Sheeting Angle for Performance Tris

[gspot 189]

I have far more experience racing keelboats than multihulls, and am finding our F-82R to be a rocket at 40 degrees AWA or lower, but above that we're low and slow.

So I took some measurements and found our jib sheeting angle to be about 11.5 degrees, and given that performance keelboats (e.g. Farr/Mumm 30, Farr 40) normally sheet at around 7 degrees, I'm wondering if our 11.5 degrees is simply too wide for efficient upwind work. 

I'd ask Ian if he were around, but he's not, and I don't own a Ouija board. The plans appear to show about 10 degrees but are not terribly specific.

I plan to experiment with in-haulers, but just wonder what other performance tris are using for standard sheeting angles?

[Lowgroove 36]

8.5-9 degrees is a good number, you just need to let it out wider once you are overpowered and trav down.

[Zonker 2,872]

Farr boats that you mentioned are optimized for upwind performance. They can sail tighter angles than you can. I'd agree 11.5 is too wide for a jib, but for a genoa it's probably OK.

An inhauler to get you 2 more degrees might be about right.

[racinginparadise 240]

we went for 7 degrees at the deck level.

here's a paste of the post in the Triple Jack rebuild thread.

Hope we are right because the coachroof stringers were placed on this line!

 

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•  #112

Posted February 10, 2020

Sheeting angle?

So, I drew lines along the new coachroof at 7 degrees from the forestay deck fitting.

This raises a few questions.

Is 7 degrees the norm?

Does anyone actually fit tracks along that 7 degree line instead of parallel with the centre line?

With higher clews does that deck angle have to increase as per the attached by Richard Woods?

 

 

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[gspot 189]

39 minutes ago, racinginparadise said:

We went for 7 degrees at the deck level.

Does anyone actually fit tracks along that 7 degree line instead of parallel with the centre line?

Good point on deck level vs. clew itself - I was actually referring to track position on the deck. 

Given that 11.5 on the deck for a blade jib is most certainly too wide!

14 hours ago, Lowgroove said:

8.5-9 degrees is a good number, you just need to let it out wider once you are overpowered and trav down.

This is more in line with what I was thinking it should be, but wanted to check that there isn't something inherently different with trimarans that led the builder of my boat to go wider.

The other limiting factor I've found is the diamond wires on the mast get in the way, especially when the mast is rotated, which leads to a more twisted jib than I'd like. Some have suggested moving the sheet car forward to put more camber in the sail and allow us to harden the leech a bit more. I also thought of under-rotating the mast to create more clearance but was concerned that would be counter-productive. 

Other thoughts other than re-cutting the sail to clear the wires?

[MultiThom 145]

1 hour ago, gspot said:

 

The other limiting factor I've found is the diamond wires on the mast get in the way, especially when the mast is rotated, which leads to a more twisted jib than I'd like. Some have suggested moving the sheet car forward to put more camber in the sail and allow us to harden the leech a bit more. I also thought of under-rotating the mast to create more clearance but was concerned that would be counter-productive. 

Other thoughts other than re-cutting the sail to clear the wires?

Most blade jibs have a hollow built into the leach (to control leach flutter without use of leach tensioning lines-at least when jib is new).  Sailmakers who build jibs for rotating masts often take the spreader location into account and put the maximum hollow at that height.  Good crew use the leach offset from the spreader as the time to stop grinding.  

My current boat has self tacker.  I have noted that pointing and speed suffer if the car is allowed too far outboard (car leash broke during a sail).  I've also noted that car position athwartships must change with wind speed, lighter breezes with less slot gap.   Consequently, I believe your tracks should angle out fore to aft so cars forward (no twist-light air) has less slot than cars aft (lots of twist, heavy air).  

[gspot 189]

2 hours ago, MultiThom said:

Most blade jibs have a hollow built into the leach (to control leach flutter without use of leach tensioning lines-at least when jib is new).  Sailmakers who build jibs for rotating masts often take the spreader location into account and put the maximum hollow at that height.  Good crew use the leach offset from the spreader as the time to stop grinding.  

My current boat has self tacker.  I have noted that pointing and speed suffer if the car is allowed too far outboard (car leash broke during a sail).  I've also noted that car position athwartships must change with wind speed, lighter breezes with less slot gap.   Consequently, I believe your tracks should angle out fore to aft so cars forward (no twist-light air) has less slot than cars aft (lots of twist, heavy air).  

