Preventer Rigging?

[SVNeko]

Originally Posted by 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.

Change unclemack to rube goldberg

[SVNeko]

Originally Posted by 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.

It will eventually work its way forward. Use and icicle hitch or prusik knot.

[UNCIVILIZED]

As originally posted:
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 - in terms of size). 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"
Thus 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.

Dockhead,
I'm going from memory in terms of sail area here, but I'm thinking that it wouldn't be overly hard to have a sheet load in the neighborhood of 2T being generated by your blade jib. Given it's size, in a moderate to fresh breeze.
- So if someone has a sail that's similar in size, & the above ratios of drum size to foil size are similar, what are the loads on the RF line going to be when the breeze comes up a bit, & they roll in 20% of said jib?

Originally Posted by Dockhead

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.

One of the BIG perks of DYNEEMA IS it's UV resistance! Especially when compared to any other type of line readily available for yachts. That's why racers use it sans cover, for virtually everything. From halyards, to attaching virtually block & fitting on the boat.

The same reason is also why its so widely used commercially. In everything from the cables in cranes, to the mooring lines on HUGE commercial vessels. Amsteel Blue has been BIG with them for decades. For it's; light weight, durability, & UV resistance, even in Equitorial Sun.

[Dockhead]

Originally Posted by UNCIVILIZED

As originally posted:
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 - in terms of size). 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"
Thus 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.

Dockhead,
I'm going from memory in terms of sail area here, but I'm thinking that it wouldn't be overly hard to have a sheet load in the neighborhood of 2T being generated by your blade jib. Given it's size, in a moderate to fresh breeze.
- So if someone has a sail that's similar in size, & the above ratios of drum size to foil size are similar, what are the loads on the RF line going to be when the breeze comes up a bit, & they roll in 20% of said jib?



One of the BIG perks of DYNEEMA IS it's UV resistance! Especially when compared to any other type of line readily available for yachts. That's why racers use it sans cover, for virtually everything. From halyards, to attaching virtually block & fitting on the boat.

The same reason is also why its so widely used commercially. In everything from the cables in cranes, to the mooring lines on HUGE commercial vessels. Amsteel Blue has been BIG with them for decades. For it's; light weight, durability, & UV resistance, even in Equitorial Sun.

OK, thanks. I didn't realize Dyneema had GOOD UV resistance. I thought for some reason it was the opposite.

So it sounds like it does make sense to use stripped Dyneema for a furling line. Maybe even stripped 12mm. It will be light and pleasant to coil (like my Dyneema halyards), and the stripped part will be lovely inside the furling drum.

[UNCIVILIZED]

Originally Posted by accomplice

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.
Yep, on this I got a bit crossed up, & goofed.

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.

Personally, I can't say that I'd use Dyneema as my line of choice for a preventer. And I'm not certain that you're espousing such either.
However, if one wants do so, then it's not overly tough to "in line" splice some type of; shock absorber, snubbing device, or length of stretchy line, into a Dyneema Preventer line. While still maintaining the continuity (more or less) of the Dyneema (Preventer) line.

On sizing Preventers & their lines, it's really pretty simple. Figure out a rough estimate of the combined, maximum loads, on both your vang & mainsheet, and then add a Very healthy safety factor to that. Then double that figure (minimum).
- Especially given that there are VERY few single line purchase mainsheets, where as many/most Preventers are (single line arangements).
And also, many people are in the habit of using knots to attach or secure Preventers to their booms. So in essence, they're then cutting the line's stength by half; on top of all of the above.

[UNCIVILIZED]

Originally Posted by Dockhead

OK, thanks. I didn't realize Dyneema had GOOD UV resistance. I thought for some reason it was the opposite.

So it sounds like it does make sense to use stripped Dyneema for a furling line. Maybe even stripped 12mm. It will be light and pleasant to coil (like my Dyneema halyards), and the stripped part will be lovely inside the furling drum.

Great!
So you're familiar too, when stripping the cover off of lines, for the necessity of having a structurally buried taper of the cover, inside of the core when you do this, right? And in addition to the buried taper, the transition of this kind of splice, is lock stitched in place.
-> The reason behind both of these things, is so that the cover & core of the line work together. And so that the cover doesn't simply slide down the core, like a snake shedding it's skin, when you pull hard on the line.

Also, there are compounds like RP25 Spinlock RP25 - Rope Treatment and Coating - 250ml | MAURI PRO SAILING which can be used to further bond the jacket & the core together, & to increase it's wear resistance. Typically they're used in very high load applications, or where the safety factor on the line is very small. Such as on a high end racer.
And there are others, like Maxi Jacket or Maxi Jacket II, which can be applied to bare sections of 12 strand lines. Like stripped Dyneema cored lines. In order to further enhance their UV resistance, & abrasion resistance. Maxi Jacket Quart | APS

The latter coating is essentially the coating which comes already pre-applied to such lines, or to Amsteel Blue, etc. And it's what makes them shiny, plus emparts some of the slipperyness to them.
Also, you can use said coatings on other types of ropes also. In locations & applications where the propensity for abrasion is high. Such as where a halyard goes over a sheave. Or a line is attached to a shackle/fitting.

