Let's talk twist ...

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Oct 26, 2008
6,043
Catalina 320 Barnegat, NJ
Mounting a new traveler ...

Several years ago I spent close to $500 for the 6-bearing traveler car and a pair of traveler controls with the dual sheaves and cam cleat. I bought this from Schaefer because the boat was rigged with Scheafer hardware and the traveler track is a 1-1/8" Schaefer track. Unfortunately, I soon discovered that the flange for the cam cleat doesn't clear my locker openings because the ends of the track stop about an inch short of the coaming. My traveler track is mounted very similarly to Radico's.

Well, now I'm re-motivated to carry this project through and I believe that I can solve my problem by buying 5' length of Scheafer traveler track and custom cutting it down to fit snugly up against the coaming. Then, the controls can be mounted at the end with just enough clearance so my lockers aren't impeded. But, I liked Radico's set-up because the working end of the control lines are at the traveler car. With mine, the working ends are at the outboard ends of the track with the fixed controls. I looked at that windward-sheeting Harken system and was liking that because they advertise that you don't have to release the leeward side when raising the windward side. What a great system for my wife! :D Besides, it seems like the Schaefer system may be slightly awkward because the sheeting system is not right in front of you when you are sitting in the cockpit.

In any case, I am faced with the dilemna of thowing out the money I already spent on the Schaefer components in favor of the Harken system which I like (and I have to look very carefully to make sure the profile of the track matches the profile of my current set-up - I can't go with low profile because the track is recessed). Installing a new Harken track will probably be a lot more work since it is not likely that any holes will match. It might be good if I could match the Harken components with my Schaefer track, but I believe that would be Metric units (Harken) to English (Schaefer) which doesn't give me much confidence. If the Harken traveler car clears my lockers when the lockers are closed, this may work because the flange for the cam cleat is on the traveler car which could be centered when I want to open a locker.

In any case, this upgrade may make my wife happy because I get the dirtiest looks when I ask for adjustments to the traveler - far dirtier a look than for any other control. :redface:
 
Jan 26, 2007
308
Norsea 27 Cleveland
Thanks Todd, that gives me something to chew on tonight. What assumptions regarding sail shape go into making a polar? If you change the sail shape (by altering any of the trim controls other than angle of attack), then do you really have a different sail with a different polar and a different max force? I'll have to see if I can find my Arvel Gentry articles.

In any case, assuming that there is 'some' angle of attack for each sail shape that produces maximum force for that shape, then amongst all possible sail shapes there should be one with maximum force overall. That would presumably be the best trim for power and speed (max force = max power). There is another issue lurking in there. In each case force should be interpreted as forward force, as heeling force doesn't really [directly] add power, force or speed. The root of my misunderstanding stems from the idea that speed and power both come from maximum force, and that should come from a single optimal trim for a given course, sail and wind. If that's so, then why is their a discussion of trimming for power versus trimming for speed?

One potential way out of this morass would be if a deeper draft greater angle of attack yields a smaller overall force but also a smaller heeling force, whereas a speed trim might yield a greater overall force, comparable forward force and an optimum amount of heeling force leading to an increased waterline and use of hull shape.
 

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Phil -
I think a better way out of this is:

Flatter 'speed shaped' sails will tend to reach the optimum possible speed.
Powered-up sails are for accelerating in conditions where the boat is always/usually being retarded/decelerated by wave action ............ and the acceleration never yields the optimum possible speed.

Powered up sails are more vulnerable to 'separation stalls' ....
Powered up and overly twisted sails will be vulnerable to have non-uniform or 'gradual' separation stalls from 'higher to lower' due to the gradient of twist and deeper draft (and because of Less 'wind gradient' at the higher wind ranges.

Offered Rx:
What sets all this to optimum (for sailing in less than survival conditions) is simply the tell-tales flying correctly (and watching the speedo). ... the 'basics'.
In 'normal' conditions, getting and Keeping the tell tales (full set + gentry tufts) to 'perfect' will 'automatically' give you the perfect shape and trim for the conditions, etc. and will cause automatic adjustment for the max. speed (speedo) attainable for the conditions at hand.

Summary: Rather than blindly assume some amount of twist, draft, 'control tension' etc., ... start with and interpret the tell tales to arrive at the proper amount of shape and trim.
Being clearly overpowered and in 'survival mode', then you can de-power based on your 'sailing preferences': blading-out, flat as a sheet of plywood, over-twisting, radical mast bend, reefing, etc. etc. etc. ... .

;-)
 
Jan 26, 2007
308
Norsea 27 Cleveland
Sounds right and adds one last piece, maybe. The shape of the sail effects more than just the amount of force/power generated.

If I understand you correctly, you are saying that a speed trimmed sail will reach max force/power/speed, sort of hitting a design limitation on performance. However, in bigger water the speed trimmed sail does not reach design speed for all the reasons mentioned above. In that case, a 'power' trim will generate the 'best case' force given the sea condition, sort of a conditional max force/power. In that case, I guess I'll return to my earlier statement that it's merely semantics and I'm just overthinking the topic. In the speed trim case the sails are trimmed for maximum power. As a practical matter, your Rx sounds good.
 
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