Mast Step

This page is divided into four sections - two for making the parts of the mast step and two for assembling them.

Thanks are due to Liam Chinnery in Australia who picked up several errors in the previous version of this page.

Mast Step Panels 1/2

This drawing shows the cutting, marking and initial assembly of the two cheek pieces and three other plates.

If you make the mast step parts as described here, you will be able to 'dry fit' them together before assembling them for real - everything needs to be a good fit, as any error here will be multiplied by 12 at the top of the mast!

It is easiest, and most accurate, to mark all mast step panels before cutting - but this cannot be shown clearly in one drawing.

The whole mast step is made too high and with a square end - after it is finished, the top is trimmed off horizontally to the right height.

The dimensions for the lines of the cheek pieces are measured at the points where the lines intersect the edge of the rectangular panel, to increase accuracy.

Mark the second cheek piece as a 'mirror' of the first - with all lines drawn on the other side of the ply. Note that one line is marked on the 'back' (what will be the outside) of the cheek pieces.

The four fillets that go in the inside corners of the mast step are made from the same 15x15 stock as the seat bearers - I used softwood and it seems strong enough. They need to have one corner chamfered as shown to provide clearance for the mast. It is tricky to plane such a small object and you may need to make up a jig to hold them during planing.

 

When fitting the fillets to the cheek pieces, use an epoxy/microfibre 'glue' (a fairly runny mix) and pins to hold it while the 'glue' sets. Pinning the fillets in place accurately is difficult from the back - you can do what I did, which is to use long pins to go right through the fillets and the cheek pieces, and grind off the excess after the 'glue' has set.

Position the fillets so that their bottom edge is on the TOP of the two lines drawn across the base - this will put the top of the fillets flush with top of the cheek pieces, but concentrate on the bottom, as this is where accuracy is needed. Make sure you position the chamfered face of the fillets the right way - towards the centre of the mast!

The front plate of the mast step is a simple rectangle with two fillets near its edges. The fillets are inset 9mm from the edges with their chamfered edges facing inwards. The bottom of the fillets are inset 9mm from the bottom edge, to allow for the step bottom.

The back plate is a simple rectangle with no fillets on it.

The bulkhead doubler is a simple rectangle. This part is used to mount the mast step on the bulkhead of the front seat/tank - the doubler is fitted to the bulkhead and the mast step 'locks' over it. The bulkhead doubler is not assembled with the mast step, but it can be 'dry-fitted' to check that it fits well.

 

Mast Step Panels 2/2

This drawing shows the cutting and marking of the remaining parts of the mast step.

The top doubler is chamfered on its underside along all front and side edges (to reduce the 'hard spot' on the seat at its edge), but leave the back square.

The drawing shows the dimensions of the hole in the top doubler which fits over the top of the rest of the mast step (ie, the two cheek plates and the front and back plates). The front and back edges will need to be chamfered to fit the rake of the mast.

The bottom doubler is similar , but without the mast step hole. Mark the line of the rest of the mast step on it as shown - this will help during assembly of the mast step.

The step bottom is a simple rectangle.

Mast Step Assembly 1/2

The previous sections provide the cutting, marking and assembly details for the parts of the mast step.

Assembling the mast step needs to be done with both care and confidence - the length of the mast will amplify all errors by 12!

The easiest thing is to 'dry-fit' (ie, assemble without glue) the parts together to ensure that everything fits as it should.

Note that the bulkhead doubler (the part shown separately in these graphics) is not assembled into the mast step - it is fitted to the front face of bulkhead B and precisely locates the mast step when it is fixed to the bulkhead.

However, it is sensible to 'dry-fit' the bulkhead doubler when assembling the mast step as this makes sure the mast step is a good fit on the doubler.

The graphics show two views of the mast step - the right hand one has the starboard cheek piece (and its fillet) and the back plate left off so you can see inside the mast step.

What might not be obvious from these graphics is that the step bottom is square to the front and back plates (and so square to the mast), but only its front edge rests on the bottom doubler (see below) - its back edge is clear of the doubler, as the bottom of the boat here slopes more than the rake of the mast.

Assemble the pieces shown here with an epoxy/-microfibre 'glue' and pins. It is vital that everything remains square so be sure all plates touch the step bottom and 'dry-fit' the top doubler to hold it all while the 'glue' cures.

Mast Step Assembly 2/2

 

The second stage of assembling the mast step is to fit the top and bottom doublers.

The top doubler locates itself, but the bottom doubler needs to be located with its aft edge flush with the back of the cheek pieces.

At this stage, you can take out the 'dry-fitted' bulkhead doubler as it restricts access and would be likely to get stuck in.

Assemble the parts using two different products:

  • an epoxy/microfibre 'glue' to stick the doublers to the rest of the mast step;
  • a stiffer filler mix which fills the wedge-shaped void between the step bottom and the bottom doubler.
  • My favourite for the second sort of mix is one third microfibres, one third silica and one third lightweight filler (hollow glass spheres or similar).
  • The same filler mix can be used to add epoxy fillets to all exposed corner joints (eg, between the doublers and the cheek pieces and front plate) - but don't put filler above the top doubler as the bow tank top goes here.

If you want an overbuilt mast step like mine, wrap some glass tapes around the front corner of the step, to reinforce the connection between the front plate and the cheek pieces.

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