Matagi

Should we rethink reefing points?

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I was fiddling around with my amateurish thoughts on designing a small catboat, a bit like the Marblehead 22, but more speed-oriented, maybe even for events like the Silverrudder etc.

When I was thinking about the sail plan, it occured to me that most sail plans show the reefing lines in the same distance to one another. This, plus the triangular shape of the main sail means that the more the wind pressure mounts, the less sail you reef, percentagewise. Add to that the fact that pressure mounts exponentially with windspeed (doubling from 15kts of wind to 30kts means roughly 5x the pressure, give or take, depending on density).

So my question is: should we not extend the distances between reef points exponentially, especially with more triangular shapes of the main sail?

To illustrate: equidistant reefing points:

SY48-Sail-Plan-1-1400x788.jpg

My idea:

catboat.png

PS: all furling main sails are satanic and must be burned :) 

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I haven't done the math (still need my second cup of coffee), but I'm pretty sure that you already reef a larger percentage of the sail as you go up.  Imagine equidistant reefing points all the way to the head (you'd never actually do this of course, you'd switch to a stronger storm sail, but for illustration).  The last one would remove half of the remaining sail area, where the first one would remove a much smaller percentage.

 

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Thanks, I think this is were my logic got twisted. I also had my second coffee now, so I can see what you mean. First reef removes ca.1/6, second 1/5, third 1/4 of the respective remaining sail area.

I was focused on the percentage of the removed sail area with regard to the overall sail area. This gets indeed smaller which each reef, but it is -at the respective point in time- a moot point, as only the remaining s.a. needs to be considered. Right?

So the correct way would be to plot the increase in wind pressure to the results of the equation: how much s.a. do you remove with each reef with respect to the remaining s.a. and at a later stage also account for changes in height of CE.

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What Corryvreckan said Plus the fact that there is more wind the higher away from the water you go, so each reef is getting into less pressure. 

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I would further add that as the sail is lowered, the lift provided by the sail (centre of force?) is also lowered resulting in less healing moment.  

Also, the sail gets 'flatter' (less chord) the higher you go.  Again, less lift from the top part of the sail for similar areas.  

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However there is a difference in rate of change of area for a triangular sail .v. a square head one as you have drawn. Can't do the maths, but the triangle area shrinks more than linearly with each reef, but only linearly if the square head gives you a sail close to an rectangle. So for your design, your thought process seems good to me - increasing spacing as you go - to give equivalent area rate of chnage/CoG change you would get with a triangle and equally spaced reef points.

 

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Sailmakers often ignore designer's sail plan reefing points anyway.

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I haven't done the math on sail area, but the distance between reef-points on my main is not constant

-- tack to 1st reef-cringle = 4'-0"  (11% of luff)
-- 1st-reef to 2nd-reef = 5'-0"       (25% of luff)
-- 2nd-reef to 3rd-reef = 6'-4"       (42% of luff)

(32' boat, 36' luff).

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You can put the reefs where ever you want on the sail.  Standard is at 12.5% increments but I have done sails with bigger jumps.  One common one is to do the first and second at 12.5% and 25% and then push the third up to 40% or even 50%.  I like to  think of it as the transition from sailing to surviving.  If you are thinking third reef there's plenty of wind to get the boat moving and the extra control and comfort of a super deep reef.

 

 

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As a kruuzer I put two reefs - 15% reduction of luff length and a second at 35% - kind of a middle ground in reduction.  I often found that if I was putting in a reef, I was going to need to put the second one in later. After the second reef, it's getting put away. 

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5 minutes ago, Elegua said:

As a kruuzer I put two reefs - 15% reduction of luff length and a second at 35% - kind of a middle ground in reduction.  I often found that if I was putting in a reef, I was going to need to put the second one in later. After the second reef, it's getting put away. 

That's my philosophy too. Were I racing a just enough reef would be OK but I want to eliminate the extra bits of the 3rd reef and I want to make the reefs count.

Were I going far offshore the 3rd reef option would make sense again.

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Using the sail plan you included in your first post for SWE 4801, I measured off the luff lengths (P) and boom lengths (E) for each reef and did the math.

  • No Reef - 100% of sail area (of course).
  • 1st Reef - 75% of sail area left exposed.
  • 2nd Reef - 50% of sail area left.
  • 3rd Reef - 30% of sail area left.
  • Next step would be a Storm Sail I'd think...

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On our last boat (big genoa/small main) the main reefs were at about 1.5 and 2.5 compared to standard reef point positions. Might as well make them count.

 

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On 5/21/2020 at 5:21 AM, Matagi said:

I was fiddling around with my amateurish thoughts on designing a small catboat, a bit like the Marblehead 22, but more speed-oriented, maybe even for events like the Silverrudder etc.

When I was thinking about the sail plan, it occured to me that most sail plans show the reefing lines in the same distance to one another. This, plus the triangular shape of the main sail means that the more the wind pressure mounts, the less sail you reef, percentagewise. Add to that the fact that pressure mounts exponentially with windspeed (doubling from 15kts of wind to 30kts means roughly 5x the pressure, give or take, depending on density).

So my question is: should we not extend the distances between reef points exponentially, especially with more triangular shapes of the main sail?

To illustrate: equidistant reefing points:

SY48-Sail-Plan-1-1400x788.jpg

My idea:

catboat.png

PS: all furling main sails are satanic and must be burned :) 

You're completely insane, but we'll let it go. We're here for you.:D You've started a good discussion.

Reefing the main is just so right when you do it at the right time.

