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.

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.

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)

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.

...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.