google-site-verification: googleffe3ebaef4e4b443.html Oztayls-Restoring and sailing a vintage scow Moth: Control lines

04 June 2013

Control lines

The control lines had seen better days so I ordered some 4mm Spectraspeed. I like this stuff very much as it is tough and has a hard low friction cover plus it does not distort and flatten as it goes around a turning point, so it performs more like a 3mm line. Nice.

The bottom of the mast had a 3/16” SS wire rope loop with five 19mm Ronstan ferruled head blocks threaded onto it for the Cunningham (downhaul), and the outhaul. The problem with this arrangement was that I found that the SS wire rope was too rigid and did not allow the blocks to properly align with the lines, so there was friction as the lines travelled through twisted blocks. I decided to remove the wire loop and replace with 3mm Dyneema. I also thought it would be cool to replace the old 19mm ferruled head blocks with lightweight Ronstan kite blocks, which have a working load capacity of 150kg and break at 300kg. Pretty impressive little blocks these. The only problem was that they have a maximum line capacity of 3mm, and I had bought 4mm. Bummer, can’t use the kite blocks here. For now, the old blocks have been returned to service, threaded onto the Dyneema loop spliced around the base of the mast. All three control lines run to clam cleats mounted on the wings where they can be adjusted while hiked.

I spliced the two upper blocks of the Cunningham to some 3mm Dyneema which are in turn attached to a hook which clips to the Cunningham eye on the sail. This makes rigging/de-rigging easier. The Cunningham system (yellow line) is a good 8:1, which is enough power.

I also replaced the outhaul line inside the boom with 2mm Spectraspeed. Where it exits the boom, I replaced the old Ronstan 19mm loop headed block with a #6 Wichard FRX ring. These rings are pretty cool replacements for control line blocks in situations like this. They are made of a very strong alloy and have a tough, low-friction coating. I like that they have no working parts and have a redundancy factor, ie. if they were to break, the control line will still work, just with more friction. The outhaul control line is the blue one.

The lever style vang is very powerful, and the the only concern I have at the moment is whether it will interfere with the daggerboard when gybing. I’ll have to watch that. I have installed a Dyneema loop around the boom and this loop attaches to the lever. The other primary Dyneema line (3mm) attaches to a shackle on the mast foot. Also attached to this shackle are two FRX rings spliced onto 3mm Dyneema. The red control line runs through three FRX blocks as you can see in the pic above and then run to the clam cleats fixed to the wings. The pic above shows the vang lever. In the pic below you can see on the left the blue Dyneema loop around the boom for the vang attachment which also passes through an eye to fix it in place. The other 2 loops to the right are the hangers for the mainsheet blocks. I have no idea how to calculate the mechanical advantage of this system, but I estimate it to be about 16:1.

The pic below shows the attachment of the clew to the outhaul. I may add a shackle here to make it easier to rig the 2mm Spectraspeed line to the clew. 2mm line can be a bit of a fiddle to untie! I also replaced the SS wire outhaul traveller line with 3mm Dyneema which has spliced loops at the ends for smooth attachment points that won’t interfere with the running block. The traveller is tensioned with an eyebolt at the inboard end. A 19mm loophead block facilitates smooth running along the traveller. Also, a thin bungee cord tied to the shackle to act as an inhaul will be fitted.

Unfortunately the Dyneema loop around the base of the mast to which the Cunningham and outhaul blocks are attached is not removable at the moment. I will think about modifying this arrangement so that this loop can be attached with a clip. If I do this the control lines can remain attached which will make rigging/unrigging so much faster!

Well, that’s the control lines all sorted. Smile


At Tuesday, 11 June, 2013 , Blogger RDG said...

Hi Oztalis,
Make it all black (don't) and it's a straightforward Batman device.

Kidding aside, I think you have managed to restore the boat in little time without losing attention to detail (well except for the one screw holding the outhaul eyelet at the rear of the boom maybe).
Splicing Dyneema string was a good thing to learn as is the use of Wichard FRX rings.

I chair your concern about the vang interfering with the daggerboard, If I see well on an earlier posted image the device was above the forward tube of the wing frame. Then again I could imagine you wouldn't bother much about raising the blade at all except for beaching.

What's next, sail it? 


At Tuesday, 11 June, 2013 , Blogger Bruce Taylor said...

Thanks for your kind words Ronny. I think I will post something about the daggerboard and the case design as I think I've discovered a quirk that looks like it gets around the problem quite nicely. Quite simple but also very clever, so kudos to the designer (Greg Marshall). Later scows moved the foredeck bulkhead forward so the casing was located lower in the dished out part of the deck, so this solved the problem and also allowed a shorter board.

The outhaul eyelet is in fact through-bolted through the boom tube and a short inner sleeve that looks like it was inserted at some stage. Judging by the ugly holes there, it looks like the clew eye was pulled out completely at one time! It's all good, really. :)


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