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Old 08-03-2010, 15:03   #91
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Interesting thread to follow

What helped with the hanked on was having someone on the helm who didn't do anything stupid / didn't make my life harder (of course as a kid a lot of blind faith involved on my part).........and something I sorely missed with hanked on sails on my 21 foot Corribee and no autopilot .
Thanks you just reminded me about one of the critical faults when using my hank-on foresail. At the moment the halyard has a habit of getting caught under a fitting at the top of the mast. Last time this happened was when I had someone inexperienced at the helm who could not control the boat. So far I have winched others up to release the halyard, but as soon as I get a chance I am going to have to get up there to see if I can modify things so this wont happen again.

Likewise, it would not be hard for the same thing to happen to me alone at sea especially if my unreliable tiller pilot did one of its malfunctioning tricks (Yes, I would like to get a wind vane, but that is a topic for another thread).

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Old 08-03-2010, 15:29   #92
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I also own a Steel H28 Ketch, (the only other one in Australia as far as we both can tell!) and have a 145% Genoa on a furler.

Cheers
I am looking forward to comparing notes. Sorry I have been a bit slack responding to date, but I have been busy trying to sort out work and family issues while trying to arrange to recover my boat from QLD.

I actually saw your post about your sail on the New Zealand H-28 Owner’s Website while I was searching around for tips and advice about sails (see, http://h28.org.nz/). It was a pity that I had already ordered a new No 2 Genoa otherwise I would have closely listened to your advice BEFORE I made the order. At the time of the order I just did not have enough money to get both the sail and a decent furler such as a Profurl at around $2,000 Aus. Likewise, I really need the sail to get the boat back to NSW and would rather be sailing than having to leave my boat on the hardstand for another month while I searched for the extra funds.

As I quoted somewhere above, I had also been reading Francis Chichester’s “Gypsy Moth Circles the World” and had decided that if a bloke in his 60’s could handle a huge wardrobe of hank-on sails on a temperamental 50’ ketch I should have no problem doing the same on my well behaved H 28?

All the best and hope to catch up somewhere in the near future!
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Old 09-03-2010, 02:22   #93
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I agree with you. The time spent on planning is more important than the amount of cash you put into a project
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Old 09-03-2010, 05:48   #94
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That is true, but I don't see how that would work in reality, apart from the issue that the sail luff can't be made strong enough. If you have this inner stay with furler, I assume it is being used for staysails too, not just for a storm jib. I can't see anyone spending the $$$ on a furler that might never get used, plus the maintenance. So, the furler is already in use for the staysail, which is used before the winds go to storm force requiring the storm jib. The staysail is the sail to use for a fresh to strong gale.
If you are in harbor and see that storm brewing or you hear it's forecast: yes, you could put the storm jib on before heading out, but I think it's madness to do so, I would hide in the tiki bar and wait for the storm to pass!
I agree 101% about the Tiki bar. But I don't know what's wrong with a staysail furler used for a storm sail, if it's sized right. Logically: if the furler can take the loads which would knock the boat down with the regular staysail, why wouldn't it take the same load from the storm sail? I never heard of the luffs blowing out. I guess the storm sail luff is shorter, so will concentrate the force over a smaller luff length, but that's got to be within reserve strength of the luff, don't you think?

The little staysail on our boat is on a massive 400S Furlex which looks like it came off a tall ship. I don't worry too much about the luff.

I had our boat in a strong Force 9 (gusting well over 50 so maybe it was really a F10) under staysail and deeply reefed main. The boat was making way and making progress upwind, and was perfectly balanced, but she was underpowered, not heeling at all, and it was really not quite enough sail out (I got into trouble when I tried to let out some Yankee; I realize now that I should have been letting out some mainsail). I think the full staysail and deeply reefed main could be used on our boat in any wind condition which the boat could take (I reckon wind will almost never be a problem; it will be sea state which becomes dangerous long before wind gets to be a problem). I don't think we need a storm jib.

A trisail however would be a good thing, much stronger and with a better shape than the deeply reefed main.

