New stays, mast rake, lee helm?

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New stays, mast rake, lee helm?

Postby geofisherman » Thu Aug 10, 2017 8:19 am

I installed new stays on my DS-II last weekend. My mast (with tabernacle) was shortened a couple inches by a PO at some point, and I had to mount the mast tangs higher for the new stays. This operation was complicated by the fact that the new forestay with QR lever was 2-7/8" longer than the old forestay (1-1/4" longer than the sidestays). It appears that I estimated the new tang positions incorrectly because I now have much more lee helm. Under single-reefed main alone with board all the way down, the boat is just about balanced sailing flat close hauled. Noticeable weather helm returns as it heals in gusts. Under double-reefed main and jib with the board all the way down, lee helm is significant. Previously, the boat was balanced with double-reefed main and jib with the board all the way down. I liked this setup because I could control weather helm with any other sail arrangement by raising the board a bit. I know I need more mast rake, but how much?

As setup now, I can tighten the sidestay turnbuckles about an inch before having to move the sidestay tangs. I can only loosen the forestay 1/2" before moving the tang. So, I suspect I will have to move the tang for the forestay. But, I am hoping that someone can give me an idea of how much I need to move the stays before I start drilling more holes.

Thanks for your help.
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Re: New stays, mast rake, lee helm?

Postby fatjackdurham » Thu Aug 10, 2017 9:22 am

whoops.... double posted......
Last edited by fatjackdurham on Thu Aug 10, 2017 9:25 am, edited 1 time in total.
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Re: New stays, mast rake, lee helm?

Postby fatjackdurham » Thu Aug 10, 2017 9:24 am

I think I saw someone say that the rake should by set by hang the halyard six inches aft from the base of the mast.

My questions since I plan to shorten my mast is, how to best level the boat on land (what and where to I use the level) and how far up the mast should the stay straps be as defined by the stay length and spreader geometry.
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Re: New stays, mast rake, lee helm?

Postby GreenLake » Thu Aug 10, 2017 9:38 am

I would have someone make up a new forestay that's the correct length for your boat. Every time you drill, you weaken the mast and moving around a tang in small increments will leave a line of holes that acts like a perforation on a postage stamp (if you're old enough to remember :) ).

You don't give the source of your stays, but I seem to remember that D&R Marine actually assembles stays when you order them; usually, they just use the stock measurements, but you can probably give them a call and ask to supply your data.

For tuning the mast rake, I recall there was a North Sails tuning guide for the DS that gave the distance from mast tip to transom. This is easily measured and independent of whether your boat is level.

(You would have to compensate a bit for your shorter mast).

However, if your boat was balanced before and you have the old stays (and old location of the tangs), it shouldn't be that hard to replicate that. That's what I did when I upgraded mine to 1/8" from the old 3/32". The old ones were fixed length and the new ones had turnbuckles. I laid them alongside each other and set the turnbuckles to where they came out same length as before. Worked like a charm (I must add that tension in my case is supplied by a mast jack, so I don't adjust the turnbuckles at all once they are at the correct length).
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Re: New stays, mast rake, lee helm?

Postby geofisherman » Thu Aug 10, 2017 10:44 pm

First, thank you all for your input.

I bought the new stays from D&R. Calling D&R and requesting custom stays would have been a good way to go. Live and learn I suppose.

I got out the tape measure this evening. My new forestay is exactly the same pin-to-pin length (15', 11.5") as the OEM specs quoted in Roger Conrad's daysailer book. However, on my boat the forestay attached to the mast about an inch below the sidestays. It was therefore shorter than the sidestays.

I agree that extra holes in the mast is not desirable. However, because the new holes will be in a vertical line, each new hole will not add much additional weakness. This is because the primary bending forces acting on a mast are perpendicular to its length and any break or buckle will propagate around its circumference. The real problem would be having additional holes in a ring around the circumference of the mast.

I can move the forestay tang down the mast 7/8" with only two new holes by reusing one of the current holes. If I got my trigonometry right, lowering the forestay tang 7/8" will increase mast rake by about 1 degree. Lowering the forestay tang 7/8" and using the remaining 1/2" of adjustment in the forestay will increase mast rake about 1.4 degrees. What I don't know is how much of a difference 1 or 1.4 degrees of mast rake will make in my helm balance. It doesn't sound like a lot. Assuming the mast is vertical now, adding 1.4 degrees of rake would be enough to move the end of the halyard 6" behind the mast if the boat is sitting level fore and aft.

