Preventer Rigging?

[s/v Jedi]

This is exactly what I always mention but most schrug it off thinking it is a non-issue.

1. It starts with the reefing points of main sail and mizzen. Each reef must lift the end of the boom further up, in order to keep the boom further away from the sea as conditions worsen and a deeper reef is set. If you want a blue water cruiser, then things like this is what makes it, not a brochure or price tag. If you don't have this then have it changed.

2. Regular polyester double braid lines for preventers so that they give a bit by stretching. But it does not stop there! Like mentioned: what happens if the boom meets the sea? Of course there are preventers that are designed to cope with that, like mine are! You simply choose a line that is not too thick which makes it stretch more. Next you look up the breaking strength of that line and install rope clutches that slip well before that force is reached. Now your designed weak point is slip of the clutch which leads to zero damage plus maximum dampening of shock loads. Not rocket science people, methods like these (design weak points, sacrifical parts etc.) have been used for hundreds of years!

[Dockhead]

These guys have rigged their preventer to a forward cleat:



And the lead looks right to me.

I notice that they have the two-part preventer line as described by Zinger and Exile. Waiting for bated breath for an explanation of why it's done that way.

For safety "fuse" I guess you could have a special link. I can't use a clutch because it's just too much of a PITA. My preventer is always on a winch, because I need to be able to adjust it to always keep it under tension. Center cockpit boat and you can't reach clutches on the rail, without getting out of the cockpit.

Wish someone would invent a remote-controlled clutch.

[Dockhead]

Concerning what rope to use --

10mm Marlowe double braid polyester has breaking strength of 3.7 tons. No way in a million years do you need more than that for a furling line, and I would guess this would be ok for preventers as well.

[transmitterdan]

Originally Posted by Dockhead

I notice that they have the two-part preventer line as described by Zinger and Exile. Waiting for bated breath for an explanation of why it's done that way.

They use the "leader" from the boom to the actual preventer line so the leader can stay permanently rigged to the boom. When not in use the bitter end of the leader is clipped to the boom near the gooseneck. It is always there ready to go. So if the boom is already out over the water it's a simple matter to rig the preventer without pulling the boom back inboard. Saves time and makes it more likely the preventer will always be rigged.

[Dockhead]

Originally Posted by transmitterdan

They use the "leader" from the boom to the actual preventer line so the leader can stay permanently rigged to the boom. When not in use the bitter end of the leader is clipped to the boom near the gooseneck. It is always there ready to go. So if the boom is already out over the water it's a simple matter to rig the preventer without pulling the boom back inboard. Saves time and makes it more likely the preventer will always be rigged.

I see -- you can rig it with the boom already out.

But I am quite used to thinking about this BEFORE letting the mainsheet out, so if this is the only purposes of having this "leader", I think I might forgo that for a simple loop (spliced dyneema) at the boom end. It's total muscle memory for me, to rig the preventer before ever sheeting out the main very far, and really no problem.

Splice a snap shackle onto a length of 10mm double braid and Bob's my mother's brother.

But this is quite like what I do now, only with a better attachment system. I was hoping to find some way to rig it permanently. Even with a "leader", I'm not seeing a good way to do this.

I'm thinking it might make sense to run it through bullseye fairleads along the rail and to a turning block at the quarter, to get a better lead to the winch. Could be needed in case I start using a bow cleat.

[unclemack]

First thought re. possible fixes for one preventer concern, that of the boom dipping in the drink and breaking:

How about a little drogue-type device/scoop suspended just below the boom end and connected by a line to the release handle of the preventer line's (side lever?) clutch, so that the preventer is released just before the boom splashes... any use at all?

Not wedded to the idea, only a couple of minutes wasted if it's rubbish.

[poiu]

My preventer goes through from the boom end, through a fairlead at the bow (amidships just doesn't work), along the side deck, through a turning block, around a cheek block and to a spare winch, or often to a cleat at the stern instead. It's dead simple and works fine. I'd rather I didn't have to rig it as it involves foredeck work.

