Mainsail reef points

[B00B00]

We would normally spec reef points based on a % of luff length rather than area. For offshore its normal to be somewhere like 15%, 30% then 50% up from the tack.
We like to keep the 1st reef just above the hounds on a fractional rig and on bigger boats with light weight rigs the other reefs are by spreaders rather than in the middle of panels. This is inportant on squaretoip mains especially although thats pretty irelevant for this case.

[StuM]

Originally Posted by B00B00

We would normally spec reef points based on a % of luff length rather than area. For offshore its normal to be somewhere like 15%, 30% then 50% up from the tack.
We like to keep the 1st reef just above the hounds on a fractional rig and on bigger boats with light weight rigs the other reefs are by spreaders rather than in the middle of panels. This is inportant on squaretoip mains especially although thats pretty irelevant for this case.

Your 15, 30 and 50% up from the tack works out reasonably close to the OPs 75,55,33% desired areas.

75% area = 86.6% of height (13,4% from tack)
55% area = 74.2% of height (25.8% from tack)
33% of area = 57.5% of height (42.5% from tack)

and by either metric, the first reef would be about 6-7ft above the tack, a lot more than the OP's measured 3.5ft. At that measured height he is only about 7% above the tack and he has about 86% of his full sail area.

To the OP: that goes well outside the parameters of "a compromise between the desired exact percentages and the best load distribution"

[wiekeith]

Carlos
Have you asked the sailmaker why he deviated from your agreed dimensions?

Doing so would probably identify whether it was a misunderstanding, incompetence or reasonable logic, based on experience, on his part.

[Carlos The Dog]

Originally Posted by wiekeith

Carlos
Have you asked the sailmaker why he deviated from your agreed dimensions?

Doing so would probably identify whether it was a misunderstanding, incompetence or reasonable logic, based on experience, on his part.

No. Why the difference is not understood. I first thought the incorrect sails were shipped. The stated luff on the main and Genoa are a good 5" shorter than agreed and the Genoa is a standard cut foot. I asked for a Yankee cut and on the sails bag shipped it states Yankee cut, but it is not.

I am more concerned as to the sailmaker shipping me the sails I bought rather than how or why I got something else.

[Carlos The Dog]

I am attaching an image from my sailmaker. Can anyone make anything of it? This is my first attempt at attaching an image. If it does not upload properly I apologize.

If the drawing is to scale then it confirms my calculations. Area calculations of drawing made from measurements (using a ruler): I get 86%, 63%, 38%. 38% is closer. The accuracy of measurements taken from a small drawing I admit are not great. Still it shows there remains a large discrepancy.

[wiekeith]

Originally Posted by Carlos The Dog

I am attaching an image from my sailmaker. Can anyone make anything of it? This is my first attempt at attaching an image. If it does not upload properly I apologize.

If the drawing is to scale then it confirms my calculations. Area calculations of drawing made from measurements (using a ruler): I get 86%, 63%, 38%. 38% is closer. The accuracy of measurements taken from a small drawing I admit are not great. Still it shows there remains a large discrepancy.

It looks like the sailmaker's starting point, 100% area, is 37.65 (I'm assuming that's square yards), whereas your specified area is 38.55, if my calculations are correct. So there's a 0.9 square yard difference to start with, which could account for the shorter luff and foot you're seeing.

[Carlos The Dog]

Hi Wiekeith;

My apology. Square meters.

[barnakiel]

Can you possibly look at your initial post, where: " ... P=48.2, E=14.4 ... " and relate these to the dimensions given in the image?

I can be doing something wrong, but I cannot see the dimensions in the drawing.(?)

P=48.2 = 14,69 m
E=14.4 = 4,39 m

???

If, so then flat area 32,24 m2 not 37,65 m2.

BTW As already mentioned, the sailmaker is not free to place the reefpoints. They must allow for batten layout, panel layout, etc. Some deviation from the order is a rule. Normally about +-5%.

But I cannot match your initial post with the image somehow. Maybe just a bad day here though.

THX,
b.

[barnakiel]

Another tip: how a sail is built, the guy on the floor could have simply misunderstood the marks on the panels and placed your reefpoints WRONGLY. Then their QC simply did not spot the difference and that's that.

They seem not to have any QC at all since you say the sails are like 2'' too short.

b.

