Friday, May 31, 2019

Shroud Tensioner

This probably won't interest most readers, but a fellow F-24 owner wanted some images.

Because the F-24 folds, a quick release of cap shroud tension is required. Pulling the shrouds aft with a tackle is a simple way. This can either be a cascade:

or a straight tackle:

A cascade places only 1/2 the load on the blocks and can thus be built using lighter gear. This is commonly done with vangs, for example, which also have a small range of travel. The only advantage of a straight tackle is that it can be adjusted through a greater range.

The PO (previous owner) probably used the blocks in a 4:1 tackle. I'm not sure why he went to a cascade, but it works very well. I assume he went to 2:1 on the blocks to avoid over tensioning, but I may go to 4:1 (the pulleys are there ) to make it easier to adjust under load, simply remembering not to yard on it.

Tuesday, May 28, 2019

The Best Rope-to Chain Splice

The Irony Spice

Joining chain to rope in a manner that allows it to feed smoothly has always been something of a challenge. Back in the day of weak chain and hemp rope, a 2-strand splice was developed to allow bulky rope to fit through a link. One strand was unlaid way back and the remaining strands go through the link in opposite directions, laying flat and sharing the load evenly. Even with the loss in strength around the link, 4 strands were as strong as the 3 strands of the rope. One of the strands would be laid back in the empty groove and terminated in the manner of a long splice, and the other back tucked like a 3-strand eye splice.

Feeds through a windlass like silk

Then ropes got smaller and stronger, and a simple 3-strand back splice or crown splice became the standard. The smaller line was as strong as BBB chain. Then we introduced G43 and G70 high tensile chain. By the time we use a rope as strong as the chain, the splice was too big for the windlass gypsy, and so the irony is we find ourselves returning to 19th century splicing technology.

It is a little more difficult to get the strains even, and the spice takes a few minutes longer, but you gonna love the way your windlass feeds. No more jams!


The name "irony splice" was coined by Brian Toss, and this method is well described in his highly-recommended book, The Rigger's Apprentice. It takes considerable practice to get the tension just right, but if you have any ability with splices, by the third or fourth try you should be in good shape.

The following instructions are for half-inch three strand rope. For larger diameters, increase the spacings proportionately.

The Irony Splice--Instructions

  • Place a light seizing around the rope about 5 feet from the end.
  • Tape each strand separately and securely.
  • Unlay one strand back to the seizing, without disturbing the other two strands.
  • Place a light seizing across the two remaining strands about 3 feet from the end.
  • Untwist the two strands and lead them through the last link of chain in opposite directions.

  • Take one of the strands and lay it into the space left vacant by the first strand that was unlaid. Be careful to maintain twist in that strand, and to choose the strand most naturally lies in that vacant space.
  • When this strand meets the first seizing and the first strand that was unlaid, join the two strands in the manner of a long splice. This will require a locking overhand knot, back tucking both strands, and tapering.
Line re-layed, tying the overhand to start the long splice join.

 Long splice finished (not trimmed), ready to do the tuck-backs at the chain end.
  • Take the remaining loose strand, still hanging loose at the last link of chain, and tuck it back at least eight times in the manner of a back splice. Taper carefully.
 Much smaller in diameter, more flexible, and much easier to feed than the common backsplice. They got prettier with practice, but this one tested at 85% line strength. I eventually reached near 100%.

Thursday, May 16, 2019

Backing Plate Testing

Breaking stuff in the name of science is always fun! Parts of this appeared in Practical Sailor in 2015, some not.

The test rig

The bolt is tightened and torque recorded until something gives.

I tested laminate samples to make sure the failures were appropriate (good bonding). As you can see, the core is failing in shear.1 layer 17-ounce biax on the bottom, one layer 17-ounce biax and one layer 6-ounce cloth on the top, 1/2-inch end grain balsa.

I replaced core with plugs--standard practice.

The Poor

Starboard showed micro cracks after 3 week. It also creeps a lot--I had to keep re-torquing for 48 hours.
Teak is a big failure. Note how the distorted washer became a wedge.

 The Best

Just 2 layers of 17 ounce biax were very impressive, holding 1.5 tons. 4 layers would be correct for 1/4-inch bolts.

1/8-inch FRP bonded  did better than 1/8 SS, particularly on rough surfaces. 1/4-inch FRP would be correct for 1/4-inch bolts.

 The Bottom Line
  • 1/8" aluminum for light duty in dry locations. Thickness = 1/3 bolt diameter minimum.
  • 1/4" FRP most places, bonded if there is high load. Thickness = 2/3 bolt diameter minimum.
  • 4 layers of 17 ounce biaxial cloth for every 1/4-inch of bolt diameter, where there is high load and irregular surfaces.
  • Diameter of plate = 5 bolt diameters minimum.
And never, ever use fender washers. They bend into cones and are LESS effective than standard bolting washers in actually distributing the load.  Buy extra thick (Bolt Depot).
 A little more if the skins are very thin. Less with solid glass.