Preventer Rigging?

[geoleo]

Originally Posted by estarzinger

Regarding Preventers . . . the first question is whether you want to redesign your boom and deck layout. The best solution I have seen is: preventor line with trigger shackle, led to block let into side or underside of boom, line running forward, and down to deck and back to winch/clutch. You stow the line with the shackle clipped to the forward end of the boom. To set it, you release the clutch, and take the line forward and clip it to a strong point. If you have two of the port and starboard you can leave both set and jibe from the cockpit.

If you dont want to redesign your boom and deck layout . . . then probably the best technique is lines fixed to aft end of boom, and led forward, stowed at forward end. With lines running from winches up the side decks to a strong turning point and back, stowed near the stays with trigger shackles. You clip the side deck lines to the boom lines to set the preventors. sure the prevent or does not bear on the upper lifeline when the preventer is set and the main has accidentally jibed, and it is nice if they do not also bear on the stays. I bent stanchions twice on Hawk before I got this sorted out.

As to line size - for the furler - yes, definitely use stripped dyneema for the part in the drum, with a cover where it has to be winched or clutched under load. For the preventor same thing. And yes, in both cases, 10mm dyneema is probably more than string enough.

You gybed with the preventor set ????

[Copprhead]

While I haven't tried this yet I'm wondering if it would be a bad idea to attach the preventer to the top end of the kicker instead of at the end of the boom.
Besides the less ideal leverage (problem for the boom?) I only see advantages:
No ropes in the cockpit / dangling from the boom end, ropes can be shorter, can stay attached at all times.
What do you think?

[Dockhead]

Originally Posted by geoleo

Overkill! Just take a 1/2 nylon dockline from end of boom to a convienient stanchion and tie a loop in it at a convient height then run the line from the stanchion thru the loop and tie a slip knot--- easy to undo and retie if you gybe. Wheww

Stanchion?

[belizesailor]

Originally Posted by Dockhead

Stanchion?

Sacraficial stanchion?

Not likely to fare well in an accidental jibe.

[estarzinger]

Originally Posted by geoleo

You gybed with the preventor set ????

Sure, many times, accidentally. That's is part what they are for!

On purpose, we would often have both preventers connected up' so we just opened one clutch, jibed, and pulled in the other and closed its clutch.

[accomplice]

I intend to some day change the way we have our preventer run, but I believe that what we've come up with works reasonably well.

We have a significant (12-14mm) line -- the preventer -- tied to a strong bail on the underside of the boom, approximately 80% of the way aft. I have a bungee cord attached to the gooseneck. A loop is tied in the preventer such that the bungee hooks into it and holds the preventer up off the bimini when not in use. The tail of the line is coiled and hung from the gooseneck.

When sailing deep down-wind, or -- more commonly -- off the wind in conditions where the sea-state and roll wouldn't keep the boom stiffly in position, we remove the preventer from the gooseneck bungee and run it forward (outside the shrouds) making fast to the forward midship cleat (approximately station 2-3). We let the boom out a few inches more than target trim, cleat the preventer, and tighten the mainsheet. We have travelled thousands of miles like this.

The biggest downside is that we must go forward to adjust the preventer. I hope to someday come up with a solution that works well on our boat yet allows control from the cockpit.

And, to Evans point, the preventer has saved us countless times from unintended gybes. In college I suffered a severe concussion (loss of consciousness, convulsive seizure) from an unanticipated gybe -- not something I am eager to repeat.

[transmitterdan]

Originally Posted by Copprhead

While I haven't tried this yet I'm wondering if it would be a bad idea to attach the preventer to the top end of the kicker instead of at the end of the boom.

Besides the less ideal leverage (problem for the boom?) I only see advantages:

No ropes in the cockpit / dangling from the boom end, ropes can be shorter, can stay attached at all times.

What do you think?

Yes, it's a bad idea. Preventer should be attached well aft in the boom. More than 3/4 is normal. Less than 1/2 could break the boom.