[Dockhead]

Originally Posted by UNCIVILIZED

Great!
So you're familiar too, when stripping the cover off of lines, for the necessity of having a structurally buried taper of the cover, inside of the core when you do this, right? And in addition to the buried taper, the transition of this kind of splice, is lock stitched in place.
-> The reason behind both of these things, is so that the cover & core of the line work together. And so that the cover doesn't simply slide down the core, like a snake shedding it's skin, when you pull hard on the line.

Also, there are compounds like RP25 Spinlock RP25 - Rope Treatment and Coating - 250ml | MAURI PRO SAILING which can be used to further bond the jacket & the core together, & to increase it's wear resistance. Typically they're used in very high load applications, or where the safety factor on the line is very small. Such as on a high end racer.
And there are others, like Maxi Jacket or Maxi Jacket II, which can be applied to bare sections of 12 strand lines. Like stripped Dyneema cored lines. In order to further enhance their UV resistance, & abrasion resistance. Maxi Jacket Quart | APS

The latter coating is essentially the coating which comes already pre-applied to such lines, or to Amsteel Blue, etc. And it's what makes them shiny, plus emparts some of the slipperyness to them.
Also, you can use said coatings on other types of ropes also. In locations & applications where the propensity for abrasion is high. Such as where a halyard goes over a sheave. Or a line is attached to a shackle/fitting.

Thanks; yes, I'm familiar with the concept. Which is not to say I'm able to do it myself -- my splicing skills have grown over the last year but that might be a bridge too far.

A bit of thread drift, but one thing I don't like about my dyneema halyards is that "snake shedding its skin" feeling. The cover doesn't seem to be bonded to the core in any way at all and I don't like the feeling. I don't trust it entirely in clutches, although I haven't had a problem with it so far.

[estarzinger]

Originally Posted by UNCIVILIZED

[COLOR=navy]
However, if one wants do so, then it's not overly tough to "in line" splice some type of; shock absorber, snubbing device, or length of stretchy line, into a Dyneema Preventer line. While still maintaining the continuity (more or less) of the Dyneema (Preventer) line.

I would (and have) argue that you don't want or need elasticity and 'shock absorption' in a preventer.

You don't want it because in a sea way it will allow the whole system to move, which will create fatigue cycles and wear - in everything from the gooseneck to the vang to the preventer itself. It is better to lock everything down so there is no movement or as little as possible.

You don't need it because, if the boom can not move, there is in fact very little shock loading in an accidental jibe. It is mostly the boom moving and building momentum that adds in the shock loading potential. And elasticity/stretch in the system actually adds shock loading when/if you correct the accidental jibe and the boom slams back into place.

There is an argument from some racers on some boats that you want a fuse in the preventer system. So that if you dip the boom in the water when it is prevented, it is the fuse that breaks rather than the boom. But #1 this is really not a problem with the vast majority of cruising boats, and #2 is not really a problem with most 'end of boom' preventer set-ups. So, I personally (after quite a bit of thought and experimentation) prefer not to have a fuse (on most cruising boats - I would on some racing boats)

[SVNeko]

Originally Posted by UNCIVILIZED

Great!
So you're familiar too, when stripping the cover off of lines, for the necessity of having a structurally buried taper of the cover, inside of the core when you do this, right? And in addition to the buried taper, the transition of this kind of splice, is lock stitched in place.
-> The reason behind both of these things, is so that the cover & core of the line work together. And so that the cover doesn't simply slide down the core, like a snake shedding it's skin, when you pull hard on the line.

Why? Its a core dependent line, so the cover should not need to carry any of the load. Simply secure it from sliding somehow.

[s/v Jedi]

Originally Posted by estarzinger

I would (and have) argue that you don't want or need elasticity and 'shock absorption' in a preventer.

You don't want it because in a sea way it will allow the whole system to move, which will create fatigue cycles and wear - in everything from the gooseneck to the vang to the preventer itself. It is better to lock everything down so there is no movement or as little as possible.

You don't need it because, if the boom can not move, there is in fact very little shock loading in an accidental jibe. It is mostly the boom moving and building momentum that adds in the shock loading potential. And elasticity/stretch in the system actually adds shock loading when/if you correct the accidental jibe and the boom slams back into place.

There is an argument from some racers on some boats that you want a fuse in the preventer system. So that if you dip the boom in the water when it is prevented, it is the fuse that breaks rather than the boom. But #1 this is really not a problem with the vast majority of cruising boats, and #2 is not really a problem with most 'end of boom' preventer set-ups. So, I personally (after quite a bit of thought and experimentation) prefer not to have a fuse (on most cruising boats - I would on some racing boats)

The preventer is only half of the system to keep the boom in place. Do I understand that you also use a Dyneema sheet?

