tuning the rig, numbers

[CHARLES SCHEAFFER]

Tuning the rig, mast numbers

I will admit this is the first time in 20 years I actually took measurements of the mast, but I am amazed how easy it was.  Curious if anyone else knows their actual mast prebend and mast rake numbers?  I have a three spreader Offshore Spar and presently have 3" of prebend and 15" of rake when the backstay is unloaded.  With the backstay fully tensioned, the mast bend goes to 4" and rake goes to 21".  It's easy to check rake at the dock, by laying a folding rule on the deck behind the mast and hanging a weight on the main halyard.  Prebend was based on holding the main halyard at the mast near the gooseneck and estimating the largest gap between the line and the back of the mast and comparing that to the width of the mast.  My mast is 7 inches front to back.

Anybody have numbers they can share?

Chuck Scheaffer Resolute 1989 C&C 34R Annapolis

[cene...@aol.com]

Very nice! Have never done it myself on my 3 spreader Offshore mast which is likely the same as yours.

I removed my baby stay years ago to stop tearing up my 155 during tacks after my sailmaker claimed that with the spreaders basically athwartship (not angled aft) that the baby stay was unnecessary. Even if I had the measurements they would not be useful for comparison. 

Re performance differences my ‘guess’ is that as long as the mainsail is cut to match the mast bend, they would be minor at least in my case with a center board model. 

Given the shallow NC sounds and marinas where I sail/race, I am glad I got the cb model so that I can go to weather better than most others with my 7.5 ft. draft upwind. OTOH, I would sure like a keel that was much thinner than my ~ 12 inch wide cb trunk!!

Compromises, compromises, etc.

Charlie Nelson

1995 C&C 36 XL/kcb

Water Phantom

Sent from the all new AOL app for iOS

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[cene...@aol.com]

Hello all;

My C&C 36 XL/kcb was delivered with the runners/check-stays run to the aft rail just about the location of the original headsail winches. They are rigged with a 4:1 purchase and are released/tightened depending on what tack we are on. Downwind they are unshackled and pulled forward.

I removed the baby stay and its purchase/track to save wear and tear on the headsail during tacks so my boat is slightly modified from its factory settings. I do have and use a hydraulic backstay adjuster and always race with a roller furling headsail. 

I just had all the standing rigging replaced after 27 years of mostly PHRF racing in the lighter airs of the Pamlico Sound/Neuse River in NC. With a PHRF rating of 120 I am usually competitive with the fleet against similar sized boats sailed reasonably well--which I manage to do most of the time. 

My question for this group, especially those with runners/check-stays rigged, is two fold:

1. Given their aft location on the quarters, the angle they make with the mast is mostly aft--I'd guess about 75 degrees from perpendicular to the mast, or maybe 165 degrees off the bow. At that angle and purchase, they certainly have a minor effect on pulling the mast to weather upwind, which I understand is their main purpose (although they may also help prevent mast pumping in serious chop). Question #1 is do I really need them as currently set-up?

2. If the answer to question #1 is yes, my next question #2 is should I move them forward so they have a better angle keeping the mast to windward and perhaps increase their purchase? I know from these groups that some run their runners/check-stays to winches to put some serious tension on them at the expense of more trimming, etc.

Before I do a sailing test with and without them, thoughts from the lists are welcome.

BTW, my mast is a relatively bendy Off-Shore spar--hardly a telephone pole--so it can be bent with the hydraulic backstay adjuster.

Thanks,

[CHARLES SCHEAFFER]

Hi Charlie,

Great topics as I'm tweaking my setup as well.  I think it's important to try different things and make the boat your own.

My R model has the three spreader Offshore Spar with runners, checkstays, single backstay with single hydraulic ram.  Is your mast three spreaders or the more common two?

