Are backstay adjusters a threat to B&R rigs?

[henkmeuzelaar]

Although the pros and cons of variable mast bend (through backstay adjustment) as a tool for controlling sail shape are already a topic of discussion in at least two other ongoing threads, I would like to flesh this particular issue out a bit further in connection with the famous (some might say infamous) Bergstrom and Ridder rig with which many Hunters are equipped.I don't claim to be an expert rigger, sailmaker or designer but it would seem to me that the combination of a B&R rig with an adjustable backstay makes for an uneasy marriage on the best of days and for a potentially dangerous relationship on the worst. The fractional B&R rig on Rivendel II, our Hunter Legend 43 (hull #1), features a fairly strongly pre-bent mast and is clearly a poor candidate for further bending through tightening of the split backstay attached to the masthead. Attempts at further mast bending through backstay adjustment would be expected to concentrate most forces at the attachment point of the genoa, some 8 ft below the 64ft high masthead. IMHO, this would be an open invitation for trouble. Although Rivendel's design pre-dates the days of the backstayless B&R Hunters, the backstay is relatively lightly built and tensioned. It's main role appears to be to prevent the mast top from whipping around when there is no full main hoisted, as the upper shrouds are quite capable of maintaining the correct amount of mast prebend specified for this particular B&R rig all by themselves. In fact, Rivendel's backstay does not even play an important role in controlling forestay tension, nearly all of which is controlled by the upper and intermediate shrouds, supported by the strongly backswept spreaders of the B&R rig...But what about the masthead-type B&R rigs on many Hunters? Is there any particular reason to believe that mast bend variations large enough to be effective for controlling sail shape, could perhaps pose a threat to the overal integrity of these rigs as well?A tiny bit of fore-and-aft play is unlikely to get most B&R sailors into serious trouble and might even make ex-racers and other sailors addicted to tweeking the backstay adjuster downright happy . Nonetheless, one should always keep in mind that pulling the masthead down and aft inevitably changes upper shroud tension (and - to a lesser extent - that of the intermediates), because of the strongly backswept spreaders and unusually far aft located chainplates of the B&R rig. So, unless my logic is "all wet", trying to increase mast bend on a B&R rig, (e.g. in order to flatten the main in strong winds) is akin to slackening off the uppers! Not exactly, the recommended course of action in heavy weather, I believe, as this might promote mast pumping and other destructive behavior aloft.Looking forward to your valued insights and comments;Flying Dutchman

 

[Steve S]

Ask Selden...

Henk,I have given some thought to adding a backstay to by fractional B

 

[newly anonymous]

thinking out loud

On a BnR rig, the diagnals control bend while the uppers control athwartships movement. So wouldn't a backstay tensioner result in slackened diagonals? If this is the case, Henk, it would seem that you'd be inviting the mast to pump in high winds. Keep in mind that I'm thinking out loud here and that my poor brain is officially on spring break in 5 hrs, 37 minutes. The other consideration, of course, is that a BnR rig is all about roach, and adding a backstay defeats the purpose, doesn't it?the link below references the BnR tuning reference page on HOW.

 

[henkmeuzelaar]

Thanx for the link, John. Who wrote this?

Unfortunately these tuning instructions do not appear to differentiate between fractional and masthead B&R rigs. Where they say:"The upper shrouds, also called uppers, keep the top part of the mast, that which is above the spreaders, from moving from side to side. When an upper is tightened it does two things. It will pull the mast in the direction of the shroud, and it will put a bend in the mast at the spreader in the opposite direction from the shroud. Example: when the starboard upper is tightened it will pull the top of the mast to starboard and push the middle of the mast at the spreader to port."the writer appears to momentarily forget that the direction of pull of B&R uppers is neither simply to port nor to starboard but quite markedly aft as well. As a result, the combined pull of the two uppers will bend the mast in aft direction (as the port and starboard vectors cancel out). However, his remark that"The intermediate shroud's function is to keep the mast from bending to either side at the upper spreader." would appear to make perfect sense. The direct reason for bringing my concerns about the potentially negative effects of backstay adjusters on both types of B&R rigs up was that the thread discussing how to add a backstay adjuster to a Hunter 31 (a masthead B&R rig, as far as I can see) did not address this issue at all. Also, in the thread on "mast prebend in mast furling" the impression was created that backstay adjusters perhaps ought to be mounted on all vessels wanting to properly shape the main. So, before too many owners of B&R-rigged Hunters fall under the spell of fanciful backstay adjusters I thought it appropriate to put a bit of a question mark behind these notions. Have fun!Flying Dutchman

