When the outhaul line on our boom derrick began to wear, we posted a note in the Voyage Yacht Owner’s Association group and sent off an e/mail to Sparcraft in South Africa.  In addition to a comprehensive reply from Garland, a fellow Voyage Yacht Owner, we received the following (His material in blue, mine in black) from Richard Stubbs of Sparcraft:

"To change your derrick line you need to do the following.

1) Disconnect the shock cord at the front end of the boom.   Make sure you tie a messenger line to it.

2) At about 276mm from the end of the boom, you will see some setscrews; these and the other set 604mm further along need to be undone.    (NB:  There are two screws on each side and one screw on the bottom of each block.  The blocks are nylon and Sparcraft pre-treated the screws with something like Tufjel - so the screws come out easily)

3) Once these are undone you should be able to remove the entire derrick mechanism out from the back of the boom.  (I attached the main halyard to the end of the boom and used the boom as a hammer to knock the blocks out.)

4) Once out you will be able the replace the line."

To replace the blocks, I tapped them softly with a leather hammer and placed them with a dowel, placing the forward one first - slowly to carefully align the screws.  The bottom one had to be placed first on the aft nylon block to pull the other four into alignment.

Please see the following photos - and read their accompanying text - for more details.

Remove two screws on each side and one screw on the bottom from each block.  Have some Tufjel or something similar on hand when re-installing to prevent adverse reaction between the aluminum and stainless.

Support the end of the derrick with the main halyard - rigged through one of the blocks.  A second person helps adjust the length.  One nylon block has come out and the second is just becoming visible.  We attached a second line to the forward end of the derrick and tied it to the topping lift - in case I pulled it all the way out.  Continue using the derrick as a hammer - tapping it aft sharply to dislodge the second block.  Be careful - you need not take the second block all the way out.  Some silicone spray helps at this point.

 As the old line becomes visible on the starboard side, tap very slowly until you can grasp the stop knot.  Attach the new line to the old at the winch end and pull it through the blocks and boom.  If you have difficulty getting the joint through the block, tap the block out a tiny bit more, unfasten the joint, and push the new line through.  The hole is quite a tight fit. 

It is hard to photograph re-assembly.  I sprayed the two blocks with silicone and tapped the inner (forward) block with a leather hammer and a dowel until it reached the screw holes.  Place a small bit of Tufjel on each hole to retard corrosion.  Fasten the screws tightly until all are in place before tightening any screw fully.  The aft block required some not-so-gentle tapping and lifting of the derrick end with the topping lift.  I had to tighten the bottom screw completely to bring the other four into view.  Then I loose fitted the four remaining screws, loosened the bottom screw and tightened all screws evenly.

The job took about 1 hour - with a second person required for about 1/2 the time.