Our blade jib is quite roachy and has battens to support the leach, which provides nice sail shape, but makes the wire clearance problem worse. 

The current cars do angle in towards the bow as desired, which preserves the sheeting angle, but unfortunately I think that needs to be moved inboard.  

Some boats (e.g. Ultimes) use low friction rings which can be positioned in three dimensions, instead of a car which moves in one dimension, so that is certainly a consideration.

[bushsailor 92]

Not sure that the 11% sheeting angle is the problem.

You should be able to sail at 45 degrees TWA using 11.5% sheeting so maybe work on other areas first. Optimum sheeting angle is around  9 or10 degrees which is only 1.5 less than what you have now

It is easy to choke a multihull by over sheeting.

Sail shape? Too full?

mast rotation? Try centering the mast.

You should be able to point as high as a mono but you will only be going the same speed as a mono as well......which would be lower vmg.

You need to work out your upwind target speed as well, maybe 9kn above 12kn windspeed at a guess. That will stop you footing off too much(easy to do because you don't have the feedback from the boat that you get from a mono. .

[gspot 189]

16 minutes ago, bushsailor said:

Not sure that the 11% sheeting angle is the problem.

You should be able to sail at 45 degrees TWA using 11.5% sheeting so maybe work on other areas first. Optimum sheeting angle is around  9 or10 degrees which is only 1.5 less than what you have now

It is easy to choke a multihull by over sheeting.

Sail shape? Too full?

mast rotation? Try centering the mast.

You should be able to point as high as a mono but you will only be going the same speed as a mono as well......which would be lower vmg.

You need to work out your upwind target speed as well, maybe 9kn above 12kn windspeed at a guess. That will stop you footing off too much(easy to do because you don't have the feedback from the boat that you get from a mono. .

I just heard offline that Randy Smythe set up his boat to sheet at around 8.5 degrees, which is three degrees less than we have. It doesn't sound like much, but in absolute terms it's about 4" / 10 cm closer to the centerline, which is actually quite a difference.

I will also try centering the mast. My understanding is that the rotating mast is most effective when reaching, so maybe it will be a net gain in point mode.

Obviously there are other aspects of our pointing technique that will require work, but  if we can get 9kn of boat speed in 12kn of breeze at 45 TWA I'd be thrilled. It should be possible based on what I've heard from other owners...

[Tom Kirkman 36]

9 degrees and let it go.

[MultiThom 145]

Work with inhauls before moving tracks.  The roachy jib may need a bigger slot than you are used to.  Have you noticed any backwind bubbles in the lee main in bigger breeze?  

[Wess 2,488]

15 hours ago, bushsailor said:

Not sure that the 11% sheeting angle is the problem.

You should be able to sail at 45 degrees TWA using 11.5% sheeting so maybe work on other areas first. Optimum sheeting angle is around  9 or10 degrees which is only 1.5 less than what you have now

It is easy to choke a multihull by over sheeting.

Sail shape? Too full?

mast rotation? Try centering the mast.

You should be able to point as high as a mono but you will only be going the same speed as a mono as well......which would be lower vmg.

You need to work out your upwind target speed as well, maybe 9kn above 12kn windspeed at a guess. That will stop you footing off too much(easy to do because you don't have the feedback from the boat that you get from a mono. .

This above.  "Its easy to choke a multihull by over-sheeting the jib."  Would add that many under sheet the main which impacts a lot including the shape of the jib (and location of the clew of the jib).  

In haulers are not going to help unless the shape of the main is such (and the forestay tight enough due to mainsheet tension) that you don't choke the slot.

[gspot 189]

13 hours ago, MultiThom said:

Work with inhauls before moving tracks.  The roachy jib may need a bigger slot than you are used to.  Have you noticed any backwind bubbles in the lee main in bigger breeze?  

We'll definitely start with inhaulers or other temporary measures before making any permanent changes. And I haven't noticed any backwind bubbles in the main. The issue is more that the jib luffs unless we bear away to several degrees below the other boats. 

4 hours ago, Wess said:

This above.  "Its easy to choke a multihull by over-sheeting the jib."  Would add that many under sheet the main which impacts a lot including the shape of the jib (and location of the clew of the jib).  

In haulers are not going to help unless the shape of the main is such (and the forestay tight enough due to mainsheet tension) that you don't choke the slot.

We still need to optimize our main shape, but I think we're getting much closer, and have also experimented with sheeting the boom slightly above centreline. 

