Mainsail reef points

[Carlos The Dog]

Hi All;

Been lurking around this forum for quite some time and finally decided to join.

I could usually find the information I want and really had no reason to post. Now I think I have one.

I bought this mainsail and I'm told that the reef points are what I asked for. I have calculated the reef points by hand but my calculations vary considerably from where the reefs are placed. What I'd really like is an independent person with access to a sail design program and calculate where the reef points are to be placed based on reef percentages. Then I can compare them to what I have.

P=48.2, E=14.4
R1 75%
R2 55%
R3 33%

This is a cruising mainsail with modest roach, camber and some bag in foot.

My hand calcs do not take roach, camber, etc. into account. But I think most (not all) of that factors out in determining reef points anyway.

[JPA Cate]

Hi, there, Carlos the Dog, and welcome aboard CF.

If you would fill in the information a little more, on your avatar, so we can tell generally what area you sail in and tell us the size of your boat, it will help us make our answers fit you, personally.

The reason is that the number and spacing of reef points depends on the kinds of sailing breezes predominate in your area. Your intended usage of the boat lets us know more about your personal needs/wishes.

For instance, the first reef in our mainsail is deep enough so that the mainsail clears the running backstays. This makes it possible to drive it without tacking the running backs with each tack, just set both of them, and forget. The third reef gets it down to about 1/4 its unreefed size, and the second reef splits the difference. Suits our use and wishes.

Thanks.

[GordMay]

Greetings and welcome aboard the CF, Carlos.

[UNCIVILIZED]

Without knowing what boat it is, it's impossible to offer specific advice, but... in addition to what Ann said, there are some other key factors to consider.

~ How well your boat shifts gears, & what sail combinations it needs in order to best do so.
As with some boats having 3 reefs is inefficient, in that each one by itself doesn’t reduce the sail plan by enough to keep the boat on her feet at the next (higher) wind strength. This is something that some boat designs are notorious for, & wizened sailmakers know which ones, & recommend the number & size of the reefs accordingly.
~ How much drive your boat gets from the main vs. headsails
~ How much weather helm each sail, or reef, imparts, or removes. So as to make her easy to steer while still making progress; both upwind, & down, in various conditions.
~ Location of the various hardware on the main, especially mast cars & battens is a big player. Since you want the reef at the tack particularly, to be well attached to the mast, so as to resist being pulled off of the spar by the loads from the clew reef. And your battens need to be well positioned to assist with sail shape, both when reefed, & not.

You also need to be aware of where on the mast the head of the sail is with each reef. As the main tends to try & pull the mast aft, & invert it at the headboard in high winds. Plus it’s best to have your heavier weather reefs setup so that the head of the main lies at the junction of a set of spreaders/shrouds. So that the mast doesn’t get pulled into a sideways S-shape, thus risking it’s failing.

And of course the position of the; Runners, Staysail stay, & Babystay, also need to be matched up in terms of position with where each reef point puts the headboard on the spar.

[Carlos The Dog]

Hi All;

Thanks for the replies.
From the replies it is clear I did not communicate what my intentions are, I'm sorry for that. I am not asking if the stated reef points are optimal for my boat. What I am asking for is help in determining if what I got is what I asked for.

What the vendor tells me is they plug the reef % into a computer and it determines where the machine? is to place the cringles. I don't think anyone actually knows where they go until after the fact.

The problem is when I first looked at the new sail the placement of the reefs looked woefully short. And my hand calcs show this by 10% to 15% difference. I doubt my ignoring the camber, roach, etc makes my calcs off by this much. But I can be wrong (actually I hope I am.)

[UNCIVILIZED]

Unless you have a square head main. or one with extreme roach, then calculating things pretty much based on the formula for the area of a triangle works.

[Carlos The Dog]

Uncivilized;

Thanks Uncivilized.

I asked for a moderate roach, camber, foot, etc. This sail is for offshore passages and I did not want a racing sail. So I assume trig calcs would put me in the ballpark. Anyway, If the roach and camber nearly extend from the head to foot then they would factor out of the calcs for the most part.

