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Old 12-01-2021, 23:51   #1
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Rigging an inside shroud upwind screecher on a cat

Has anyone got any experience setting up a screecher sheeted inside the shrouds for upwind? How did it work?

Any feedback on what sheeting angle worked on your cat? My reading so far shows anything from 7 degrees to about 12 degrees from centerline, but I've seen photos that are a lot wider than that.

This assumes the screecher is cut a bit flatter, (maybe 55% midgirth?) for upwind light air, and would need to be sheeted quite flat and tight, I'm assuming.

Were you able to sheet to an existing winch, and if so, where is it located?

I'm thinking I'd probably need to use an in-haul to get a tighter sheeting angle.

Any photos of how it is set up would be sweet, thanks
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Old 13-01-2021, 01:25   #2
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Re: Rigging an inside shroud upwind screecher on a cat

No photos yet as we’re just setting up and getting a design finalised for a light air upwind screecher on our boat. The angle between the tack and the sheeting position is a tad over 12 degrees, which is slightly less than the angle of the genoa sheeting position that our sister ships have (the mouldings for the track and winch are on our cabin top, even though we have a self tacking jib).

We’re using the moulded winch platform as the location for the pad eye and LFR that will be used for sheeting the screecher, redirecting the sheet through the stern quarter turning block and back to a cockpit winch.

The key factor is cutting the leech hollow enough so that it won’t foul on your cap shrouds. If you have diamond stays on your mast then those have to be accommodated. The cut will likely be similar to a genoa and should allow for greater luff sag than a genoa would have when supported by a forestay.

If you must use an outboard sheet position then barber hauling the sheet inboard will work. But a sail that is cut for use outside the shrouds may not fit inside them. How much clew overlap is there of the shroud? Bow full is the leech? But even if it fits inside the shroud, the sail is likely too full in the luff.

As an example, the screecher that came with our boat sets outside the shroud with a 13.5 degree sheeting angle. But the closest we can sail, fully trimmed in, is about 40 degrees AWA. This is due to the fullness in the luff, typical of a sail designed for close reaching rather than upwind.
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Old 13-01-2021, 03:02   #3
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Re: Rigging an inside shroud upwind screecher on a cat

My screecher sheets to my jib tracks on the coach roof. Sheeting angle, measured from the tack to the line of the track, for the jib is 9.8° and the screecher 8.2°.

The screecher is slightly bigger at 65sqm than the mainsail at 63sqm and is flown from a 1m long prodder.

Screecher is cut with a high clew to allow it above the coach roof and to clear the A-frame on the forward beam that can be a issue with tight sheet angles.

As Fxykty says the leach needs to be slightly hollow cut to clear spreaders and the luff cut to accommodate any sag. I don't have runners so my shrouds are a long way aft so no issues.
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Old 13-01-2021, 16:16   #4
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Re: Rigging an inside shroud upwind screecher on a cat

Thank you both for your responses, very helpful

Light air upwind passagemaking will be important to us in the tropics, so trying to get it right, first time. Finding it hard to find cats with an inside shroud rigged screecher that will give good upwind light wind performance to see how it's done. Will be very interested to hear how you go with both of your boats.

Our rig is somewhat different, it is a center masted, cutter rig with no spreaders but with lower, intermediate and cap shrouds. The lowers & intermediates are from carbon chainplates at the forward side of the bimini hardtop/turret, about a meter behind the mast, the cap shrouds are back another 750mm from that.

So fitting the screecher between the outside shroud and the intermediate, with 1.25m between them, doesn't seem like it would give us much more sail area and risks contact between the screecher and either of the shrouds.

But I've drawn the screecher clew to be just forward of the shrouds ( about 500mm behind aft edge of mast) so I can install an LFR inhaul along the leading edge of the bimini hardtop to be able to adjust the sheeting angle between 7 and 13 degrees. That still gives a flat screecher with a foot of about 9.5m and area of between 90 & 95 sqm by my reckoning, so looks like that will have to do for an upwind sail.

The sheet will contact the bimini side edge as it leads back to the spin winch located on aft gunnel pedestal, so I was thinking of putting some polished 316ss sheet along the bimini edge as rub protector & maybe put (moveable) chafe guard on the sheet at that contact area???

This exercise is just so we can plan the re-enforcements required and to wrap our minds around any showstoppers or limitations before we sit down in front of a sailmaker to nut it out and see what cut and material will work as an upwind and (compromised) reaching sail.

