What is the purpose of the rear stay adjuster?

[Squidd]

I mean what is the advantage...? I have seen single line hydraulic pull downs, glorified turnbuckles with big wheels, and all sorts of contraptions to "squeeze" a split rear stay...

What for and when do you yank it...??

(picture borrowed)

 

[philwsailz]

If I may take a stab at it... From this layman's terms...

There are two scenarios I think about, and it involves the difference between a fradctional and a masthead rig.

On a fractional rig, the backstay can be tensioned, which introduces a bend in the mast.
This has the compound effect of flattening the main and applying tension to the forestay. pulling the draft of the jib forward. Both sails are affected in a manner which is beneficial in higher wind speeds, removing belly from the main and blading out the jib.

On a masthead rig, I am not sure you see adjustable backstays as much, but if it is present, tightening the backstay will move the CE of the main aft slightly, as well as tensioning the forestay. in this scenario, you are not introducing any mast bend, so no flattening of the main, but the jib can be affected by the increased tension, moving the jib's draft forward.

This is just how I have interpreted the information I have taken in. No doubt someone else will chime in with a more appropriate and factual answer, but these two examples give the best descrition of how I understand the backstay tensioner and when to use it.

 

[Squidd]

I should mention I have a masthead rig and split back stay with no known adjuster...

so question is do I "need" one...?

 

[philwsailz]

I should mention I have a masthead rig and split back stay with no known adjuster...

so question is do I "need" one...?

To my mind, probably not... You can manually tune mast rake by loosening and tightening fore and aft backstays to compensate for or add the desired amount of weather helm. Beyond that the only other benefit, (again only as I understand it) is tweaking the jib, which can be similarly accomplished by tightening jib halyard or adding a simple cunningham.

 

[Sandy Stone]

If you are not a racer or a tweaker, you'll probably get along just fine without a backstay adjuster. If you are (either one) you'll probably like the ability to tension the headstay going upwind in a breeze, reducing heel and increasing pointing ability. I agree, you probably won't bend the mast much on a PY26, so no flattening the main.

 

[rardiH36]

I have a masthead rig and several years ago I did add a squeeze type tensioner (like the one in your photo) to improve upwind performance by reducing the jib's headstay sag in anything more than a light breeze. The advantage is noticeable to me.

I also had been uncomfortable cranking down really hard on my bow/stern turnbuckles and maintaining the higher tension 24/7/365. When not at the boat, then tensioner is relaxed.

Philwsailz, you are right that a backstay tensioner on a masthead rigged boat doesn't induce the mast bend effect as for a fractional rig. But it does induce some since the lower forward stays tend to keep the middle part of the mast from moving back as the aft stay tension is increased. But the extra induced bend is only an inch or two on my boat. Probably has little effect on my mainsail trim.

 

[Gunni]

On your boat it would be there to take the sag out of your forestay when the genoa was powered up. They put a lot of head sail on the PY26, and the standing rigging is not that robust. So when see your forestay bending off to leeward more than about 6 inches, tighten up.

 

[Squidd]

On your boat it would be there to take the sag out of your forestay when the genoa was powered up. They put a lot of head sail on the PY26, and the standing rigging is not that robust. So when see your forestay bending off to leeward more than about 6 inches, tighten up.

I've seen that...where my jib downhaul is pulled straight and the forestay curves out a good 3"-4"...

 

[RichH]

The answer is very very simple .... the sailmaker who cut your jib/genoa EXPECTS that the forestay on your boat to be at a fairly precise tension.

You adjust the forestay tension via the tension in the backstay. That precise tension will cause predictable sag in the forestay wire when the headsail is windloaded, and the sailmaker will cut away a smooth curved shape from of the luff (called 'luff hollow') to meet this expected and very predictable sag that develops in the wire, typically for 12-15 knots of windstrength. Of course at differing windstrength the sag will be lesser or greater depending on the windstrength, so the sailor should adjust that backstay tension up or down to return that curved luff shape that the sailmaker put into the sail.