In my racing, we found the runners and checkstays were unnecessary below ten knots of wind and most of my races were frustratingly below seven knots.  We did have a handful of strong wind races and we reefed down for a few starts.  I believe the runners and checkstays straighten the mast when the backstay is applied.  They limit the amount of bend and prevent inversion.  The previous owner of my boat rigged the runner/checkstays closer to the centerline on the transom as many J-35's have done.  He had bunji cords pull the slack tails to the backstay at around ten feet above the deck.  This puts them aft of the mainsail leech.  At the time, I didn't understand that setup and returned the rig to design.

Retractors:  I took an idea from U20 sailboats and rigged bunji cords to pull the runner/checkstays forward to the chainplates and hold them out of the way.  These work great for singlehanding and I can send you pictures.  However it adds lines that create a spider web look and I'm sure some crew members wouldn't like climbing out of the cockpit under the bunji cord to get onto the rail.

The R model was designed w the runner tails running forward to turning blocks and up to the outer winches on the cabintop.  I recently added clutches to the lines so I can free up that winch after setting the runner/checkstay tension.  Sometimes I need to adjust halyard tension.  Haven't sailed enough to judge this setup.

Have you ever measured your prebend and mast rake?

Chuck

[cene...@aol.com]

My mast has 3 spreaders like yours but the runner tails were not rigged to run to any winches on my XL. Actually the main tail of the entire combination (runners/check stays) has a 4:1 purchase and finally exits thru a cam cleat on the last block which locks the runners. The runners/checks, probably like yours, are rigged so that the highest one is connected to the lower one and the lower one has an additional 4 or 6 to 1 purchase with a smaller cam cleat so that the shorter lower one can be adjusted separately of the longer higher one. 

Since my rigging replacement I have not measured the rig but previously IIRC my rake was ~ 12 inches which was in the ball park of recommendations from the lists. 

Since I no longer have a baby stay, I cannot bend my mast much since I have nothing to hold or pull the middle of the mast forward--only the hydraulic backstay to pull the top aft (and the runners/check stays to prevent too much bend). OTOH, the 4:1 purchase is such that the crew pulls up to tighten the purchase so they can get the runners/check stays pretty tight without going to a winch. In fact when I saw them run to a winch from some boat on the list, I was concerned that using a winch, especially if there was already a purchase on the line, would be too much and pull the attachment bail out of the deck!

Downwind, we usually unclip the single connection of the runner/check stay on the deck and let it be loose to avoid interfering with the main--although I have used bungee cords at the deck level to pull them forward, out of the way.

I probably have to answer my questions with some on the water tests with the runners as rigged, unrigged and rigged more forward to keep the mast from sagging too far to leeward upwind. Too much sag to leeward has got to be slow and/or reduce pointing especially in a breeze. In light air, like you I could probably forget about them!

Based on where they were rigged at the factory/dealer yard, their main effect is clearly to steady the mast fore and aft. Whether their existence was to improve performance/safety/etc. or merely to give a racy look to what is a cruising boat is an open question. The reason I suspect this is that my non-swept spreaders don't seem consistent to me (or my sail maker) with the need for a baby stay--especially a baby stay mounted on a track with some purchase and then run to a winch could but a heck of a bend in the mast with non-swept spreader---but to what end?

Charlie

PS: This issue has become more important as one of my competitors is a well sailed J34C rated at 111 vs my 120. We finished tied for 1st place last weekend in 12-15 knots with identical 1,1,2,2,2 records. The good news is that this was the first time in years that I ever beat him, the bad news is that he took the last race and hence the regatta! He can stay with me upwind apparently at about the same angle so I need to get everything I can out of my boat. Most other competitors cannot point with me so I usually get to the weather mark first. OTOH, my LWL is only 30 feet and his is closer to 34 so downwind, without a kite, he will overtake me if don't gain enough going upwind. Hence my inquiry about the checks.

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[David Knecht]

Hi Chuck- I have measured my mast at times, but was never sure about the rake measurement.  "From the gooseneck" can have 2-3” of variation depending on where you actually put the ruler.  I have been unsure if this is a height indication (back of the mast where the boom attaches) or an along the boom indication (tack attachment point?).  Where did you put it? Dave

S/V Aries

1990 C&C 34+

New London, CT

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[Francois Rivard]

Hi Chuck, 

I have a different mast (2 spreaders / no runners)  

My pre-bend is also 3" (My main is specifically cut to work with that prebend)  but my rake is closer to 13 inches in the summer / about 10-11 in the winter.   

