Mast Tuning and Spring Fever

Chuck-

It really depends on your sail and mast- I got a "mast bend test" from Helen at Goodall's and tested my mast- It was the outer limit (or beyond) for what Helen listed as "average" numbers- Meaning (to me) that I have a quite "bendy" mast. So my numbers (even if I were using your mainsail or vice versa) might not work on your mast-

I had just added the adjustable spreaders prior to SF to my boat- I had recieved advice on setting the rake at 48-50mm (I used 49mm), I have my spreaders very close to the maximum 700mm wire-wire width (this changes with rake- at 49mm I moved the little end "pieces" out one hole to get this) and the prebend at 30-33mm. HOWEVER- I measured my prebend BEFORE I removed my old spreaders (and my boat had been very fast in light air but was overpowered in heavier air) and it was only 23mm!! So when I got to SF I had mine set at 30mm- Went out sailing (in the relatively light air Thursday) and the leeward telltales in the middle of the sail (the max prebend is above the spreaders) wouldn't "fly" while all the others were- To me this meant the middle the sail was being "sucked" forward too far and was too flat (and you could see this looking up the sail while powered up) and I had too much prebend (if I let the downhaul all the way off it went away- But that's no way to sail fast!!) so that evening I reduced the prebend to ~26mm (I also figured it was going to be light air and I would have some fairly hefty crew weight so fuller rather than flatter would be better anyway) and Friday my sail looked good (to me) w/ nice even curve all the way up and when the wind came up that evening was still able to downhaul and control the boat.

Now- Why do I think I can "get away with" less prebend than the "gurus" say and even NEED it to get my sail looking good? I think it's because I have a "bendier" mast so the downhaul, etc. has more effect to depower it than a stiffer mast so less prebend is needed. These prebent wingmasts are different animals than I was used to- It has taken me awhile to figure them out.

Hey- Did you see the Macho Man results for Day 2?

Looks like Mike's Taipan smoked EVERYBODY from the results but I'm not sure they sailed same time/course etc.-

It was good to see you in Georgia-

Hope that helped-

Kirt

Chuck,

I asked the same question a while ago (before a forum crash - I think the info is gone). Below are the responses that were posted.

Since the topic of T4.9 tuning has been brought up – I’d like to ask the people who have been sailing the T4.9 a while to comment on diamond wire and spreader setup. I’ll list a few specific questions below, but please feel free to comment in any way you like. Please quantify where you can (instead of just leaving everything in terms of ‘more’ and ‘less’). I’ve seen the page on the AHPC web site regarding wing mast tuning, but I would also like to hear other opinions and a few numbers.

1. How much prebend do you put in the mast for light air (8kts and under)? Answers for both sloop and uni configurations would be great (along with your typical crew weight).

2. Do you make changes to the rig for large differences in wind velocity – or have you found that one setup works well for most conditions?

Any advice/experience you’re willing to share is greatly appreciated.

Thanks,

Kenn Newbury

Kenn,

Most boats in Australia hover around 30mm prebend.

And leave this set pretty much for all conditions. Set the diamonds, spreaders and prebend to suit your mainsail and your crew weight.

antony.

062

Kenn-

I was told by Goodall's it should be around 20mm (3/4-7/8 of an inch) and that's what I have been using in all conditions-

Less gives you a fuller sail, more gives you flatter. I have still have the "old style" spreaders (CF w/ 2 "slots" for setting rake- been using rear slot)- One trick is to use a little less prebend but rake your spreaders back considerably- This allows you a fuller sail w/ light downhaul but when really downhauling/sheeting hard the raked spreaders flex the mast more longitudinally and will induce more fore and aft bend (essentially providing more "prebend" except it's really "post" bend now I guess??)-

Hope that helps-

Kirt

Kirt Simmons

Taipan #159, "A" cat US 48

For Sloop (Crew weight = 120 kg)

spreader rake ~ 55 mm

we do not measure pre-bent, instead diamond tension is ~ 32 on the Loos Gauge Style A (old type).

We do not change the static setup of the rig (except stay tension) for varying wind speeds.

If you have a boat with the factory settings (i.e. new), it is wise to stay with these settings for a while. (see J. Boyer's instruction on how to sail with the wing mast).

Gebhard.

We have about 2" of spreader rake with about 7/8" prebend right now - seems to be working OK. Our 'factory settings' were about 2 3/8" rake and 1 1/8" prebend. We seem to be doing better in light air now, but I'm not sure how much I can attribute to the spreader/diamond wire changes versus learning the boat (we also tried different jib and main luff tensions). Except for coming in after Friday's SF races (GPS said we were doing about 24MPH on a jib reach w/ only one person on the wire . . . the most fun part of the day), we haven't had a chance to sail in a moderate to heavy breeze yet - hopefully we will still be able to depower enough.

Kenn Newbury

T4.9 USA226

Kirt,

Can you describe the mast bend test?

Thanks,

Kenn Newbury

T4.9 USA226

Kenn-

Yes I can, and I took photos (before SF) so I will send to Wouter to put on the Web page w/ the photos if that's okay.

Helen can give you the text, sorry I don't have here w/ me!

Kirt

I just finished the spring fever picture pages

Wouter

Thanks Kirt and Ken for the numbers. I am going to take a look at my mast this weekend.

Chuck

Chuck, Kenn and everybody else-

Wouter should have gotten the photos and text yesterday from me-

E-mail me if you want the text and diagrams (the photos are a large file!)-

Kirt

Thanks Kirt,

The will be up in a few days.

Wouter