As above it seems that when we get the main into a good pointing shape with slight helm pressure the jib starts luffing, and when we bear away to address that the main stalls. It's like we can't get the main and jib in sync in point mode.

We also have some good photos of us and a Sprint 750 on the same point of sail, same race, same location, and the Sprint's jib is sheeted in further with less twist. But ours is already in as far as it will go.

[MultiThom 145]

7 minutes ago, gspot said:

We'll definitely start with inhaulers or other temporary measures before making any permanent changes. And I haven't noticed any backwind bubbles in the main. The issue is more that the jib luffs unless we bear away to several degrees below the other boats. 

When I've seen those symptoms together I have sometimes found that the jib halyard is not sufficiently tight.  

[gspot 189]

51 minutes ago, MultiThom said:

When I've seen those symptoms together I have sometimes found that the jib halyard is not sufficiently tight.  

That has definitely been part of the challenge - the jib halyard tends to slip a couple of inches before the clutch bites. 

I've tried to create a pseudo-Cunningham for the jib to address this but it's still a work in progress. 

[MultiThom 145]

7 minutes ago, gspot said:

That has definitely been part of the challenge - the jib halyard tends to slip a couple of inches before the clutch bites. 

I've tried to create a pseudo-Cunningham for the jib to address this but it's still a work in progress. 

I had similar issues with main halyards (especially uncovered halyards).  I inserted a bulk (small diameter line cover) into the core where it goes through the clutch.  Held much better.  Often had to retighten jib halyard using cabintop winch after sailing a while (just like mainsail halyard).   Also, on some small boats (eg weta), some folks use a cunningham on the halyard above the clutch to give 2:1.  

[Loose Cannon 60]

20 hours ago, gspot said:

I just heard offline that Randy Smythe set up his boat to sheet at around 8.5 degrees, which is three degrees less than we have. It doesn't sound like much, but in absolute terms it's about 4" / 10 cm closer to the centerline, which is actually quite a difference.

Randy also sails with 'small groove flatter sail' by my eye and he cranks the mainsheet for a piano wire tight leech and as a result a tighter headstay.  IF you are capable of driving in that groove upwind, have at it.  He can - I can't (I am only a national champion - he is an otherworldly driver.)

 

[gspot 189]

8 minutes ago, Loose Cannon said:

Randy also sails with 'small groove flatter sail' by my eye and he cranks the mainsheet for a piano wire tight leech and as a result a tighter headstay.  IF you are capable of driving in that groove upwind, have at it.  He can - I can't (I am only a national champion - he is an otherworldly driver.)

 

Yeah, I don't think we'll be able to emulate Randy! 

In the monohull world I've found that most reasonable helmspeople can steer to a 10 degree sheeting angle, so I think that's a more reasonable target.

That's still about 2" / 5cm inboard of where our cars are at the moment, so should be quite doable with inhaulers. 

[Dave_S 1]

Deleted

[MultiThom 145]

On 2/18/2021 at 9:13 AM, gspot said:

We'll definitely start with inhaulers or other temporary measures before making any permanent changes. And I haven't noticed any backwind bubbles in the main. The issue is more that the jib luffs unless we bear away to several degrees below the other boats. 

We still need to optimize our main shape, but I think we're getting much closer, and have also experimented with sheeting the boom slightly above centreline. 

As above it seems that when we get the main into a good pointing shape with slight helm pressure the jib starts luffing, and when we bear away to address that the main stalls. It's like we can't get the main and jib in sync in point mode.

We also have some good photos of us and a Sprint 750 on the same point of sail, same race, same location, and the Sprint's jib is sheeted in further with less twist. But ours is already in as far as it will go.

One other thing to take a look at is mast rake.  If the mast is too far upright, you aren't getting as much jib luff tension as you would like since with no backstays (as you are used to having with a monohull) the forestay tension comes from the mainsheet.  Lots of stuff you have to play with to dial in an fboat.  Can take more than one season and change with new sails.  I usually started with mast rake and changed rake so the boat slowly rounded up going to weather (tried to get 5 mississippis after letting go of tiller before I had to rescue the boat from irons).  That being said, current boat has a mast rake like a Hobie 18 and I still have lee helm (but it points much better than my F242 did).

Main sheeting to weather (F242) was (in typical wind) sheeted above centerline so last 8" of middle batten was parallel to boom.

My F242 didn't need haulers for jib positioning, but other F242s did.  Either their skippers were fussier or their jibs were different cut or their tracks were in different spot.