Forestay advice please

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kirielad

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Hi,

Sorry if this has been covered before (I did a search - honest!).

I have a question regarding the tension (or rather the lack of) in the forestay of my Feeling 720.

The rig is 7/8 fractional, with straight cap shrouds / spreaders (no intermediates). 2 lower shrouds either side, an adjustable backstay and Plastimo 608 r/reefing up front (no turnbuckle / bottle screw fitted). All simple stuff .

I should also say there is not a great deal of mast bend apparent when sighted from deck level.

My question is in 2 parts really;

1, Can anyone provide guidance on the correct way to apply tension to the forestay (the backstay would does this 'to an extent', but I thought this was purely to apply a temporary bend in the mast to change mainsail shape?). Should the aft lowers be doing this job - i.e putting in some mast bend and tensioning the forestay?

2, Is it worth fitting a bottle screw on the forestay so that there is overall mast angle adjustment? At the moment using the existing 'Plastimo meccano' fittings it's not really possible.

Any pointers / advice gratefully received.

Thanks
 
[ QUOTE ]
the "Rigging Instruction" booklet

[/ QUOTE ] Or go directly to it HERE

Well worth downloading and saving! Fractional rigs can be quite complex to set up and the Selden book covers the variations that are possible.
 
The answer to the sceond question is no you don't need a turnscrew in the forestay.. The static tension on the forestay is achieved with tension on the cap shrouds which should attach to chain plates which are aft of abeam the mast. So the more collective tension on the cap shrouds the more tension on the forestay. If this tension tends to bend the mast middle forward then this is taken out byt he lower shrouds also going to chain plates aft of abeam the mast.
From thois et up o0f nearly straight mast for light winds you then crank on the backstay to put bend in the mast to take fullness out of the main sail for strong winds. In bending the mast even more tension will be put on the forestay.
Warning though you will not be able to take out all the forestay sag. The jib should be cut (concave in the luff) to allow for some sag.
Don't try to get too much tension as this may bend the boat .
IMHO olewill
 
With straight cross-trees the cap shrouds won't tension the forestay. Nor will the lowers, which just control the bend. kirielad's cap shrouds will be level with the mast, so it's really only the backstay which will tension the forestay. The mast angle adjustment is usually provided by a series of attachment-points for the forestay.

Most rigs now have swept spreaders which is quite different.
 
The rig is covered in the Selden book but they say it requires runners!

Picking up on the Plastimo reefing/ bottle screw question. There are two variations available of the Plastimo gear with different length "Mecano" side plates. longer ones for use with a bottle screw, shorter ones without (at least for the smaller sizes) Plastimo's website gives the details. The long ones (11 holes) are normally for use when the gear is retro fitted to an existing forestay and bottle screw without lowering the mast. when fitting to a new forestay the shorter plate (5 holes) can be used without a bottle screw. Fine adjustment of mast rake is only possible with a bottle screw though.
 
[ QUOTE ]
With straight cross-trees the cap shrouds won't tension the forestay. Nor will the lowers, which just control the bend. kirielad's cap shrouds will be level with the mast, so it's really only the backstay which will tension the forestay. The mast angle adjustment is usually provided by a series of attachment-points for the forestay.

Most rigs now have swept spreaders which is quite different.

[/ QUOTE ]

That goes to the heart of it really. Tightening the cap shrouds, set as they are inline with the mast will I suspect only pull the mast downwards, creating a downwards load but not any bend / forestay tension.

Interestingly, the aft lowers are substantially strengthened below decks, (as are the caps), however the forward lowers are just bolted through the deck (presumably just to prevent the mast inverting).

Thanks to all for the replies.
 
A word on tensions: and sorry if this is already obvious -

1. On a fractional rig, the aft stay does not connect with the incoming forestay tention so will only give you a measure of prebend in the mast - it will have little effect on a sagging forestay. Most rigs specify no more than 5 degrees of bend to be inserted this way - I wince when I see more because it has little effect in the middle of the mast - where the benefit is wanted on the mainsail - and does subject the top of the mast to unwarranted stress.

2. All forestays sag to a degree, and on fractional rigs can only be tensioned well if the spreaders are swept back to give leverage on the mast. If sag is exceptional additional tension can be applied through the standing mast rigging: the heavy sag in strong winds can only really be reduced, if this is desired, by reducing the foresail - ie load.

It's said that mast rigging is tensioned to the full when it twangs if hit with the back of the hand. If yours is already there, that's it my friend!

PWG
 
My apologies for missing the fact that the shrouds are square to the mast.
If the backstay is cranked on but the forestay is till not tight enough because the mast bends. There are 2 options both drastic. One is to fit running backstays connects to the same level as the forestay or you can fit jumper struts to the top of the mast which in effect make the mast less bendy so get the backstay tension to the forestay.
Jumper struts are a pair of short spreaders mounted at about 60 degree angle form one another facing forward and fitted just above thee forestay attachment. Stays run from the intermediate shroud fittings over the jumper struts to the top of the mast. They will need bottle screws and as you tighten them the mast will bend forward at the top (too much) or be much more rigid against bending aft at the top when the backstay is pulled on.
I do wonder if you aren't expecting too much as you can't avoid all forestay sag. olewill
 
A mast with pre bend has an overall height which is LESS than the same mast in its straight form. So it stands to reason that when sailing in moderate breeze the mast remains bent because not enough wind in the mainsail to straighten it /forums/images/graemlins/grin.gif main full + full genoa with plenty of power, wind pipes up, mainsail power pulls bend out of mast, ie straightens it making it longer, tightening forstay makes for tighter luff flatter sail, less heel, I think that was the plan when fractional rig was devised /forums/images/graemlins/smirk.gif
 
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