Reef Points on a Genoa - SailNet Community
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Reef Points on a Genoa

Is there a formula to determine the size of a Genoa as you furl it?

For instance I have a 150% roller furling headsail, I would like to mark it at the 120% and 110% points. My assumption is I would need to know the foot length and measure along it. Correct? Or is there more to it than what I am assuming?

Thanks,
Dick

Sabre 34
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Old 03-06-2013
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Re: Reef Points on a Genoa

First of all, few sails, even with foam luffs can be reefed more than 10% to 15% without ending up with a very poor shape, too poor a shape to be reasonable for heavy air sailing.

With a reasonable reefing range, there will be some amount of reefing that will still have sheet leads that actually end up on the jib sheet track. It takes some experimentation but once determined you can mark the track position for the block and coorelate that with a certain amount of reef. Due to creep, you will need to change that lead over sailing time, but it will give you a rough starting point.

Jeff

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Old 03-06-2013
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Re: Reef Points on a Genoa

If you do want to do this, the 150% represents the length of a line intersecting the clew at right angles to the luff/forestay (LP).. For instance if your J measurement (forestay to mast along deck) was 10 feet, a 150% would measure 15 feet. So marking that LP line at 12 feet, and transposing that to the foot parallel to the luff would give you a ballpark 120% setting.

However as Jeff indicated, performance will unlikely be particularly good esp if beating. Better than being overpowered, of course, but not nearly as good as a proper 120/100/whatever.

Ron

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Old 03-06-2013
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Re: Reef Points on a Genoa

Here's your approximate dimensions for a Saber 34 Mk1 .... just measure along the foot to arrive at your desired 'markings'.

If these 'marks' will be used for long distance cruising consider to add 'chafe patches' along the foot and leech where the rolled up sail comes in contact with the "roll" .... just triangles 12-18" on an edge patches made from adhesive backed 'insignia cloth' ... just a 'stick on', replaced every 1-2 years, no need to sew down. Sailrite.com has it.

data
J = 14 ft. (Tack to mast dimension)
LP 150% = 21.2 ft.
(assuming the sail is almost a 'deck sweeper '... clew is fairly low to the deck ..... ) ....

@ 150% = 22 ft.
@ 120% = 17' 7"
@ 110% = 16.0 ft.

Roller reefing such a sail is possible to an approximate area reduction by 30% maximum:
• IF the sail is constructed with 5-6oz. DACRON cloth or dacron cruising laminate,
• IF you have a reefing-furling system (need a free rotating 'top swivel')
• IF the backstay tension is at or above 15-20% wire tension. To INSURE that the forestay doesnt develop significant 'sag' when reefed.
• IF the Sail has a foam luff and/or the sail was 'cut' specifically for roller reefing
• IF When you roll up to 'reef' that roll is TIGHT !!!! ie.: You apply somewhat heavy resistance to a jib sheet when you pull in the furling line, etc.

That 30% max. rolled up reduction is only an estimate of max. 'roll' before the shape develops a 'severe bagginess' in the middle panel section at the position of the 'new' luff area. Many times you cant roll to this 30% max. reduction because of how the sailmaker cut the 'leading edge' shape.
If this sail was a 'stock' sail cut for 'cruising' you 'might' get a 20+% roll-up (120% LP); if this sail was a 'race cut sail' (flattish luff entry shape) you'll probably get up to 30% but with 'some' bagginess behind the 'roll up' developing.
You'll have to 'test' how the sail roller-reefs and then set your 'marks' to those dimensions in its variably rolled up state in close to 'actual' windspeed and sea state conditions to see if you 'can' roller-reef to these area reductions; once 'bagginess' behind-the-luff develops due to 'roller reefing' you wont be able to 'point' as well as before as when the sail was fully 'unfurled'. Only 'trials' in actual conditions will indicate 'how much'.

If you 'can' reef to 30%, consider to use Garhauer EZ glide fairlead car adjusters Garhauer Marine Hardware -5857845 ..... to reset the proper car fore/aft position 'from the cockpit'.

Hope this helps. ;-)

Last edited by RichH; 03-06-2013 at 11:10 PM.
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Re: Reef Points on a Genoa

Thanks for all the great info. I did do the math and came close to the great info from RichH.
I usually prefer a headsail in the 110-120 range, but this is the headsail that came with the boat. The boat was located in CT, where the winds are generally fairly light. We live in Maine, and will be spending a year moored in RI so the wind strength is an issue. I may opt to have another headsail made.I have a drifter for those light wind days.

Again, thanks for all the info.

Dick

Sabre 34MKI
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Old 03-07-2013
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Re: Reef Points on a Genoa

Quote:
Originally Posted by Dharmabum View Post
Thanks for all the great info. I did do the math and came close to the great info from RichH.
I usually prefer a headsail in the 110-120 range, but this is the headsail that came with the boat. The boat was located in CT, where the winds are generally fairly light. We live in Maine, and will be spending a year moored in RI so the wind strength is an issue. I may opt to have another headsail made.I have a drifter for those light wind days.

Again, thanks for all the info.

Dick

Sabre 34MKI
Dick--

We have a 155 with a foam luff that one can, theoretically, reef; and, we have lead blocks positioned by multi-part tackles whereby one can reposition the sheet leads as necessary when reefing. In fact, however, with any more than two or three rolls of the foil, the sail becomes so inefficient because of the size of the roll along the foil, it's a pretty useless arrangement for anything tighter than about 60º apparent (IMHO). We only set that sail when we're going to make a very long trip in relatively light air and so need the size most of the time but do need to roll it down in squalls. The rest of the time it sits in our garage. For the most part we use a 135 and were I to do it over, we'd have no more than a 110-120 as our primary head sail. Friends of ours with the same boat as ours have been in the Caribbean for the last two years and report that they never use more than a 100.

Given the foregoing, I suggest that a new smaller sail is likely the best option if you can afford it.

FWIW...

PS: The Sabre 34 is a great boat. I'm sure you'll be very happy with her. I helped a friend race a 34--"Intermezzo"--for several years and really liked the boat.

"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."

Last edited by svHyLyte; 03-07-2013 at 08:35 AM. Reason: Add PS
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Old 03-07-2013
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Re: Reef Points on a Genoa

Even if your genoa doesn't get all baggy when rolled in, wouldn't it make sense to just roll it in enough to get the performance you want regardless of what the sail area is?

Valiant 32
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Old 03-07-2013
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Re: Reef Points on a Genoa

My race brain says it does not work well

My cruise brain and my real life experience say a 150 foam luff rolls down plenty small and the boat keeps moving just FINE

1970 Cal 29 Sea Fever

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