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Yes, it does. But why is it called a gale sail and not a storm sail? I have no use for something like that when it's only usable for gales because I fly my regular staysail for that. I am afraid when they don't want to state it is a storm sail because there must be a reason for that.
I think you're reading too much into the name, which is nothing but catchy advertising. "Gale" rhymes with "Sail" and sounds appealing. Also "gale" in the English language generally refers to any kind of shrieking bad weather at sea. It was Beaufort who somewhat artificially defined a "storm" as being more intense than a "gale". In common speech, they are synonyms. In all the literature, the "Gale Sail" is described as a "storm sail", which is certainly what it looks like to me.

That being said of course there are big disadvantages to using any storm sail on the forestay, as we've discussed. I just thought of one more -- in storm conditions you would be a lot happier working some distance away from the bow, where an inner forestay is, than at the very bow of the boat, where pitching forces are at a maximum and green water may be coming over. I wouldn't want to launch that Gale Sail on a forestay in bad conditions.

So even if the Gale Sail looks good I guess that a removeable inner forestay (maybe best of all a Solent stay) and proper hanked-on storm jib is a much more optimal solution.
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Old 09-03-2010, 06:47   #95
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Last evening, we picked up our two jibs newly fitted with hanks.

It is hard to work on the foredeck in heavy weather. Hanks are the least difficult solution for heavy going. They are also the most difficult solution for easy going. Experience has it that the hassle of hanks in light air is truly tiny compared to the hassle of RF in difficult conditions.

We recognize that we are odd-balls on this subject, too.
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Old 09-03-2010, 10:49   #96
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The little staysail on our boat is on a massive 400S Furlex which looks like it came off a tall ship. I don't worry too much about the luff.
Pls. read back my explanation on how the luff of a sail that goes on the furler is constructed. It is the weakness of that construction in the sail that I was talking about. They use very heavy sail cloth for storm jibs but that cloth can't be used there because it wouldn't fit into the small channel of the foil.

I don't remember who mentioned it but using the lighter cloth at the luff isn't okay. When you put that logic to work, you could use the lighter material for the whole storm jib... which they don't.

Quote:
I don't think we need a storm jib.
My sail plan doesn't have one, nor a try-sail. But I found one case where a Sundeer 64 was overpowered with just the staysail. It wasn't clear if they used the reef point in it, but it was the same as ours with bronze hanks. It ended up shredded.

Under the worst conditions we would go to just the main sail with 3 reefs. After that it is survival under bare poles. The account mentioned above stated that after the staysail was shredded they did fine under bare poles at 7 knots boat speed.

cheers,
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Old 09-03-2010, 11:50   #97
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Nick...Say your running before the wind... is a fully reefed main better the a handkerchief storm jib on an inter-stay..?

I have been out in close to 50 knots with the later albeit mounted on the fore-stay and she practically steered herself with out any worry of a jibe to contend with...or any sensation of being turned head to wind...we had little swell to contend with though.

I know the wind factors quadruples as the velocity doubles so Just picking your brain here...I just don't like the picture in mine of an accidental jibe it those conditions.
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Old 09-03-2010, 15:36   #98
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Stillraining:

It depends on many factors. For ketches and schooners, using a main alone can be better than using a jib alone. But that main must be designed to be used instead of a trysail, with a 3rd very deep reef, heavier sailcloth etc. Also preventers that are adjustable from the cockpit must be rigged. A trysail is always better than a main.

At 50 knots we would have main and mizzen 3 reefs, main 3 reefs or taken down completely and staysail. When it changes to a sustained 55 knots I would have to make a decision about keeping sailing or going to sleep-mode (hove to). When I keep sailing I will probably continue with just the main with 3 reefs but when that is down already I might select the staysail with a reef in that. When hove to, we will only have the mizzen up but every boat needs something different and most need a jib for that.