 

[newly anonymous]

agreed .......... Phil?

I'm thinking of so many other complications it's almost dizzying. Chainplates for example. On my h410, with it's aft-swept arch, a backstay set far enough aft to allow boom clearance would have to be anchored almost a fathom behind the transom. What that means is that you'd have to go to runners, which would be working in direct opposition to the diagonals. That and the fact that runners are inherently evil. ........... By the way, I don't know who wrote the article about tuning the BnR rig. I'm guessing that Phil would know. Are you there Phil?

 

[Phil Herring]

I believe it was...

...the guys who designed the mast, Mr. B. and R. I'm haivng a brain cramp and can't recall if if it was Lars or not, but I'm pretty sure they are the source.

 

[Stu Sauer]

Backstay adjustment & shroud tension

I have had an 8:1 purchase on the four wheel component split backstay on my 1986 Hunter 28.5 since the mast was first stepped. By the way, when I directed similar questions to the Hunter folks, the response was : "Why would you want to bend the mast; we don't recommed that."So I worked out the installation myself and have been using 2 to 4 inches of additional mast bend which will completely flatten the main. As far as this having an effect of slightly loosening the shrouds, I think they may become marginally looser, causing the mast to slightly fall off to leward. This seems OK with me because it would serve to de-power the upper portion of the sail.The only mast pumping I've noticed is a kind of wind induced harmonic vibration in the mast when the sails are down and we're in the slip.If there were significant issues in using this backstay adjuster I guess I would have noticed something by now, seeing that the 28.5 has a fairly slim mast section for a 37'-4" high mast head rig (41 feet from waterline). The 31 and 34's appear to have comparatively heavier cross sections.

 

[Cliff Ruckstuhl]

Bergstrom & Ridder

Rig Designer'sCliff

 

[Alan]

Lars "from Mars" Bergstrom

..was the primary culprit of this design. When I spoke with him a number of years ago about it he told me that the original design had no backstay adjuster BUT it was designed with a headstay adjuster. I don't suppose you guys want to spring for a hydraulic headstay adjuster,....well neither did Hunter, so they never put them on the boats. Gee I wonder why?? P.S. The B & R rig is probably the strongest design on the market. I had a backstay adjuster on my old 34 for years and it really got a workout. I can't believe that a backstay adjuster could do any harm to that rig!!

 

[henkmeuzelaar]

That nugget of info makes a lot of sense, Alan!

On larger vessels, any idea of a rapidly adjustable forestay might as well be forgotten. Even on smaller boats the cost and technical complications involved would seem to make a forestay adjuster quite impractical, I fear.What I personally still hope to learn from this thread is whether there is any wisdom out there regarding the theoretical (e.g. performance-related) and practical (e.g. tuning-related ) differences between the fractional and masthead B&R rigs.Have fun!Flying Dutchman

 

[Wanderer138]

