Mast bend & Sail match…….again…..

[Finn]

I’m looking to buy a 2nd hand sail & wonder if I’m trying to match both the fore/aft & side/Side numbers or just the F/A will suffice?

My mast numbers are (allegedly):

F/A
0
62
83
63
0
Tip 443

S/S
0
60
90
86
0
Tip 355

Also, whats the general consensus on changing mast bend? A spot of sanding?
Looking at the 85kg(ish) recommended numbers on the spreadsheet I have, this mast is stiff F/A & soft S/S for me.
Ideally I’d like it to be a bit softer F/A to allow for more mast bend for less leach tension.

[GBR1501]

the for and aft are quite modern numbers… the side is soft… ive got a couple of second hand sails that will fit the for and aft numbers… email me if you are interested…ive got them on the for sale board..

[Finn]

Giving this a bit more thought… I guess the mast is bent sideways to one degree or another most of the time and the luff curve is a combination of both the F/A & S/S numbers.

When I use a sail that is cut for a needlespar bluetop (F/A 0/79/117/99/0 tip- 555, S/S 0/73/135/123, tip- 565, acording to the numbers I have) on the Ceilodh (sp?) the head doesn’t twist off and depower in any where near the fashion that the sail that is cut for the mast. I guess that, at the given wind speed the sail is expecting the mast head to be 200mm further to leeward, but could of course be due to a myriad of other factors that have never occured to me….. :?

so….if the sail in question is cut for a mast that is stiffer S/S then the head will open up earlier on the this mast assuming the F/A numbers match.

So, I wonder how much windspeed 10kg at the mast head roughly translates to……?

[davecooper]

I wonder how much windspeed 10kg at the mast head roughly translates to……?

Pretty much any windspeed beyond the point where you are fully hiked, I think. Assuming you’re sailing your boat upright (like we all are, natch!) the side force on the mast has to equal the righting effect of you sitting out.

Dave

[Finn]

@davecooper wrote:

I wonder how much windspeed 10kg at the mast head roughly translates to……?

Pretty much any windspeed beyond the point where you are fully hiked, I think. Assuming you’re sailing your boat upright (like we all are, natch!) the side force on the mast has to equal the righting effect of you sitting out.

Dave

Ahhh, interesting point. Assuming that the sailor can provide enough moment to do so.

I figured that the F/A bend would also be effected by aerodynamic drag at high wind speeds. More so than the S/S bend which as Dave points out is limited to the righting moment produced by the sailor. The F/A bend could be greater as the stern is being pushed down reather than the boat being tipped over sideways.

I’m sure this discusdion has some practical application. …. :roll:

[davecooper]

Holy Gramoly, Finn! No, your rig is pulling the boat forward (I hope!) not pushing it backward, so it’ll be depressing the bow, not the stern.
For the same reason, it’s certain that the fore and aft bend is all accounted for by the mainsheet tension. Even in the most dramatic gusts, I don’t think you’ll see the sheet go slack as you sail up the beat!

Dave

[Finn]

Sailing to windward in 30 knots the top 1/2 of my sail is flapping, only creating drag. I too would hope that this drag is more than offset by the forward drive in the lower part of the rig. In lesser breezes, I’d agree the mast bend is largely down to mainsheet & kicker. In the gusts something is going on that causes the leach to soften & open(cunningham) while the mainsheet is pulling the boom toward the centerline of the boat rather than down, keeping the sheet loaded.

So, do sailmakers adjust luff curve for S/S bend or just F/A, I wonder.

[davecooper]

Sailing to windward in 30 knots the top 1/2 of my sail is flapping

You wuss! Try hiking a bit

In the gusts something is going on….

Yup, I start swimming!

Dave

[leech]

Finn, have you checked your rake lately? Your mast might be too upright. I’ve played around a bit with mine lately and it does make quite a difference.

[Finn]

Lee, I agree, the mast on the boat is a tad upright ATM, which is an attempt to combat balance issues due to luff shape……In order to flatten the luff shape of the sail (so the boat will point nicely) I need to bend the mast quite a bit, which can only really be done via leach tension (mainsheet or kicker). This also pushes the draft aft in the sail, which along with the hard leach, results in more weather helm, hence the mast is set a little upright. The luff looks nice, but the leach doesn’t flow. In certain conditions it works really well, but most of the time the leach is too tight.

So, in a nutshell, I’m trying to get the sail to do something it doesn’t really want to do.

Options are:
1: Make the mast softer F/A (not really plausable)
2: Point lower
3: Get the luff curve of the sail re-cut (a more realistic option)

The appropriate course of action is to have the luff re-cut, then rake the mast back a bit, but in the mean time i’ll just ease the mainsheet a tad point a bit lower.

[Finn]

@Finn wrote:

So, do sailmakers adjust luff curve for S/S bend or just F/A, I wonder.

I’ve managed to speak to a sailmaker who tells me that while the software can design for S/S bend, it is largley disregarded because the S/S is constantly changing.

[Author]

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