Sadler 25 conversion..

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  • 02 Jul 2020 23:37
    Reply # 9075001 on 8800878

    Thanks guys- slap bang in the middle of the hatch it is then. 
    Incidentally I definitely want the sail on the port side as this puts you on starboard tack when raising sail saving the indignity of having to give way to anyone around in a busy anchorage just as I’m gathering way..

  • 02 Jul 2020 22:33
    Reply # 9074874 on 8800878

    Having worked on a number of fiberglass boats I can say that they are rarely symmetrical, the worst I have come across was a Peterson 33 on which the back-stay was 90 mm off center. It never seems to make a lot of difference so don't worry about it and no one has ever noticed until things were measured to the last millimetre.

  • 02 Jul 2020 20:25
    Reply # 9074653 on 9073515
    Anonymous wrote:

    In using a plum line from the mast position on the  centre line of my fore hatch, I was puzzled to find that it didn’t fall to the centre line of the V berth.

    After loads of measuring I’ve found that the coach roof is offset 20mm or so to port (ie port side deck is narrower than starboard).


    While I suspect the strength is enough and would point out that in other discussions about offsetting the mast the "looks" has generally been deciding factor.... my glib response would be: So, put the sail on the Starboard side of the mast and the sail will be close(r) to centre.

    If the hull and cabin have been designed with the mast slightly off centre, strength should have also been taken into consideration and centring the mast may actually weaken things. You may find the Port side of any bulkheads there are slightly thicker than the Starboard side, for example.

    If you take as an example an extruded square as the hull and cabin, There is the possibility of racking. However, adding an X brace at the point where the racking force occurs will keep the top plane in position with the bottom plane. If the top plane is stiff enough, it doesn't really matter where that force is applied. So having the mast offset will not make it more prone to bending the boat to the side.

    The real issues are that most boats are not flat on the bottom and so moving away from center or the keel means less available bury for the mast and may also mean the foot of the mast does not have the strength of the keel. So long as the bury is still 10% of the mast height that is not a problem. A properly made mast step should not have a problem transferring the load from keel over by 20mm as most are much wider than that and so will still be tied into the keel anyway.

    The one other obvious thing is the the centre of moment will be shifted to one side. How much this affects the motion of the boat depends on beam at the WL, hull shape around WL, mast weight, machinery weight and placement, etc. If these things have already been designed for an offset mast, that might already be reason for leaving "well enough alone".

  • 02 Jul 2020 10:16
    Reply # 9073515 on 8800878

    In using a plum line from the mast position on the  centre line of my fore hatch, I was puzzled to find that it didn’t fall to the centre line of the V berth.

    After loads of measuring I’ve found that the coach roof is offset 20mm or so to port (ie port side deck is narrower than starboard).

    This means that the edge of the mast socket hole is only 20mm at it’s narrowest, from the V berth bulkhead on the port side, and 60mm on the Starboard.

    Is this asking for trouble structurally, ie -will a socket wall thickness of 20mm at it’s narrowest bonded to 10mm bulkhead be too weak?

    If so I could offset the mast to starboard by 20mm to give 40mm at the narrowest point both sides as in this photo (and put up with the no doubt endless observations from strangers that my mast doesn’t look centred).

    The V bulkhead is 10mm fibreglass. I will be filling in the locker holes with 9mm ply.

    The mast socket is 54mm of plywood on top of 54mm of mast step, as per Arne’s method.

  • 18 Jun 2020 15:53
    Reply # 9045174 on 8800878

    Hey thanks Arne..


  • 18 Jun 2020 10:12
    Reply # 9044679 on 8800878
    Anonymous member (Administrator)

    Paul

    Over the years I have rigged three junks with softwood wedges and metal partners. I think the best version is the one I use now, on my 26’ Ingeborg’s mast. Here I made many narrow wedges with a very fine wedge angle and with the shown nose on top to ensure that they will never fall through. The main part of the partners is a cylinder, not angled in any way, so the wedge is resting against the upper part of it. This dents the wedges a tiny bit, but I think that is just good. The fine angle of the wedges has ensured that none of them has tried to creep upwards. Just as important as the wedges, is the making of a watertight mast coat. It both protects the wedges and keeps the v-berth down below dry.

    Good luck!

    Arne

    (PS: See page 9 on wedges, and this one about the mast coat)

  • 18 Jun 2020 09:02
    Reply # 9044566 on 8800878

    Thanks David, softwood wedges it is then(Was just trying to cut corners).

    Apologies if the answer is hiding in plain sight, I have  spent several hours scouring both PJR and the website, and googling to no avail..

    Can anyone advise as to the simplest method of achieving a tapered hole at mast socket and partners?

    In both cases I’m using several layers of plywood, which obviously is not glued up yet.

  • 17 Jun 2020 07:50
    Reply # 9042227 on 8800878

    PJR recommends a taper of 1 in 50, or ~1.2˚ and a self-holding machine tool taper, eg Morse, is ~1.5˚ . In both cases, the heel socket or hole through the partners should be tapered, but at only 2 - 3mm in 100mm, it's not too onerous to do.

    These plastic wedges seem to have a taper of 2.5 - 5˚ and being made of a slippery material can't be relied on to self hold. I have used wooden wedges with an angle of 5˚ and a disc of plywood above them, bolted down to the partners to keep the wedges from slacking off. These are a bit easier to knock out when unstepping the mast.

    I can't really see that these plastic wedges have any advantages over spending an hour with a saw and a piece of softwood to make wooden ones.

  • 16 Jun 2020 12:06
    Reply # 9040167 on 8800878

    ...I was thinking I could separate each u shape ( to use individually to better conform to mast radius), and fish them in pairs top and bottom.

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