Where the backstay tension goes

Like Stu's 86 H28.5, my H23 has a "bendy" mast with swept-back spreaders, split back-stay and chainplates aft of the mast step. The mast is very slender and light and gets its stiffness from the standing rigging. Here's how it works.First off, I think "prebend" is an incorrect term. "Pre-bow" (as in "bow and arrow") is more accurate. The first step to tuning the rig is to tension the upper shrouds. As upper tension increases, the middle of the mast bows forward. The swept-back spreaders act like an arrow and heighten the effect. The masthead barely moves aft, if at all. As Henk noted, tensioning the upper on one side would bow the mast to the opposite side. By tensioning both uppers equally, side bend is cancelled out, but the forward bow remains, in fact it's doubled. When the desired amount of bow ("prebend") is achieved, the lowers (which are attached to the mast at the spreaders) are tensioned to stiffen the mid-mast. Typically the tension in the lowers is about half the tension in the uppers.With a properly tuned rig, the boat can be safely sailed with the backstay completely slack or even missing, just like a B

 

[Wanderer138]

Difference between masthead and fractional rigs

To me, a fractional rig would be easier to bend/bow than a masthead rig. The B

 

[Arlyn Stewart]

B&R backstay adjuster - baby stay

Basically, the B&R rig is a commitment to one tuning setup, hard for more wind or loose for light air with little real ability to tune on the fly with a backstay tensioner because the tensioner will produce looseness in the uppers and loss of forward forces of the radical raked spreaders as it draws the masthead aft. This is especially true for mast head rigs. This looseness of course can result in mast pumping or aft bend which actually makes the main fuller. There is a way to make the backstay adjuster functional in firming up both the jib and main, but it means holding the center of the mast forward as spreader forces are relaxed by the backstay tensioner with an alternate method... a baby stay. On my 25 foot boat, a traditional baby stay was not possible as there is no hard point between the mast and stem and even if there were, a baby stay would not leave room to tack the jib well. The solution is one to the stem which works for cruising but wouldn't be worth the effort for a day sailor or racer as the baby stay has to be released for tacking. I call it a running baby stay, not related to point of sail but because its running rigging rather than standing rigging. It is rigged from the spreader to the stem and of course has to be self retracting. Here is how it works. A low stretch line is rigged from the spreaders to near a block at the mast base and has a ring affixed where two more lines make to it. One is a bungee which feeds thru the block and back to the spreaders. The bungee provides the retraction of the baby stay to the front of the mast. Another low stretch line, actually my pennant line for my drifter is shackled to the ring and of course feeds thru a block at the stem and then back to the cockpit. When the baby stay is wanted, the pennant line is hauled firm by a cabin top winch. To tack, the line is released where the bungee retracts it to the mast allowing full freedom for the jib to tack. It works great for the coastal cruising I do on the Great Lakes. A bonus is that my boat uses a CDI furler which has an integrated halyard and with no traditional forward lowers (baby stays) there is no redundancy for a forestay failure. The use of the running baby stay offers a measure of safety ( always a plus while cruising) as well as allowing use of a backstay tensioner on the B&R rig to gain the ability to power or depower the rig.

 

[Stu Jackson]

Still Not Sure

After relentless discussions about this topic over the years, I'm still not sure Ii get the concept.I fully understand bending the main and flattening the mainsail.But, and this is a BIG but, most of our boats just do not have the mast designs that would allow that to happen.Our C34 has a tree trunk for a mast. All our backstay adjuster does is tighten up on the forestay a bit.So, gang, what's all the discussion about mast bend? I understand Hunter rigs are very different, but given the cross section of the spars I've seen on Hunters, new and old, I just don't see anyone being able to bend them enough, or at all, to affect the mainsail.Maybe on A Cup boats, and certainly on smallr dinghies, but not on our 25 to 35+ foot recreational boats.Hope you can help me better understand this.Thanks,Stu

 

[Fred Ficarra]

Masthead B&R

I've read and studied the posts here several times from start to finish. The only explanation for Henks' (and others) concern about bending a B&R, seems to be as it applies to fractional rigs. My H34 is mastheaded. I trashed the split backstay to simplify for our bimini. The adjuster is now Navtec. I can't imagine not being able to add tension. The masthead tension aids both genoa and mainsail shape. And the Navtec works really well.

