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#1 2007-07-17 00:08:58

Guest

Rig Tuning

I have finally got my 27 under sail with lots of help from the forum, thanks to all!  I have noticed that the boat sails about a 1/2 knot faster on a starboard tack than on a port and I have more weather helm on a port tack than on starboard.  I have checked the mast according to the "Black Arts" instructions and everything looks good.  Does anyone have any ideas as to what is causing the difference in weather helm/speed?  One more thing I have noticed is that the boat has a port list of a couple of degrees at rest.
Speed checked with GPS, on Lake Michigan (no current)
Dave Green
"Bart" MKII #245

Last edited by (2007-07-17 01:29:30)

#2 2007-07-17 01:17:24

Guest

Re: Rig Tuning

You cannot trust a speed indicator to be accurate on the C&C 27's or any other boat if the paddle wheel is off center.  The speed in which the water travels around the hull on the submerged side is different from the up lifted side.  I just had this discussion with a naval architect last week. 
As far as the weather helm, your rig may be tipped to one side creating the feeling...just check to make sure your rig is vertical to the deck...
"IRIS"
1975 C&C 27 MKlll
Hull #453
Kittery Point, Maine

#3 2007-07-17 01:47:24

davidww1
Member

Re: Rig Tuning

The port list could be the weight of batteries on that side. Put more junk on the starboard side.

If you've followed the Black Arts instructions, and the mast is both evenly tensioned and centred at the dock, the spreaders might be the issue. If the spreader ends are free to move fore and aft, and particularly if one has more play than the other, you can experience a distinct difference from one tack to the other. See the possible remedies <a href="http://www.cc27association.com/fixes/various/various.html">here</a>.

David Weatherston
Towser, Toronto
C&C 27 Mk IV


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#4 2007-07-17 22:27:53

Guest

Re: Rig Tuning

Dave, when you note more weather helm on port tack, are you also experiencing a greater heel angle?
I am guessing that your port shrouds are not as tensioned as your starboard? I would be surprised if 80 pounds of batteries in a 2-ton boat would be the cause.

#5 2007-07-17 23:35:55

Guest

Re: Rig Tuning

I have attempted to balance the boat (moving stuff to starboard) with some success.  Tension of the stays seems equal.  Heel angle seems to be greater to port.  Maybe I'm just being overly picky, but the boat just seems to go faster and sail better to starboard.  This may just be my perception.  One thought, if the keel is not centered, would this cause the boat to be stiffer on one tack or the other?  I thought that I noticed that it seemed to be very slightly cocked when it was hanging in the slings prior to launch.
Dave Green
"Bart" MKII #245

#6 2007-07-18 00:38:24

davidww1
Member

Re: Rig Tuning

>Maybe I'm just being overly picky...

If it feels wrong, it probably is wrong. What you need to do now is find out how wrong and why. Try to get another experienced sailor on board to double-check your findings (particularly to ensure that your sail settings are identical from tack) and find out:
<ul><li>What is the difference between pointing ability from tack to tack? Go head to wind to establish wind direction, then sail upwind on either tack in an area where wind will not be distorted by land, carefully noting compass direction. Calculate the wind angles on either tack.  They should be roughly the same. Five degrees signifies a tuning error. Ten degrees is a major tuning error or something else.
<li>At the same time, note the boatspeed. As was pointed out earlier, your knotmeter won't be perfectly accurate (but there's no way it should be inaccurate to 1/2 kt. from tack to tack). Lay your hands on a GPS and measure speed with that (you can also use it to validate your compass at the same time).
<li>If there are differences, run through the tuning guide once again. Tick off every item as you double-check it (I can't tell you how many times I've torn my hair out, only to discover that I've missed some glaring deficiency). Measure the position of the masthead and check the shroud tensions.
</ul>
When you've done all that, then and only then should you consider something as improbable as your keel being visibly off centre. Read <a href="http://antwrp.gsfc.nasa.gov/apod/ap070717.html">this</a> and follow the Adelson link to the <a href="http://web.mit.edu/persci/people/adelson/illusions_demos.html">illusions</a>-- you'll never trust eyeball measures again.

David Weatherston
Towser, Toronto
C&C 27 Mk IV


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#7 2007-07-18 09:32:36

Guest

Re: Rig Tuning

As for the boat leaning to one side. We put a fully loaded camera bag in the boat the other day and noticed that at rest it caused a small but noticable movement of a couple of degrees to that side until we placed the bag in the v berth. I would echo the solution to put more junk one one side.

