What percentage reduction in sail area is 1st and 2nd reef

[tudorsailor]

So I have in-mast furling (no debate to be started on this). I can reef as much or as little as I like, but there are no reefing marks as there are on the head sail.

Is there a standard amount for sail reduction for headsail or mainsail 1st and then 2nd reefs.

If I wanted to mark my sail for those reductions how would I calculate where to put the marks?

TudorSailor

 

[Angele]

Using the highly technical method of taking a ruler to a photo of my boat, the reefing lines on Angele are 10% (reef 1), 25% (reef 2) and 40% (reef 3) of the way up the leech of my mainsail.

Not possible to use the same method to measure distance along the boom (photo taken from the leeward side of the boat and unfurled genoa obscures the gooseneck) but, as the shape of the sail triangle is constant, you ought to get the same result.

 

[bedouin]

The ORC specification for a deep reef in the main (so you don't need a trysail) reduces the area to 40% - and most boats would have that as a 3rd reef

So I suppose 1st reef of -20%, 2nd reef of -40% and 3rd -60% sounds about right.

 

[Angele]

The ORC specification for a deep reef in the main (so you don't need a trysail) reduces the area to 40% - and most boats would have that as a 3rd reef

So I suppose 1st reef of -20%, 2nd reef of -40% and 3rd -60% sounds about right.

Just to avoid possible confusion, the numbers in my earlier post relate to distance along one of the sail sides. Obviously the reduction is sail area is the square of that number.

So, reef 1 - 0.9 squared is 0.81, so a reduction in sail area of 19%, etc.

reef 3 is 0.6 squared, 0.36 or a reduction of 64% !

I therefore concur with Bedouin's numbers.

 

[davidej]

Dont forget a square rule will apply

If you reduce the foot by 10% you will reduce the area by 19% (.9*.9) - 20% will be 44%


Too late - some has already explained that!

 

[prv]

Dont forget a square rule will apply

If you reduce the foot by 10% you will reduce the area by 21% (.9*.9) - 20% will be 44%

So it sounds like the two techniques roughly agree on 20/40/60

Pete

 

[Lakesailor]

Yer but.
If you reef the sail onto the boom whilst you are reducing the sail area you are also reducing the height of theCoE of the mainsail.
Whilst that will happen to a certain extent on an in-mast reefing sail (because the luff is longer than the foot) it won't be as much for a given % reduction.

 

[davidej]

Yer but.
If you reef the sail onto the boom whilst you are reducing the sail area you are also reducing the height of theCoE of the mainsail.
Whilst that will happen to a certain extent on an in-mast reefing sail (because the luff is longer than the foot) it won't be as much for a given % reduction.

Not so - it makes no difference whether you wind it in or down.

If you reduce the foot by 10% you will reduce the luff by 10% - the sail will be 19% less in area and will be in the same position on the mast.

This assumes the sail is a right angled triangle - a shaped roach might make a slightl difference

 

[Tranona]

So I have in-mast furling (no debate to be started on this). I can reef as much or as little as I like, but there are no reefing marks as there are on the head sail.

Is there a standard amount for sail reduction for headsail or mainsail 1st and then 2nd reefs.

If I wanted to mark my sail for those reductions how would I calculate where to put the marks?

TudorSailor

Bit of a pointless exercise. One of the great benefits of a furling mainsail (either in mast or in boom) is that your sail size is infinitely variable and you are NOT restricted to effectively 3 fixed sail areas. The 2 or 3 fixed reefs on a slab reefed sail are just a compromise.

Adjust the sail area to suit and use the outhaul to change the shape of the sail depending on point of sail.

 

[Angele]

Bit of a pointless exercise. One of the great benefits of a furling mainsail (either in mast or in boom) is that your sail size is infinitely variable and you are NOT restricted to effectively 3 fixed sail areas. The 2 or 3 fixed reefs on a slab reefed sail are just a compromise.

... agreed, but at least it gives him a guide as to how the degree of furling at a given time compares to what you would get if you were restricted to 2 or 3 slab reefing points.

As someone who has never sailed a boat with a furling mainsail, I know I would find that informative.

 

[lw395]

I would suggest putting some markers on the main and jib systems, so that when you find some settings that give you good balance you can repeat them easily.

 

[Lakesailor]

Not so - it makes no difference whether you wind it in or down.

If you reduce the foot by 10% you will reduce the luff by 10% - the sail will be 19% less in area and will be in the same position on the mast.

This assumes the sail is a right angled triangle - a shaped roach might make a slightl difference

I don't agree. I could work it out if I could be bothered, but I'm not that fussed really.

