Mainsail position/trim with Asymm . . .

[Clark]

For optimum performance, where should the mainsail be when broad reaching with an asy spinnaker? First inclination is to let it out as far as it will go with some belly introduced with the outhaul+halyard+vang. I've wondered if pulling it in to get some lift off the back of the main and to funnel air to the spinnaker works any better.

TIA

 

[Stu Jackson]

It would seem to be based on how fast you are moving. Then the apparent wind angle would determine the position and the wind speed the trim of the main.

 

[CharlieCobra]

The best sail I ever had with my Asso was with the chute flown "by the lee". I had everything else up on a broad reach and the chute ended up being happiest by the lee after a gybe. The main and staysail seemed the feed the chute and keep it happy as seen below.

 

[Clark]

So something of a 'wing & wing' right Charlie? I do plan to experiment with a number of configurations. I have a little experience with an Asy; just wanted some tips for getting higher on the learning curve.

 

[CharlieCobra]

Yep, it was by accident as the chute didn't want to fill after a gybe. We gybed back, were slow with the chute and noticed it was very happy where it was. I later hoisted the staysail for grins and it was even better. The wind was 8-12 and we were doing 7 knots under this configuration or just over hull speed. We gybed a few more times and brought the chute to the lee on purpose each time. I have flown that sheet as close as 60* apparent on a reach at times with it sheeted in hard like a big Genny effectively. It's easily one of my most effective sails. Just go out and experiment with it in wind to 15 knots. I will fly mine up to about 25 knots offwind if wanting a rush but that's pushing it with an 800 sq ft sail. I did have it self deploy in a 50 knot gust once but that's another story entirely.

 

[Joe]

I think you should still be able to use your main's leech telltales on that point of sail. The spinnaker can help funnel the air on the main.

What you might consider is experimenting with your twing (you do have twings on your spin sheets, right?) Anyway, try cinching the twing down a bit to close the leech on the spinnaker and see how that effects the main. Then try other settings. If possible you may try moving it forward or back a bit... but normally there is an optimal position for the sail.

Also, experiment with tack height in combination with the twing and sheet. See how that effects the airflow off the back of the main.

Track all the changes with wind, sea and boatspeed data.

After experimenting with these combinations, check you notes ... analyze... then you'll be able to logically come up with the right trim strategy for each given situation.

 

[RichH]

Clark
The best position for the mainsail/boom angle from the centerline is determined by the SPEEDO !!!!!!!

After the Asym is set/shaped to perfection... then watch the speedo for the HIGHEST speedo reading as you adjust outhaul, 'boom off the centerline angle', halyard tension, etc. etc. After gaining the highest possible speed, then 'reset/reshape' the Asym again to perfection and then repeat the trim/shape with the main (and while watching the leech tell tales)..... while watching the SPEEDO.

WATCH THE SPEEDO !!!!!!! It will automatically 'correct' for different wind and wave patterns. The GOAL is to be as fast as you can possibly go (in the right direction) and the only 'instrument' that can tell you that is the SPEEDO.

 

[Clark]

Sage advice Rich, Thanks. Experimenting with this stuff is a blast . . . I hope to report back results after a few runs.

 

[RichH]

Using the speedo, and taking/recording notes, is the 'ultimate best' way of getting optimization of sail trim & sail shape.

Without getting into very complex aerodynamics, which is NOT 'intuitive', the speedo gives you an extremely precise and ultimately SIMPLE way to empirically (simply from observation of the *results*) analyze any change in sail trim and equally important - sail 'shaping'.

The speedo gives an extremely easy method to evaluate 'any' changes in sail shape/trim. The logic of this 'speedo method' should be astoundingly profound as it easily *validates* those changes in trim/shape.

Why do 'anything' if you cant 'prove it'. The speedo takes out 99% of the 'guesswork'.