adding inner forestay

Discussion in 'Sailboats' started by urisvan, Mar 13, 2012.

  1. urisvan
    Joined: Nov 2005
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    urisvan Senior Member

    hello,
    last year i added an inner forestay and runner to my sail boat for heavy weather sailing. A rigger in Turkey did the work and i was not with him while he was drilling my mast to make the connections for the forestay and runners. i think the connection on the mast is a little bit higher than it supposed to be.
    I want to change this connection and lower it a little bit. I am a little bit afraid that the holes of the existing terminals that will leave there when i move the terminal will weaken the mast. what do you think about it?
    At the monent the inner forestay is attached by a T-terminal and the runners are attached to the mast by a 12 mm bolt.
     

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  2. michael pierzga
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    michael pierzga Senior Member

    Hmm...I dont understand what you are trying to achieve ?

    Your present setup looks good.

    Why lower the inner forestay ? A cutter with a big staysail is a pleasure to sail.

    Why the extra aft lower ? the angle is so sharp that all you will do is add compression. Inner forestay opposed by running backstay is better because the angle is bigger...less compresion.

    If you do add the additional aft lower, investigate the present chainplate scantlings. It will become highly loaded.
     
  3. urisvan
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    urisvan Senior Member

    i also dont want new drama and effort.

    what i only want to do is, make a safe setup to survive in heavy weather.

    i am thinking that the innerstay is too high so it adds too much compression. what i know is the rigging should be designed for RM of the vessel. Lets think a scenerio of heavy weather that we are sailing only with staysail, and the boat is heeling 40 degrees because of the transverse load produced by the wind and transfered to the mast by the forestay fitting on the mast. Ok, the angle between the runner and the mast is bigger comparing to extra lower but the load on the runner should be very high because, the transverse component of the strain of the runner needs to compansate the transverse load, so it will produce too much compression. doesn't it?

    i am planning to reduce the compression force by lowering the terminal and i am planning to use the runners additional to extra lowers.

    i am open to all arguments. what i want is safe sail in a storm.

    cheers
     
  4. michael pierzga
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    michael pierzga Senior Member

    Is you must sail in heavy weather you use a small sail. Sailing at a 40 degree heel angle is not recommended. In heavy weather you want the boat to stand upright and move slowly, deliberately.

    A cutter rig is beautiful because it allows you to carry a big sail plan. The bigger the stay sail the better. The double head sail rig is effective and versatile. 99 percent of a yachts life is spent in fair weather...

    I wouldn't retard the sail plan forward by moving the inner forestay down. Far better to devise the proper sheeting angle for a heavliy reefed staysail .
     
  5. urisvan
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    urisvan Senior Member

    of course i dont want to sail with 40 degrees angle it just can happen with a sudden gust.

    i have a 100 percent genova and mainsail with three reefs. And my staysail is 7 square metre. Up to 6 fore i use 2 reefed main and genova, in 6 force i roll genova only a little. I did not experienced, but this year i think i will see 6-7 force; i am planning to use 2 reefed main and 7 m2 staysail. If i encounter 7-8force i am planning to sail with three reefed main and staysail. And if it is more than 8 force i will sail with only staysail.

    the question is "is it safe to use this staysail on that inner forestay and runner setup in that circumstances or do i need a change"?

    regards
     
  6. Perm Stress
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    Perm Stress Senior Member

    Holes for the lower attachments will be far enough from the previous ones, they will not create significant chain-effect weakening of multiple holes.

    As to additional lower shrouds (together with runners to handle longitudinal forces), they are only really useful for current set-up, as new stay in the middle between transversal staying points put bending load on the mast. While the mast is stayed so as to have almost exclusively compression load in it.

    If you lower the stay attachment as per sketch, additional shrouds will be not that necessary.
     
  7. urisvan
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    urisvan Senior Member

    hello Perm,

    first i think you say that this lowering the terminal will be necessary.

    and i did not understand you clearly, did you mean that if i lower the terminal like that only the runners will be enough?
     
  8. Perm Stress
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    Perm Stress Senior Member

    I did not say lowering is necessary.
    Yes , if you lower the terminals, runners only could be enough.
    As can be judged from the photo, runners are anchored quite far from the centreline -so much the better -they will provide a little bit of transversal support too.
    Is their anchoring point far from maximum beam on deck?
     
  9. urisvan
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    urisvan Senior Member

    actually the boat is a classical english boat and it is pretty narrow. beam is 265 cm. that means half beam is 132cm and the width from runners anchor point to centerline is around 105-110
     
  10. Perm Stress
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    Perm Stress Senior Member

    What is the height from deck to intended location of inner stay?
     
  11. urisvan
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    urisvan Senior Member

    around 780 cm-800cm. Now it is about 920cm from the deck.
     
  12. urisvan
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    urisvan Senior Member

    i can not give precise measure because the boat is at distance
     
  13. Petros
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    Petros Senior Member

    Not likely the old holes for the bolts in the mast will make any difference in the strength of the mast, there is a hole in it now, if it has a bolt in it or not it is already weakened.

    As far as making the mast stronger, it appears to me that you have a complex loading condition. If you lower the point where the lateral shrouds are attached, the length of mast above the attach point will get larger, and it is possible it will put more compression and bending loads on the upper part of the mast. The side stays (running over the spreaders) will also put compression on the mast when it is loaded in bending from the top, it seems to me if there is a genoal on the fore stay that runs to the top of the mast, it is possible in a gust that the compression loading can be increased if the attachment point is lower.

    It is difficult to know for sure looking at the picture, but that mast is not a simple cantilevered column, but rather more like a truss. If you load a truss the wrong way it could actually hold less load. You will get failure from bending in members that were intended only to take tension and compression loads.

    To know for sure you would need an accurate drawing of the rigging geometry, and the loading conditions you are trying to accommodate. Are you loading from the top of the mast, or from the point where the lower fore stay is attached? Are considering the mainsail will be up, if so to what reef point?

    I would just leave it the way it is for now, unless there is a particular condition you are trying to accommodate, than you should get some professional guidance before you make any changes.
     
  14. Perm Stress
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    Perm Stress Senior Member

    Than in front view, angle between mast axis and runner will be : arctan(100/800)=~7.1 degrees. Not a lot, but just enough to provide some side support worth mentioning.
     

  15. Perm Stress
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    Perm Stress Senior Member

    There is no way an inner stay could load a mast in compression above his attachment point.
    As to compressed column, for so long as unsupported lengths between staying points are not increased, load-carrying capability is not decreased.
    While compression force in the mast as such is largely determined by righting moment of the boat. Staying arrangement can change this only a little amount. (Here I do not mean drastic change of shroud base width, for example).

    .... it is possible in a gust that the compression loading can be increased if the attachment point is lower. ....

    The sail force will be greater, because CE is lowered, but heeling moment created by this force will be the same (because stability of boat remain the same), as well as basic compression force in the mast.
     
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