Why different setups? 

More rake = faster in light air (as I often see in the summer) because you get more overall power but it's at the cost of some weather helm when the wind picks up. 

Less rake= faster in heavy air with a balanced / hands free helm hard on the wind up to about 10knots apparent.  That helps reduce the drag-brake effect from the rudder fighting weather helm and also reduces the need for furling/reefing. 

-Francois

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[CHARLES SCHEAFFER]

Thanks for the reply.  I may have a little too much rake. I never measured my headstay length and need to remove the headsail to establish that.

Saturday, we had no problem with weather helm in 5 to 10 knots until we hit some gusts of about 12 or 14 knots and had to drop the traveller or apply too much rudder angle and suffer the braking effect and excessive heel. 

Francois,

Curious where/how you took those measurements?  Also, could you measure the rake and prebend with full backstay on?

Thanks,

Chuck

 

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[Francois Rivard]

Hi, 

I forgot to add that the weather helm is also directly related to the size of your headsail.  Those settings are effective with my current 135 genoa.

About the measurements: 

• They are taken with the backstay off
• The prebend is "Eyballed" by having a halyard that's taut / against the mast and looking at the mid-mast distance between the mast and halyard. The best place on my boat to "Eyeball" is from inside the cabin, looking through the small Lewmar hatches located on the ceiling above the saloon table. 
• The rake is measured using the distance between the halyard and gooseneck keeping the halyard taut using a bucket.  That technique is outlined on the tuning section on the C&C site. 

-Francois

 

[cene...@aol.com]

Hey guys--great discussion!  I may have to measure my numbers for comparison! 

As I understand rake, it is determined by the head stay length and measured at the dock and with the mast not under backstay tension. 

Mast rake is a measure of how far the mast is angled aft from a straight vertical per a Quantum on-line rig-tune article.

The Internet suggests 1-3 degrees of rake for bigger boats like ours. That being the case, unless the head stay is changed, the rake is constant unless you move the mast base--not something our boats are usually rigged to do.

Thus I am curious Francois how you change the rake between sailing seasons?

Charlie Nelson

PS:  Per the same on-line article:     

--- pre-bend, which refers to the amount of bend that has no backstay tension 

This can only be set with the shrouds unless you change the rake. With non-swept spreaders like mine, pre-bend as defined by Quantum is close to zero. OTOH, with swept back spreaders, pre-bend can be set with the shrouds without back stay tension. 

FWIW

-----Original Message-----
From: CHARLES SCHEAFFER <csche...@comcast.net>

https://groups.google.com/d/msgid/cc-3436/803138282.631681.1661184982582%40connect.xfinity.com

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[CHARLES SCHEAFFER]

Hey Charlie,

Glad you are joining this discussion.  I'm hoping to learn from others how they setup their boats, and possibly improve my boat's setup.

I measured my mast at the dock with and without backstay tension.  I wanted to know how far the extreme backstay would change bend and rake.  I think I explained my method well enough already, but I guess I'll have to do it again and video it, so others understand how I got numbers.

FWIW, Headstay length can be changed by adjusting the furler drum turnbuckle.  Backstay length on my R model can also be adjusted by turning the threaded fork fitting on the ram.  The furler turnbuckle has about a three inch range and my backstay has the same.  The previous owner of my boat used a simple rigging toggle to add two inches to headstay length for lighter wind races, a technique explained in a tuning guide for the venerable J-35.

Background: I just completed a 4 1/2 year refit and the mast was out that whole time.  It's possible I changed the headstay length when I removed the furler from the headstay and cleaned and flushed it out.  I made some changes to acommodate the new bowsprit and may have upset the length.  I also had to have my backstay ram rebuilt so it was on and off a few times before I got out sailing. 