[wiekeith]

Originally Posted by barnakiel

Can you possibly look at your initial post, where: " ... P=48.2, E=14.4 ... " and relate these to the dimensions given in the image?

I can be doing something wrong, but I cannot see the dimensions in the drawing.(?)

P=48.2 = 14,69 m
E=14.4 = 4,39 m

???

If, so then flat area 32,24 m2 not 37,65 m2.

BTW As already mentioned, the sailmaker is not free to place the reefpoints. They must allow for batten layout, panel layout, etc. Some deviation from the order is a rule. Normally about +-5%.

But I cannot match your initial post with the image somehow. Maybe just a bad day here though.

THX,
b.

I agree with that. So the sailmaker's drawing indicates that 100% area is actually greater than the area specified by the OP by 5.4m2.

So the sail delivered, if made to that drawing, would be larger, not smaller!

Maybe I'm having a bad day too Barnakeil

[wiekeith]

Originally Posted by Carlos The Dog

... I asked for 75, 55, 33% and I was told that is what I got. But upon inspection it is more like 88, 69, 46%. The reefs are about 3' different each. For the first reef I expected around 6'5" up from the boom I got 3' 5" same difference for the rest...

Now here's a crazy thought. The sailmaker drew the plan you've shown, with the appropriate 75%, 55%, 33% reefing points. Realises he's got the dimensions (P & I), and hence the area, too large, so takes 5.4 m2 off, from the base of the sail plan to correct for this, which reduces the P of his original plan by about 3'.

However, when somebody comes to fitting the reefing points they take the measurements from the head of the sail down, as on the original sailmaker's plan.

This would explain the 3' or so lower that all the reefing points are, and (I've not done the calculations) would give effective reefing areas of 88%, 69% and 46%, perhaps?

[Carlos The Dog]

Originally Posted by barnakiel

Can you possibly look at your initial post, where: " ... P=48.2, E=14.4 ... " and relate these to the dimensions given in the image?

I can be doing something wrong, but I cannot see the dimensions in the drawing.(?)

P=48.2 = 14,69 m
E=14.4 = 4,39 m

???

If, so then flat area 32,24 m2 not 37,65 m2.

BTW As already mentioned, the sailmaker is not free to place the reefpoints. They must allow for batten layout, panel layout, etc. Some deviation from the order is a rule. Normally about +-5%.

But I cannot match your initial post with the image somehow. Maybe just a bad day here though.

THX,
b.

You have P and E correct. and yes the "flat" area is 32,24 m2. I am assuming the 37,65 m2 on the drawing takes the camber, roach, curve of luff, etc. into account. So if you take PxE and divide by a factor of 1.71 instead of 2, out pops 37,65 m2.

[barnakiel]

Originally Posted by Carlos The Dog

You have P and E correct. and yes the "flat" area is 32,24 m2. I am assuming the 37,65 m2 on the drawing takes the camber, roach, curve of luff, etc. into account. So if you take PxE and divide by a factor of 1.71 instead of 2, out pops 37,65 m2.

You may be mixing up cloth area and mold area. You sure there is 5.4 m2 extra mold area in a 32.2 m2 main ???

I will look up our gennaker ratios to see it this holds water.

And if you look at the image you attached, the P and E are nowhere to be seen. Different values are give.

Yes/No/Anything in between?

I'll be back ;-)
b.

[barnakiel]

OK.

I have looked up our main and the extra 20% of area (roach about 10%, camber ads another 10%, etc.) IS fine.

Back to your image, some values given there are: 13.65 cm, 4.07 cm, etc. Nothing matches the actual sail dimensions and the scale is not 1:100 either (as could be assumed to simplify the calculations, when done mentally).

Let us know when you hear back from the sailmaker.

I think as long as the required reefed SA is withing some 5% of your request, the job is done fine.

Now what? Are you taking the sails back to the loft?

b.

[wiekeith]

Originally Posted by barnakiel

Back to your image, some values given there are: 13.65 cm, 4.07 cm, etc. Nothing matches the actual sail dimensions and the scale is not 1:100 either (as could be assumed to simplify the calculations, when done mentally).

Not sure if this helps, but the ratio 13.65:4.07 is 1:0.3 (which is the same ratio as the OP's P:E)

With this ratio, and an area of 37.65 m2, it gives a P of 52'.

Edit - the above assumes a triangle, of course.