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11-10-2024, 06:40
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#1
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Moderator
Join Date: May 2014
Boat: Shuttleworth Advantage
Posts: 2,700
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Reefing line load
Just curious what reef lines would take the most load. The first reef or the third reef.
Obviously the wind acting on the third reef will be stronger but the area is much smaller.
A lot depends on the given wind strengths relating to when you reef.
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11-10-2024, 07:31
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#2
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 6,936
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Re: Reefing line load
Interesting question.
Ultimately the load on the reef line will be determined by the wind load on the sail.
As an example, the first reef may be taken in, when the wind is at, say 25 knots. Being as that the mainsail gets reefed from the bottom up (assuming a non in-mast furling system), the larger square footage of the mainsail of the lower portion of the main gets taken in first.
As the wind pipes up, the second reef may be taken in, at say 30 knots. Though the sail area is now smaller, the wind load will be higher, remembering that the wind pressure goes up as the square of wind velocity, it, in other words, the wind pressure at 30 knots likely being double that at 25 knots. So, although the sail area is now smaller, the wind pressure is much higher.
I'd have to take pen to paper to figure this one out, as the mainsail also gets dropped during this process, which is also a factor to be considered.
Without doing some math, could not put a precise number on this, but going from actual at sea experience, I'd be inclined to think the second reef is the higher load.
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11-10-2024, 07:35
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#3
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Registered User
Join Date: Sep 2019
Posts: 557
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Re: Reefing line load
Doing some guessing...
I would assume wind pressure is highest at 90 deg (beam reach)
Here is a table showing some wind pressure values: windforce
If you know or can guestimate the area of sail at each reef point you could estimate the force on the sail.
Then you could assume that the reefing line geometry was similar in the way sail pressure was related to line tension.
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11-10-2024, 09:25
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#4
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 6,936
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Re: Reefing line load
If you assume a main is 500 SF in area, and the first reef takes in 15%, that leaves you with 425 SF. Using the figures above, 2.5 lb/SF at 25 knots = 1063 lbs.
The second reef takes in another 15%, so now you have 350SF, and with wind at 30 knots, that is 350 x 3.6 lb/SF = 1,260 lbs, an increase of about 18% over the first load.
Just something to chew on.
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11-10-2024, 09:39
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#5
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,804
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Re: Reefing line load
In my mind, the last reef is likely to see the highest load. As you lower the center of effort by reefing the sail, the amount of load on the sail that can be tolerated without the boat becoming overpowered should increase. So it's entirely possible the last reef will need to handle load right up to the point of the sail coming apart.
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11-10-2024, 10:06
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#6
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Registered User
Join Date: Aug 2006
Location: Skagit City, WA
Posts: 25,731
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Re: Reefing line load
For a rough idea just find the wind force for the wind speed at which you go to each reef point and maybe for the maximum wind speed you would leave the sail at that reef point. Determine the Sq Ft of each reef point. Make yourself a table.
Reef 3 example:
Reef at 40 knots,
Maximum usage of Reef 3 = 60 knots
SQ FT of sail at reef 3, = say 100 sq ft
Wind Force at 40 knots = 5.2# per sq ft
Wind force at 60 knots = 25.6# per sq ft
Tension on each Reef line ~ = 1/2 of wind force
at 40 knots the force is 520 lb, line tension at 50% is maybe 260 lb
at 60 knots the force is 2560 lb, line tension at 50% is maybe 1280 lb
Figure a safety factor of 3 for line sizing. Even a 3/8" dacron line is good for about 4050#
Not to worry.
__________________
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11-10-2024, 10:19
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#7
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Writing Full-Time Since 2014
Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 10,045
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Re: Reefing line load
Interesting way to calculate, but ultimately, I think we make too many assumptions and are thus incorrect.
I'm going from a multihull point of view. Might be different, because we reef to gusts not sustained wind.
---
Let's assume we are comparing right at the reefing point, which means lifting a hull. The heeling force is equal. In fact, this is not true; in strong conditions considerable heeling force comes from windage on the hull, cabin, tramps, mast and rigging, and from the action of waves (the boat is on a slope, and then flies off the top of a slope). Then let's assume the center of force is lower. Thus, the tension required to keep the same shape in the sail when the sail is smaller (lower) at the same force is proportionally lower. But the pressure required to generate the same heeling force is higher. Both of these are linear with the size of the sail, so the end result is not much different. The key factor, IME, is that we are getting heeling from waves and constant windage factors, so that the sail is contributing a lesser portion of the heeling force when reefed. Thus, the sheet load when reefed is somewhat less. This squares with my experience; I grunt the hardest on the tackle and winches when beating with full sail right at the reefing limit. At the same limit with a reef in the sheeting loads (jib and main) are less. Not a lot less, but less. Even less with the 2nd reef. Not a lot, but less.
But this is NOT the whole story. Nearly every story I know of tearing a sail or damaging the traveler is during a rough jibe, and those are more likely in rough conditions, when the boat yaws when you didn't expect it. The sheeting loads are less off the wind, but the jibe forces can be considerably greater than windward sheeting forces. I've put instruments on this. Normal jibes are typically less, but a rough jibe can be many times greater.
---
Bottom line: I think there is a reason the are all the same. There's not much difference, on the average. There is also not much point in having lines stronger than the traveler. Would you rather break the ...
The reef line is cheaper and much easier to fix on the fly. I think most often it is an old sail that splits first.
