Rig tuning 101 or.....

Dimitri-2000X-Tampa · Post by **Dimitri-2000X-Tampa** » Sat Jun 03, 2006 4:08 pm

Since I lost my lower shroud out sailing the other day, I used it as an opportunity to re-tension my whole rig. My shrouds were pretty well balanced before although slightly looser than I would like so I adjusted all 4 by exactly one click on the slot adjusters. I ended up with the Loos gauge pointing at 32 for the lowers and 37 for the uppers. This corresponds to 200 and 300 lbs respectively for the 5/32 inch shrouds. I think this is plenty tight enough now. I was able to easily get twice as much tension as that using the standard mast raising gear and not even torquing it much...thats the beauty of the mast raising gear and I doubt that you could ever achieve this sort of tension by pinning the forestay without a mast raiser.

Since I already had one lower loose, I disconnected the other lower and then tightened the two uppers first. Interestingly, with the lowers disconnected, I only got about 33-34 on the uppers at first which corresponds to about 240 lbs. When I connected the lowers, it raised the tension on the uppers by 60 lbs. This seems to imply that the lowers actually pull against the uppers which it would then follow means that it does not add any mast bend, in fact, maybe it even reduces it. This was something I used to wonder about. Its a lot easier and more efficient tuning the rig using the mast raiser versus trying to tighten the slot adjusters when under tension...thats a job better left to turnbuckles.

Anyway, this is the tightest I've had it before so I hope it improves my dismal upwind performance some. This has been the main reason I haven't shortened my forestay (although it always stays as short as possible with the turnbuckle), I don't want to potentially reduce my upwind performance.

Lease · Post by **Lease** » Sat Jun 17, 2006 5:34 pm

This thread has been very useful for rigging, but there is one point (that may be there,but I missed) still to explain.

What is the best datum to use for levelling the boat on the trailer?

I'm thinking the top of the centreboard case (26X), but wonder if that is the right place.

delevi · Post by **delevi** » Sat Jun 17, 2006 7:06 pm

Dimitri is right regarding the lowers. The lowers counteract the mast bend induced by the uppers, which is why you should set the uppers first to lock in the desired bend. More important for an M than an X since with an M, you can't create mast bend on the go with the backstay. Of course keeping the mast straight (w/o bending to either side) is the time-consuming part.

Frank C · Post by **Frank C** » Sun Jun 18, 2006 12:56 am

Lease,
Can't guarantee the CB case is actually level, but seems a good first guess. (I've always adjusted my mast while on the trailer - means just level the bootstripe, which mine does float to.) Fact is, you could use it for both length & beam - maybe by mounting one of those center-bubble disks that the RV guys use, just at the aft corner of the CB trunk.

Boblee · Post by **Boblee** » Wed Mar 12, 2008 3:19 pm

ModsNote: Mid-thread time lapse here is 21 months. It's not a problem, just useful info when judging context. ~fc

Think I have a handle on the adjustments but my impression has always been that the mast rake should be set on the water and in the

case I would imagine with ballast in as that drops the nose at least 2".
Our dealer here recommends tightening the forestay turnbuckle to reduce weather helm but obviously not as far as mine as my mast was way forward in comparison to the ones he had tuned and I only have about 1" bend.
The X's all had more rake and much more bend in their masts.
Stupidly I did have access to a guage and got too preoccupied with other things to take advantage of it (for three weeks)

If I make the nose heavier with an extra water tank should I adjust rake to suit

or try and balance it while it is full and as it empties

Terry · Post by **Terry** » Wed Mar 12, 2008 3:33 pm

I did mine on the hard because I never know what the waterline will be throughout the year. Most times it is me and the Admiral adding weight aft, sometimes it is two full tanks of gas or two empty tanks. Sometimes my 50 litre water bladder is full, sometimes it is empty. Sometimes we are loaded for a 5 day cruise, early in the season we are loaded for only daysailing. Sometimes I have two dozen water bottles in the forward hatch sometimes only a few. Sometimes extra passengers but in future I plan to solo. The weight fore & aft will vary throughout the year as will the waterline so now where and how do I set the mast rake???? I used the bootstripe as an average waterline.

Boblee · Post by **Boblee** » Wed Mar 12, 2008 7:21 pm

I think setting to the boot stripe has to be as good as any and then balance the boat to suit but am pretty sure mine is either slightly forward or straight which makes it well forward when the ballast is in.

Currie · Post by **Currie** » Thu Mar 13, 2008 6:26 am

I set my mast rake to the design-waterline - while on the trailer. What I did is square myself to the mast base, back up about 300' and photograph it (on a stepladder) with a digital camera. I then measure rake and bend with photoshop-type software (I use Corel).