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Old 09-03-2010, 15:44   #99
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I have 3 reefs in both main and mizzen...by "deep reef " is that a differently larger spaced one on the last one?...Mine appear to be all evenly spaced.
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Old 09-03-2010, 16:10   #100
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Nick...Say your running before the wind... is a fully reefed main better the a handkerchief storm jib on an inter-stay..?

I have been out in close to 50 knots with the later albeit mounted on the fore-stay and she practically steered herself with out any worry of a jibe to contend with...or any sensation of being turned head to wind...we had little swell to contend with though.

I know the wind factors quadruples as the velocity doubles so Just picking your brain here...I just don't like the picture in mine of an accidental jibe it those conditions.
SR,

Running I would think you want your sail's center of effort forward of your keel, so whatever does that.

You need the trysail or deeply reefed main if you're hoving-to or trying to reach.
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Old 09-03-2010, 20:22   #101
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The furling unit isn't strong enough.

OK, lets take a closer look at that shall we. Ill use a Beneteau 45 as an example (I=15.8m, J=4.6m) A racer cruiser, so a proportionally bigger rig than most cruising boats.

Taking a storm sail of 25% fore triangle area (ISAF say max 5% height of fore triangle squared its about 25% for most boats) = 9.2m2.

Calculate dynamic pressure in system: P=0.5d x V2 x A (This is a simplistic approach I agree it doesnt consider the healing of the boat or the fact that the wind is not perpendicular to the sail, but its good enough to determine the ball park force and ensures a certain degree of inherent contingency)
D= density of air = say 1.2 kg/m3
V= velocity of wind = 65 knots (start of hurricane in Beaufort) = 33.4m/s
A = Area of sail = 9.2m2

Therefore, dynamic pressure in the system (P=0.5d x V2 x A) = 6,115N or 627kg force.
.
So the answer is to buy a roller furling with a SWL of more than this apply safety factors as you see fit (Id suggest something significant to account for gusts over 65kts, say 1.5+).

Unfortunately, furler manufacturers dont seem to publish the SWL of their systems, but no matter, we can make some assumptions and work it out. Take this mid range cruising furler from Profurl: (click here)

Rated for 13m to 15m boats, so suitable for our Bene 45 example. Rated for a max sail area of 80m2. Now the assumption we make is to assume that a Bene 45 would be expected to carry a full headsail up to somewhere in the 20-25knot range (well use 22knts, 11.3m/s). If this is a reasonable assumption to make, then it is also reasonable to assume that the manufacturer would design his system to have a SWL of at least this (I suspect it is much higher)

So P=0.5d x V2 x A in 22knots with full sail area in this case works out to be 6,129N or 625kg force.

About the same force in the system as for 65kts with a storm jib.

This should not come as a surprise!!

The whole point of reducing sail as wind increases is to reduce the force that attaches its self to the boat - too much, we broach, too little we stall, but the forces attaching themselves to the boat (via the sails, via the furler) remain roughly the same.

If the forces were to increase significantly - say a gust of 80 knots coming through - the system may exceed it's SWL (depending on your safety factor) for a very short period of time until you heel or broach or whatever happens to spill the wind, but it is unlikely to exceed MWL or fail completely.


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Old 09-03-2010, 21:49   #102
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Bewitched,

In principle, your post is right. The first number should have been 6,158N but that still puts it in the same range. However, I think you skipped some factors:

1. The luff of the storm jib is much shorter than that of the genoa. This means that the transfer of power from the sail to the furler is done over a smaller area. I have no numbers for "I" for a storm jib but guess it's about 40% of the genoa? In that case, the tension on the luff-to-furler area is increased by 250%. In numbers: at genoa I=15.8m so tension is 6,129 / 15.8 = 388N/m. For the storm jib I = 0.4 x 15.8 = 6.32m. 6,158 / 6.32 = 974N/m so 2.5 times as high. How much would the safety factor be? double?

2. shockloads. I've been out of school for too long so don't remember the formula's. We have to consider acceleration and mass. How would that compute?

