rigging question

ShipsWoofy

ShipsWoofy

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Oh I love Winter, my list of jobs is getting longer by the day.

I could really do with some advice if you will....

I have a bridle arrangement on my front forestay. How tight should I expect to get this. I was fairly horrified this year in a F7 how much bend I was getting even with the genoa reefed. It is a bigger sail that I bought last year and this was the worst weather we had sailed in since.

My aft stays are pretty tight which should pull the forestay up, though I do have a turnbuckle at 50% on the forestay. The mast is mounted above the saloon door and over-tightening could result in compressing the roof, or even as warned by one rigger, pulling the hulls and actually warping the boat.

If I grab the bottom of the roller reef I can shake it fore and aft so there is some slack there.

arrangement>>

Top_Cat_Refb_fore02_lrg.jpg


Anybody familiar with bridles able to tell me how taught my set up should be or what I can expect. Reading Multihulls sites it seems forestay sag is quite common, but how much?

Thank you in advance...



<hr width=100% size=1><A target="_blank" HREF=http://www.topcatsail.co.uk>Woof</A>
 
The genoa tack is well above the deck. So when you sheet in you pull the forestay aft with the sheet. This effectively shortens it, thus it sags. Clearly the bigger genoa aggravates the problems, as does sailing with it reefed.

There is no easy/cheap solution. You want to stop the aft movement of the tack. The normal way of doing that would be to fit a compression strut running aft (in other words a bowsprit) but I don't think that would be practical in your case.

Other HT's have had their rigging slacken because there was a gap between kingpost and deck and the glass joint, over time, has delaminated allowing the deck to drop. But I doubt if that is your problem
Sorry!

<hr width=100% size=1>Richard Woods of Woods Designs for quality sailing catamaran designs
www.sailingcatamarans.com
 
If the bridle was at 45 degrees, then you'd have to tension them along their axis by 41% more than a straight stay to achieve the same down force (x square root of 2 to be precise). This isn't to say that it is physically possible to do!


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There is a great danger in overtightening the rigging on a multihull, that you actually damage the boat. This is compounded on yours, cause of the bridle arrangement. This is obviously a class problem, and would be surprised if there is not a specific tension recommended by the designer/manufacturer. Having seen other twins out , this arrangement would appear to cause more sag than I have on my catalac (but I do tension a lot more than most other catalacs). Have you considered changing the bridles for solid rods, and adding another solid rod down to the bridgedeck (i.e. in line with the forestay) this would provide a better angle for tensioning, whilst not adding the full force of the stay to a new point on the deck.

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To get on and off when we beach her. It was built by the previous owner and is a brilliant addition to the inventory.

<hr width=100% size=1><A target="_blank" HREF=http://www.topcatsail.co.uk>Woof</A>
 
Thank you Richard. I have read your reply a couple of times and it makes sense to me now. Perfect sense.

So unless getting the forestay bar tight and controlling the position of the bridle to stop it moving aft, at all, sag is something I will have to live with. I will have to reef more too.

I wonder if I might see any benefit from a solid forestay instead of wire, or is that inclined to bend just as much?

<hr width=100% size=1><A target="_blank" HREF=http://www.topcatsail.co.uk>Woof</A>
 
any type of forestay will bend as much. to get any stiffness you'd need a spar several inches across.

you'll never get a really tight luff with that rig but it really doesn't matter. if the genoa is cut as if for a racing mono the sag of the luff will mean it won't point well (this is one of the main causes of poor windward performance on multis). if the sail is cut with a curve in the luff it will set fine, the problem is getting a sailmaker to believe that's what you want. they prefer to think in terms of humungous backstay tensioners.

i'll be down at millbrook tomorrow, would you like me to ask pip patterson about it?

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Posted your question on another forum, and was given the following response:
<blockquote><font size=1>In reply to:</font><hr>


I don't have numbers for any particular boats, It would be helpfull to know what the designer chose as a maximum allowable tension, then it's recommended to set your backstay (having handtightened both stays to give the desired rake) to 2/3 of that.
Unfortunately the question came in too late, Pat Patterson died two weeks ago. Brian North may have the specification I guess as he sold new boats for many years (till the moulds were smashed up).
<font color=red>ALL Multihull owners ~ One important point when tuning your own rigging - if you constantly have to tighten the rig to maintain the desired state of tune, then the hull may be distorting under load</font color=red>. If this is likely, release all rigging tension and consult professionals.

<hr></blockquote>



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If Richard Woods says there's no easy/cheap solution, you can be pretty sure there ain't.
Have you tried the <A target="_blank" HREF=http://homepages.rya-online.net/htowoa/>Owners' Association</A>?

<hr width=100% size=1><font size=1>Nobody is perfect.
I am nobody.
Therefore I am perfect.</font size=1> /forums/images/icons/wink.gif
 
richard

sounds like you are the man who may be able to answer my question- how much tension do you need in a forestay to get a given degree of sag? (obviously this depends on luff length and sail area).

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I have an arrangement on my cat that is a solid chuck of metal about 2' ish high coming up from where your anchor sits. It has the effect of making your headsail bigger and lowering the angle from your genny track.
Cant take a photo at the moment cos I am in Malaysia and wont be back to my boat until end of Jan.
I will try to put on here the ones I have.


<hr width=100% size=1>
Gaelic_Cat.thumb.jpg
 
I know I'm a boring ol' onehuller, but looking at your pic, the only way i could see of getting a tight f.stay would be to take a tackle down to the fwd x-beam and heave on that - but is the structure up to it - would you need a spreader above and below the x-beam with stays to the bows to resist the bend?.

It would seem that if you rely only on the bridle you're never going to harden up the f.stay because the bridle angles are too shallow to allow them to assert much of a vertical component.

I may, of course, being talking rubbish!

<hr width=100% size=1><A target="_blank" HREF=http://www.writeforweb.com/twister1>Let's Twist Again</A>
 
the common arrangement these days is called a 'seagull striker' (opposite of the old dolphin striker below a bowsprit). it is like a diamond stay and resists the tendency of the front crossbeam to be bent upwards by the forestay tension.

the original twins probably doesn't have a suitable beam inside the leading edge of the bridgedeck so couldn't support this arrangement.

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Dont know if this helps Jules. As Chris points out you may not have a beam between the hulls for it. Mine is a dam great bit of 4" pipe.

Seagull_Stricker.sized.jpg


Sorry its also the best picture I have with me. You can just about make it out to the left of the electric power point.


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Gaelic_Cat.thumb.jpg
 
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