David
Westwind Mark 5

#8 2007-07-18 09:55:19

Guest

Re: Rig Tuning

Hi Dave,
You must be learning a lot about your new boat and you've come to the right place for some willing help. Just a couple of thoughts to add to the mix; ---

    I know that the holes in my toerail are not symmetrical side-to-side and your boat may be the same and if so, the Genoa will be sheeting differently on one tack than the other. Take a tape-measure and measure from the tack fitting backward along both toerails to verify that the snatch blocks are indeed even, side to side. ( I also found that the base of my mast must be placed 3/16" off centre (to port) in the Aluminum mast step so that it ends up centered between the upper shrouds-- see Rig Tuning- Black Arts)
    As others have already said, in your search for tack-to-tack speed differences,  ignore your knot meter. Instead, rely on a GPS but in your hunt for some apparent differences in speed between port and starbord tacks, don't just look at the speed over the bottom provided by the GPS. Pick (or first, go and set) a weighpoint directly upwind from a starting point and then put a "Go TO" command into the GPS for that weighpoint and sail upwind toward it from the start point.  Watch your VMG toward the 'target' on each tack (hopefully in the same wind/wave conditions) and compare that to the "speed over the bottom" on each tack. That will tell you a lot about boatspeed and leeway differences tack-to-tack.
   Another very good possibility for leeway/helm/speed differences tack-to-tack is a rudder post bent to one side (from a former grounding) - Ashore , viewed from astern, the rudder obviously should hang directly in line with the keel. You mentioned your perception that the keel seemed 'canted' when in the slings -- Is it possible that the keel is indeed straight and that a bent rudder post made the keel look slanted???

   Good luck in your determinations-- Keep us posted because this is turning out to be a fun exercise trying to solve this puzzle !!
Regards, Clare Jordan  , Aragorn

#9 2007-07-18 22:09:17

Guest

Re: Rig Tuning

Many good suggestions!  I especialy like the idea of checking the VMG.  As for checking rudder and keel alignment, it will have to wait utill haulout.  I will report back with my findings.
Dave Green
"Bart" MKII #245

#10 2007-07-18 23:57:39

Aragorn
Member

Re: Rig Tuning

"as for checking the rudder and keel alignment, it will have to wait until haulout"

Hi again Dave,
   Not necessarily. If you swim and have a snorkle/mask, a major bend in the rudder post will likely be apparent in clear water viewed from astern with the tiller centered. Or, to detect a lesser bend, with a tape measure, a snorkle and some help in the cockpit you could measure, say, from the aft corner of the rudder up each side of the boat to some fixed reference, say, the casting at each corner of the transom to determine if these measurements are equal.

Clare

Last edited by (2009-09-08 00:02:19)


<U>SAIL FOR SALE </U>_
#2 Genoa for 27' Mk.111 by North Sails . Tri-radial cut, Norlam fabric, built 1998-- good shape . Window, tell-tales and draught stripe. Stitching etc. checked ;2001/2002 . #6 Luff tape .
Replacement Genoa is on order for 2004 racing season but there's some cruising years left in this one -$ 550 asking price. phone 613 498-2029 or e-mail <A href="mailto:bosco@ripnet.com">bosco@ripnet.com</A> <img src="emoticons/icon_frown.gif">Brockville)
;
;

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#11 2007-07-19 23:17:53

Guest

Re: Rig Tuning

I think I have a pretty good eye for things and there are no major alignment problems with either the rudder or keel, unless someone took my boat out and ran it aground with out telling me!! (Kidding)
In the black arts section on tuning it was mentioned how "J" owners verify that the keel is centered, and this is where I got the notion that it could be an alignment problem.  I am interested to know how critical keel centering is to boat performance.  Is a minor deflection (1 degree or roughly 1" at the bottom of the keel) a problem or not? 
As my father used to say about a car's front end alignment "I can't tell you if it's right, but I can tell if it's wrong!"
Dave Green
"Bart" MKII #245

#12 2007-07-20 01:57:36

foroadmin
Administrator

Re: Rig Tuning

I don't think you could determine if the keel were off centre without a fair bit of expense and effort. These boats change shape significantly when they're out of the water, so you'd only get an accurate measurement if you hauled the boat after some time in the water and measured it immediately in the slings.

Would it matter? J/35's have relatively deep and high-aspect-ratio, fine and carefully shaped keels on a canoe hull, so there is value in optimizing at the level described in Black Arts. We have relatively blunt, low-aspect-ratio, roughly shaped low-performance keels on a slack-bilged hull. There is going to be so much turbulence and inefficient flow around our keels, I would be deeply surprised if 2 inches made any difference. (Nor do most of us want to fling money at our boats the way J/35 sailors do &ndash; Toronto has a big J/35 one-design fleet and if you want to compete at the top, you join the "arms race".)

