Blue Peter Dinghy - Adjustable Mast-step Mk2

The first sliding mast cup attachment worked really well (in theory), but when I started shaking the mast strongly to emulate gusts etc, the HDPE proved too slippery and it was moving. No good at all.

I got hold of some polypropylene and I cut and joined this into a couple of blanking plates like for the shim under my mast gate, then drilled, routed, and finally cut to size using the original as a template.

In fact, I noticed the mast appeared to lean to port, so checked this using a plumb-bob and line from the mast joint by placing a bolt through the upper mast rest tube. After some school level trigonometry, I was able to calculate that the mast was leaning by a scary 48mm (1.42°) from true. A little more trig and I was able to fix this by moving the mast cup 8.5mm to port relative to my fixing points (centralised in the mast step). The mast looks a little odd being so asymmetric in the mast step, but it's more important it is true relative to the hull shape. I have checked the dagger board slot and that conforms with the new true of the mast, so that is also now in alignment which is great. I hasten to add that I'm pretty sure it isn't all perfect, but anything would have been better than the original state! If I'm lucky the boat may even sail nicer as a thankyou.

In the picture below, you can see my setup:

  • The spirit level was used to check gunnels being level at multiple points across the hull, there was another I used to double check the floor of the cockpit (which slopes)
  • The plumb-bob to align the mast with vertical
  • The masking tape on the gate on which to mark the movement of the plumb-bob bow-stern
  • The plastic electical conduit wedged down the daggerboard slot (n.b. this bends, but I tried it both ways to take an average - I don't have anything long and thin enough that doesn't bend). The daggerboard is seriously warped, so useless for this task
  • In the background, a polypropylene crate from which I extracted the pieces to weld together to make the new adjustable cup holder (identical design to the Mk1, just offset).
Plumb-bob line and an admittedly flexible plastic tube in the daggerboard slot

All that remains now is to invert the boat, get the mast (or a shorter emulation) set vertical, and check by eye that the bottom of the hull looks symmetric... If it doesn't I've probably made things worse - so, lets avoid this task for a while.