Adjustable Backstays

[sidon]

I am looking at buying some form of adjustable backstay tensioner for my jeanneau 37. I looked on the bavarias at southampton and their system seemed o.k. I am going down this route as I am trying to take the sag out of the forestay,as I have facnor furling gear fitted, and when my local rigger checked he said the only way to remove this was with an adjuster. My boat has twin backstays and is used for cruising as well as racing, therefore I dont want a single backstay which falls right in the middle of the stern impeding access to the cockpit. Has anybody got any ideas which system to use, your advice would be greatly appreciated. Thanks in anticipation.

Simon M

 

[Twister_Ken]

Quick question

Does it actually have twin backstays, or a single backstay which terminates above the deck at some point and then has two stays coming down to the quarters?

 

[sidon]

Re: Quick question

Unfortunately in my cas it has 2 seperate backstays.

 

[Twister_Ken]

Re: Quick question

Not fractionally rigged I guess?

To get forestay tension without twisting the mast you have to increase tension in both backstays pretty well equally. The only way I can think of doing this (at least quickly!) would be to put a bridle between the backstays, then pull that down with multi-part tackle or a lever to pull the stays towards each other, but it doesn't seem exactly seem pretty.

It might be worth talking to a rigger to see whether it would be sensible to put a single, split backstay on.

 

[Twister_Ken]

or if the mast is keel stepped

it might be possible to use some chocking at the partners to increase forestay tension.

 

[kdf]

Friend of mine has SO 37 and I was looking at doing the same thing for her. It might be possible to remove one of the backstays at the masthead, then bring down the single remaining one to a point maybe 2-3 metres above the deck, and then split it from there to each quarter. You can then put the adjuster on one side and it would tension the lot.

You do need to talk to a rigger. I don't know if this is possible but I suspect it is.

 

[billmacfarlane]

Doesn't Bavarias have a fractional rig which means that the backstay tensioner is more to do with controlling the shape of the mainsail rather than tensioning the forestay ? I'm not sure which type of mast the Jeanneau has but if it's fractional with swept back spreaders I'm not sure that a back stay tensioner will help. One of the mags last month had an article about how to correctly tension a fractional rig. Maybe someone knows which one ?

 

[kdf]

SO37 is masthead but the principle is the same. THey currently have two bottle screws but I think he's looking for something that can be easily adjusted from the stern. The article in the mag was all about fractional rigs.

 

[qsiv]

Re: Quick question

May not be pretty - but costs very, very little and generates immense power.

I also have twin backstays, but have a pair of hydraulic rams to do the tensioning. Beware the loads can be immense. We regularly run 22000 lb in the hydraulics - if I remember correctly this equates to about 6 tonnes of load in my case.

The advatage of the bridle is that you arent interfering unduly with the rig or the loads it was designed for. Presently the tangs at the masthead are each designed to take half the total backstay load. If you chage to a single backstay and diuvide it 10 foot or so abiove the deck, all the load will now be taken through a single tang, and you may well be beyonf the design limit.

 

[Guest]

If as mentioned the masthead fitting is suitably strong and I would say it most likely is, get rid of the twin backstays and have bridal with adjuster on one leg, hydraulic is the easiest to use.

Cheers

Lash

 

[Twister_Ken]

Re: Quick question

Not disagreeing, but with true twin backstays, the angle between them is pretty narrow, so to get much tensioning through a bridle means putting it fairly high up, and pulling it down a long way = lots of string

 

[Chris_Stannard]

Banana Boats

Be very careful if you fit an adjustable backstay. There is a limit beyond which you should not go in tensioning it. I have a Selden mast and in the instructions with it there is a way of calculating the maximum tension that you should put on the rig.
There can be a problem with masthead rigs, with adjustable backstays, or fractional rigs with check stays, that if you wind too much tension on you can make the boat banana shaped and over time this will become permanent. I have seen a Sigma 33 in this state from using the winches to wind the check stays on. Of course it is self defeating in a way because if you start pulling the boat out of shape you are not making the forestay tighter.

My advice would be to ask Jenneau, or the designer if you know who it was, what their recommendations would be and how much tension you can impose safely on the boat.

You can also partially overcome the problem of the forestay allowing the genoa becoming too full by increasing the halyard tension a bit. That is a question of trial and error to see how much tension you need in various wind strengths and then, if you are serious about your racing, marking the halyard to know how much you need. The forestay tension can also be increased by bring the main traveller to the centre of the boat or slightly to leeward and pulling the sheet down hard.

One last thought, if you do fit a tensioner, remeber that initalilly you should set the tension up and then set your genoa halyard tension, as if you pull the mastheas back you do increase the tension.

Chris Stannard

 

[charles_reed]

Re: Banana Boats

I'd certainly agree about the dangers of using backstay tensioners on masthead rigs.
Far better to try genoa halyard tension before going to the backstay tensioner

 

[qsiv]

Re: Quick question

I wouldnt have a bridle slide down slide down (theres potentially a lot of friction)- I'd seize a purchase horizontally (above head height) and simply pull them together. As the rig is masthead, and one isnt looking to deflect the head of the mast aft by more than an inch or so in order to increase the forestay tension you wouldnt need large deflections to generate the loads.

 

[Roberto]

Re: Banana Boats

Even if the banana shape is not permanent, it has a few funny effects on the boat, tried first hand with excessive tension on backstay:

propeller shaft misaligned, turn on engine before releasing tensioner and it goes vlakvlakvlak

rudder shaft friction increase, if fitted with a deep skeg it can almost become impossible to turn

internal door opened, various hatches out of alignment...

 

[Peter_H]

We have a Beneteau Oceanis 361 which also has twin backstays. We were also looking at a backstay tensioner sytem as there was excessive sag in the forestay when going to windward.

Our local rigger put us off the idea since he thought the swept back spreaders on the masthead rig would be a problem. His thinking behind this was that since the spreaders are swept, the cap shrouds contribute to pulling the masthead back as well as the backstays and so both the backstays and the cap shrouds contribute to forestay tension. Therefore if the tension of the backstays is altered using the tensioner it will also alter the tension of the cap shrouds and so could lead to lateral instability in the mast. A way of getting around this would be to leave the backstay tension constant. However, it has already been mentioned that leaving a high tension can lead to the boat bending and becoming damaged.

I do not know enough about rigging to verify whether this theory is correct but i have found that tensioning the cap shrouds does slacken the backstays and vice versa, so there is certainly some truth behind the theory.

However, on our boat we have greatly improved pointing ability by slackening the rig and starting tuning again from scratch. This has decreased forestay sag considerably. A good tuning guide can be found at the beneteau owners assocaition website (it is designed for an oceanis 411, but will be virtually the same for most standard rigged boats). The site is www.beneteauowners.com. Go to library, then 'rigging and tuning' and the guide was posted on 23rd jan 01. I hope this helps!

 

[kdf]

Re: Banana Boats

Agreed - however no amount of forestay tension will have any impact on a sagging forestay. The weight of the furler alone will cause the stay to sag to leeward which kills your pointing ability. The only real way to cure this is to pull the masthead back either via the caps or the backstay.

The SO 37 has two bottlescrews, one at the end of each backstay. You can safely assume that if your new single backstay can not tension beyond the limit of the current bottlescrews the you will not damage anything.