Hear, Hear!!!
Muchas Gracias.
On Thu, 11 Oct 2001 07:13:56 -0700
Mike Guccione <innove8@pacbell.net> wrote:
> Great information Harry. We all appreciate it. Thanks.
>
> -----Original Message-----
> From: owner-santana3030@sailpix.com
> [mailto:owner-santana3030@sailpix.com]On Behalf Of Harry
> Pattison
> Sent: Wednesday, October 10, 2001 8:41 AM
> To: innove8@pacbell.net
> Cc: Santana 30-30 Mailserver
> Subject: RE: mainsail trim
>
>
> Mike,
> This is a pretty good article in general sort of terms,
> and pretty true for
> boats such as a Santana 30/30. The drag he is referring
> to under the boom is
> aerodynamic drag from eddies that form of the end of any
> airfoil. The
> flatter the section is, the less the eddies will form. Of
> course like
> anything else you can always overdo it. In light air
> conditions where you
> need power you will need the bottom of the sail fuller
> than you do in
> windier conditions.
>
> As far as trimming the main you should be looking to have
> the boom at or
> near centerline with enough twist so that the back end of
> the top batten is
> parallel to the centerline. You will find that in under 8
> knots of wind the
> top telltale will not flow back all the time, but it
> should be streaming
> back about 1/2 of the time. The lighter the wind, the
> less it will stream.
> As the wind increases the top telltale will stream more
> and more. By the
> time you get to about 11 knots of wind it should be
> streaming all the time.
> If you can't get the top telltale to stream it means you
> either have the
> sail sheeted too tight (too little twist) or the sail is
> too full. That is
> why even in light air you need to sail with at least some
> backstay on.
>
> Once you get the top telltale streaming while the boom is
> trimmed to
> centerline and the top batten parallels the centerline
> you have about the
> right combination of twist and depth. After that as the
> wind increase you
> will need to flatten the main to reduce healing. As you
> increase mastbend
> you will need to sheet the main tighter and tighter
> because as the main gets
> flatter the upper leech becomes more and more open. As
> long as you can keep
> the boat from healing too much you want to keep the twist
> in the main about
> the same. When you reach the point where the main is
> about as flat as you
> can get it you will need to start letting the leech twist
> even more to
> depower the boat.
>
> It is hard to talk about trimming the main without also
> talking about
> headstay tension and checkstay tension. You should always
> think of the
> checkstays as a control of headstay tension, NOT as a
> control of mast bend.
> If all you want to do is change the mast bend you don't
> need checkstays.
> Just put on more backstay to bend the mast and let if off
> to straighten the
> mast.
>
> Checkstays are for controlling headstay tension. If you
> are sailing along
> and have the main trimmed just the way you want, but find
> you are not
> pointing because the genoa entry is too round, what do
> you do? Put on more
> backstay which will increase headstay tension and make
> the jib flatter. This
> will also make the main flatter so now you have to pull
> the checkstays
> tighter to reduce mastbend back to its original amount.
> Now the main will be
> the same shape as before, but the headstay will be
> tighter and the jib entry
> will be flatter.
>
> Harry Pattison
> Elliott / Pattison Sailmakers
>
> -----Original Message-----
> From: Mike Guccione [mailto:innove8@pacbell.net]
> Sent: Tuesday, October 09, 2001 3:46 PM
> To: Harry Pattison
> Cc: Santana 30-30 Mailserver
> Subject: mainsail trim
>
> Guillaume sent me this article from scuttlebutt about
> mainsail trim.
> I used to try to keep my leech tighter and straighter
> than I do now. Cliff
> has taught us that by adding twist you lose a lot of
> weather helm and
> therefore drag. What do you think about this article?
> What is the latest
> thinking in mainsail design. What advice can you give the
> fleet for trimming
> the main on a Santana 30/30. I also don't understand what
> they mean by
> "lower third should be flat to reduce drag under the
> boom". What drag is
> there under a boom?
>
>
> MAINSAIL TRIM
> (Pete Colby distills mainsail trim in a story published
> on the SailNet
> website. This excerpt explains what the main should look
> lie.)
>
> The maximum draft (shape) should be located at 38 to 48
> percent back from
> the luff.
> The lower third should be flat to reduce drag under the
> boom.
> The middle third needs a bit more shape. This section
> promotes lift with its
> longer chord length (the luff to leech straight-line
> measurement). The added
> area accelerates flow, thus increasing the lifting force.
> The top third is a bit trickier. It is designed with as
> much depth as it can
> take. The added depth increases surface area, giving the
> airflow a longer
> runway on which it can accelerate. Depth also reduces the
> effects of drag,
> by giving the airflow more time and area to generate lift
> before it reaches
> the turbulent leech. Further, depth creates a twist. In
> other words, under a
> given sheet tension a main with more depth up high will
> fall off, or twist,
> to leeward. Seen from behind, the sail looks like a fan
> blade. The twist
> flattens the curvature, reducing the chance of
> separation. And twist also
> combats surface friction. The air moves faster the higher
> it is, and a
> faster-moving breeze approaches the sail at an angle aft
> of that of a slower
> breeze. In order to maintain a uniform angle of attack
> (the angle where the
> apparent wind direction intersects with a straight line
> from the leech to
> the luff), you need to turn off the leech. A greater
> angle of attack creates
> more lift. - Pete Colby, SailNet website
>
>
>
>
>
>
Received on Thu Oct 11 10:42:32 2001