Rope-Stropped Wooden Blocks

There is nothing that can make your boat look saltier than to fit it with old-fashioned rope-stropped wooden blocks. Of course, you can't buy them; or at least I have not found them (I have now; see below), and probably could not afford them if I did. So the answer for me was to make my own.

The blocks shown here were made for my Bobcat. They use fully modern self-contained ball-bearing sheaves, so they are functionally equivalent to the metal-shelled ones you can buy ready-made. Bobcat's plans call for 1/4 inch line; these blocks will take up to 5/16 inch line, so you can use a slightly bigger mainsheet for a better fit in your hand.

Theoretically, these blocks could be made strictly with hand tools and a lot of experience/skill. However, a drill press and a router will save you a lot of time and grief; if the axles are not perfectly perpendicular to the cheeks, the sheaves will not fit properly. A bandsaw is also nice for rough-shaping the blanks. Most of your time will be spent rasping them to shape and sanding them.

Materials

Six are required for Bobcat. To make these, you will need:

• Two feet of clear hardwood stock, 1-1/8 inch square
• One foot of 1/4 inch brass rod for axles
• Six Harken #160 self-contained sheaves
• Six stainless or bronze thimbles for 1/4 inch rope (round preferred; I could not find any)
• About 12 feet of 1/4 inch Dacron twisted rope
• One spool of whipping/seizing twine
• About 2 cups of raw linseed oil, and a dairy-style plastic container for it.

The picture shows an exploded view of a block ready to be assembled.

(The thimble is missing, as I was still trying to locate round ones when this picture was taken.)

The dimensions and basic design of the blocks are shown here.

If you have CAD software, you can download this drawing in DXF format and print it to scale. If you have (or are willing to obtain) a copy of DeltaCAD, you can download the original drawing and work from that.

Procedure

As they are quite small, it is much easier to work with them while they are all still part of the same piece of wood. Draw or mark the locations of each of the blocks along the piece of stock, allowing for the widths of the saw kerfs made when separating them later. While still joined together, do the following:

• Drill 1/4 inch holes for each of the axles
• Drill 1/4 inch holes at ends of blocks for the strop guides
• Drill 1/2 inch holes for each end of the sheave slots
• Join the 1/2 inch holes to make the sheave slots
• Square off the hole at the end of the sheave slot closest to the axle
• Cut or plane off the corners end-to-end to save much rasping later

Now cut the blocks apart, and rasp them to shape by eye. Don't worry if no two are alike; that is part of what gives them their character.

This picture shows some blocks in various stages of completion. (You may notice that these instructions incorporate the benefit of hindsight; the corners are still clearly on these pieces.)

Once the shells are complete, they can be finished in linseed oil. And I mean "in"; I put them into a dairy container and filled it with raw linseed oil, and left them there for three days to soak. On taking them out, I wiped them down thoroughly and hung them on a wire to dry (about another three days).

You may instead wish to varnish them with a clear hard finish. I chose linseed oil because the blocks will not show dents to the finish, and should I ever wish to do so they will be much easier to refinish.

Assembly

While the shells are sitting in linseed oil, cut six pieces of brass rod to length for the axles. Ideally, these will sit flush with the cheeks for maximum bearing surface against the shell. Make six rope grommets for the strops; it may take some trial and error to get the correct length. Put the shell and the thimble into the grommet, apply some tension, and seize the grommet tightly between the shell and the thimble. Make sure that the squared end of the sheave slot is opposite the thimble and the rounded end closest.

That's it; go and install them on your boat!

Notes

The sheaves used for these blocks are rated by Harken for 300 pounds maximum working load, and 2000 pounds breaking load. This should be plenty for the mainsheet and halliards of a sailing dinghy; after all, you have to hold on to the end of that rope, and 300 pounds would probably pull you out of the boat.

If the block does collapse for any reason, it will not fail completely. Even if the shell or the sheave were to completely disintegrate, the line led through the block is still captive in the grommet.

The original idea for these blocks came from a book called “The Marlingspike Sailor”, by Hervey Garrett Smith. It is full of all manner of interesting things like this, and worth a read.

Boatbuilder Robert Albers makes beautiful rope-stropped wooden blocks out of lignum vitae and bronze. If you don't have either the tools or the time to build your own, you can buy them from him. (Considering the effort that goes into these, I think his prices are very reasonable.) He also steered me to Sailrite, who have round brass thimbles.