Blue Peter Dinghy - Adjustable Mast-step Mk3

The finished product

My previous attempt (Mk2) worked, it even had the mast vertical, but, it fractured in use. The polypropylene wasn't up to the task. To rectify this, I initially scrapped the entire idea and made something resembling a pair of chip (edible kind) buckets, with an adjustment screw between them. I thought this would make for an easier to adjust item, while being very solid in steel. What I found on fitting the item was that despite making a mock up in cardboard first, getting the mast to slot into place was not possible without rocking the contraption towards stern slightly.

Here's the cardboard model that I used to check it was going to work as I hoped without causing issues for the mast install (something must have gone wrong because I couldn't later get this to work in any way with the metal version 😒)

I used the metal spindle shown to link the items, but the actual spindle would be an m6 if I recall correctly bolt. The size of which only has impact on the exterior of the device, hence the weird blob of cardboard attached to the outside giving the max dimensions of this rod.

My net with a ruler for scale
My net with a ruler for scale
The finished product

Here are a few pictures showing the cardboard model being turned into a steel item

Partially made (exterior cup only)
Almost fully made, checking sizing
Almost fully made, checking sizing

After spending too long building this, I changed tack back to the working Mk2 version. I cut out several copies out steel with differing slot sizes that when stacked make a shape identical to the Mk2 version (but in steel). To get the pieces to bind together, I scrapped the first nut being attached to the mast cup (it wasn't possible to get it tight enough to function using finger strength). I now use a long socket wrench to tighten this nut straight onto the stack of metal. This pins the bolt in the right place ready for the cup to be placed on top before my yellow domed nut is affixed above to stop the cup floating off.

The finished item in steel with cup removed so it is all visible.

 

To maintain friction between the steel plates, I've added a special ribbed washer (Nord-Lock) under the nut. This acts like a star washer, but is reusable. 

So far, the boat has had limited use, but the feature works fine. If I have the time and inclination, I may make a more drastic fix by cutting out a hole in the mast step into the hull interior, then resealing it allowing a larger longer mast step to be inserted. This would permit an Optimist style adjustable mast step to be made and fitted.

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