sails...goofing around

mixmkr

mixmkr

Well-Known Member
Ok…. I have this old sail...yes it's soft and comfortable and I added the windows years back. No draft to the sail, so it must be close, if not original to my '69 Sunfish. Oddly, the roach is scalloped or 'curved in' . You can't see it in the pictures, but the luff...or side that goes up the upper spar, actually slightly curves the other way...I guess an attempt at some sort of vertical belly! The foot is basically straight with no real apparent "belly" to the sail along that edge. For fun, laid out the line to emulate the shape of those "hi-tech" sails. I'm beginning to think that adding a huge roach like those tech sails, IN THIS SAIL, would be basically the same as raising the gooseneck higher up the mast.....and a little more sail area too. So...the boat will flip easier!
Wondering 'out loud' if messing around like this is just a total waste of time...or just a 'minimal' waste of time ;-) I'll never use this sail as I have several newer others, so this one can be ripped apart and made a lab experiment.
If others would like to "wonder out loud" as well, that would be appreciated. I have no idea what I'm doing in sail design, but I can rip seams, add draft, add fabric and actually think that I'd do it neatly too....since I can sew pretty decent. The peanut gallery needs to start hollering so I can determine a direction....or do I just go sailing on my other fishes ;-)
btw...I DO like to experiment with stuff like this and work on boats, as much as I like getting out on the water...so...that's to be considered.
Lastly....a draft with less belly (than the newer design), adding more sail area...especially up higher.... that might be best?....oh...and I have NO idea who made this sail, as there are no markings or indications on it anywhere. It IS cleanly stitched and doesn't look "home made".
 

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battens are a given with the roach. I didn't lay the rope out very good either....too rounded...especially compared to the sails in the hi-tech thread. Why the float....or am I hearing sarcasm?
 
'scuze my "rapid fire photoshop". This is more in line with what I'm thinking. The dashes are the outline of the sail now, and of course the red lines simulate approx. batten placement.
 

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There are two issues with what you are showing. 1) You will move the center of effort way back with this plan. You gooseneck will need to be waaaaay back to ccompensate. I don’t think you will be able to get under the boom as the boom needs to angle up to be able to get under.

2). The sail is getting more square in shape. For better performance it should get taller and have a shorter chord length as those transparent sales have. Instead it is staying the same height and getting squatter.
 
Yeah....i see that now. I don't believe they changed spar lengths....except the foot was 18" shorter...and some decided to then cut the excess off the boom. So...how do you get the rig higher without moving the center of balance aft? Probably need to cut the luff (more towards the bottom and less at the top) so the upper spar can angle more vertical.
Im wondering if there is a way to get perimeter dimensions and I'll deal with the broadseaming somehow and guesstimate in creating some draft. Maybe I'll call the Furrar sail loft and see how "helpful" they might get. Dang...Id pay for dimensions or templates of the panels.
 
OK..not quite lined up.. BUT...move the whole rig forward as shown (and make sure the mast can still tie on to the upper spar).. then cut/add cloth to fill out the turquoise lines for the new shape??
 

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Odegaard’s original post mentions the designer moving the center of effort forward. Odegaard’s post on the Sunfish Listserv says the next version is taking 14 more inches off the foot. So it’s hard to say exactly what they are doing and the pics help but don’t give the whole story.
 
Right... I read that and tried to use the pictures as best I could to figure out what they did. The above last pic...you can see I moved the whole rig forward (watch that you can still attach the upper spar to the mast)...Then trimmed off the luff..more at the bottom and added to the roach. Hopefully keeping things halfway balanced, but higher aspect....also thinking a flatter sail might be better for that too, since the sail now extends up higher to limit the healing aspect. Probably all for nothing... but the picture of the hi-tech sails look nice and they allude the boat DOES sail better, specifically pointing.
 
Mixmkr already knows about a lot of this but to expand the discussion for others...

A sail on a boat is very similar to a wing on an airplane, sailplane or hang glider. It's just positioned at a 90 degree angle to that of a wing on an aircraft. The trick when trying to increase performance is to be able to create as much lift as possible while at the same time minimizing drag.

The easiest way to do this is by increasing the aspect ratio of your wing or sail. That is, in the case of a sail, making the sail taller while at the same time making the foot shorter. A common way of doing this is to add more chord (distance from the luff to the leech) near the top of the sail while taking that same amount of sail square footage away from the foot area.

The picture below is of an Intensity Sails Power Head sail. You can see that they have added sail to the top where the luff and leach on the Standard sail used to just meet as a point at the tip of the mast.

They have added this extra foil area up top by having a very stiff transverse batten that supports this extra "roach" area. Another plus to having this type of square shape at the top of the sail rather than a point is the square shape creates less drag for a given size than a point. In other words, a significant portion of the total drag of a wing comes from the vortices that exit the wing tip.

If I were to try to increase the performance and power of a Sunfish sail, this is where I would add sail area while taking it away from areas that are the most aft of the center of effort (COE) of the sail.

This keeps the position of the center of effort close to the center of lateral resistance (the daggerboard's lift, COLR) and keeps weather or leeward helm from resulting when the COE and the COLR are moved further apart. You then just use outhaul, cunningham and vang forces to fin tune the position of the COE.

Just like how you would use the vang and cunningham to bend the upper section of the Laser mast to flatten the foil up top on the Power Head sail in the picture and allow the leech to twist open and remove the power from the top of the sail when the wind increases.

That is the approach I would use if I were to start playing around with a Sunfish sail. I think adding a lot of roach material to the middle red batten area in your creative photo might move the COE back, particularly with soft cloth that can be hard to hold the COE in one place.

Relating to that, using thick, stiff sail cloth that doesn't stretch would be my material of choice. Also, in the time it took me to write this, you posted some more points that I covered in my post so you're on the right track. By all means, do continue with your tinkering! Would love to see the results. :)

- Andy

intensity-sails-power-head-sail-for-the-laser-1.gif
 
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Or... if Mixmkr could do this, it would look pretty cool.

One of the most aerodynamically clean (ie, low drag) wing tip configurations out there can be seen in the photo below. It's the wing tip of the hang glider I fly.

vq-race-wing-tip.jpg


Where the end of the wing goes from straight to starting to curve is where a carbon fiber tapering wand is plugged into the outer section of the leading edge of the glider and then bends under load as you tension the wing. You can see how the very tip of this stiff wand supports the "leech" of the wing near the tip... much like the transverse batten on the Intensity Power Head sail.

So, one could mount a fiberglass wand to the tip of upper boom of the Sunfish and attach upper most end of the leech on the Frankenstein Sail and there you go. It would look wicked. By the way, they used to have this exact set up on windsurfing sails... with a fiberglass wand coming out of the top of the mast.

- Andy
 
Would I attach the batten actually to the upper spar? Have you seen a "flicker"? A batten coming off a masthead, horizontal pointing backwards...to hold an adjustable backstay off a large roach mainsail. It then "bends" in line with the backstay, when the stay is tensioned. I'd think a super stiff upper batten, angled upwards would be the only feasable way.
 

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I agree. Having an upper batten like in the last photo of the Australian 18 Footer "Gotta Love It 7" would be the best bet.

- Andy
 
Hobie's latest trimaran runs an angled batten from the tack to the furthest part of their loosefooted mainsail. (Furtherest-most-distant part).
 
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