Had purchased a new mainsail from a local manufacturer in Montreal . He used Pentex material and was cut , plotted by Prosail system. Beautiful sail but I swear it doesn't perform as well as the (at least 15/20 yr old ) Smyth mylar .With the old Smyth , the cat seamed to accelerate much easier with less air. Had many more capsizes from what seamed more instantaneous accelerations . Now either my sailing abilities greatly improved over one year (highly doubt) or new sail not as good. Does the cutting (full vs flat ) have that much to do with the sails performance ?
I know Smyth made great sails , but this one was well into the delimitation stage.

Yes, absolutely. Shape matters more than material. Most sailmakers are used to slower boats and fixed rigs. You're boat is neither, and requires a different twist profile than most. This issue is why I won't use one of the half a dozen competent sailmakers locally to do my F18 sail designs-it would take 3 shots to sort of get in the ballpark with someone who has a lot of fast multihull experience, and that experience in a sailmaker is rare. In the U.S you have Glaser and Smyth designing quick multihull sails, Sail Technologies has fast A-Cat sails, and EP also has some good work going on (sailmaker for Performance Catamarans for many years).

This does make sense ,now.Thank you for experience . Might take the old sail out again . I have a Glaser jib that I had a great deal on and can see the great workmanship . A new Glaser main runs at $2300 + 1.33 % CAD exchange ! Will have to start putting some money aside.

Try putting the sails up and taking pictures of their shape. Also, lay one on top of the other and look for differences. The most likely area that you are going to find changed is the luff curve. It might be that the new sail is cut with more or less curve and therefore you need to retune your mast to get the most out of it.

i know of several good and experienced sailors that went from classic to modern sails on legacy cats. it took a while to tune the mast, and get a feel for the nuances and learn how to optimize their sailing for the new cut sails.

When EP made the square top for my 5.5SL (was pin top). They also recommended the correct mast settings.
If your sail maker can't or don't know. Then compare then old to the new sail and see where the differences are. If fuller or flatter. The determine what to adjust to accommodate the sail shape.

How can you tell visually if sail is Fuller or Flatter ? I usually sail with combined crew weight of 380 and believe I should be looking at a fuller cut sail. Considering mast settings, you are talking about mast rake and bend or just from the down haul ? I appreciate all your tech experiences . I hear all these terms but not sure how they will affect sail trim .

Rake and bend are separate adjustments; rake is just your forestay/shrouds and moves the center of effort forward/backward relative to your centerboards/rudders. There are some other things to consider, but this is most of what you need to know.

Bend is the "shape" of the mast; think of it as a bow/arrow setup. Your spreaders and diamond wires are the string and the tighter and/or further back you set them, the more curve the bow has. You want the bend of your mast to match the shape of the luff of your sail, so if the new sail has more or less luff curve than the old one you will need to change your spreader sweep and diamond wire tension accordingly.

The simplest suggestion I could give would be to lay the sails over each other and stake the heads down, then pull them tight by hand and see which one sticks out in front of the other at the luff. That should give you and idea what direction you need to go with your mast.

If you want to see the shape, raise the sail, connect the boom, set the rotation and sheet the sail. Now lay under the sail and look up the luff. You can pull on the downhaul/cunningham and watch the shape change. If you're really interested, you can take pictures of both sails and compare them side by side.

There are other things you could do as well, but this will answer all of your questions.... the others start getting harder.



Edited by wlrottge on Aug 07, 2020 - 05:54 PM.

Hi emmettv,

An old style pinhead sail and the newer flat top sails are two very different beasts, and your concern is not uncommon. Expect your learning curve to be steep because there are so many variables, like:
Downhaul
Mast pre-bend and rotation
Mainsheet trim and leech twist
Outhaul control of the camber

Your sailing will get better when you are better at trimming this new sail using the same old controls that now have a different effect on sail shape.
Ask your sailmaker for advice on these settings as they apply to your new sail.

--
Sheet In!
Bob
_/)_____/)_/)____/)____/)_____/)/)__________/)__
Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
--

Lots of great knowledge,here .
Thank you all ,will go out today to experiment .

emmettv

I should have been more specific, so here goes:

An old style pinhead sail and the newer flat top sails are two very different beasts, and your concern is not uncommon. The flat top sail takes advantage of the wind nearly 30 feet up, which is usually stronger and cleaner (on general principles) than the wind on the water. They are also made of different, generally better, materials than the dacron you may be used to. (Know that I still race with my 30 year-old original Prindle pinhead sail). Expect your learning curve to be steep because there are so many variables, like:

Downhaul, which is now used as much to control pre-bend in the mast as flattening the luff.

Mast "pre-bend" changes the bend in the mast profile from side to side, to front and back. This creates a better profile to the oncoming wind, opens the jib slot, and changes the relationship between the downhaul and the sail shape. Most flat top sails are cut and sewn to take advantage of pre-bend.

Mast rotation is, in general, used more moderately with a flathead sail.

Mainsheet trim and leech twist are different in a flathead due to the cut of the panels and the type of material used for the sail.

Even the simple outhaul control of the camber in the lower part of the main is exaggerated with the newer materials and cut.

I strongly encourage you to contact the maker of your flathead sail and ask for advice on all these points, especially setting pre-bend.
Your sailing will get better when you are better at trimming this new style sail using the same old controls that now have a different effect on sail shape.

--
Sheet In!
Bob
_/)_____/)_/)____/)____/)_____/)/)__________/)__
Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
--

If you want a good explanation, Andrew Landenberger wrote a good article that's been posted several time in various places.

https://www.landenberger-…ow-does-a-wing-mast-work

emmettv-
Here is an older article on mast pre-bend that does a good job of explaining the concept.
https://www.thebeachcats.…436&g2_imageViewsIndex=1

--
Sheet In!
Bob
_/)_____/)_/)____/)____/)_____/)/)__________/)__
Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
--