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Old 15-10-2014, 07:04   #31
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Re: Second forestay on a catamaran?

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Originally Posted by UNCIVILIZED View Post
Option B, in lieu of a typical Staysail stay, is a Solent stay. One mounted just inside, & a small distance below the primary headstay.
Aye, this is what I was referring to. Didn't know the proper term.
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Old 15-10-2014, 07:25   #32
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Re: Second forestay on a catamaran?

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Originally Posted by monte View Post
An option worth investigating are the storm jibs that wrap around the existing furled jib. I think they're called a storm bag or something
Yes.

Aside from obvious benefits, these may have some shortcomings:

- if you wrap round the genoa (on most boats) they will be too far fore for upwind work,

- if your furled sail is massive, the flow will be very poor, again: bad for upwind work,

You may opt for a storm sail that will be set from a point between the mast and the bow (NOT from the bow). This lets you work both up and downwind courses.

I think, if you think you need a storm jib at all, then go for a proper kit: small, high aspect, heavy, flat, orange and set close(r) to the mast.

A storm jib set from the bow may be fine when your rig is seriously fractional, but is less than perfect when you have a typical large fore triangle setup (common on many modern boats).

Another bene of having your clew closer to the mast is when you set it and douse it you are further away from where you do not want to go.

Cheers,
b.
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Old 15-10-2014, 07:37   #33
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Re: Second forestay on a catamaran?

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Originally Posted by UNCIVILIZED View Post
Guys,
I was typing when that "Storm Bag" thing was posted. I have ZERO doubts that in the real world, as they show it rigged, it's a non-starter. And also in that video it's not even blowing 25kts.....
Ok, I get your point. And no, I'm not trying to buy myself out of thight situations. But having been a professional mountain climber myself, I quite understand your point, I've been there myself.

So back to the topic, and I'm really interested in your opinion.

Let's assume, I have a genoa on the forestay. As Helia 44 pointed out, it should not be a problem to use it partly furled, but as I pointed out before, I would not really feel too comfortable with that once the going gets tough.

Now, to use a storm bag or something like that, there seems to be a concern about putting too much load on the forestay. So thats no option.
And with all thats been said so far including Barnakiel just now, the forestay for the storm jib should be set from a point between the mast and the bow.
As I mentioned earlier, I can't see, how this could be done on any of the FP's, because they don't have a solid structure aft of the bow, just trampoline.

Any insight how to solve the problem?
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Old 15-10-2014, 10:10   #34
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Re: Second Forestay on a Catamaran?

IMHO

Where the storm jib (clew) attaches, depends on a couple of factors. Some of them:

- what storm strategy you have (up- or down-wind or mixed),
- what rig you have (fractional, big main/fore ratio, small main/fore ratio),
- what your boat is (mono, multi, light vs. heavy),
- etc.

Lack of attachment point is a minor glitch as Hobbies too have for sails set without such a point ... run Spectra strops to each side (each hull) then set the jib from mid-point.

When the rig is fractional with strong domination of the main, I would leave things as they are and fly the storm jib (if required) from the forestay.

Alas, if the mast is set well aft (cutter rig) or when the rig is designed around equal SA spread (or worse, with a dominant fore triangle area) then I would very seriously consider if my storm jib could be flown from a point well aft of the bow(s).

I am attaching links to two images of how this matter got sorted on two cats prepared to sail in any weather.

http://www.latitude38.com/LectronicL...18/clubmed.jpg

http://www.zeglujmyrazem.com//wp-con...lists_(42).jpg

(actually on Club Med there was another, more inner jib too)

Cheers,
b.
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Old 15-10-2014, 19:01   #35
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Re: Second Forestay on a Catamaran?

To setup an attachment point for an inner forestay/staysail stay, you want to do what I tried to say, as did Barnakiel. On the inside of the hulls, where you want the staysail stay to be mounted, you'll likely want to build some ring frames or small bulkheads. And if you like, a fore & aft stringer on the side of the hull where the attachment points for the inner stay's cross wires will be.

These will both reinforce the hull against the load, as well as spreading it out, from the forward (cross beam) bulkhead, back to the main structure of the boat, where the forward portion of the hulls meets the bridgedeck.

Then, from the padeyes, you run wire or Spectra lines from each hull, to a central connective plate (above the trampolines), which is what you attach the new stay to. And you do the same/similar for the tack of the sail.

Like I stated earlier, it'd be wise to talk to the designer/an engineer prior to doing this. Just so that you know that the loads from such a setup are okay. And for peace of mind, it wouldn't hurt to run the recommended modification past a private design/engineering firm as well... or even in the first place.
Racing sailboats have major structural modifications done to them all the time, & not just rudders & keels. Albeit, they're planned out by engineers first, to ensure that the changes are safe, & make sense.
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Old 16-10-2014, 03:16   #36
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Re: Second Forestay on a Catamaran?

Swiss Mocha,

We encountered John Hitch, aboard his cat, "Xit" on one trip north in New South Wales, Australia. His boat had no mainsail whatsoever. Huge spreaders, swept aft on the mast, and 3 roller furler sails all along the centreline. He came zipping past us one day, [no emoticons], and the next, to windward, we did better than he, but with his hull lengths he was clearly the faster boat under most conditions. Unusual design, but surely did give fast cruising. You can google on the boat and find out more about it if interested.