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11-10-2024, 11:04
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#8
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 6,936
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Re: Reefing line load
For the 35 odd years that I've been afloat, my reef lines have always been 3/8" and never had a lick of problem with that size.
You could probably use a thinner line, but I prefer the 3/8" from simply a handling point of view.
To clarify, that is the line size led to the reef clew. Once the sail is down, I have a several buntlines to wrap the sail to the boom, which are 1/4".
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11-10-2024, 11:11
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#9
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,792
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Re: Reefing line load
Depends on how strong the wind is.
Assuming you 'reef to conditions' the 3rd reef will become the one most loaded - just because a boat driven in higher wind will also have to overcome higher waves. And a boat driven in such (sea state) conditions needs an additional oomph of energy to get going. So the forces that could otherwise (in flat water) be proportional, will now be disproportional. And there will be more variation in cyclical loading too.
Now if you are not 'reefing to conditions' then you probably should.
b.
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11-10-2024, 13:00
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#10
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Writing Full-Time Since 2014
Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 10,045
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Re: Reefing line load
Quote:
Originally Posted by barnakiel
Depends on how strong the wind is.
Assuming you 'reef to conditions' the 3rd reef will become the one most loaded - just because a boat driven in higher wind will also have to overcome higher waves. And a boat driven in such (sea state) conditions needs an additional oomph of energy to get going. So the forces that could otherwise (in flat water) be proportional, will now be disproportional. And there will be more variation in cyclical loading too.
Now if you are not 'reefing to conditions' then you probably should.
b.
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If you reef to conditions, then the load on the sails at the reefing point is always the maximum heeling force which the hull form and keel can produce. This can only be less in strong conditions, with windage and waves knocking the boat over. Yes, you would like more power, but the the maximum upwind power cannot be increased. It can only decrease once the reefing point is reached.
Of the wind is a different subject. Must boats can carry more sail dead down wind well past the point of instability. That's always a good way to break stuff.
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11-10-2024, 13:19
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#11
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Registered User
Join Date: Mar 2007
Location: Santa Cruz
Boat: SAnta Cruz 27
Posts: 7,055
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Re: Reefing line load
From a different viewpoint. I have generally used 1/2 in dacron reefing lines, and have broken several first reef lines. I have never broken a 2cnd reef line. In boats with 3rd reef points, I usually don't use the third reef because the line is too long and heavy to leave in, so I just drop the mainsail entirely.
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11-10-2024, 15:12
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#12
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Moderator
Join Date: Nov 2011
Location: aboard, in Tasmania, Australia
Boat: Sayer 46' Solent rig sloop
Posts: 29,579
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Re: Reefing line load
Our boat is Solent rigged, so the interplaying with the wind may be very different. The main is partially battened, and ~560 sq. ft. Short tacking on the wind is difficult, requiring rolling up the whole sail, because the slot is so narrow. Normally, we use reef #1 between 20 and 25. Then we go to the staysail with the genoa rolled up. By 30, we want to use the #2 reef, and depending on our heading (into or off the wind), might go down to the 3rd reef by 40. We can roll up the stays'l partway, or sail on it alone, or just use the 3rd reef by itself if loafing along at 45. The wind strengths and heel angles determine the load on the reef lines, I think, with bigger seas and cross seas and I hear what Don said about the weight of that length of 10 mm spectra we use for our reef lines. It is a big bundle in the cockpit. But, very pleased to have the use of the 3rd reef. However, I don't do deliveries, like he does, and his decision makes a lot of sense, too.
Ann
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11-10-2024, 16:42
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#13
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Registered User
Join Date: Aug 2021
Location: PNW
Boat: 35 Ft. cutter, custom
Posts: 2,713
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Re: Reefing line load
The load on those lines primarily comes from two sources.
1, the initial tension, (even with no wind).
2, wind pressure.
The wind pressure is not linear with wind speed, it increases as the square of the velocity of the wind.
The total load on the clew is also affected by how close and how tight the foot of the sail is constrained, and at what angle the clew line intersects the sail relative to the closest line that secures the foot.
The ability of a boat to "stand up to its sail" is also a factor, as well as how deep each reef goes.
As a result, without actually incorporating strain gages on the three lines, (halyard, tack, clew,) all is speculation, and all is variable among individual boats.
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11-10-2024, 16:54
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#14
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Registered User
Join Date: Aug 2009
Location: Lake Macquarie NSW
Boat: Chamberlin 11.6 catamaran
Posts: 971
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Re: Reefing line load
I think it is pretty easy to work out the loads - just work out the loads in the opposing system - the mainsheet.
I reckon, roughly, that there will be little difference. If there was then there would be significant differences in the system resisting the wind pressure - the main sheet.
Although the mainsheet has more leverage (shorter foot - same length boom) on the third reef but the amount of difference is little if the sheet load is similar.
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11-10-2024, 17:16
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#15
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Registered User
Join Date: Aug 2021
Location: PNW
Boat: 35 Ft. cutter, custom
Posts: 2,713
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Re: Reefing line load
^ in the grand scheme of things, with the more-or-less-instantaneous changes in loading from wind, wave, angle of attack and roll, pitch, yaw, sway, surge, heave, any figures obtained would be bouncing around like a BB in a boxcar over a section of rough track.
In the end, the question in this thread is an exercise of "Majoring in minors".
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