Herb,

  I'll basically agree with Rob and Arto: work on trimming those sails to get some airfoil curve that will generate forward lift to pull the boat where you want it to go. 

  The difference between well-trimmed sails and poorly-trimmed sails is huge.  On a boat where leeway is prevented by a foil, which needs a good flow of water over its surface to be effective, instead of a long keel, which prevents leeway by brute surface area, sail trim can easily mean the difference between tacking through 90 degrees and tacking through 150 degrees.  Or, in this case, shunting.

  After getting a new traveler for my catamaran, which allowed me to properly trim the main (no vang on this boat), I doubled my boat speed in some circumstances.  Traveling my boom down off the centerline until the lowest telltale fluttered straight of the leech, and then using the mainsheet to adjust twist so the higher telltales lined up, made all the difference in the world. 

  Case in point: I was not able to tack the boat on the mainsail alone, regardless of the wind speed, before the new traveler.  After the upgrade, the boat tacks fine in light wind with just the main up.  Being pulled by 90% of the sail is vastly more effective than being pulled by 40% of it.

  There might be two good ways to do this:

  a) Get a good sailmaker with racing experience to come out on the boat with you, look at the sails, adjust trim, and then potentially re-cut them and/or get better battens.

  b) Get serious about testing all the variables. 

    - You could put up a few dozen telltales for testing purposes, particularly along the leech of each sail and on each side (windward/leeward).  You wouldn't want all these telltales for normal sailing because it's too much information to process, but for pure testing, they're useful.  Taped-on cassette tape is a great way to test cheaply.

    - Go out on a good steady wind day with an omnidirectional wind meter and a knot meter or GPS.

    - Find a good sail angle by letting the boom out until the sails luff and then bringing it back in to the point where they fill.

    - Trim both sails to get good telltales.

    - Record your boat speed as a percentage of wind speed at different amounts of curvature in the sails.

---

  Ben has a good point about flat sails, but he's also sailing a lightweight rocket with a small diameter mast that's not likely to spoil much wind over the sails, and a sail that has a nice airfoil shape even when it's close to flat.

  If you can adjust the boom relative to the mast, that would be ideal.  But if not, you'll definitely need to play with the draft.  If you've got a big mast, followed by a sail with no draft (there's almost no curve in the top half of the mainsail in the photos), it's possible that most of your sail will be either shadowed by the mast or in its turbulence.  You may need more draft than someone with a rotating wing mast, just to get more of your sail into smooth air flow.

  Again, telltales can help with this.  A few columns will tell you where the sail is stalling and where it isn't.

  Personally, I'd probably see if I could lure an expert onto the boat for a day with offers of food, beer, and a sail on a proa.  Or just spend some money on a consulting fee.  It all depends upon how detailed you want to get with your testing, as well as how many days you want to devote to it.

        - Mike
 


Arto Hakkarainen wrote:

 

Looking again at the pictures it seems that the slot between jib and mast is quite open (hard to say from this angle). Also the sheeting is from the reef point of the jib which is probably optimized for hard wind. Hard to tell without tell tales though. If I was trimming there I would try to pull the jib sheet corner down (and perhaps also a bit to the center but down pull is more important) to make the leach tighter and to close the slot a little while also adding some curve to the jib at the same time.

 

Arto

From: bjarthur123 <bjarthur123@yahoo.com>
To: harryproa@yahoogroups.com.au
Sent: Tuesday, October 18, 2011 3:22 PM
Subject: [harryproa] Re: Sangduennoi

 

i don't understand why, but according to the following page, flatter sails are better in the lightest of airs:

http://www.uiowa.edu/~sail/skills/racing_basics/chap2.shtml

seems to work on my weta in 5 knots or less. if i loosen the downhaul to deepen the camber in such wind, the leeward telltales stall on my main. and i'm never first to the weather mark, as i typically am otherwise.

conversely, deeper is good in 10-15 knots. beyond that i start flattening to reduce power.

ben
weta #358, "gray matter"
ithaca, new york

--- In harryproa@yahoogroups.com.au, "heinrich_meurer" <meurer@...> wrote:
> looking at the photos it appears that there is very little wind. In such conditions flat sails and the wrong mast rotation and the attempt to steer into the wind at all costs kills boat speed.