I have a poly doublebraid sheet and preventer and never had the boom moving or shockloading. To the contrary, I use the stretch available to tension sheet and preventer and when one stretches a bit, the other takes up any slack by stretching a bit less. Works great

Dockhead: the forward blocks for my preventers: for the main they are close to the bow cleats and for the mizzen they are at the midships cleats. My main preventers are 105' each of which 60' is between block and the bitter end on the winch.

[estarzinger]

Originally Posted by s/v Jedi

The preventer is only half of the system to keep the boom in place. Do I understand that you also use a Dyneema sheet?

I have a poly doublebraid sheet and preventer and never had the boom moving or shockloading. To the contrary, I use the stretch available to tension sheet and preventer and when one stretches a bit, the other takes up any slack by stretching a bit less. Works great

Yes, we also had a dyneema sheet (and vectran 3dl & spectra sails). A polyester sheet sort of damps some of the advantages of sails like those.

But I agree with you that polyester is just fine - it is reasonably low stretch, especially if you tension it right up. (but I might add, that even if you have and like a polyester sheet, I would still suggest there are advantage to a dyneema preventer)

What I was offering was an option against the "shock absorber, snubbing device, or length of stretchy line" suggestion in a post further above, which I took to mean a truly elastic section of nylon or rubber snubber sort of material. I do not think that is useful in the preventer.

If you do want extra (nylon level) stretch anywhere, I would suggest you put it in the traveler line. That is the most effective place to soak up jibe shock with minimum effect on sheeting control and unnecessary movement in bumpy conditions. There is a debate about whether putting elasticity there is a useful trade-off or not, but not much debate if you want to put elasticity in that is the place.

In the transpac, both Stan Honey and Jim Corenman (both winners of their classes) mostly did racing 'slam jibes' (eg did not sheet in much if at all, just jibed and let the boom fly across) and both found nylon dynamic climbing line useful in their trav control lines to soak up this shock loading and cushion its effect on their rigs.

[neelie]

Evan,
Interesting that you recommend against having any stretch or give in the preventer. I'm not sure I am convinced (yet).

My intuitive feel is that a bit of give or stretch in the system minimizes shock loading and therefore can't be a bad thing.
As usual, I have absolutely no data to back up this or any other subjective assertions I make.
However, 60 feet of 1/2 inch nylon under a bit of tension has worked fine for us. In light airs and rolly seas the available stretch in the system never seems to come into play.

I guess it depends on the degree of allowable give in the system?

[estarzinger]

Originally Posted by neelie

Evan,
Interesting that you recommend against having any stretch or give in the preventer. I'm not sure I am convinced (yet).

My intuitive feel is that a bit of give or stretch in the system minimizes shock loading and therefore can't be a bad thing.
As usual, I have absolutely no data to back up this or any other subjective assertions I make.
However, 60 feet of 1/2 inch nylon under a bit of tension has worked fine for us. In light airs and rolly seas the available stretch in the system never seems to come into play.

I guess it depends on the degree of allowable give in the system?

Well, I am not trying to sell it; so if you are happy fine

But I can suggest that there is a trade-off between shock absorption vs fatigue cycles. And while shocks are more obvious, my experience would suggest the shock on a tightly low stretch prevented boom are not so very high and there is more long term damage from extra fatigue cycles. Lots of fatigue cracked goosenecks and vang lugs and such.

I personally would have considered 60' of 1/2" nylon to be very stretchy - that's essentially a chain snubber spec designed to maximize stretch. Out of curiosity, with your preventer set and a full main and an accidental jibe in 25 kts of breeze, how far toward the center line does the preventer stretch allow your boom to go? When we used nylon the boom would go about half way to the centerline, and then had a lot of momentum (sail pressure plus the elasticity spring back of the nylon) when it slammed back.

We started off with nylon, switched to polyester and liked it better, and switched to dyneema and liked it best. But again, if you like it, great and be happy and I will not argue at all.

[s/v Jedi]

The traveler lines... right, I didn't think of that... need to ponder on it for a while
About the stretch and how far the boom comes in during gybe with preventer set: you take out most of the stretch by tensioning it. I never had an accidental gybe with preventer set in heavy weather, but I did test it in 25 knots with 11 knots boat speed and the boom came back about halfway to midships with no shock from the boom. That still left the sail with 7 full 3/4" round battens snapping to the other tack that made a racket.

[estarzinger]

Originally Posted by s/v Jedi

I never had an accidental gybe with preventer set in heavy weather, .

you are a much better man than I

actually, with your boat you probably usually sail hotter downwind angles to get better vmg.