Mast Movement when beating

thomashoebus

thomashoebus

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How much movement of the top of the mast when beating in a rough sea is acceptable? The movement is fore-aft so i could tension the backstays but the tension looks ok. there is a slight aft rake. Not to much because my main sail is a roller reefer. Perhaps i should nevertheless put more tension on the backstays but when is it to much and when ok. Probably there is a maximum sagging of the headsail as a rule or so.
Boat is oceanis 440 - masthead rig - roller genua and roller main.
 
The fore and aft support for the middle of the mast comes from the intermediate side stays which should be set somewhat aft of abeam the mast pulling against an inner forestay. Assuming this is your stay set up then I wouldn't think you should see any fore and aft movement of the middle of the mast. This set up is usually very stable.
If you pull on the backstay then the forestay will stretch or straighten eventually putting more pressure on the inner forestay. ie pulling the whole mast aft in rake . This will make the intermediate shrouds looser.
So my suggestion is to tighten uip the intermediate side stays (shrouds). You will probably find when sailing hard that the lee intermdiate shroud is quite loose while the windward remains tight. The leeward looseness can allow the middle to move forward and to windward. Don't expect tension on the lee shrouds but do take some of the slackness out.
NB I am notr so much in favour of high static stay tensions but rather that stay tension should be set to make the mast straight and well controlled when sailing hard to windward. good luck olewill
 
Ok but the movement is not in the middle of the mast but in the top. So do i just have to tension the backstay then en check that theintermediate stays don't come to loose?
 
What I have sometimes found is that, although it appears that the top of the mast is pulling forwards, it is the centre of the mast bending aft, requiring more tension on the forward lowers if fitted or the baby stay if fitted. If baby stay is fitted look for flexing of the deck allowing a an aft bend in the mast at mid height. It may not be sensible to keep tensioning the backstay/forestay to cure what could be a mid height tension problem.

John Lilley
 
There is no babystay fitted. What I could do is 1 or 2 turns on the forward lowers and 2 turns on the backstay. Then check the tension of the forestay. I can't tension the forestay itselfbecause it's a furling genua without this options so i always have to tension it by the backstay i presume.
 
If the top seems to be bending back and forth, have a look at the forestay sag. Is that bending and straightening significantly too? If so, yes, this is your masthead moving, and taking some slack out by tightening the backstay would be a good move (plus re-setting the other stays as necessary to remove mast bend).

Mind you, there will always be some fore and aft movement of the jib luff - and the mast head. It's a matter of degree.

It's your jib cut that tells you if things are too slack. If you can't sheet it in enough to remove that baggy bit in the miiddle . . . ah. But that could be caused by a stretched sail . . . oh well. Too many variables. I give up.

So, as you guessed, it all depends on the cut of your jib, so to speak.
 
There are huge loads put on both rig and sails. All rigs are a little bit different, other than on a boat exactly like yours. The rig would be covered by insurance but it could be very inconvenient if it fell down.

To get a local reputable rigger to look at your problem and make some adjustments will cost not a great amount whilst providing lots of peace of mind.
 
I was going to chip in with some musings, but that advice to get a rigger on the job is wiser. It's a lot of canvas and metal to get wrong.
 
OK Thomas all of the above is good. I missed the "top" of the mast bit but it my yet be the middle moving. In which case the forward intermediates should be tightened but make sure the mast remains straight both fore and aft, and sideways.
Then of course the backstay should have a fair bit of tension. This may straighten the luff a little but don't expect to be able to get enough tension to make the luff of the jib bar straight. olewill
 
Most yachts' rigs 'pump' to some extent when heading into a heavy seaway. The cause is the flexing of the hull. Lightly-built modern yachts flex far more than old-fashioned strong ones. The rig will have been designed to cope with the modes of flexing of that design of hull in the sea-states it will encounter in the kind of use it is sold for.
If it is to be driven beyond its intended use the rig should be set up by a professional: parts of the rig, and perhaps the hull/fastenings might need to be beefed-up.
I am not familiar with the Oceanis range, but many yachts have an adjustable tensioner on the backstay, which actually tensions forestay and lowers as well. (by bending the hull) If you have one, it should by wound up before driving the boat hard; and relaxed afterwards. You do not want to premanently distort the hull!
Hope this gives food for thought.
 
I would download Selden's PDF on rig tuning and get a good tension guage. Then have some fun. Rig tuning is abit off a black art, like sail trim, and all part the fun.By all means pay a rigger but be there and ask why he does what he does. He may fudge a little ( you pay to see the cards and lessons are extra) but you will get a good idea what to do. Rigs do need constant attention and vigilance so better to learn now.

PS it takes a long time to set up the more complicated rigs like yours so the rigger will not be cheap.
 
One other observation...

If your Oceanis is similar to mine, and many other models, then it'll have twin backstays, and a tang on the rear of the mast that splits the attachment to the two stays.... its not unheard of for this tang to become 'slotted' and/or the attachment to the mast (which is a rounded nut that sits in an associated cup) to become worn, and thus allow a bit of movement.... worth checking....
 
Mast head often appears to move ... you detect sagging of forestay / genny foil or backstays ... but is often due to mid section bowing fwd or aft ... this effectively shortens the mast and then fore / aft stays give a bit.

It is common and unless excessive is not a problem. You may be able to tension this out to a smaller factor by tensioning internediates and maybe adding a turn on fore / aft stays .. but then you may start to compress your deck. I have a good indicator of compression - my loo door sticks under the mast backing plate !! So I slack of till door just scrapes through !

You say that you cannot adjust forestay due to furling gear ... unusual unless you have foil + rod integral gear .. normnally you can lift the furling gear after unlocking the bottom tangs or fixings so that you can work the bottle screw inside ... the forestay BS.

The advice to get a rigger on the job is not a bad idea ... costs - but the knowledge you gain from it is worth it. Once you know the "sound / twang" of the rigging after he sets it up - you can reproduce later .....
 
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