Ann
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Old 16-10-2014, 03:33   #37
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Re: Second Forestay on a Catamaran?

I know that boat, even have an old cartoonish drawing of it. Neat concept.

PS: Being that it's relevant to the topic, I'll add it in here. Though it, & some other key formula's are to be found on Harken's website. But the formula for figuring out wind load on a sail, headsails in particular, is:
Wind Speed Squared (in knots) x Sail Area (in square feet) x 0.00432 = sheet load in lbs.

For the metric version, or the "correct" way to figure loads on a mainsheet, you'll have to visit their site (or adapt & convert). I can say that I've never understood their mainsheet formula, as the loads surely don't equate to a jib of the same size. Gotta' ask'em one day. But perhaps the difference is to account for the more violent shock loads when one accidentally jibes a main. Whereas such an accident with a foresail isn't anywhere nearly so likely to shake the fillings out of your teeth.
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Old 16-10-2014, 04:10   #38
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Re: Second Forestay on a Catamaran?

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Originally Posted by Ann T. Cate View Post
Swiss Mocha,

We encountered John Hitch, aboard his cat, "Xit" on one trip north in New South Wales, Australia. His boat had no mainsail whatsoever. Huge spreaders, swept aft on the mast, and 3 roller furler sails all along the centreline. He came zipping past us one day, [no emoticons], and the next, to windward, we did better than he, but with his hull lengths he was clearly the faster boat under most conditions. Unusual design, but surely did give fast cruising. You can google on the boat and find out more about it if interested.

Ann
Actually, I think that two of the stays went to the bows, carrying "genoas" or whatever trick names you guys have for spraddle-legged foresails, while there was one that was indeed center line carrying what I would term a staysail. A strange boat and a strange rig, but it seemed to work well for
John. Went like clappers off the wind!

Jim
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Old 16-10-2014, 05:31   #39
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Re: Second Forestay on a Catamaran?

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Swiss Mocha,

We encountered John Hitch, aboard his cat, "Xit"....
Just looked it up, interesting design.... Thanks für your post!

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Old 16-10-2014, 05:42   #40
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Re: Second Forestay on a Catamaran?

Quote:
Originally Posted by UNCIVILIZED View Post
I know that boat, even have an old cartoonish drawing of it. Neat concept.

PS: Being that it's relevant to the topic, I'll add it in here. Though it, & some other key formula's are to be found on Harken's website. But the formula for figuring out wind load on a sail, headsails in particular, is:
Wind Speed Squared (in knots) x Sail Area (in square feet) x 0.00432 = sheet load in lbs.

For the metric version, or the "correct" way to figure loads on a mainsheet, you'll have to visit their site (or adapt & convert). I can say that I've never understood their mainsheet formula, as the loads surely don't equate to a jib of the same size. Gotta' ask'em one day. But perhaps the difference is to account for the more violent shock loads when one accidentally jibes a main. Whereas such an accident with a foresail isn't anywhere nearly so likely to shake the fillings out of your teeth.
Metric is Wind Speed Squared(in knots) x Sail Area (in square meters) x 0.02104 = sheet load in kg.
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Old 16-10-2014, 09:05   #41
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Re: Second Forestay on a Catamaran?

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Metric is Wind Speed Squared(in knots) x Sail Area (in square meters) x 0.02104 = sheet load in kg.
But the load is (IS IT?) clearly different between an upwind work and reaching.

This is because upwind a sail is a foil (a wing) while downwind it is just an obstacle to the wind.

So this formula represents which situation?

b.
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Old 16-10-2014, 09:14   #42
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Re: Second Forestay on a Catamaran?

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But the load is (IS IT?) clearly different between an upwind work and reaching.

This is because upwind a sail is a foil (a wing) while downwind it is just an obstacle to the wind.

So this formula represents which situation?

b.
I think, as far as physics go it doesn't matter. But what do I know, I sucked in physics
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Old 16-10-2014, 09:24   #43
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Re: Second Forestay on a Catamaran?

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I think, as far as physics go it doesn't matter. But what do I know, I sucked in physics
OK. I see. Maybe the forces are the same but differently distributed.

My half guess was from what we can feel on the sheets but also from the fact that the flows are radically different.

b.
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Old 16-10-2014, 09:31   #44
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Re: Second Forestay on a Catamaran?

Another factor worth considering is that for an upwind situation, the jib must be actually slightly bigger than results from a simple Wind/Force/SA downsizing.

This is because often in heavy wind upwind sailing there will be disproportionately more wave and the boat will need more than proportional power to drive thru.

So to say, for a fully loaded SA 100 sq ft at 15 kts we need a bit more than 25 sq ft SA at 30 kts. Etc.

Not a huge difference, but it is there.

b.
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Old 16-10-2014, 09:51   #45
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Re: Second Forestay on a Catamaran?

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Originally Posted by barnakiel View Post
But the load is (IS IT?) clearly different between an upwind work and reaching.

This is because upwind a sail is a foil (a wing) while downwind it is just an obstacle to the wind.

So this formula represents which situation?

b.
My guess is this is calculated based on downwind. On a downwind run, it's mostly about how much wind can you block and a new kevlar high tech sail and an 20yr old baggy sail will block about the same amount of wind.

Once you start moving away from downwind, sail shape and trim start playing a huge impact on the aerofoil properties and those change with the heading relative to the wind, far more than the change in apparent wind would account for.
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