What I also don't know is if I can make this change without using up all of the 1" of adjustment remaining in the new sidestays. Can anyone tell me from experience how much you have to adjust sidestays for every 1/2 or 1" of change in the forestay?
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Re: New stays, mast rake, lee helm?

Postby GreenLake » Fri Aug 11, 2017 2:46 am

I believe you should answer the question by comparing the length of the new to the old stays (and adjusting for any change in tang location). If you are in the ballpark on that with a reasonable amount of adjustment left either way, you should be fine.

The reason I come back to duplicating your old setup is that you say it worked and that we don't know whether it takes one or two degrees of change in mast rake, or some other value, to get there from the way it is now. Without knowing that number, it's hard to know ahead of time whether you have enough adjustment left. Your estimation is that 1.4 degrees corresponds numerically to an offset of 6" from the vertical at the mast partners. So far so good. But we don't know whether your mast is currently vertical, or raked forward. If it is actually vertical or slightly raked aft, the 1.4 degrees should possibly just get you there, if it has a bit of forward rake now, that won't be enough.

Based on simply trig, the elongation on the shrouds due to mast rake is far less than for the forestay. There's a secondary effect if you need to increase the forestay tension without decreasing the mast rake by adding forestay tension, the shrouds would also elongate a bit due to the overall increase of tension in the rig, and then you'd need to remove that elongation by adjusting the turnbuckles if you'd want the geometry to be stable.

Overall, I'd expect that you can run the full length of the forestay adjustment (at constant forestay tension) without going the full range of adjustment on the shrouds to compensate. At the angles in question (projected on the lateral plan) whatever trig function it is might be approximated as linear, so the range of adjustment would be proportional to the ratio of angles you get, which is something like 1:3 ?
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Re: New stays, mast rake, lee helm?

Postby geofisherman » Fri Aug 11, 2017 1:02 pm

Thank you again Greenlake. Most helpful.

I used the same measurements to calculate my current mast rake and got 0.1 degrees of forward rake. But this really depends on how accurately I measured everything, so I don't want to rely on it.

I was trying to duplicate my old rig setup (with different tang locations), but I failed to think about the different angles between forestay and sidestays when I drilled the first set of holes. Tonight I will measure the old forestay and use trig to calculate how much further up the mast I need to move the tang from the old location to duplicate the geometry of the old setup.

You raise a good point about the stays stretching. I suppose mast bend is also a factor. These complicate my attempts to duplicate the old rig because I was never able to get proper rig tension with the shorter mast. Instead, I relied on the jib halyard and wire luff of my intensity jib to tension the rig. This is the primary reason I started this project, and I figured that, as long as I was moving stuff around, I might as well replace the old stays. I also wanted the QR forestay lever.
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Re: New stays, mast rake, lee helm?

Postby GreenLake » Fri Aug 11, 2017 2:27 pm

If you are using trig and dimensions, go and calculate where the mast tip will end up in relation to the transom. Depending on how much shorter the rig is due to the non-standard mast length, there may be a small correction, but otherwise you can compare that number with the North Sails tuning guide.

The point of using those numbers is that they do not depend on knowing what is "vertical". (A boat on a trailer is most likely not level in the same way it is when floating). If your setup produces about the right value compared to the tuning guide with the turnbuckles not hard at either end of the adjustment range, then you should be able to further fine tune your rig based on any issues from non-ideal weight distribution. Mast rake really is measured relative to the water's surface.

Think about it: if you sailed your boat bow down far enough, you'd loose the rake as the mast would come forward (and you'd also change the center of lateral resistance from hull/foils) and this would change the balance of your rig.

The instructions from NS read:
To measure the aft rake of your mast, hoist a tape measure on your main halyard and hold it tight at the intersection of the transom and rear deck. This measurement, without your jib up and your rig set “snug” (no play in any shroud or forestay), should be 24 11” to 25’ 1”.


Just plug in the theoretical mast length and you can use these numbers directly.

By the way, having the wire luff take significant tension is actually how I understand sails with that feature should be set. That allows you to control the luff-sag of the sail based on the wind conditions.
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Re: New stays, mast rake, lee helm?

Postby geofisherman » Fri Aug 11, 2017 3:48 pm

Thanks again Greenlake. I will do as you suggest and modify the North tuning guide to fit my mast length and measure the mast-head-to-transom distance before adjusting anything.