[wiekeith]

Originally Posted by Carlos The Dog

Hi All;

Been lurking around this forum for quite some time and finally decided to join.

I could usually find the information I want and really had no reason to post. Now I think I have one.

I bought this mainsail and I'm told that the reef points are what I asked for. I have calculated the reef points by hand but my calculations vary considerably from where the reefs are placed. What I'd really like is an independent person with access to a sail design program and calculate where the reef points are to be placed based on reef percentages. Then I can compare them to what I have.

P=48.2, E=14.4
R1 75%
R2 55%
R3 33%

This is a cruising mainsail with modest roach, camber and some bag in foot.

My hand calcs do not take roach, camber, etc. into account. But I think most (not all) of that factors out in determining reef points anyway.

I don't have a program for calculating this, but some scribbles and a calculator gave me the following results for P:

R1 75% P=41.6
R2 55% P=35.7
R3 33% P=27.6

I can give these results absolutely no guarantee - please free to ignore

[Carlos The Dog]

Thanks Wiekeith. That is close to what I got, except for the 1st reef I have P1= 26.4'

[wiekeith]

Originally Posted by Carlos The Dog

Thanks Wiekeith. That is close to what I got, except for the 1st reef I have P1= 26.4'

Well mine was a quick calculation on my part

Interestingly, feeding 26.4 into my calculations actually gives 30%. I was working to 33%.

How far out from your calculations were the actual dimensions of the sail?

Edit: When I say dimensions I mean P dimensions for reefing points.

[StuM]

Uncivilized made some good points - it's not good to place the reef points on a main "willy-nilly" based on just percentages, there are other more important consideration.

It's likely that the sailmaker placed the reefing cringles at locations which are a compromise between the desired exact percentages and the best load distribution based on the number and location of battens and mast cars for the full sail.

[Bleemus]

Originally Posted by StuM

Uncivilized made some good points - it's not good to place the reef points on a main "willy-nilly" based on just percentages, there are other more important consideration.

It's likely that the sailmaker placed the reefing cringles at locations which are a compromise between the desired exact percentages and the best load distribution based on the number and location of battens and mast cars for the full sail.

What he said. As a former sailmaker there is more to it than just percentages.

[Jim Cate]

Further, worrying about a few percentage points difference in reefed sail area is a waste of worry time! You'll never be able to tell the difference in performance... just not that critical in the real world.

Jim

[Carlos The Dog]

To get around the batten cars and such, a few percentage points I would not worry about, the sailmaker and I agreed on this. However, it is not a few percentage points. 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.

That is why I'd like to find a sail maker that can give me reef points locations based on a similar design. Or if one of you have had a similar sail made you can give me the reef locations.

Thanks all for your comments.

[UNCIVILIZED]

As stated, we can't give you good reef locations without knowing a lot more information. Much of which that's already been asked about, but is still unanswered.
How many spreaders, how far apart?
Deck or keel stepped?
Fore & Aft Lowers, or Babystay? Babystay height?
Runners, or Runners & Checks?
Swept spreaders or No, & if so, what angle?
B&R rig?
Bendy rig with lots of controls, or tree trunk?
Cutter or Solent Stay? Attachment point height for same?
Number of battens, locations, hardware type & location on the sail?
Jib: Hanks or Furler?
Jib sizes?
Staysail sizes?
Keel & Rudder configuration? Including CLR?
Height & location of CE? Including with various sail combinations?
LOA, LWL, Beam, Displacement?
SADR?
Predominant wind conditions? Upwind downwind, both?
High windage or low? Including arch, davits, bimini, panels, dinghy...?
Heavily loaded, or light?
Sailing plans?
Sailing Style?
Crew number, & levels of experience?

I could keep going, but all of the above & a lot more play into this. And without such information, our guesses are just that, guesses. So as you may have figure out, sail design & making is about a lot more than cutting out some panels, & sewing a few miles of straight lines. And it's also why rigging shops & sail lofts tend to be located next to one another.