I have often though that the line pre-stowed on the boom would be useful as it would save laying down a boom length of line, plus as Transmitterdan pointed out, would avoid having to sheet in if you realised you needed a preventer after giving it a go without. I in contrast to you am not so good at judging it and do this a lot. The boom line has a further advantage of requiring a shorter dedicated line for the preventer and less coiling afterwards. Downside is it isn't too pretty and will flop around a little I expect. I haven't fitted one, though am within a gnat's whisker of giving it a go. It could be a thin dyneema single braid (but as strong as the main line). I expect as you will have enough stretch for shock absorption in the bulk of the main preventer line.

[UNCIVILIZED]

Originally Posted by Dockhead

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".

P/S = Port & Starboard. Not a new term. And yes, RF = 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".

So if your boat's 14' wide, & you have a 16' boom, how do you clip a preventer line to the boom's end (or anywhere near it) if the main's fully eased out?

You can't. It's physically impossible to reach a bail at the boom's end when it's eased out; unless you climb onto the boom, snake out to it's end, & then attach the line. Not a problem if you're racing, but not really an option for most cruisers.

Thus; either you leave your preventers P/S (Port & Starboard) rigged all of the time, or you have lines permanently affixed to the outboard ends of the boom P/S, which reach almost to the mast (ergo my reference to cleating them to the boom there). And which are connected to the other part of your preventer, when the boom's eased out.
These parts of the preventer are left at the rail, when not in use.


2. Is it realistic to expect the whole system to stand up to the snatch load from the "full main taken violently aback"?

YES, BTDT, Many, Many, Many times.
Not everyone continually trims the preenter as they adjust the mainsheet. Especially those who aren't well seasoned sailors. AKA easily 1/2 of most crew on boats with more than 3 people onboard.

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.

The strength of the blocks needed, & thus their attachment points was covered.

And me, I WANT a preventer which STOPS (AKA Prevents) the boom from swinging across regardless of the why. Even & Especially if, the boom gets dunked in the water at speed. For then, the energy in it as it swings (or rather, is SLAMMED) is HUGE.
And if it swings across with any speed, it can easily kill someone, or bring down a rig (SIC).

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.

Even with all of the boats out there with swept spreaders, the majority of sailboats don't have such. Walk the docks & see for youself.

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?

When a sail is furled, most of it's roller furling (RF) line, is wound onto the drum. And thus doesn't get much UV exposure.
But a big part of the reason for using Dyneema is that it's fairly immune to UV as compared to other ropes.

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.

I'm unclear as to which loads on the RF line you're stating are modest. Except, perhaps, for when a sail is completly rolled up. That's the only time when the loads on the RF line will be "small".

[UNCIVILIZED]

Originally Posted by Dockhead

I see -- you can rig it with the boom already out.

But I am quite used to thinking about this BEFORE letting the mainsheet out, so if this is the only purposes of having this "leader", I think I might forgo that for a simple loop (spliced dyneema) at the boom end. It's total muscle memory for me, to rig the preventer before ever sheeting out the main very far, and really no problem.

How does this work? Because as soon as you fall off 10 degrees (or less) from close hauled, the boom's no longer over the deck, & thus you can't reach it's end (or anywhere close there to) to attach a Preventer to it.

Splice a snap shackle onto a length of 10mm double braid and Bob's my mother's brother.
And in English (or rather, American) this means?

But this is quite like what I do now, only with a better attachment system. I was hoping to find some way to rig it permanently. Even with a "leader", I'm not seeing a good way to do this.

You can use a leader, which is always connected to the boom's outer end, & most of the time it's connected to a line which leads to a STOUT deck block at the shrouds (perpendicular type). And from there, the line goes back to a Primary cockpit winch.
But at some point you're going to run into;
- Poor lead angles
- Interference with the shrouds
- Interference with the jib or spinnaker sheets/guys

Basically, there's no free lunch here. You're going to need to connect & disconnect things at times. And you pretty much need to use a leader, so that you're not trying to reach the boom's end, when it's 15' out over the water.

I'm thinking it might make sense to run it through bullseye fairleads along the rail and to a turning block at the quarter, to get a better lead to the winch. Could be needed in case I start using a bow cleat.

The line which goes through a deck block at the shrouds (above), can be run aft to a turning block on the boat's aft quarter, & then to a Primary or Secondary cockpit winch.

[Dockhead]

Originally Posted by UNCIVILIZED

The line which goes through a deck block at the shrouds (above), can be run aft to a turning block on the boat's aft quarter, & then to a Primary or Secondary cockpit winch.