Screecher sailcloth selection for the tropics is a whole other topic.......
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Old 14-01-2021, 01:43   #5
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Re: Rigging an inside shroud upwind screecher on a cat

I have had 3 screechers. The first was Cuban and designed by Gary Martin. Spectacular sail terrible material. The second was a Doyle NZ, Genesys string sail, too heavy, terrible shape, terrible material. The 3rd was made from a material called Code Zero by Dimension Polyant from a batch that was made for a one off campaign and sadly no longer available. I has a very light taffeta on a single clear net reinforced membrane.

They were all used in the tropics, the Cuban lasted 9 months, Doyle Genesys 1 year, CZ is 12 years old and due for replacement but still useable, just.

The key to upwind sailing with a screecher is to keep everything light, the boat, the sail, the sheet(s). IMO it should not have UV protection, this makes it too heavy. Take it down when not in use. I use a single line drum rather than a continuous furler as it is easier to deploy and stow in my case into a dedicated front apron locker. I also have a net on my bow prodder to make access easy. I only use one sheet on the screecher as it cannot be tacked or gybed. If you were racing maybe this would be different but it is easy to furl it, tack, walk the sheet round and unfurl it.

Size wise mine is a tiny bit bigger than the main and gives a good balance once in the groove you can let go of the wheel. It is only useable up to 10 knots (12 knots gusts) apparent. It is possible to get down to 30° AWA but performs best at 34-35° AWA in the right conditions we can exceed TWS.

With your mast further aft, an arrangement better suited to off the wind, you may have to experiment a bit so I see your need to understand before spending out. If the screecher is a lot larger than your main there may be a tendency towards lee helm.


I have PM'd you a link with some pictures.
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Old 14-01-2021, 04:20   #6
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Re: Rigging an inside shroud upwind screecher on a cat

Great feedback, Tupaia. Very much appreciated

I thought DP Code Zero was still available, I was speaking with DP last week here in Oz about it. But will check further. Thanks for the heads up on that. I was interested in your comment that after 12 years it is still somewhat useable. A sailmaker in Langkawi told me he has found CZ is still damaged by mildew caused delamination as it has a film on one side, so it bears further investigation. He suggested a lightweight Hydranet Radial cloth for better durability & UV resistance.

Have you tried sheeting it outside the shroud to reach? Is it versatile enough to give some reaching capability?
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Old 14-01-2021, 09:37   #7
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Re: Rigging an inside shroud upwind screecher on a cat

Upwind screaschers for cats your size do need to be built strong. The apparent winds can get quite high even in 10 kt or less true winds. The Code 0 CZ, line from Dimension is available in a few different constructions. The CZ90 or CZ120 Silver may be up to the job for this. Other options for performance cruising are, warp dacron in a heavier weight, and the Carbons with double lite skin taffetas.
The sheeting angle should be close to 10 degrees for good upwind sailing but, 12 degrees will work. The clew can be slightly aft of the shrouds if enough hollow is cut into the leech. If drawing this to scale, the clew can be farther aft than the 2D drawing as the foot s never pulled straight.
Sheeting to an existing genoa track is the simplest way to go. Otherwise, adding a block or short track at the 10 to 12 degrees off centerline, using the tack as the apex may be needed. Best to sort this out with the length of the bow sprit before contacting the sailmakers for quotes.
In addition to this, the bow sprit and whisker stays need to be very strong as well as a high tech, low stretch, 2 to 1 halyard for keeping optimum shape. These sails need very high luff tension for upwind sailing. The luffs need a low stretch, anti torque, luff rope as well.
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Old 14-01-2021, 10:34   #8
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Re: Rigging an inside shroud upwind screecher on a cat

Interesting about the CZ still being available, if it is then I will be using it for the replacement. It does discolour with mildew but this has not caused any delamination. Aging is mainly cracking but after 12 years I think this is acceptable. As I said it is only up when flown so UV has not been an issue. It tends to be used in calm dry conditions so is usually stowed dry.



