What does a backstay tensioner on a fractional rig boat do?

[maxwell edison]

Can someone help me understand what use is made of an adjustable backstay on a fractional rig boat please?

After many years of sailing a masthead rigged boat with a non adjustable backstay my life is going to change.

Next year I will be getting a Sadler 290. She has a 7/8 fractional rig with an adjustable backstay pulley tensioner which allows plenty of tension to be added to the backstay to flatten the main in strong winds thereby reducing the need to reef down earlier. Or so I read in one of the reviews of the boat.

Is that it then? When the wind gets up I haul in on the tensioner, and when it goes down I let it off? Or is there more to it than that? How do I know how hard to haul it in or let it off? Come to that how do I know the starting point for tension?

What I would really like is for someone who knows about these things to tell me what this tensioner is for. When do I use it? How do I use it. What does it do?

In case a bit more detail helps the Sadler has 56 sq m sail area. Of which, the main is 29 sq m and the headsail 27 sq m. She weighs about 5.3 tons, has a ballast ratio of about 46% and an AVS of about 144 degrees.

Finally, what changes am I likely to experience in a fractionally rigged boat compared with my masthead rigged boat.

Thanks

Max.

 

[AIDY]

Backstay tension is normally cranked on when beating to windward (should make the boat point better) and reduce weather helm. On a reach / run slacken off. not required in light airs.

fractional rigs normally require reefing earlier, i put my first reef in around 15knots upwind.

 

[dt4134]

It bends the mast slightly. The effect is that the middle part of the luff of the mainsail is pulled forward and the sail flattened which reduces the power in the mainsail. In conjunction with tightening the outhaul and putting more tension on the main halyard you can manage the power in the main and delay the point in a building breeze when you have to reef.

It will also tension up the forestay and take some of the sag out of it which will also tighten up the luff of the headsail, which is also good in a building breeze.

 

[Nick_Pam]

If you run "Backstay Tension" through the google search engine, one of the responses you will get is This

Nice simple explanation of a really black art!!!

Nick

 

[bbg]

What he said.

Tension the backstay upwind in stronger winds. Ease it as the wind drops or when off the wind.

With experience you will be able to see the shape of the sail flatten as you crank on the tension. It is also interesting to stand at the base of the mast and look up before and after it is tensioned - you will probably see a difference.

 

[MarkGrubb]

your description sounds about right. I've raced on a boat with a hydraulic device that we'd pump to tension the stay and flatten the main. The affect was most noticed by the helm. If the helmsman was fighting the wheel he would pump on some backstay tension to flatten the main, the affect of this was to make helming much easier by reducing weatherhelm in the gusts, and also often gave a few tenths of a knot extra speed. Then in the lulls, ease the tension to put more power in the rig.

We'd think about reefing once the backstay was fully tensioned and the mainsheet traveller was at the end of the track.

Best thing is to get out and practice and get a feel of how it affects speed, weatherhelm, pointing etc.

 

[MarkGrubb]

if you have a running backstay then you'll also have to learn to gybe again /forums/images/graemlins/smile.gif.

 

[ex-Gladys]

Backstay doesn't flatten the main it eases the leech. When blowing, the fullnes in the main is pushed aft, and you use outhaul and halyard tension t heave it back forward. When you can do that no more, you bend the mast to let the leech open up, because the belly moving aft has hooked the leech and that gives weather helm

 

[KenMcCulloch]

[ QUOTE ]
if you have a running backstay then you'll also have to learn to gybe again /forums/images/graemlins/smile.gif.

[/ QUOTE ]
I don't think maxwell edison (majoring in medicine?) mentioned a running backstay. If he has one I hope he has the other as well.

 

[rwoofer]

Actually the backstay does both. The forestay acts as a pivot point, so above it the mast is pulled back, which opens up the leech. Below the forestay, the mast actually moves forward and this is what flattens the sail. This forward bend is usually more pronounced higher up the mast, which is why you have two further aids to flattening the sail - the vang and the flattener. The vang works by pushing the lower mast forward and the flattener works by pulling in the bottom third of the main, much like an outhaul.

Now if you have got running backstays on too tight you can undo all of that flattening effort!

Edit: And I nearly forgot that on super flexible masts you can use the cunningham to flatten the main as well in addition to it's more typical use of pulling draft forward. On our old twin trapeze dinghy the cunningham was actually the number one flattening device and you could completely blade the main with it.

 

[jb2006]

I agree with rb.

The backstay will also tighten the forestay as mentioned above but this is a lesser effect on the fractional rig. If a fractional rig has running backstays these tension the forestay much more efficiently - the backstay will still supply bend if the runners attach to the mast at the same height as the forestay. They seem to be a rarity now except on boats with huge rigs

 

[Boatmik]

Howdy,

It depends on the rig a lot. AND THE STYLE OF SAILING.

A few years ago I sailed on a racing boat with some Grand Prix type sailors on a boat with backstay and runners.

They used a reasonable amount of runner tension but almost never used any backstay.

The mainsail was trimmed in the same sort of way a racing dinghy mainsail is trimmed. As power became too much more vang, cunningham and outhaul.

Sheet was dumped in the bigger squirts - but never any backstay tension.

I would guess the reasons are.

1/ The sailmaker has spent a lot of time getting the right shape into the sail to match the mast bend characteristics. Bend the mast at top and you lose the shape designed into the sail.

2/ If you tighten the backstay you lose the gust response of the mast. It might reduce power in the gusts, but the mast won't straighten up in the lulls to power up the boat, tighten the leach and help the boat maintain height.

Just like sailing a dinghy.

After that experience I would be much more careful about tightening the backstay prematurely.

Michael Storer

 

[rwoofer]

Sounds about right for very flexible masts, but for normal cruising masts you won't get anywhere near the effect, which is why the backstay becomes important again.

There are many types of running backstays and sophisticated ones have multiple take-off points, but by they time you are playing with those you should really know what you are doing.

 

[Rob_Webb]

Lot's of info here, including some slight inconsistencies but hopefully you get the gist of it.

One other mode not mentioned is to keep sufficient backstay tension on to support the top of the mast if you are running under a masthead kite (don't know if that is in your repetoire).

 

[maxwell edison]

No the Sadler 290 does not have a running backstay. And no I have never majored in medicine but, well done, you have got the source of my forum name, and that of my present boat, right!

Max