 

[Tranona]

... agreed, but at least it gives him a guide as to how the degree of furling at a given time compares to what you would get if you were restricted to 2 or 3 slab reefing points.

As someone who has never sailed a boat with a furling mainsail, I know I would find that informative.

Not sure of the logic of that. Fine if you are trying to replicate the restrictions of slab reefing, but pointless if you are taking advantage of the increased flexibility of furling. Irrelevant, really to try and compare with what you might do on a different boat with a different system.

I can see some sense in marking points that you find appropriate for specific conditions, but my experience with furling sails is that you get to know how much sail area you need, and it is so easy to adjust fairly accurately rather than "is it time for a 20%+ reduction in area" etc.

 

[Angele]

I can see some sense in marking points that you find appropriate for specific conditions, but my experience with furling sails is that you get to know how much sail area you need, and it is so easy to adjust fairly accurately rather than "is it time for a 20%+ reduction in area" etc.

That is why I would find the marks useful.

On Angele, I know what effect I have from putting in a single (slab) reef on the main. By definition, the amount of sail area I reduce each time I put that reef in is a fixed amount.

By contrast, rolling away a few turns on the genoa is less of a precise measure (and, I can only assume that doing the same with a furling main, without marks on the boom is even more guesswork, since you can't easily count the turns inside the mast). I do, however, have a vertical line on my genoa - put there by the sailmaker, and not at my request - that marks the single reef point. If I furl away to that point I get a consistent level of reduction in "hairiness", such that I know in advance whether that is likely to be enough, or whether to put in another turn for good measure according to the conditions.

I find the mark useful.

 

[lw395]

It's also good to have a known setting for the jib, you can set the fairlead position to suit.

 

[mjcoon]

I don't agree. I could work it out if I could be bothered, but I'm not that fussed really.

I vote against you too (and thought that before I read davidej's refutation & explanation).

The fact that you cannot readily write some counter-logic suggests that you were wrong. "... if you fail to mention something that you later rely on in court..."

Mike.

 

[Tranona]

That is why I would find the marks useful.

On Angele, I know what effect I have from putting in a single (slab) reef on the main. By definition, the amount of sail area I reduce each time I put that reef in is a fixed amount.

By contrast, rolling away a few turns on the genoa is less of a precise measure (and, I can only assume that doing the same with a furling main, without marks on the boom is even more guesswork, since you can't easily count the turns inside the mast). I do, however, have a vertical line on my genoa - put there by the sailmaker, and not at my request - that marks the single reef point. If I furl away to that point I get a consistent level of reduction in "hairiness", such that I know in advance whether that is likely to be enough, or whether to put in another turn for good measure according to the conditions.

I find the mark useful.

But there is still no point in replicating the fixed reefing points of a slab reef sail! By all means give yourself some marker but not at fixed 205 etc points. As I say, if you did have a furling main you would very quickly get used to not having fixed points, but adjusting your sail area to suit the conditions. You can mark it on the boom, on the outhaul line, or more likely just eyeball it.

 

[Lakesailor]

I vote against you too (and thought that before I read davidej's refutation & explanation).

The fact that you cannot readily write some counter-logic suggests that you were wrong. "... if you fail to mention something that you later rely on in court..."

Mike.

OK. Show me calculations and diagrams that show the CoE moves the same amount for each scenario. Or can you cannot readily write some logic?

 

[jordanbasset]

Not sure of the logic of that. Fine if you are trying to replicate the restrictions of slab reefing, but pointless if you are taking advantage of the increased flexibility of furling. Irrelevant, really to try and compare with what you might do on a different boat with a different system.

I can see some sense in marking points that you find appropriate for specific conditions, but my experience with furling sails is that you get to know how much sail area you need, and it is so easy to adjust fairly accurately rather than "is it time for a 20%+ reduction in area" etc.

Agree with that, one of the advantages of the furling main is it's flexibility, you soon learn on your own boat how much sail to leave out and if you get it wrong it is a matter of seconds to take some more out or pull some in.

 

[mjcoon]

OK. Show me calculations and diagrams that show the CoE moves the same amount for each scenario. Or can you cannot readily write some logic?

I myself cannot better davidej's explanation; with geometry as simple as that I just "do it in my head".

Or could Google for "congruent triangles"; there are lots of diagrams there, though they don't mention "CoE" . To a first approximation (as davidej said, there are second-order effects such as roach and perhaps sail cut) the CoE will move in the same way as the centroid, which can be Googled for too...

HTH, Mike.