3. luff construction. As showed in point 1, the forces on the luff will be much higher for the storm jib, but we are limited to using the same material there in order to fit it into the furler groove. Unless someone tells me that that material can easily handle 2.5 times the force too, it ain't much use if the furler stays together but the sail tears apart.
This is what's sewn onto the luff, and the cloth is 8oz dacron:

cheers,
Nick.
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Old 09-03-2010, 22:45   #103
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Nick - I agree that it is a rough and ready calculation and doesn't cater for all the forces at work. But I do believe it errs on the safe side - hugely so actually .

You mention the length of the luff (40%) - it could be a reasonable assumption (65% max according to ISAF). It certainly adds more force into that particular element of the system - but remember, much is transferred to the mast/deck by means of the halyard. But there is already much contingency within the assumptions of the calculation itself.

It assumes that the load is acting perpendicular to the full area of the sail. (a 45 deg heel would 1/2 this load - add in an angle of attack to the wind of the same order and you are down to 1/8 the force), it assumes that the boat does not heel with as the force is applied - which of course it does - an additional force of only a few 10's kg of force would cause additional healing and thus the wind would spill, reducing the force attaching itself to the boat.

The calc is for dynamic loading, but if you want to go OTT with safety factors, the max shock loading factor that you could apply is around 2.0. This would represent 65knots in one direction, coming to a complete stop and then coming at 180 deg at 65 knots in an instant. It's not going to happen. I suggested 1.5 in my earlier post.

The principle to follow is:
Establish the loads that the system will take. You can take this as far as you want
Add safety factors as you see fit
Specify the system appropriately.

Same approach for any system taking load on the boat

If you follow this approach, I believe will find that a roller furling that is rated for the headsail of a particular boat will be sufficiently strong enough to hold a storm jib on that boat.

As for the strength of the storm jib where it attaches to a luff groove - I don't know what material is used or it's strength. Maybe ask these guys, they all produce such a sail.

Quantum

UK Halsey

North Sails

Or maybe these guys - sailing in the 1998 Sydney Hobart in horrendous conditions, using sails in luff grooves and going on to win overall

Midnight Rambler
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Old 09-03-2010, 23:56   #104
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Hi Bewitched,

I understand that you err on the safe side. But those errors cancel each other out when you compare the genoa- to the storm-jib scenario. For example, the halyard transfers much of the load but it will do that for both scenario's. If the load is equal but the luff only 40%, then the forces at the luff increase by a factor of 2.5 regardless of other factors; the 2.5 stays 2.5.

For shock loads I do not mean caused by 180 degree wind shifts. What does happen is that the jib collapses in the lee of a wave, or it can gybe. This is a regular occurrence in storm conditions and it fills again in a violent and explosive way.

I don't think any of the links you posted concern roller furling storm jibs. I still don't know if these are made or used because I never met someone who had one. People who say they have it, are really talking about a staysail, not a storm jib.

Also, the racing foils are much stronger than cruising roller furler foils. For starters, they are one single piece. But we weren't talking about racing equipment anyway.

cheers,
Nick.
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Old 10-03-2010, 01:43   #105
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Nick,

I really don't want to get into batting "have you considered this, you've missed that" type of postings back and forth. I freely admit the calc doesn't cover every force in play - it doesn't consider that the jib sheet takes a significant portion of the load for example (30%??).

And by the way, you can't increase the force in the system. Adding 250% because the luff is only in connection with 40% of the stay is like me saying the force on a hank is 10,000% more because each one is only in connection with 0.1% of the stay. Clearly this is not the case.

Shock loading - the max is 2.0, less for the scenarios you mention.

Rather than talking calcs, how about adopting a more high level approach to establishing the spec of this system?

I'd suggest that a furling system with a SWL of slightly more than the halyard or sheet blocks (with the necessary adjustment for the sheet / halyard angle) and a lot less than the rig is what is required. That way the blocks explode before your expensive furler system, but everything is sure to go before the rig.

I'd be surprised if the headsail furler specified for the boat in question doesn't already fit nicely into this little window.

Roller furling storm jib - no I've never come across one either. But I've still not heard a convincing arguement against them.
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