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Jib sheeting angles


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So according to various sites, jib sheeting angles should be somewhere between 7deg and 15deg. 

But what plane gets used to measure the Jib sheeting angle? 

Is it right angles to the forestay? Or right angles to the mast?  Or something else? 

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It is the angle from the centre line. i.e. the bottom picture in your drawing.

Apparently some of the TP52s can have sheeting angles of 3 degrees!

 

 

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Yeah - good luck with that on my Lotus 9.2, she's a bit broad in the beam for 15 degrees. In fact haul her in too tight and she stalls. I have tested as much as I can on a steady wind day, using a waypoint and the chartplotter VMG.

What I have discovered, for my boat, is that you need a polar diagram to give your best point of sailing. The maths bears this out. Hard on, if say your speed is 4knots and your VMG is say 3.2 knots... if you bear away by 10 degrees and your speed rises by more than 10%, you are winning.

For the my Lotus, my best VMG in smooth water is at 35 to 40 degrees to the wind, and in rough water add another 5 degrees. Boats designed for pure racing, will get better angles of course, and I remember my last trip on of the old Americas cup boats, and the bloody thing was operating close hauled at 16 degrees to the apparent wind!

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1 hour ago, ex Elly said:

It is the angle from the centre line. i.e. the bottom picture in your drawing.

Apparently some of the TP52s can have sheeting angles of 3 degrees!

Yes, but is the plane at right angles to the luff through the clew (the LP measurement), or parallel with the deck (the J measurement)?

Both the blue and green lines are 15degrees but from a different anchor point. 

So they end up in very different places on the deck depending on which you use as the anchor. 

I understand it's the angle, but what's not clear is what plane to measure the angle across. 

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I've understood it's the blue line in lower sketch, based on a line from forestay base to centre of mast.... be interested to see other interpretations 

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Blue line all the way, can’t sheet a sail as per green line

The angle as per forstay comes down to sail cut and how you are using that sail in relation to wind strength and sailing angle

IIRC there’s 10 hole positions from light to heavy for a #1 on a 1020, maybe more

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You can sheet the sail to the green line. It is the LP which is a line at right angles from the luff through the clew to the deck? No? 

So assuming the blue line, the angle would be measured from the sail tack, I presume and not the J measurement point? 

Although on CD, with the furler, it's about the same location... 

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Unless you have a barberhauler setup or like the new pogos low friction ring  double line systems you will be set to the angles setup by the design and as stated above slower and wider boats will have a wider angle.

Then you need to maintain the gap between headsail and main. Overlapperes are harder to sheet closer than blade type sails

Biggest gains I’ve seen is outboard sheeting headsails once you crack sheets at all, this stops the leach from hooking

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15 hours ago, alibaba said:

Yeah - good luck with that on my Lotus 9.2, she's a bit broad in the beam for 15 degrees. In fact haul her in too tight and she stalls. I have tested as much as I can on a steady wind day, using a waypoint and the chartplotter VMG.

What I have discovered, for my boat, is that you need a polar diagram to give your best point of sailing. The maths bears this out. Hard on, if say your speed is 4knots and your VMG is say 3.2 knots... if you bear away by 10 degrees and your speed rises by more than 10%, you are winning.

For the my Lotus, my best VMG in smooth water is at 35 to 40 degrees to the wind, and in rough water add another 5 degrees. Boats designed for pure racing, will get better angles of course, and I remember my last trip on of the old Americas cup boats, and the bloody thing was operating close hauled at 16 degrees to the apparent wind!

On our 9.2 that equates to about 100mm off the spreader when hard on. A bit more in the light.

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On 5/04/2022 at 5:23 PM, alibaba said:

Yeah - good luck with that on my Lotus 9.2, she's a bit broad in the beam for 15 degrees. In fact haul her in too tight and she stalls. I have tested as much as I can on a steady wind day, using a waypoint and the chartplotter VMG.

What I have discovered, for my boat, is that you need a polar diagram to give your best point of sailing. The maths bears this out. Hard on, if say your speed is 4knots and your VMG is say 3.2 knots... if you bear away by 10 degrees and your speed rises by more than 10%, you are winning.

For the my Lotus, my best VMG in smooth water is at 35 to 40 degrees to the wind, and in rough water add another 5 degrees. Boats designed for pure racing, will get better angles of course, and I remember my last trip on of the old Americas cup boats, and the bloody thing was operating close hauled at 16 degrees to the apparent wind!

Does your Lotus have inhaulers? I'd suspect not... just tracks running fore/aft beside the cabin. As such your sheeting angle is limited by where the track is fitted to the deck, you can never get a narrower sheeting angle then what the track is without inhauling. The problem with tracks set at a relatively wide angle is attempts to help the boat point higher by sheeting the headsail in harder just lead to a very closed leech and removal of twist which tends to stall the sail. A inhauler gives the ability to narrow the sheeting angle without reducing twist or closing the leech.

Think of it as the traveller on the mainsail. 

No inhaulers (and a wide sheeting angle) would be like having the mainsail traveller all the way down to leeward. There are limits to how much adding more mainsheet tension will help before it starts to hinder performance. 

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3-degrees-of-seperation-768x432.jpg

TP52 Med Cup boats are nuts, TWS 14 knots, TWA of 36°-38°, Jib lead about 3.2° off centerline r.  9.1 knots boat speed

 

Also that jib likely costs more than my entire boat!

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I've heard they sheet them so close on the Patiki's the leeward shrouds go loose and the spreader just hops out of the way. 

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9 hours ago, Ed said:

3-degrees-of-seperation-768x432.jpg

TP52 Med Cup boats are nuts, TWS 14 knots, TWA of 36°-38°, Jib lead about 3.2° off centerline r.  9.1 knots boat speed

 

Also that jib likely costs more than my entire boat!

Yeah, but obviously lightly loaded, old mate is trimming it without mechanical advantage!

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31 minutes ago, Dave said:

Yeah, but obviously lightly loaded, old mate is trimming it without mechanical advantage!

No. No he’s not. At 14 knots of wind and 9.1 of boat speed on a 52’ boat? The jib sheet runs aft from the low friction ring. The line he holds runs to the foredeck hatch, likely to the kite?

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16 hours ago, John B said:

I've heard they sheet them so close on the Patiki's the leeward shrouds go loose and the spreader just hops out of the way. 

basically yes, they often use bungees to stop the annoying rattle from rigging screws flopping about

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