If there is too much sag in the wire because of too little tension in the backstay or too much windstrength, the headsail will become radically draft aft and the leech can 'hook up' to weather ... causing the boat to excessively heel over, slow down, and the boat to begin to 'skid' to leeward and unable to 'point' as a worst case scenario. 'Skidding off to the lee' will be felt, erroneously, as 'weather helm'. Skidding is usually a direct result of 'too loose' forestay!!!! The same bad shape of the jib/genoa can happen if a sailor applies too much jibsheet tension, tension that causes the forestay to radically sag.
If too much tension in the forestay, which can happen in 'very light' winds when not 'easing' the backstay tension, the draft in the jib/genoa will move forward and the leech will 'open' (distance between the leech and the mainsail will increase) ... and the all important luff shape will become very 'rounded' ... easily causing/allowing separation stalls to occur because the low speed air doesnt have much energy in it for the airflow to stay 'attached' at the now 'greatly rounded' luff shape.

So, the backstay causes proper tension in the forestay. Correct forestay tension determines the SHAPE of the jib/genoa, especially as most 'plain vanilla' jib/genoas were designed to be flown in 12-15 knots of windspeed and with the forestay near about 15% of wire tension !!!!!!!
Further, gorillas on jib sheet winches, can easily over tension the jib/genoa sheets and totally destroy the 'shape' of the all important LUFF SHAPE.

For the recreational sailor, backstay (forestay) tension can be a major SAFETY concern, especially in the higher wind ranges.
;-)

http://www.ftp.tognews.com/GoogleFiles/Matching Luff Hollow.pdf

 

[shemandr]

If you are not a racer or a tweaker, you'll probably get along just fine without a backstay adjuster.

Once again, I have to add you don't have to be a racer or tweaker to appreciate enhanced upwind performance. It is simply a joy to sail when any boat is properly trimmed. Good sails, good running rigging and sail controls are worth their expense.

 

[py26129]

Squidd

I put a back stay adjuster on my Py26, similar to the pic you attached.

The main reason it is there is to tension the forestay while beating. We wre racing quite a bit at the time and it made me feel better on the beats.

Practically speaking, especially if you're cruising, you don't really need it unless you want to squeexe the last .5% or performace out of the boat.

Matt

 

[onecoolair]

I mean what is the advantage...? I have seen single line hydraulic pull downs, glorified turnbuckles with big wheels, and all sorts of contraptions to "squeeze" a split rear stay...

What for and when do you yank it...??

(picture borrowed)

I helped race a friends Tartan Ten a long time ago......We used the back stay to bend the boat...

 

[Jackdaw]

I helped race a friends Tartan Ten a long time ago......We used the back stay to bend the boat...

This is a lot more common that you might think.... Lots of older racing boats answer questions about how much backstay to dial in with answers you would not expect...

'Until the the companionway hatch wont close.'

'Until the head door pops open'

 

[onecoolair]

This is a lot more common that you might think.... Lots of older racing boats answer questions about how much backstay to dial in with answers you would not expect...

'Until the the companionway hatch wont close.'

'Until the head door pops open'

So True!!! ....... You just reminded me of another who got one those first off the line Legend 45s....

 

[Joe]

Then there was the Americas' Cup race in San Diego a number of years back where backtstay tension bent the boat so much it folded in half, like closing an open book, and sank. I'm thinking it was one of the Australian boats..... but I'm too lazy to look it up... I just remember the event.

Regarding the question.... I learned that on a masthead rig the backstay tension is used to adjust sail trim related to headstay tension.

I can't see how a jib downhaul duplicates the backstay tension effect.... unless it's rigged to the tack or luff cringle, making it a jib cunningham, but that affects luff tension more than headstay sag.

On a fractional rig, the backstay adjuster affects sail trim related to mast bend.... headstay tension is less affected but also less critical on the fractional set up. The headstay becomes the fulcrum point for bending the spar.

