Square Top vs Pin Head

Technical discussion of ARC products
gahamby
Professional
Posts: 252
Joined: July 24th, 2012, 7:02 am
Boat Make/Model: SuperCat 15#315
Location: Falls Church VA 22042

Re: Square Top vs Pin Head

Post by gahamby »

Thanks Bill, in this instance I would not shorten the foot, just add area at the top?
Bill Roberts
Expert
Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Square Top vs Pin Head

Post by Bill Roberts »

Yes, make the square top anywhere from 25% to 40% as wide as the foot of the sail.
The factory is using 40%. No Change to the foot.
Go for it.

If you don't have an experienced sailmaker with square top sails in your area,
maybe Tom Haberman could do it for you.
gahamby
Professional
Posts: 252
Joined: July 24th, 2012, 7:02 am
Boat Make/Model: SuperCat 15#315
Location: Falls Church VA 22042

Re: Square Top vs Pin Head

Post by gahamby »

Copy that, Bill. This has off season written all over it. Does that top batten need to be more robust than the stock '84 vintage round fiberglass ones I'm currently using. I know the top battens will have to be longer.
Bill Roberts
Expert
Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Square Top vs Pin Head

Post by Bill Roberts »

The gaff batten does need to be a little stiffer than any of the other battens in the sail. If you have Tom fix your sail, he can supply you with a correct top/gaff batten at that time. Was your sail built in 1984? If so, you might need a new one.
gahamby
Professional
Posts: 252
Joined: July 24th, 2012, 7:02 am
Boat Make/Model: SuperCat 15#315
Location: Falls Church VA 22042

Re: Square Top vs Pin Head

Post by gahamby »

Bill, my sail appears to be original equipment. The sail, however was the good news of this rescue cat. Except for a shabby head board (replaced) and an improperly riveted clew plate(brass to stainless, refastened w/ stainless) and the battens being totally wrapped in black electrical tape (removed, long day) the sail was beautiful.
I can't see replacing it. The most abuse this sail gets is in hoisting and striking. I don't really want to get a Mylar sail. There's kind of an upper limit to the amount of money I'm willing to plough into the old girl. It's a damn fine little cat as is. I wouldn't mind a little more get up and go, however. I tip in at #200 and I tend to squash her a bit. I'll explore this option after the season concludes. GH
Bill Roberts
Expert
Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Square Top vs Pin Head

Post by Bill Roberts »

gahamby, if the sail is in good shape, stay with it. Maybe it spent several years
not used. Fresh water sailing is much easier on sails than salt water sailing.
At your weight don't sit in the back of the boat and make it squat. Keep the knuckle
of the bow underwater and you will have the boat trimmed out pretty good.
Good Sailing.
gahamby
Professional
Posts: 252
Joined: July 24th, 2012, 7:02 am
Boat Make/Model: SuperCat 15#315
Location: Falls Church VA 22042

Re: Square Top vs Pin Head

Post by gahamby »

[img]
square%20top.jpg
[/img]

Bill, am I on the right track here with the sail. Granted this is a rough take.
I am trying to break myself of the habit of sitting aft
By knuckle do you mean the top of the top stripe?
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Bill Roberts
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Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Square Top vs Pin Head

Post by Bill Roberts »

gahamby, good to hear from you.
The knuckle at the bow is the intersection
of the stem and the keel. So you have it right.
Keep those blue stripes at the bow just underwater on
all points of sail and in any wind condition and
you will have the hull trim just right. In light winds,
you will be sitting forward at the main beam. You
might want a cushion to sit on. On a windy day, you
will be sitting back at the rear beam reaching going fast
downwind. The point is, you are going to be on the move
keeping that hull trimmed out just right.
I like your square top line.
Kevin Keller
Professional
Posts: 362
Joined: September 24th, 2006, 2:56 am
Boat Make/Model: SC-20, ARC22
Location: Honolulu

Re: Square Top vs Pin Head

Post by Kevin Keller »

Bill,
In your locked post you mention tightening the downhaul will open the leach. I have Aquarius supplied Kevlar sails on my 20 and 22. Tom says to tighten the downhaul just enough to get the wrinkles out. I'm wondering with such a strong material does that still apply to the Kevlar sails?

Thanks for sharing your knowledge. We all appreciate it.

Kevin
Bill Roberts
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Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Square Top vs Pin Head

Post by Bill Roberts »

Hi Kevin,
To get the leech near the top of the sail to twist off and depower, you have to put the downhaul on firmly.
This will increase mast bend even with the same mainsheet tension. When the mast bend near the top of the mast exceeds the round in the luff curve built onto the sail near the top, the major leech load travelling up the leech will migrate forward in the sail and over to the mast a few feet down from the top of the mast, below the square top. This leaves the square top area of the sail with little or no load in it and so the wind pressure pushes it off to leeward and that part of the sail produces no thrust and becomes streamlined, low drag. The center of effort in the sail migrates to a lower height in the sail and overturning moment is reduced; the sail is depowered. This should work very well with a Kevlar sail.

Kevin, on another subject, I think I have seen pictures that you have put on the forum. I am having no success doing this.
I click on "attach" at the bottom of the page.
Then click on "add files" which brings up your stored photos in your computer.
Then I type in the name of that photo and click on "open".
Progress stops there. No picture, no nothing and no more options.
What am I doing wrong?

I have a sailing picture with spin and vector diagram showing the relative wind direction.
These two pictures would be very helpful to you and others if only I could put them on the forum.
Help Please.
Kevin Keller
Professional
Posts: 362
Joined: September 24th, 2006, 2:56 am
Boat Make/Model: SC-20, ARC22
Location: Honolulu

Re: Square Top vs Pin Head

Post by Kevin Keller »

Hi Bill,

Regarding posting pictures. I use an Apple but I would think it is similar to using a PC. I hit the "Attachments" link, then "Add files" and then navigate through my computer to find the picture and select it. I don't type in anything. I haven't done it in a while but let me add a picture now to see if that is still correct.

If you can't upload it, send it to me via email and I will upload it : kevkeller@hotmail.com
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