The more I think about it, the more it seems to me that I need to be using the bow cleats for the preventer. Any other lead point doesn't allow much of the strength of the line to be used to "prevent" the main in case of any stress. And I wonder if I might not need to continue using 12mm double braid for the strength. Which is about 5 tons breaking strength, compared to 3.7 tons for 10mm.

Concerning the necessity of a leader -- I'm trying to figure out whether this would be a "eureka!" moment, having it, after a lifetime of sailing without it. Maybe it would be luxury. Hmmm.

I've just never felt it was a problem rigging it while the boom is centered, and centering it if necessary for this purpose. An important point of discipline in my sailing is never let the boom out beyond the limits of the traveler without the preventer rigged, and certainly NEVER sail without evening out the tension between mainsheet and preventer. I can't imagine leaving it partially slack so that it could swing around and impart snatch loads. You could break things easily, so I never do it.

[Cheechako]

On the boom I liked to just use a loop/strop around the boom.
ie: it's a endless loop, pass it around the boom wherever you want it, then thru itself to attach the preventer to. It's a "soft" attachment and less stress when shock loaded.

[Dockhead]

Originally Posted by UNCIVILIZED

I'm unclear as to which loads on the RF line you're stating are modest. Except, perhaps, for when a sail is completly rolled up. That's the only time when the loads on the RF line will be "small".

It's all relative. But how great can these loads be? You have all of the purchase of the furling drum to reduce these loads. Maybe 100kg max? I can't imagine that the difference between 2 tons or 4 tons or 5 tons of breaking strength, for a furling line, makes the slightest difference.

The load is zero when the sail is all the way out. Also zero when the sail is all the way in. The only time it has any load at all is during furling, or when reefed. The loads are so light that note that many people recommend never using a winch.

I like the idea of partially stripped Dyneema because the stripped part will be fantastic inside the drum, and it will reduce windage, too. But when the sail is all the way furled, the furling line is all the way out except for the couple of turns of reserve you have on it. So it will be almost entirely exposed to UV. Does this not degrade Dyneema? I thought that's why we want polyester covers on them.

[accomplice]

Originally Posted by UNCIVILIZED

When a sail is furled, most of it's roller furling (RF) line, is wound onto the drum. And thus doesn't get much UV exposure.
But a big part of the reason for using Dyneema is that it's fairly immune to UV as compared to other ropes.

On most furling systems with which I'm familiar, the furling line is wound onto the drum when the sail is un-furled. One may maintain a few wraps when the sail is furled, but most of the line is not wound on the drum when furled.

With respect to preventer line sizing, I did have a 10mm double braid preventer part last fall. I cannot say the line was new, but its failure did surprise me. The forces involved are not small. Dyneema offers strength and UV resistance, but not much stretch.

[SVNeko]

Originally Posted by transmitterdan

They use the "leader" from the boom to the actual preventer line so the leader can stay permanently rigged to the boom. When not in use the bitter end of the leader is clipped to the boom near the gooseneck. It is always there ready to go. So if the boom is already out over the water it's a simple matter to rig the preventer without pulling the boom back inboard. Saves time and makes it more likely the preventer will always be rigged.

OK, but mine are always rigged and coiled at the mast. No need to clip a second line on and can be rigged in a minute without bringing the boom in. Just uncoil and lead out to the block and back to the cockpit.

[SVNeko]

Originally Posted by s/v Jedi

This is exactly what I always mention but most schrug it off thinking it is a non-issue.

1. It starts with the reefing points of main sail and mizzen. Each reef must lift the end of the boom further up, in order to keep the boom further away from the sea as conditions worsen and a deeper reef is set. If you want a blue water cruiser, then things like this is what makes it, not a brochure or price tag. If you don't have this then have it changed.

2. Regular polyester double braid lines for preventers so that they give a bit by stretching. But it does not stop there! Like mentioned: what happens if the boom meets the sea? Of course there are preventers that are designed to cope with that, like mine are! You simply choose a line that is not too thick which makes it stretch more. Next you look up the breaking strength of that line and install rope clutches that slip well before that force is reached. Now your designed weak point is slip of the clutch which leads to zero damage plus maximum dampening of shock loads. Not rocket science people, methods like these (design weak points, sacrifical parts etc.) have been used for hundreds of years!

Monohull issue only.