 

[s sauer]

Backstay Adjuster

We have a six part purchase on a split backstay adjuster on a masthead B&R rigged 1986 Hunter 28.5. The double spreader mast head rig does bend with backstay adjustment and does flatten the main as an important means of depowering. We had our sailmaker measure the rig with adjuster on and off when he designed the luff curve of a new main and he was a little surprised at how much adjustment was possible. The sail fits the rig beautifully and has maximized adjustment potential. With a Tufff-Luff Headfoil on the headstay we are able to adjust the luff curve with the backstay adjuster. Checking specs, the mast section on the 28.5 is the same as a J29...it does bend.

 

[Scott T-Bird]

I say add it to your boat!

Squidd, if you are thinking about adding the backstay adjustment, I say do it. Especially if you like to use a larger genoa, it will make a very noticable difference in your pointing ability and reducing weather helm. On a masthead boat like ours, the purpose is to reduce the leeward sag in the forestay, which is significant when the wind is over 15 knots.

I made this improvement a few years ago and it is the most significant sailing performance improvement I made ... and I don't race. It just makes the helm behave so much better! It's a very easy DIY project and very worth the expense. If done right, it won't contribute to "rigging clutter", either. I think I'd make a change on mine though to use the blocks on a ring arrangement like the one you show. My Johnson split backstay adjuster, like the one you can see here ... http://shop.sailboatowners.com/prod...ay+Adjusters&gclid=CJ7bp-f6kLYCFUWd4AodnG0Ayw has too much friction, I think. Mine is set-up for 7/32" stays and I used a much thinner wire for the tensioning set-up, but when eased, it doesn't want to ease without manually pushing the rig upwards.

I remember one day I was sailing with my sister, and for fun we went with the 150 genny, and reefed the mainsail on the upwind legs in about 18 to 20 knots apparent. Because I was shaking out the reef every downwind leg, it was a lot of work and I forgot the backstay on one occasion when we turned upwind. (On a small lake, we make more direction changes in a weekend than many cruising sailors make in a season). Since it was eased for downwind sailing, it had to be tensioned significantly for the upwind sail, considering the wind conditions.

Anyway we were sailing along with my sister at the helm when I finally sat back to catch my breath and I noticed she was struggling with the helm. I tensioned the backstay and said "how's that?" She said "wow what a difference ... I don't have to use nearly as much effort!" And that coming from someone who didn't know what sail trim adjustments would do exactly.

 

[watercolors II]

A quicker sail adjuster

The next time you’re out sailing and someone else is at the helm and you’re close hauled into the wind, go forward to the forestay. If the forestay is tensioned correctly and all the tell tales on the headsail are breaking and flying at the same time, you’ll see the forestay bent forward and outward to the sail side of the boat. This twisting of the headsail luff allows the leech area of the headsail to be consistently shaped from bottom to top. If the angle of tension buy the headsail sheet is correct the back end area of the headsail will be parallel with the side of the hull from bottom to top and the slot between the headsail and mainsail will get smaller and smaller consistently as you look up.

Make sure you can see this first!

Take the sheet block for the headsail and move it backwards 6 inches to a foot, go forward again. The tension on the forestay has not changed so it will look the same but, by changing the angle of pull on the leech and foot of the headsail the leech area of the sail has changed. With the tension of the sheet the same on the headsail, you’ve added tension to the foot and lessened it on the leech allowing the top 1/3 of the sail to twist off away from being parallel with the hull, thus de-powering the top third of the sail. The slot will not get consistently smaller as you look up but, be wider at the top till it makes a sharper curve at the very top. This wider slot at the top of the two sails help de-power the mainsail a little. De-powering means more control and less heel when the wind picks up.

Lessening the tension on the mainsheet without changing the traveler will allow the mainsail to twist a little at the top, de-powering it also.

Now, with a backstay adjuster you will be adding twist to both sails instantly without having to reset each sail to de-power. Go back to the first paragraph and when you see that description have the helmsman grab the backstay on your boat and have him pull or push it sideways as hard as he can. What you’ll see is more of the description in the second paragraph.

A quick pull on the backstay tensioner of my Catalina 22 means 5 degrees less heel and better helm control in a puff. Unsheeting the backstay sets both sails where they were before the puff.

So, the backstay tensioner is another quick sail adjuster that can be accomplished by other sail controls or rigging adjustments.