler and so cannot easily measure forestay tension without removing the drum. The split back stay wire rope is too thin for my loos, but it's about "medium tension"... haha and has little effect on the rig other tan bending the section above the forestay. All I could really check after the fact were the three main shrouds-which is where the action seems to be on this rig, and again, the tensions are based on how much prebend you need to match the cut of your main. I need to take some prebend out because the main does not rig as nicely as before the new standing rigging was installed. And forestay tension seems ok with no excessive sag in big wind (which I avoid anyway when possible).

 

[Dan_Y]

So here are the Loos gauge PT-2 numbers for a '91 H30 fractional rig with swept spreaders. The shrouds are uppers or cap stay (1/4-in 304 1x19), intermediates or check stays (3/16 304 1x19), and lowers (1/4 304 1x19). Uppers induce prebend, intermediates keep the mast straight under load, and lowers arrest excessive prebend. Sorry, I don't know the naming convention a pro rigger uses so U=upper, I=intermediate and L=lower. The sequence reflects my tuning of new rigging as it stretched a bit and trying to get the right prebend again. Also did not want to exceed 15% of wire breaking strength. The forestay was cut dead on to the original length because I was happy with rake and pointing versus amount of weather helm. Rake is about 18" on this 42'? mast. Before the new rigging the mast would sometimes pump going thru chop to weather, so the rig needed more tension.

Old Rigging: PU:32.9, PI: 5.5, PL:30.2 --- SL:32.9, SI: 6.8, SU:33.7

New Rigging: PU:36.8, PI:15.5, PL:32.0 --- SL:32.6, SI:16.0, SU:36.3
% Breaking 14.4. 8.4 9.5. 9.9. 8.9. 13.8
(tensioned eyeballed by rigger when sighting mast on the hard)

Decided to back off tension a tad:
8/3/13: PU:34.7, PI:16.0, PL:30.1 --- SL:30.5, SI:16.0, SU:34.5

8/25/13: 1st sail, 15 knts. When pointing high, lower was loose on leeward and top 1/3 of mast bending off to leeward. Excessive sail at bottom of mast and horizontal wrinkles. Too much for Cunningham to pull out. Should have sighted mast and checked shrouds before changing rig... but what do I know about this??? I'll bet the mast was bending to leeward big time given that the intermediates were not very tight on the old rig.

9/7/13: Tighten intermediates to stop mast from bending off and tighten lowers to keep tension when loaded and stop excessive prebend.
PU:36.0, PI:18.0, PL:33 --- SL:33.0 SI:18, SU:36.0
Good adjustments. Sailed '14 season this way but finally realized there is too much prebend creating horizontal wrinkles that weren't there with old rigging. Need to reduce upper tension and retune. Back stay not excessively tight. I'll update these numbers next month.

 

[jscardam]

Hi Dan_y,

Just curious if you are still tuning your rig as noted above?

I have a '91 30T and I have more prebend than I care for. I have been snooping around online for some hints and your post seems to be the closest to what I am looking for.

What steps would you recommend to reduce prebend?

Thanks,
Joe

 

[fbcoache]

So here are the Loos gauge PT-2 numbers for a '91 H30 fractional rig with swept spreaders. The shrouds are uppers or cap stay (1/4-in 304 1x19), intermediates or check stays (3/16 304 1x19), and lowers (1/4 304 1x19). Uppers induce prebend, intermediates keep the mast straight under load, and lowers arrest excessive prebend. Sorry, I don't know the naming convention a pro rigger uses so U=upper, I=intermediate and L=lower. The sequence reflects my tuning of new rigging as it stretched a bit and trying to get the right prebend again. Also did not want to exceed 15% of wire breaking strength. The forestay was cut dead on to the original length because I was happy with rake and pointing versus amount of weather helm. Rake is about 18" on this 42'? mast. Before the new rigging the mast would sometimes pump going thru chop to weather, so the rig needed more tension.

Old Rigging: PU:32.9, PI: 5.5, PL:30.2 --- SL:32.9, SI: 6.8, SU:33.7

New Rigging: PU:36.8, PI:15.5, PL:32.0 --- SL:32.6, SI:16.0, SU:36.3
% Breaking 14.4. 8.4 9.5. 9.9. 8.9. 13.8
(tensioned eyeballed by rigger when sighting mast on the hard)

Decided to back off tension a tad:
8/3/13: PU:34.7, PI:16.0, PL:30.1 --- SL:30.5, SI:16.0, SU:34.5

8/25/13: 1st sail, 15 knts. When pointing high, lower was loose on leeward and top 1/3 of mast bending off to leeward. Excessive sail at bottom of mast and horizontal wrinkles. Too much for Cunningham to pull out. Should have sighted mast and checked shrouds before changing rig... but what do I know about this??? I'll bet the mast was bending to leeward big time given that the intermediates were not very tight on the old rig.

9/7/13: Tighten intermediates to stop mast from bending off and tighten lowers to keep tension when loaded and stop excessive prebend.
PU:36.0, PI:18.0, PL:33 --- SL:33.0 SI:18, SU:36.0
Good adjustments. Sailed '14 season this way but finally realized there is too much prebend creating horizontal wrinkles that weren't there with old rigging. Need to reduce upper tension and retune. Back stay not excessively tight. I'll update these numbers next month.

What are you currently using now with several years of trial and error with your tensions?
Thanks David

 

[Dan_Y]

Hello David
We sold the boat after getting everything just right… one day on a rough day in the bay the Admiral said “we need a bigger boat”…so we traded up to a Hunter 36.
Dan