[s/v Jedi]

We also tie the preventers around the boom, using available padeyes only to keep them from sliding. Same for the sheet: attached around the boom.

Related: we used to have wire running backstays which we replaced with Amsteel blue and now we gibe into the set backstay to absorb the shock.

[neelie]

I have never used a boom brake. But it's occurred to me that a boom brake set for maximum resistance would keep the boom fixed in position in light airs.

If this is true then the argument for a dedicated preventer set-up becomes less compelling. Especially as they come with the advantage of not needing extra lines and walks to the mast to reset preventers for the opposite gybe.

Anecdotally, boom brakes do a good job of controlling the energy in any gybe. Thus it is entirely plausible that they can replace preventers.

[UNCIVILIZED]

For a Preventer, you want a setup which will Prevent the boom from coming across of it’s own accord, should you accidentally gybe. And that will let you ease the boom across in a controlled fashion, once you’ve sorted everything else out, following an accidental gybe.

A simple, functional way to do this is much akin to the one described by Estarzinger.
You have substantial lines, preferably ones with some stretch (like nylon) attached P/S to pad eyes or bails on the outboard ends of the boom. Which are long enough so that they can be cleated off to horn cleats P/S on the sides of the boom, up near the gooseneck, when not in use.
Where they terminate in eye splices, preferably with metal thimbles in said splices.

Then, on deck. Positioned approximately where a spinnaker guy block would be, you want blocks P/S, which are strong enough to withstand the force of the boom, carrying a full mainsail, violently caught aback.
So, strength wise, on par with a spinnaker guy block.

Through which, are lines P/S, which have trigger snap shackles, designed to be connected to the thimbles in the eye splices in the lines on either side of the boom.
These lines are led through their respective deck blocks, & then back to cockpit winches; Primary or Secondary. Possibly though a turning block, enroute, & or a line clutch.
The reasoning for being led to such powerful winches, is so that the boom can be gently eased through it’s full 180 degree arc (needs be), following an accidental gybe.



Regarding RF control lines, from how ones sees them commonly rigged, when walking the docks, I don’t think that some sailors fully comprehend the forces placed upon them. Especially when one considers that these lines never get a rest from being out in the weather & UV, 24/7.

That stated, somewhere around 10mm - 11mm is about as small a loaded line as one can reasonably grasp well enough to pull on with substantive force (although bigger is better in this regard). Ditto on the self-tailing jaws of winches on mid-sized to bigger boats. Where this particular line is under a lot of load. Especially when you consider that on a moderate to large size vessel, the load on a jib sheet may exceed 1 ton at times (double that, or more on vessels like Dockhead’s). Particularly if the jib's half furled up in a heavy blow.

So... as to the math, for calculating this line’s size/strength.
On a Harken MK III, Unit 2.5 - Roller Furler. Which is sized for a boat of 12m – 14m
The circumference of the bare furling drum is 12"
The circumference of the bare (semi-teardrop) foil section is 4.5"
So the RF Line does have some built in mechanical advantage over the Jib Sheet. Call it 3:1 if you like.

Such that, to oppose the loads on the jib sheet, the RF line, needs to be a minimum of 1/3 the strength of the jib sheets. In addition to being extremely UV resistant. And for a 10mm – 11mm Dyneema line, the BS = 3-4t, WLL = 25% of that.
So, such is a realistic minimumally sized, & type of line for this application.

However, the part of this line which never gets back to the cockpit/winch, doesn't need a cover, given Dyneema's UV & chafe resistance. So with a Dyneema cored line. One can strip the cover off of that section of the line, & do a proper taper & bury of the cover into the core, structurally. Including lock stitching it into place after this is done.

Thus, you get “the best of both worlds” so to speak. A strong, small diameter, durable control line, on the drum of the furler. While the part which you handle from the cockpit is fairly easy to grip by hand, & to put onto a winch drum/into the jaws of it's self-tailer. And or, to lock off in a line clutch, so that the furler stays fixed in place.

