Latest News: Forums Technical Mast prebend (again).

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  • #4087
    Davdor7038
    Member

    Dave Doran here. Hoping someone can help me with this problem. Recently bought MKII 7038 (circa 1980 and seems to be very original) and have been trying to set up the mast but having problems getting prebend. I have searched the forum but cannot find anything to help with this particular problem. The Mast is actually inverting when jib tension is applied. The Mast seems to be the original Proctor mast complete with NON-adjustable spreaders. I have tried numerous foot positions and vernier adjustments following reading of the Wayfarer Book and have managed to get 150kg tension on the shrouds using the Highfield Lever (measured using a Loos pro gauge) but cannot get prebend. The mast is inverting forward giving an inversion of about 25mm at the shrouds. I think the problem may be with the spreaders. Compared to the most recent Wayfarer Book dimensions,
    my spreaders are; 489mm long (508mm recommended).
    Distance from outer edge of luff groove to a line drawn across the spreader tips is 141mm (200mm recommended)
    Distance across the spreaders from tip to tip is 965mm (965mm recommended)
    Vernier adjustors on shrouds are HA/4272 and Highfield lever is HA/4160.
    The spreaders do not seem to have been modified or shortened and as I say are NON-adjustable which means I cannot pull them back to try to increase prebend.
    I have tried various Mast Foot Track Pin positions (Track is a Stainless Channel) which whether track pin is forward or fully back didn’t make any real difference to the lack of prebend. As I say, the boat seems completely original including those spreader dimensions which is why I am surprised I can’t get it to work. The spreaders are held in by 2 small machine screws and locknuts. I took the spreader off on one side to see if I could pivot the spreader forward into its housing ( tip back) but there is zero movement available. Any suggestions/solutions gratefully received as I don’t where to go from here. s
    Sorry about such a long post. Regards, Dave Doran

    #5126
    triton
    Participant

    No expert but here is my view.

    Your spreaders are short in length but the distance between the shrouds at the spreader is 965mm, which is the recommended distance.
    In achieving that correct distance with the shorter spreader length, the spreaders have been angled further forward than normal.
    By doing this, it fails to exert sufficient pressure to induce bend.

    Spreader length is quite critical and is normally set according to the usual crew weight.

    Crew weight under 23 stone: 505mm
    Crew weight 23 – 24 stone: 515mm
    Crew weight over 24 stone: 525mm

    All measurements taken from mast wall to shroud.

    It would appear that new spreaders are required.
    This may be a cheaper option but you will still need to adjust the spreader angle by re-drilling the bolt holes.
    http://www.tridentuk.com/sailing/product-Spreader_Length_Adjuster-1_SN500_801_01.html

    Check that they are suitable if considering purchasing.

    #5125
    Swiebertje
    Participant

    Without the pressure of the boom, sail and kicker most masts often need some persuasion. With the tension on, try to push it hard forward. Most masts then jump in to place with an audible “ping”.

    #5124
    Colin Parkstone
    Participant

    That ping only comes about if you have a space behind the mast heel to a stop bolt in the mast step.
    Next point i would make is that your spreaders are not back far enough at the tips, they will only bend the mast backwards being so far forward.

    Maybe take the spreaders out and redrill the pivot hole near the front of the spreaders which will allow the spreader to move forward at the inboard end??

    Try taking the spreaders off, see if the prebend gets better in the right direction and then offer them up to the bracket to see if you have any chance with them.

    This MAY?? indecate you may be in for some new ones.

    Next, does the mast hit the front of the mast gate, if so your to far forward!!

    Spreaders can be cut about to allow you to use them for each class, not all spreaders are made for the backet you have so you may have new spreaders in an old bracket.

    Good Luck,

    C P 😕

    Ps, are you near any other Wayfarer clubs who maybe able to help?

    #5122
    Davdor7038
    Member

    Thanks, Gents, for the input. Colin, I will certainly try redrilling the pivot hole to allow more backward movement of the tips. I had a browse through a Proctor Mast handbook (cost 50P !!!!) that came in the paperwork that I had forgotten about. A couple of points came to my attention.
    1. Apparently the spreader tips end fitting, can be adjusted outward up to an inch on either side. They are held in by a small self tapper screw. If it is not seized in position, I will first try extending the tips to give me about 20mm more each side (to increase slightly the 140mm from the luff groove which I currently have). Obviously this will also increase my spreader span from the 965mm which it currently is. Would this be very harmful to the mast or rigging ?

    2. The Proctor handbook mentions that on an “E” section mast, the halyards should run down the luff groove and not through the main chamber at the front of the mast which they do on my boat. Does it make any difference? I was thinking that if the pull of the Jib halyard was down the luff groove, the mast would be more inclined to pull forward, though the spreaders will obviously have much more effect. As I won’t be near the boat for another few days, I don’t know anyway if the mast has the necessary holes to run jib and mainsail halyards down the luff groove.

    On actual rigging. each time before tensioning the Jib halyard, I pulled the mast back to the Foot Track Pin. Is this the way to do it or should the Track pin be left out and only inserted after prebend has been obtained.The mast rake was within limits.

    As the nearest active Wayfarer club is about 50 miles away I thought I might try the forum first for help.

    I will let you know how I get on after I get back to the dinghy and try (a) extending the tips and (b) possibly redrilling the spreader holes. Thanks, Dave

    #5121
    triton
    Participant

    I think most alloy masts of that era had an E section.
    Type I mast was tapered towards the top and the mast was sealed in an effort to prevent inversion and halyards ran down the luff groove.
    It also had an adjustable gooseneck, so no Cunningham was essential.

    Type II mast was similar but not sealed. The gooseneck was fixed and halyards ran down internally within the mast.
    As your dinghy is 1980 vintage, then it probably used this mast.

    I don’t think just lengthening the spreaders will overcome the problem. The spreaders will need to be angled further back to exert more bend pressure.
    Any bend is measured by pulling the main halyard tight against the mast next to the gooseneck. Now measure from the back of the mast to the taught halyard at spreader height.
    You are aiming for a gap of one and a half inches.

    When rigging, stand the mast in the dinghy with the shrouds in position. The mast should be up against the heel pin but without the tabernacle pin in position.
    You then apply the required tension and rake.

    Does the tabernacle pin fit the hole without touching the sides of the mast.
    If not, then the heel pin needs adjusting.
    (New edited version………thanks Colin)
    If the pin hits the back of the mast…………move the heel pin back.
    If the pin hits the front of the mast………..move the heel pin forward.

    If the holes in the mast foot give too big adjustments, then use some spacers such as a 5p piece.

    Don’t forget, if you make any adjustment to the spreaders, then the whole rig will need to be adjusted and measured again.

    #5113
    Colin Parkstone
    Participant

    Should that be the other way round Norman ??

    If the pin hits behind the hole in the mast then the bolt in the track needs to move AFT, not forward ?

    Inside the mast or in the luff groove, does not mater I would say so keep as you are.

    The foot pin will need to be left in after you have done all your setting up and the pivet pin has to be in place when you race.

    You have the older type of spreaders and bracket,it may be hard to get the newer type of spreaders to fit your bracket.

    I think the important thing for you to do is to get the spreader tips to the proper position which is aft in your case, they will only be working against pre bend as they are.

    Pre bend in a mast is not the same for each sail make,each sailmaker can make a sail with differing luff round so 11/2 may not be for your make of sail, find out how much it shoud be from the makers info or be prepared to change this for your sail.

    More Good Luck

    C P 😕

    #9528
    triton
    Participant

    Hi Colin

    You are correct, I must use my reading glasses more often.
    I have edited the original with acknowledgment to your good self.

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