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49er Mast trim issue - request help


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Hi, I finally am about back to going out on the water after a two or so health related break and thought to rig everything up and trim yesterday in preparation.

Then noticed that apparently I forgot even more than I thought. :(
Issue is that I don't get the numbers I expect and reach the limits of the adjustment screws. I reckon I just need to play around with the three stays until it works again, but have no idea where to start right now and could use a heads up if anyone spots the obvious problem.

Right now if I set things for winds 20kn+(survival for myself) I get rig tension measured with the loose gauge as follows.(second LG is just one digit higher across the board)

Forestay 31
Uppers 18,5
Main 31
Lowers 24
Prebend 205mm

First of all, Prebend is measured using the distance between a halyard touching the lower spreader and the gooseneck, correct?

I expected to see 300mm ish prebend and tension on the main shrouds to be around 35 as well as the lowers not above 20.
But as is I can not ease the lowers anymore to get the tension right as well as create more curvature and am puzzling over what I am clearly doing wrong.

My next idea would have been to go up a few holes with the uppers, tighten the lowers significantly and loosen the main shrouds and see if that gets me anywhere.
But as said, trial and error and yesterday it was getting dark by the time I called it a day and to seek outside advice first.

 

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Most 49ers measure their bend with the shock sailing (or similar) device: http://www.shocksailing.com/product-49er-bend-device_271.html, set the bend device against the bottom spreader, lay the jib halyard in the device,  have the halyard be just barely touching the mast near the southern spars sticker, and then measure from the level of the boom fitting to the halyard. Typical numbers for bend are between 8-30 mm depending on wind speed and crew weight. 

If your lowers are loose and you are still not at the desired bend then you need to bring down your primary shrouds to induce bend, it seems like you are just running too little tension on your main stays and are compensating by easing an excessive amount of lowers. With greater tensions in the primaries the mast will bend more and you wont have to be easing so much lowers. Lower stay tension is not necessarily important, it is more critical that you have the correct bend, I have seen teams with soft bottom sections running 24 on the lowers and teams with very stiff bottom sections running ~10.      

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The southern spar logo. The one that is about halfway between the lower spreaders and the gooseneck? No wonder I got gibberisch... I mean, measured nonsense.

It is good to know that there is a high variance in the lowers' tension possible. Though I did not really ease them for more bend(see my measuring mistake. Will try the weekend and note where I actually end up) but because I got such high numbers...

Well, time to see if I can get the bend right and the rest to fall in line. Then slowly learn over time...

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Well, measuring prebend like that got me in the ballpark. Or at least we did not embarass us too much sailing yesterday. Though felt the need to get into better condition :D

One thing I struggled with though is what construes correct mast curve?

As is when hoisting the main I get significant pressure on the lower battens. Enough to make it difficult to raise and bolt rope wanting to pull out. I know that this isn‘t normal behaviour.

Any ideas on how to fix that? The battens are in their „softest“(most in) position already as per base trim. 

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Good old parifin, otherwise known as candle wax, is very likely the best sail track lubricate available.

1/2'ves the friction, works for 20+ sails, and keeps on getting better and better each time you use it.

~~~~~~~~~~~~~~~~~~~~~

99.9999% of the sailors I know, and I know some damm good 49er sailors, measure pre-bend as a displacment fwd of the boom GN and it's a number like 12mm or 14mm.    ( I simply don't understand a number like 205mm and I am not sure it's a good way to measure pre-bend.)

I know all the guys talk about base settings, and how many turns they go up (or down) as the wind freshens (or dies).   Base setting is at 10 knts (from memory) and 20-24 turn up is not un-common, as it gets fresher, 20 knts is bloody fresh. 

Given the new mast is being rolled out now, let me get you some generic numbers.   It will be Wednesday, when I go beer can racing (on a Farr 40) but the AST is at the top of my ramp.      I have been meaning to do this for years, so it's good motivation.

Re batten's.    Again 99.9999% of the sailors I know, set their batten tension so they are just so, and they don't re-adjust other than to take them back to being just so.

Just so is, pull the main up, tip the boat on it's side, pull a bit of main sheet tension on, just enough to lift the sail off the ground, then get about 10% camber in the batten, (you push inwards) and adjust the tension so there is just the slightest hint of puckering on the "inside of the curve" batten cloth, so the concave side.   

Then don't touch it for a month.

As for getting it up the mast, the problem with square heads is there is about 1/2 the mast bend, so it can be tough.   Look what the poor windsurfers go through.

Try and aling the boat so the battens are perdendiculart (as in stearming drirectly aft, along CL) to the sail track (first 100mm) as your pulling the main up, so main reversed (backwinded), nose of the boat 15-20° to leeward. 

 

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On 9/27/2020 at 10:11 AM, JulianB said:

( I simply don't understand a number like 205mm and I am not sure it's a good way to measure pre-bend.)

It really wasn't. Using the method everyone seems to be using, and I was just not remembering, my numbers fit again. At least for a rough setting that has the rig and boat feeling alright at our level of capability. Nevermind speed comparisons.

We went shortly before 20kn ashore. Fun but flipping is so easy. And a good choice considering afterwards it was gusting up to 30kn...

 

On 9/27/2020 at 10:11 AM, JulianB said:

I have been meaning to do this for years, so it's good motivation.

That would be great! I have some outdated, 2017, numbers picked from some guys in Kiel but also have talked with quite a few casual 49er sailors that don't have that kind of access and struggle to set up their secondhand 49er on their own. Likely immensely helpful if the class association could update their files too...(may have to write them sometime)

On 9/27/2020 at 10:11 AM, JulianB said:

As for getting it up the mast, the problem with square heads is there is about 1/2 the mast bend, so it can be tough.   Look what the poor windsurfers go through.

Try and aling the boat so the battens are perdendiculart (as in stearming drirectly aft, along CL) to the sail track (first 100mm) as your pulling the main up, so main reversed (backwinded), nose of the boat 15-20° to leeward. 

Am a freeride windsurfer, can confirm that 8+sqm sails take quite a bit of force to get bend and tension right. So nice since the ratchet mast bases exist.

Thanks for the tip with batten/wind alignment. Have had it just straight into the wind up to now and will try it next time on the water.
I am already waxing the bolt rope and that really does help. But I have to clean the track as I had some dirt stuck from longer disuse.(lots of things flying through the air here with autumn storms)

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On 9/27/2020 at 10:11 AM, JulianB said:

Then don't touch it for a month.

Wait, I just realized. Do you mean to leave them tensioned in the sail while storing it?
I know it is the way to go with the windsurfers and in that way it would make sense here too but I did have it stored warm and dry the last two years with everything loose.

I guess that would explain why it was a tight fit even at the least batten tension...

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The 49er and 29er working sails have material in the batten pockets that can handel and sustain the tension that you put on them.

So if I was likely to sail in the next 2 weeks (or less), if you put on the right tension as explained, then there is not much need to "de-bone" them.

But if I did not forsee myself sailing for say a month, then I would.

 

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Thanks again Julian.
Really, it is so great to be able to solicit help from you here on these matters.

If I get lucky there are still a weekend or two to get out on the water before it gets too fresh here for doing it for fun and I switch fully to windsurfing.(even quicker rigging and virtually no worry about gear and weather. Worst case it is a minute back to the beach as opposed to capsized in cold water...)

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