[cene...@aol.com]

Thanks for this explanation--so your boat (and probably mine if I looked closely!) has a means to change the fore stay and back length somewhat to adjust the rake--very nice--I will have to have a better look at mine. 

It still seems to me that this would also require that the mast base be able to move forward or aft along the metal piece where the mast sits, basically pivoting slightly where it goes through the deck 'partners'--if I have my nautical terms correct!! Thus the triangles formed by the fore stay and mast and the back stay and mast can be 'tilted' while keeping the mast straight--no pre or other kind of mast bend.

Once the rake is set, the bend is applied, unless your spreaders are swept aft.

On another note, you mention you added a bowsprit. I have entertained that idea but I think the rating hit may not be worth it locally. 

Charlie

[CHARLES SCHEAFFER]

FYI, just read some interweb posts and likely I measured my mast rake incorrectly.  I should have taped a folding rule to the top of the boom, touching the back of the mast, and should have taken readings where a weighted main halyard crosses the boom.  I'll redo it and report back.  If there is no mast rake, the reading will be zero.  Actual rake will vary but should be 6 to 16 inches.

Chuck S

[Francois Rivard]

Hi Charlie, 

The rating hit can be zero depending on the length of the sprit. 

-Francois

[CHARLES SCHEAFFER]

Hey Charlie,

You should be able to see the rating penalty for adding a sprit, on the webpage for your local PHRF group. 

Here is the calculation for my installation based on Chesapeake Bay PHRF.  I mounted three deck padeyes to set the sprit to three projections: zero projection for docking, another padeye at 44.5" for a 3 second penalty, and a third padeye at 60" projection for a 6 second penalty.  If I apply for a PHRF rating, I expect to get a 3 second hit for the sprit, and a 3 second credit for using a 139% headsail so they should cancel out and my rating should stay at 96 or 99. 

I'm sure the assym will be easier to handle than a regular spinnaker, but not as fast dead downwind.  We'll have to sail hotter angles and sail longer distances, but that will be much better than the other option; jib and main alone.

Adding a sprit is not cheap.  The Selden cost me about $1300 and I found sails used.  I had a sock.  I'd like to have a topdown furler to make it possible to furl and unfurl from the cockpit, but that would cost another $2500.   The other negative is how the sprit will block using your anchor locker, but you could store the sprit further back on deck to clear the lid.

Chuck 

[cene...@aol.com]

Our local PHRF (NCPHRF) has what I believe are higher penalties than Chesapeake--OTOH, I don't think they have ever rated a sprit added boat!

The penalties appear to be additive and only address a sprit length (ASPL) up to 115% of J--a  6 second hit. If the girth(AG) is larger than the 180% of J, say 200% of J, there would be another 6 second hit and if the spin maximum luff(ASML) is = to 110% of J, another 6 second hit.

OTOH, if I went down to a 135% headsail, I would get a 3 second credit. All in, I would be looking at a potential 15 second hit to have a sprit that extends a maximum of 25" beyond J and would have a 135% headsail vs. a 155%. If I kept the 155%, I would have an 18 second hit!

If I keep the asymmetric girth and maximum luff length to the same as my symmetric kite, I would only suffer the sprit length penalty of 6 seconds, unless I matched your lengths. In that case, the penalty would be at the committee discretion!

Bottom line, it seems that adding an asymmetric would penalize me so much that I doubt it would be worth it in time, trouble or cost!

Charlie

 

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[Francois Rivard]

Here's a few other data points on the potential speed of an Asym. 

1)  Our boat's Polars favor hotter angles / I have experienced it racing with the very similar 99's.  In 3-10 knots the best polar angle is 141 - 146 Degrees.  NOT 180 degrees.  In fact you don't get close to 180 until 20 knots which is 176 degrees.  20 knots on the sail is 28+ true if you figure boat speed.  

- I've tried quite a few times to go deep and "Bee line" to the leeward marker in an effort to avoid the potential screw-up caused by a gybe only to look at my hotter angle / gybing competition getting to the mark far ahead of us... 