I humbly admit I find the idea of measuring mast-rake to the water (i.e. to plumb, not the design-waterline) rather odd. Mast rake balances the boat, which is determined primarily by center-of-effort (mast-rake), and center-of-lateral-plane (under-water profile). Measuring mast-rake to plumb considers the former, but ignores the latter.

I can imagine three skippers - one with weather-helm, one with lee-helm, and one with neither, all arguing that they have a 0-degree mast-rake (to plumb). The difference of course being that they sit on their actual-waterlines differently. By referencing the mast rake to the design-waterline (the stripe), at least one variable is normalized (locked to the boat itself), then the skippers can discuss the boat's stance.

FWIW, I believe balance is more sensitive to waterline stance than to mast rake. Tipping your boat forward a couple of degrees will move your CLP more forward than the CE, increasing weather-helm (decreasing lee-helm). Although this is arguable too, and dependent on how much board and/or rudder is down.

Balancing the boat comes down to tweaking your own rigging, no matter how you measure mast rake, but this thread has made me realize that we've been comparing apples to oranges with our numbers

Point being, if you say your mast rake is 2 degrees aft (to plumb, on the water), I have to ask - with how many people on board? How heavy is your engine? etc.

Cheers,

~Bob

c130king · Post by **c130king** » Thu Mar 13, 2008 8:37 am

Bob,

How to you change rake on an

with no backstay?

Thanks,
Jim

Scott · Post by **Scott** » Thu Mar 13, 2008 8:44 am

How to you change rake on an MacGregor 26M with no backstay?

Combination of forestay length and shroud tension. rake is primarily determined by forestay length.

I believe balance is more sensitive to waterline stance than to mast rake.

I agree but the waterline stance as you put it is the baseline for the rake. "Waterline stance" is not a static measurement, however rake in relation to waterline stance at mooring should be. If not you will need to readjust based on loading at time of launch.

Catigale · Post by **Catigale** » Thu Mar 13, 2008 10:03 am

Thinking about this - isnt the mast rake and bend less relevant with respect to the boat waterline, but more important relative to the boom geometry - which would dictate sail shape??

Bawgy · Post by **Bawgy** » Thu Mar 13, 2008 11:20 am

I would not think so since the boom angle is determined by the mainsheet or vang and can vary many degrees

Love MACs · Post by **Love MACs** » Tue Mar 18, 2008 5:53 pm

All very interesting information. And I think I follow both procedures. My real question is a little more mundane and perhaps a little novice. Is this at all necessary? At what point does this tuning truly need to be done? I think I get the idea that it will improve sail shape and mast rake, but is this just for the racing enthusiast who/wants needs to get a few more kts from his boat or is this a real problem for the average sailor? Or rather is this just a tuning up tip for those that have the time and inclination?

I do see the point of all if you lose or brake a shroud and need to equalize the new and old.

Allan

Trouts Dream · Post by **Trouts Dream** » Tue Mar 18, 2008 6:25 pm

If you set the lowers first they will increase in tension when you set the uppers as it is the uppers that induce mast bend. By the same token when you increase the lower shroud tension it will decrease the mast bend and therefore decrease the upper shroud tension. Either way they are related and you can set either way, I just find it helps to understand the cause and effect.

Currie · Post by **Currie** » Wed Mar 19, 2008 5:20 am

Trouts Dream wrote:If you set the lowers first they will increase in tension when you set the uppers as it is the uppers that induce mast bend. By the same token when you increase the lower shroud tension it will decrease the mast bend and therefore decrease the upper shroud tension. Either way they are related and you can set either way, I just find it helps to understand the cause and effect.

Trout, did you mean to say *increasing* lowers tension *increases* uppers tension?

I think of the mast as being bent like a "bow", wedged up into a wire "crotch" formed by the forestay and the upper shrouds. It's bowing because the spreaders are swept, pushing the middle of the mast forward. The bent mast alone will hold everything securely, but it may pump somewhat because the "bow" is not very stong. The lower shrouds, try to pull the bow straighter, by pulling back at the middle. With the mast trying to stand straighter, we should see increased tension in the uppers and, to a lesser extent, the forestay. Now the whole setup is very strong. Yes?

Cheers,
~Bob

P.S. I agree everything's related, and may take a few rounds of adjusting to get everything just right.

On Edit: Basically I use Moe's approach

MacGregorSailors.com

MacGregorSailors.com

Rig tuning 101 or.....