Blue Peter Sailing Dinghy - Centre Main Conversion

With a Topper, centre main conversion is trivial as you can get to the bottom of the dagger board holder. With the Blue Peter, it is a twin skinned hull so reaching inside to apply nuts is impossible. The solution recommended to me by a couple of members of of my (Reading) Sailing Club was to install an access hatch. This worried me a lot due to "what happens if I mess it up?! - I've ruined my son's boat!", but in actual fact, was a relatively trivial exercise and I think it looks really neat. Thank you Brian and Richard.

With the access hatch installed, I was able to drill holes through the dagger board housing for the pully block mounting feet and I inserted a piece of wood on the inside to spread the load across the fibreglass and alleviate any risk of it damaging the fibreglass when shock loaded in a sudden extreme gust and a gybe perhaps.

The block is just a simple one, no ratchet or anything fancy. I was going to buy one, but then I was offered this one for free - Thank you Brian! I'm really pleased with it and a ratchet is totally unnecessary due to the added friction of the extra pulley blocks. Note, the mainsheet shown is an 7 or 8mm one I use for my laser, but I bought a 6mm one for this boat because there was too much friction in the blocks for it to feed smoothly on days with light wind.

Installed Access hatch and centre main block.
 
Here you can see how I've added a block to the boom - a fabric loop through a  metal ring. (in the same way as for a topper - no rivet - as it would weaken the aluminium boom)
The mainsheet is orange, the blue rope to the end of the boom is holding it in position only for tacking practice (normally the sail does this)
 
Sailing the Blue Peter Dinghy At Reading Sailing Club, UK
Sailing the Dinghy At Reading Sailing Club
Here my son is sailing the finished product.
 
As you can see, he's using the standard tiller here. Later I added a tiller extension so that he could switch sides during a tack or gybe as in a Topper
 
Note that the wind here is incredibly low, but, combined with a light boat and light passenger, everything works really well. I've actually reefed the sail one turn if I recall correctly and it all means I've no trouble instructing from my kayak without getting breathless!... on a windy day, I got much more of a workout!