That said, this isn't a place to go for a cheap, or average duty line. For should it break, then you're faced with a wildly flailing jib, at perhaps the worst possible of times. Which, if it’s not controlled, & swiftly dropped on deck, & stowed; it would at best, shred the sail. And possibly, could even cause the headstay to break, perhaps dropping the mast. So, IMO, 10mm – 11mm Dyneema cored line is the minimum size for a 12m – 13m boat.

[Phoenician]

From Yachting World, a review of boom brakes and preventers:

Tested: boom brakes and preventers, including Walder boom brake and Wichard Gyb’Easy – Yachting World

[Dockhead]

Originally Posted by UNCIVILIZED

For a Preventer, you want a setup which will Prevent the boom from coming across of it’s own accord, should you accidentally gybe. And that will let you ease the boom across in a controlled fashion, once you’ve sorted everything else out, following an accidental gybe.

A simple, functional way to do this is much akin to the one described by Estarzinger.
You have substantial lines, preferably ones with some stretch (like nylon) attached P/S to pad eyes or bails on the outboard ends of the boom. Which are long enough so that they can be cleated off to horn cleats P/S on the sides of the boom, up near the gooseneck, when not in use.
Where they terminate in eye splices, preferably with metal thimbles in said splices.

Then, on deck. Positioned approximately where a spinnaker guy block would be, you want blocks P/S, which are strong enough to withstand the force of the boom, carrying a full mainsail, violently caught aback.
So, strength wise, on par with a spinnaker guy block.

Through which, are lines P/S, which have trigger snap shackles, designed to be connected to the thimbles in the eye splices in the lines on either side of the boom.
These lines are led through their respective deck blocks, & then back to cockpit winches; Primary or Secondary. Possibly though a turning block, enroute, & or a line clutch.
The reasoning for being led to such powerful winches, is so that the boom can be gently eased through it’s full 180 degree arc (needs be), following an accidental gybe.



Regarding RF control lines, from how ones sees them commonly rigged, when walking the docks, I don’t think that some sailors fully comprehend the forces placed upon them. Especially when one considers that these lines never get a rest from being out in the weather & UV, 24/7.

That stated, somewhere around 10mm - 11mm is about as small a loaded line as one can reasonably grasp well enough to pull on with substantive force (although bigger is better in this regard). Ditto on the self-tailing jaws of winches on mid-sized to bigger boats. Where this particular line is under a lot of load. Especially when you consider that on a moderate to large size vessel, the load on a jib sheet may exceed 1 ton at times (double that, or more on vessels like Dockhead’s). Particularly if the jib's half furled up in a heavy blow.

So... as to the math, for calculating this line’s size/strength.
On a Harken MK III, Unit 2.5 - Roller Furler. Which is sized for a boat of 12m – 14m
The circumference of the bare furling drum is 12"
The circumference of the bare (semi-teardrop) foil section is 4.5"
So the RF Line does have some built in mechanical advantage over the Jib Sheet. Call it 3:1 if you like.

Such that, to oppose the loads on the jib sheet, the RF line, needs to be a minimum of 1/3 the strength of the jib sheets. In addition to being extremely UV resistant. And for a 10mm – 11mm Dyneema line, the BS = 3-4t, WLL = 25% of that.
So, such is a realistic minimumally sized, & type of line for this application.

However, the part of this line which never gets back to the cockpit/winch, doesn't need a cover, given Dyneema's UV & chafe resistance. So with a Dyneema cored line. One can strip the cover off of that section of the line, & do a proper taper & bury of the cover into the core, structurally. Including lock stitching it into place after this is done.

Thus, you get “the best of both worlds” so to speak. A strong, small diameter, durable control line, on the drum of the furler. While the part which you handle from the cockpit is fairly easy to grip by hand, & to put onto a winch drum/into the jaws of it's self-tailer. And or, to lock off in a line clutch, so that the furler stays fixed in place.