So, under most racing conditions, the A2's operating angles of 115 to 160 degrees definitely jives with the boat's designed-in ideal speed operating parameters

2) The asym's square footage is going to be flirting with 1400 sq/ft. That's almost 2X the size of the conventional spins I'm flying.  It has to count for some potential added speed... 

-Francois

[David Knecht]

Hi Francois- 

If I understand our polar charts correctly, that is 140-146 TWA?  Correct?  

I have also never been sure if the downwind data are for spinnaker or non-spinnaker. 

 In addition, does it take into account a whisker pole to go wing on wing at a somewhat deeper angle.  There is a huge difference between 160-180 TWA with a whisker pole vs. without.  I have tried to measure VMG to a downwind mark in non-spinnaker racing deep angle with pole vs. shallower angle without and did not see much difference.  Dave

S/V Aries

1990 C&C 34+

New London, CT

I will admit this is the first time in 20 years I actually took measurements of the mast, but I am amazed how easy it was.  Curious if anyone else knows their actual mast prebendand mast rake numbers?  I have a three spreader Offshore Spar and presently have 3" of prebend and 15" of rake when the backstay is unloaded.  With the backstay fully tensioned, the mast bend goes to 4" and rake goes to 21".  It's easy to check rake at the dock, by laying a folding rule on the deck behind the mast and hanging a weight on the main halyard.  Prebend was based on holding the main halyard at the mast near the gooseneck and estimating the largest gap between the line and the back of the mast and comparing that to the width of the mast.  My mast is 7 inches front to back.

Anybody have numbers they can share?

Chuck Scheaffer Resolute 1989 C&C 34R Annapolis 

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[Francois Rivard]

I'm pretty sure it's with the Spinnaker.  As mentioned, much more competitive at hotter angles. As for TWA vs AWA , They are closer together going downwind. I pay more attention to AWA as it's what the sails "see" and sailing to 140-150 AWA is definitely faster in light air. The boat is so much more powered-up.  Easier to coast through the lulls with momentum when you have some... 

-Francois

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[Jim Morse]

Francois,

Thank you for details like this.  I figured the asym wanted hotter angles but i would have guessed more like 150 or 155.  Where did you find polars for the asym?  I too have been checking out anything for the 99 as more tuning help seems to be published 

Jim Morse

On Aug 23, 2022, at 3:27 PM, Francois Rivard <jeanfranc...@gmail.com> wrote:



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[cene...@aol.com]

I had my boat measured for an ORC certificate so I have a complete performance package for it.

The measurement involved on the hard keel measurements, etc. and in the water measurements for displacement, etc. so I believe them. 

My boat has a centerboard so they may not pertain in detail to other 36s of this era with wing or deep keels.

 

In general, however, it shows what Francois describes--much faster VMG at hotter angles even with a symmetric kite. 

Charlie Nelson

-----Original Message-----
From: Francois Rivard <jeanfranc...@gmail.com>
To: CHARLES SCHEAFFER <csche...@comcast.net>
Cc: cene...@aol.com; cc-...@googlegroups.com <cc-...@googlegroups.com>

[cene...@aol.com]

For example--downwind with mast head kite:             

True Wind Speed        AWA

    6.3                            103

   8.5                             123

  10.6                            130

  12.7                            153

  16.9                            169

   21.2                          172

   25.4                          172

The polar plot is nowhere 'smooth' but in less than 10 knots, stay less than 130 AWA is the message.

Charlie

    

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[Francois Rivard]

Hi Jim, 

My polars are the base polars that originally came from C&C so they are showing downind angles for a conventional symmetric kite. Polars for an asym will no doubt be different and my sense is that they will lean towards the hotter side of the spectrum.  

The A2's recommended angles come from the sailmaker. UK says 108-155, some others say 110 - 160 YMMV. 

I think it'll work well. 

-Francois

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[Mark Janda]

Sent from my iPhone

On Aug 23, 2022, at 5:37 PM, Francois Rivard <jeanfranc...@gmail.com> wrote:



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