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Skip Novak had a good heavy weather series of videos. In one he shows how much easier it is to put in a 4th reef than set a trisail.

On the boat, when putting in the 2nd and 3rd I've never thought they were cut too deep...

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Point already made, on a square head the amount you take in on a reef is different than a pin head.

Points not yet made: On a catboat, there is no headsail to change down or strike, so reefing the main is all you got. Therefore they should typically be deeper than the main on a sloop. Secondly, you will find on a wishbone rig a couple of new problems. As you reef, the reefed clew moves up and forward. The original foot and bunt of sail remains where it was. With deeper and deeper reefs, there is a larger uncontrolled bunt of sail hanging below the wishbone. On a daysailer maybe you can deal with this, but in weather it can get to be a problem. Less of a problem on a square head as the leach is more vertical. For this reason I would keep the leach as vertical as possible in the lower part of the sail. On your drawing I'd try going straight up or nearly to the third reef. I speak from experience. Also that first one hardly does anything, make it three, first two vertical leach, next one set forward as needed and you'll have few problems. 

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17 hours ago, European Bloke said:

Skip Novak had a good heavy weather series of videos. In one he shows how much easier it is to put in a 4th reef than set a trisail.

On the boat, when putting in the 2nd and 3rd I've never thought they were cut too deep...

This might be the one you are referring to. There are a couple more segments from the series on reefing that are really good as well.

 

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On 5/21/2020 at 5:21 AM, Matagi said:

I was fiddling around with my amateurish thoughts on designing a small catboat, a bit like the Marblehead 22, but more speed-oriented, maybe even for events like the Silverrudder etc.

When I was thinking about the sail plan, it occured to me that most sail plans show the reefing lines in the same distance to one another. This, plus the triangular shape of the main sail means that the more the wind pressure mounts, the less sail you reef, percentagewise. Add to that the fact that pressure mounts exponentially with windspeed (doubling from 15kts of wind to 30kts means roughly 5x the pressure, give or take, depending on density).

So my question is: should we not extend the distances between reef points exponentially, especially with more triangular shapes of the main sail?

To illustrate: equidistant reefing points:

SY48-Sail-Plan-1-1400x788.jpg

My idea:

catboat.png

PS: all furling main sails are satanic and must be burned :) 

But if you have a furling main you have an infinite number of reefing possibilities as in, 'I think I will go with 7 1/2 reefs'. it actually works that way when it is blowing like snot. When we crossed from Cocos-Keeling to Rodrigues in the Indian Ocean the wind was abaft the beam in the 25 to 35 knot range. We used a fairly full 135% and a tiny bit of furled main - much less than a third reef. Certainly far from survival condition and the Monitor loved the balance. We had a great sail.

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A furling main on a free standing wishbone rigged cat isn't happening. 

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I've never seen any sail reefed with any type of furling that didn't make me want to throw up in my mouth a bit 

My dad's 3.5knsb had roller furling on the boom. That was shit. We've all seen a variety of ways to reef different sails by rolling them in different ways, the thing they all have in common is being shit.

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In (or behind) Mast Furling has multiple downsides:

  • Large heavy spar sections.
  • Inability to use mast bend as a shape control
  • Often requires a cloth weight that isn't heavy enough for sailing loads.
  • Reefing moves the center of effort forward faster than it lowers and with a roller reefed headsail, you get terminal lee helm.
  • Unless it is completely unrolled, you can't do anything with it when the furling fails. 

There is a huge difference between the old roller reefing booms of the 60's and 70's and In Boom Furling products of today. Modern boom furling reefs very nicely, but they are still a mechanical system with lots of potential to fail at the wrong time. At least if a boom furling system packs it in, you can still drop the halyard and get the sail down. 

There may be physical limits such as track reinforcement for reefed head positions or fixed sheave positions on the boom which define where reefs need to be. The latter will often require the reef be placed higher in the sail than before because the sail girths are larger. The locations of battens and slide attachments has to be factored in as well.  Probably the most important consideration for reef placement is the users. Every reef adds mass to the leech of the sail and increased the tendency to flog. Cruising sails should have deeper reefs than a race sail. 

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38 minutes ago, A3A said:

In (or behind) Mast Furling has multiple downsides:

  • Inability to use mast bend as a shape control

And precludes a freestanding mast as the OP has depicted. 

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On 5/24/2020 at 3:32 AM, fufkin said:

This might be the one you are referring to. There are a couple more segments from the series on reefing that are really good as well.

 

The reef line going "through" the sail to avoid it falling to leeward is clever. First time I see this.

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On 5/22/2020 at 2:46 PM, Autonomous said:

That's my philosophy too. Were I racing a just enough reef would be OK but I want to eliminate the extra bits of the 3rd reef and I want to make the reefs count.

Were I going far offshore the 3rd reef option would make sense again.

I think 40% is the minimum reduction in luff length is what is required by many offshare racing rules for a third reef if you don't have a trisail. My idea was to get close to that with the second reef.  It balances my staysail nicely with one reef. 

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21 hours ago, Panoramix said:

The reef line going "through" the sail to avoid it falling to leeward is clever. First time I see this.

I love every bit of it, very thought through. Would be a total overkill on my Waarschip ;)

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On 5/27/2020 at 5:08 PM, Panoramix said:

The reef line going "through" the sail to avoid it falling to leeward is clever. First time I see this.

It's a little bit like the Dutchman system - vertical lines going through grommets in the sail so when the sail is dropped it comes down in a somewhat flaked fashion.

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