If any difference were discernible, it would be another of your ones &ndash; 1 degree, 1 inch and maybe a 1 per cent tack-to-tack difference, a value that could easily be cancelled out by any number of other variables. But you've been talking about major differences tack to tack, so I really believe that you need to look for a serious discrepancy in the way your rig behaves from tack to tack.

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#13 2007-07-24 23:48:42

Guest

Re: Rig Tuning

I have retuned the mast using a halyard to toerail measurement and moved it a couple of inches (3-4) at the top of the mast (about 1/2 of an inch at the chainplate) and retensioned the stays.  Unfortunately the winds were so light last weekend I didn't get a good feel for any change. 
Does this seem like a significant adjustment to you?  Thanks!
Dave Green
"Bart" MKII #245

#14 2007-07-25 07:02:04

Aragorn
Member

Re: Rig Tuning

Hi again, Dave,
   If you're telling us you moved the top of the mast laterally 3 to 4 inches this past weekend to get it centred over the boat, then that is a significant change and could well have accounted for the tack-to-tack speed differences you reported earlier however, you first told us on July 17th that you had tuned the rig according to the "Black Arts" directions which would have centered it then.....????  I can't understand ..... What's up with this mast ??--    I couldn't see that a shroud could stretch 1/2"!( the amount you found you were apparently 'off' in your chainplate measurement) Are the outboard ends of each spreader twisted into the shroud properly with the 'retainers' on the underside of each spreader and are they pinned at the inboard ends with cotter pins ?? Is the rubber there in the spreader socket and is it in good shape??
 

Clare Jordan,  Aragorn

Last edited by (2009-09-08 00:02:58)


<U>SAIL FOR SALE </U>_
#2 Genoa for 27' Mk.111 by North Sails . Tri-radial cut, Norlam fabric, built 1998-- good shape . Window, tell-tales and draught stripe. Stitching etc. checked ;2001/2002 . #6 Luff tape .
Replacement Genoa is on order for 2004 racing season but there's some cruising years left in this one -$ 550 asking price. phone 613 498-2029 or e-mail <A href="mailto:bosco@ripnet.com">bosco@ripnet.com</A> <img src="emoticons/icon_frown.gif">Brockville)
;
;

Offline

#15 2007-07-25 12:34:33

Guest

Re: Rig Tuning

My mistake was to have a "helper" the first time I tunned the mast!!!  Live and learn.
I'm only guessing at the 3"-4" movement at the top, but it was 1/2" at the chain plate.  The spreaders are mounted correctly, rubber is good etc. 
I have put more tension on the shrouds than the yard did when they originally "tunned" the mast.  In the "Black Arts" it says the upper shrouds should be "really, really' really ridiculously tight", I don't think I have them that tight (what ever that means), but they are significantly tighter.  I have noticed that after all this the spreaders are no longer flat, they have a slight "V" to them.  Is this an indication the upper shrouds are too tight?  I'm at the point where I'm thinking of buying a tension gage, because "really, really tight" is not a good descriptor for me!!!
I will be out again this weekend, hopefully with better wind and let you know.  Thanks for the help all of you have lent!

Dave Green
"Bart" MKII #245

#16 2009-09-06 22:36:35

windyday
Member

Re: Rig Tuning

"If the spreader ends are free to move fore and aft, and particularly if one has more play than the other, you can experience a distinct difference from one tack to the other. See the possible remedies <a href="http://www.cc27association.com/fixes/various/various.html">here</a>."

How is that Spartite holding up? I need to find a way to firm up the spreader bases.


---------------------
1974 Mark II C&C 27


---------------------

1974 Mark II C&C 27

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#17 2009-09-08 00:13:27

davidww1
Member

Re: Rig Tuning

I think the Spartite is underperforming, but at this point I can't tell why. I'll have a look at it when the mast comes down at the end of October. If it has compressed or broken down, I'll look for the hose referred to by Ken Pole in a thread called 'Loose Spreader':

"After an extensive search, I found suitable heater hose for the inboard end of my Mark III's spreaders at a truck supply shop. It has an outside diameter of about 1-5/8" and a wall thickness of about 3/16". My spreaders are 1" aluminum pipe which has an O.D. of 1-5/16" so the hose is a snug fit. It costs $2 an inch up here and you'll need no more than 5" to do both sides."

David Weatherston
Towser, Toronto
C&C 27 Mk IV


David Weatherston
Towser, Toronto
C&C 27 Mk IV

Offline

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