I do use it downwind, sometimes wing on wing with the jib and or main. It is sheeted via a snatch block on the midship cleat. After getting this sail we retired our spinnaker. It did offer slightly better performance downwind but with a lot more effort. We can furl the screecher without leaving the cockpit so we are happy to fly it at night unlike the spinnaker.
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Old 14-01-2021, 11:13   #9
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Re: Rigging an inside shroud upwind screecher on a cat

Why not use a barberhauler (in-haul) and/or twing setup? Then you can sheet to any block aft and adjust the vertical and athwart-ship feed angle. If reaching off you can go outside and open the slot, if upwind you can try running inside the shrouds. Much less precision on where hardware has to go and more flexible setup. Many newer performance rigs are going this way.
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Old 14-01-2021, 11:18   #10
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Re: Rigging an inside shroud upwind screecher on a cat

Like this, but the track is not needed at all, put the twing outboard, and the turning block can be nearly anywhere aft.
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Old 14-01-2021, 19:14   #11
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Re: Rigging an inside shroud upwind screecher on a cat

Quote:
Originally Posted by davecalvert View Post
Upwind screaschers for cats your size do need to be built strong. The apparent winds can get quite high even in 10 kt or less true winds. The Code 0 CZ, line from Dimension is available in a few different constructions. The CZ90 or CZ120 Silver may be up to the job for this. Other options for performance cruising are, warp dacron in a heavier weight, and the Carbons with double lite skin taffetas.
The sheeting angle should be close to 10 degrees for good upwind sailing but, 12 degrees will work. The clew can be slightly aft of the shrouds if enough hollow is cut into the leech. If drawing this to scale, the clew can be farther aft than the 2D drawing as the foot s never pulled straight.
Sheeting to an existing genoa track is the simplest way to go. Otherwise, adding a block or short track at the 10 to 12 degrees off centerline, using the tack as the apex may be needed. Best to sort this out with the length of the bow sprit before contacting the sailmakers for quotes.
In addition to this, the bow sprit and whisker stays need to be very strong as well as a high tech, low stretch, 2 to 1 halyard for keeping optimum shape. These sails need very high luff tension for upwind sailing. The luffs need a low stretch, anti torque, luff rope as well.
Thanks Dave, and I would like to investigate CZ90 Silver further and compare to some other materials. Is Warp Dacron pretty much like Hydranet Radial, or what is the difference? What about heavier Stormlite?

I think we've got the strength built in, for the sail. Our halyard is 2:1 and so is the continuous furler tack which can be pulled down by our capstan easily. The prodder is a boom section (not pretty, but strong & functional) and the nacelle longeron & composite forebeam are built strongly and engineered to spread the loads.
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Old 14-01-2021, 19:17   #12
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Re: Rigging an inside shroud upwind screecher on a cat

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Originally Posted by Tupaia View Post
Interesting about the CZ still being available, if it is then I will be using it for the replacement. It does discolour with mildew but this has not caused any delamination. Aging is mainly cracking but after 12 years I think this is acceptable. As I said it is only up when flown so UV has not been an issue. It tends to be used in calm dry conditions so is usually stowed dry.



I do use it downwind, sometimes wing on wing with the jib and or main. It is sheeted via a snatch block on the midship cleat. After getting this sail we retired our spinnaker. It did offer slightly better performance downwind but with a lot more effort. We can furl the screecher without leaving the cockpit so we are happy to fly it at night unlike the spinnaker.
Thanks, that's what I was hoping to hear. We would try the wing & wing before deciding whether an Oxley Bora is still useful.
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Old 14-01-2021, 19:20   #13
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Re: Rigging an inside shroud upwind screecher on a cat

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Originally Posted by zstine View Post
Why not use a barberhauler (in-haul) and/or twing setup? Then you can sheet to any block aft and adjust the vertical and athwart-ship feed angle. If reaching off you can go outside and open the slot, if upwind you can try running inside the shrouds. Much less precision on where hardware has to go and more flexible setup. Many newer performance rigs are going this way.
Yep, that's where we're headed if we can get the angles right. I keep forgetting what a great resource L-36.com is, I was just looking at it again yesterday. Thanks for posting that picture of the twing.
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Old 15-01-2021, 01:34   #14
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Re: Rigging an inside shroud upwind screecher on a cat

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Originally Posted by BigBeakie View Post
Thanks, that's what I was hoping to hear. We would try the wing & wing before deciding whether an Oxley Bora is still useful.

Contrary to the obvious when wing on wing I found it better to have the screecher on the windward side and the jib on the leeward side with the jib sheeted a little harder. The wind exiting the front of the jib keeps the screecher from collapsing even with very low apparent wind.
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Old 15-01-2021, 04:00   #15
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Re: Rigging an inside shroud upwind screecher on a cat

Nice hint on the wing setup! Thanks, I'll file that in the memory bank
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