PDA

View Full Version : Adjustable Backstay



Alchemist V274
09-10-08, 07:29
Stoopid Question 1./forums/images/graemlins/grin.gif

Not being a racing sort I have heard of but not used an adjustable backstay but I do like to sail fast.

I have noticed some sag to leward on the furling genoa luff, particularly when sailing to windward in F4 - 5- how much is acceptable? How is it measured? Should I estimate the distance of the sag in the middle part of the forstay from vertical?

Is it worth putting some sort of block and tackle arrangement on Flipper's split backstay? (There is one stay from the masthead splitting about half way down.) Presumably this would reduce the sag? However the mast is pretty big all the way to the top so not sure I could induce any 'bend'.

eastcoastbernie
09-10-08, 10:23
Stupid Answer No 1:

I have an adjustable backstay. It's there mainly for show to con people into thinking I know what it's for. There are normally too many other things to think about to bother with it.

When my rig was set up, I seem to remember the shrouds and forestay being set up gradually until it was all reasonably tight with the mast nicely straight (side to side) and top to bottom. The backstay was then tensioned so the top part of the mast was tilted back.

As I undestand it, you have the backstay tension as hard as you can possibly get it when going upwind. My worn out brain cells are telling me that as it gets windier you put on more backstay tension which has the effect of flattening the sail hopefully delaying the time when you will have to reef. (Racers only, cruisers will want to reef in good time.)

Then downwind, you let the backstay tension go enough to make the mast straighten up (I suppose). I haven't tried it cos I'm not sure I have the muscle to get the tension back on when going upwind again.

MoodySabre
09-10-08, 10:28
Thought you'd know all about adjustable stays /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

FullCircle
09-10-08, 10:33
Stoopid Question 2.


Is Flipper a Masthead or Fractional Rig?
Frac rig more 'tuneable' than masthead, but not always a disadvantage.


The backstay tension is let off downwind to nmove the centre of effort forward. I have known certain scalliwags winching theor mast forward on a spare halyard. Ahem.

Backstay tension can be useful.
Mast should be set up with some pre bend in the middle ish, and mast rake too.
Application of backstay, as ECB points out, is to flatten to main by additional mast bend.

Can induce pumping or inversion of the mast, depending on the rake of your spreaders, and the amount of pretension. Thats mainly why I have a babystay in the middle (but watch this space in 2009).

Usually you have a bit of backstay on up to about 12 knots, and then apply it gradually untill you need to reef.

Not a whole answer.

rudolph_hart
09-10-08, 11:02
I've found they make quite a difference to forestay tension (=reduced sag=pointing higher) on mastehead rig. On fractional rig (or masthead with in-line spreaders without aft lower shrouds) it also adjusts mainsail shape, by bending the centre of the mast forward & flattening the main.

I've had 3 different types of tensioner:

1. On a masthead Listang (backstay split above deck, like yours), with a block on each wire 'split' coupled together, which were pulled downward by a tackle, so pulling the 'split' wires togther.

2. On a 3/4 tonner (tapered 3/4 rig, single backstay) which had an alloy lever pulled downward with a tackle (same as used for boom vangs on Hunters and Sigma 33's)

3. On Dehler 34 (7/8 rig, backstay split above deck) Stbd 'split' wire runs through block attached to lower end of backstay. It's then tensioned by a 4:1 tackle fixed to Port hand. As a safety measure, a wire strop interconnects the tackle blocks, in case the line is accidentally let fly /forums/images/graemlins/blush.gif. This arrangement gives sufficient power to induce pre-bend in the untapered mast to adjust mainsail shape.

The other types of tensioners I've seen are wheel driven bottlescrew and hydraulic (with a bilgepump-type handle).
Hope this is of help.

Alchemist V274
09-10-08, 13:04
Thought I would miss some vital information! Masthead rig, forestay, baby stay at front. Shrouds with in line spreaders and stays from half way up mast at sides. Backstay split as described.

I have set the mast up vertically - front / back & side to side. Not tried to put in any rake.

Bit concerned that I may induce pumping or inversion of mast - sound rather worrying. /forums/images/graemlins/shocked.gif

Mast is coming off over the winter so want to set it up right when it goes back up.

FullCircle
09-10-08, 13:30
Peter,
suggest using Dave of DRS Rigging at Southminster when putting it back.
I cant easily see where you would gain much benefit, except to get the rig correct when you put it back up. He will also give you a rig survey to mollify the insurance folks too.
Tell Rigger bloke if you have weather helm or whatever, and he will move it accordingly.
My fine craft has no backstay tensioner, and about 40 mm of rake, with about 1/3 of mast section pre bend. I will increase this to 1/2 mast section when I remove the babystay for next season, with approx 15% loading in the shrouds.