That said, this isn't a place to go for a cheap, or average duty line. For should it break, then you're faced with a wildly flailing jib, at perhaps the worst possible of times. Which, if it’s not controlled, & swiftly dropped on deck, & stowed; it would at best, shred the sail. And possibly, could even cause the headstay to break, perhaps dropping the mast. So, IMO, 10mm – 11mm Dyneema cored line is the minimum size for a 12m – 13m boat.

Thanks; very useful and thorough! I don't understand your terminology "attached P/S" etc. which must be current racing terminology which I don't know, and which didn't exist back in the stone age when I was racing myself, but what you suggest is very detailed and clear nevertheless. "RF" I guess is "roller furling".

So, a couple of questions:

1. Why does everyone use a line attached to the boom end which is attached to another line? What's the purpose of this complexity? Why wouldn't you just use a single line (for each side) snap shackled to the boom end? Clearly I'm missing something here. I would have thought that the pre-rigged preventers could be simply left out at the rail when not in use, then clipped to a bail at the boom end in order to put "into action".


2. Is it realistic to expect the whole system to stand up to the snatch load from the "full main taken violently aback"? I don't think any of my gear is up to that except perhaps the primary winches. What I have ALWAYS done with preventers, is to prevent any snatch loads from developing in the first place by ALWAYS keeping tension between mainsheet and preventer, so that the boom can't swing around and develop a snatch load. So the maximum load is just what the sail can produce when taken aback by an accidental gybe, which is not that huge. Thus I would not have thought that a really large line would be needed. I am planning to use my pad-eyes at the rail forward, installed for my blade jib twings, for the turning blocks. I've now had them installed permanently (by Lallow's at Cowes) after having experimented last year with them mounted temporarily (you and others greatly helped me figure that out last year). They are pretty strong, not through-bolted but tapped and glassed into a heavy alu strip which is part of my hull-deck joint, but I'm sure they'd be ripped out if they were subjected to the snatch load of a swinging boom, so why bother with more strength in any other part of the system? I guess they are not stronger than 10mm double braid rope.


3. I had to laugh when I read about your "180 degree arc of the swinging boom". I wish! Aft-swept spreaders, anyone? One of the compromises we make for cruising. Although I have to say that even a racer should like the massive rigidity of my rig -- for heavy weather work at least. Even if it compromises main sail trim downwind.


4. Concerning using stripped dyneema rope for a furling line -- it occurs to me that the naked part will be exposed, when the sail is furled. Thus subject to lots of UV exposure on a cruising boat since we leave the sails up all year round. Right? So maybe unstripped dyneema, 10mm, with a polyester cover, would be the thing. I can't imagine how I could break 10mm double braid in this application, because the loads are very modest, but I guess one wouldn't want to take any risk, and the lightness of dyneema will be very pleasant for this application.

[Dockhead]

By the way, one way to impart massive loads to the preventer would be if you dip the boom in a heavy sea. But that would break any preventer, I reckon.

My solution to that has always been to just never use the mainsail in conditions where the risk of that is significant. Tie off the boom amidships.

[SVNeko]

Originally Posted by Dockhead

4. Concerning using stripped dyneema rope for a furling line -- it occurs to me that the naked part will be exposed, when the sail is furled. Thus subject to lots of UV exposure on a cruising boat since we leave the sails up all year round. Right? So maybe unstripped dyneema, 10mm, with a polyester cover, would be the thing. I can't imagine how I could break 10mm double braid in this application, because the loads are very modest, but I guess one wouldn't want to take any risk, and the lightness of dyneema will be very pleasant for this application.

massive waste of $$

Also, consider stretch, which in some situations can be your friend. Not needed in a furling line, but in a preventer, I think you'd want some. I had dyneema cored lines as my daggerboard lifting lines. Sometimes the boards would catch in the trunks and not lower all the way, leaving the lines slack. When the board dropped, with zero stretch the lines would blow up my clutches. Switched to poly line and the problem went away due only to the slight stretchiness in poly lines.

[barnakiel]

Agreed. In my book, the preventer is a dynamic line, not a static one (to use the climbing analogy).

Nylon and not oversize probably best?

b.