One more question: The North guide references "the intersection of the transom and rear deck". But, my DS-II does not have a rear deck, and I've never seen a DS-I with a rear deck up close. Would the equivalent point be at the outer lip of the transom, or the inner lip of the transom?
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Re: New stays, mast rake, lee helm?

Postby GreenLake » Fri Aug 11, 2017 6:47 pm

I bet they mean "top edge of the transom". Just as the way they suggest you hoist the tape measure will make the other point the rear sheave a the mast top.

(For calculating, you can use their numbers, but plug in the nominal, unshortened, length of your mast. You will need to measure the (horizontal) distance from mast partners to transom for your calculations.)
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Re: New stays, mast rake, lee helm?

Postby geofisherman » Sun Aug 13, 2017 9:09 pm

The project is complete. I ended up using the Dieball tuning guide found on the DS Association home page because it provided more dimensions.

I measured 130" from the end of my transom to the base of the mast inside of the cuddy (only path to stretch a tape straight). This is line a on the drawing. The Dieball tuning guide says 132 +/- 1" for this distance. So, I went with 131" since my measurement was to the inside of the cuddy.

My masthead is 264.25" above the cuddy. This distance should be ~270.75" for a class-spec mast. This is line b on the drawing. I subtracted 3/4" from these values because that is how much my mast shortened when tensioned the rig.

The Dieball tuning guide gives a target of 300-303" for the masthead-to-transom distance with proper rig tension.

Using the class-spec measurements and the Dieball values for a and c, the angle between lines a and b (angle C on drawing) should be 90.68 degrees. I kept this angle constant and used my mast height to calculate the target masthead-to-transom distance for my mast. This came out to 295.7".

I then freed the forestay and used the jib halyard to hold the mast up while I tightened the backstays to reach this measurement. Once I had the proper rake, I discovered that I needed another 3.1" of forestay length (Or, I needed to move the forestay tang down the mast). So, I measured the distance from the base of the mast to the stemhead (x in drawing), calculated the angle between this line and the mast, and used my target forestay length to find how high up the mast I needed to place the tang to keep the angle constant. It needed to be only about an inch above the factory location.

Since the new forestay is longer, I will be sailing with more mast rake. Looking at the boat, the rake is noticeable. But, I still have adjustment in the forestay if I find the weather helm too much.

I have a week vacation on Umbagog Lake coming up, so I will post an update after sailing the boat in a variety of conditions.

This online calculator took all of the work out of calculating lengths and angles: https://www.calculatorsoup.com/calculat ... osines.php
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Re: New stays, mast rake, lee helm?

Postby GreenLake » Sun Aug 13, 2017 10:53 pm

Nice.
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Re: New stays, mast rake, lee helm?

Postby Tipster1 » Sat Aug 26, 2017 8:49 am

How about raising the mast? My PO also shortened mast after incident leading to lee helm. I fashioned some lifts from PVC trim to fix it and it worked.
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Re: New stays, mast rake, lee helm?

Postby DigitalMechanic » Sat Aug 26, 2017 11:38 am

I just posted a very long winded response to a rigging question over here

https://forum.daysailer.org/forum/viewtopic.php?f=12&t=5585

See the part about dealing with a short mast, or running out of room to tighten shrouds.

My advice would be to put the tangs back where they were (so the mast will be in spec), and then shim the mast from the cuddy using shaved castings and/or wood block (I have a wood block sandwiched between 2 shaved mast castings on my boat). It has lasted 2 years so far and the boat sails fine :wink:

Take a look at the response in the post I linked, it may help you setup the standing rigging and get the tension you are looking for.
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Re: New stays, mast rake, lee helm?

Postby geofisherman » Sat Aug 26, 2017 8:07 pm

All,

Thank you for your input. I decided not to raise the base of the mast b/c it would raise the tabernacle. I already have trouble with jib sheets catching it from time to time.

This week I had a chance to sail the boat with the new shrouds and the tuned rig in a variety of conditions. I used everything from double reefed main alone in gusts up to 20 mph to full main and jib in light winds. Under full main and reefed main with jib, the helm is neutral until the boat starts to heal at which point reasonable weather helm returns. I get a neutral helm under main alone with the board about 3/4 of the way down. The lee shroud does not start to go slack until I am almost overpowered (single handed). So, I think the tension is OK. I'm still playing with the jib fairlead positions for different conditions, but I am happy with the new setup.
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