 

[henkmeuzelaar]

This is the deal, Fred:

On a conventional rig the pull of the backstay against the forestay controls mast bend, whereas the shrouds mostly control sideways play (and thus help the mast stay in column).On a B&R rig, whether masthead or fractional, most of the functions of the backstay, including mast bend, have been taken over by the shrouds in general and the uppers in particular. That's why for all practical purposes the backstay is no longer needed.Unfortunately, by adding the function of providing mastbend to the shroud's original function of keeping the mast in column, these two functions have become a lot less independent of each other.Consequently, the use of an "extra" backstay to amplify the mast bend function of the shrouds unavoidably also influences the shroud's original function of keeping the mast in column. In fact, since the shrouds are being loosened by the increased pull of the backstay there is now also less shroud tension available to keep the mast in column.........This is the reason for the concern that has been voiced by me and others. Theoretically speaking, the correct way of providing additional mast bend for a B&R rig would either be to increase the tension on all shrouds (but primarily on the uppers) or to increase tension on the forestay.Have fun!Flying Dutchman

 

[Fred Ficarra]

But, to counteract headstay sag one needs

backstay tension. With my new hydraulic ram, I'm finding that about 1.5 tons looks great. And yes, the Leeward shrouds do loosen but it sure beats a curve in the headstay. Olaf doesn't like that.P.S. Lets say I had no backstay. I set the shroud tension with a Loos (sp) guage after commissioning last summer. We followed the recommended tension but kept to the lower side of the range for my size boat. Are you saying I should have used higher tension and not worry about messing with the backstay?

 

[henkmeuzelaar]

Two comments, Fred

(1) In principle the headstay on a B&R rig can and should be tensioned by increasing the combined aft pull of the uppers and, to a lesser extent, the intermediates.(2) A sagging headstay is a nuisance (although at times a very annoying one) whereas - to me -a sagging mast poses a threat...Flying Dutchman

 

[Arlyn Stewart]

B&R dynamics

A B&R rig eliminates the traditional forward lowers (baby stays) and sometimes the backstay. The reason for doing away with forward lowers is to more easily move jib tracks inboard for better pointing. With the forward lowers eliminated, an alternative method to hold the middle mast forward is needed. This is what the radical raked spreaders do... push forward on the middle mast section. If a backstay on such a rig is used and it has a tensioner and enough slack exist in the forestay to draw the mast head aft, the uppers will loosen and the forward force on the spreaders will be compromised which will allow the middle mast to bend aft (undesirable) under load. For this reason, B&R mast head rigs are not thought to be candidates for a backstay tensioner without compromising proper shroud tensioning. The story is somewhat different on a fractional rig where pulling the masthead aft doesn't result in aft bend in the mast but has the desired effect of adding prebend.A 25 foot boat certainly has a light enough mast to experience bend. Without the running baby stay I discuss up the thread, I experience about two inches of aft bend in the mast if a back stay tensioner is firmed up. The running baby stay will easily hold 1.5 inches of prebend which equates to 3.5 inches difference in the mast bend and considerably less power in the mainsail and jib of course when the tensioner is hardened.

 

[Fred Ficarra]

Henk and Arlan

I was going to reply last night but wanted to study your posts some more this morning. OK, here it is. As the owner of a masthead B&R H34 since 1986 and during that time, always used added backstay tension and traveled many thousands of miles at sea, I have not seen the detrimental behavior you guys speculate as a possibility. The upper shrouds do loosen under backstay tension but that's it. Henk, I am in a quandary. Last month you thought all B&R rigs were fractional by definition. Now you're postulating the behavior of my rig as if, well, you were in on the design, testing and production of it. With all due respect, why? I'm really torn. I gobble up every word you write. But your concerns, I'm not seeing. Hey, you know what? We are talking about SAILING! And while I've got your attention, hows Rivendel? Specifically, any flood damage?