I would have preferred to make the blocks of stainless steel, but cutting and accurately bending and drilling even 1/8-inch stainless was beyond the capability of my equipment, so I choose aluminum. Aluminum can be hand-sawn easily with a hacksaw blade with 24 teeth per inch, but I also used a miter saw with a 10-inch diameter 60-tooth carbide-tipped blade that cuts through aluminum like butter with a very straight clean cut.
I made the bottom channels from a 12-inch length of 1/8-inch aluminum channel, 2 inches wide with 1-inch sides. I made the rope-retaining arches from a 48-inch length of 1/2-inch x 1/8-inch aluminum strip. This was available from my local aluminum supply shop for $15.
I needed to make one row of six sheaves, a row of three, one of two, and a single, but most sailboats won’t need that many and would therefore require less material.
MAKING THE BOTTOM CHANNELS
I first cut the channel into 1-inch wide pieces to form the base for a two-sheave block. I needed five of these.
The next drilling operation is critical. It might be possible with a hand-held electric drill, but it’s much easier and more accurate with a drill press. Both legs of the channel need to be accurately marked 3/4 inch from the bottom outside of the leg and in the center. I drilled a 1/4-inch hole at these marks from both sides of the legs. This hole position allows the sheaves to rotate clear of the bottom of the channel by 1/16 inch and the lines run out the top of the sheaves at the very lowest point: about 1 inch off the deck.
Next I drilled and countersunk two 1/4-inch holes in the bottom of the channel 5/8 inch from inside the channel and in the center. This was to locate the attachment screws beneath the sheaves. As a final finish to the channels, I rounded the square sharp corners of the legs with a flat file.
The rope-retaining arches
To form the arches, I cut the 1/2-inch aluminum strip into 5-inch lengths so I could more easily bend each around the mandrel. I clamped the socket/mandrel hard in the vise, then marked the center of the strips and clamped one to the socket in the center with Vise-Grips. This is to ensure that the aluminum strip will fold evenly round the mandrel in a perfect half circle, otherwise it will bow upward and not form correctly. I also cut some lengths of spare strip to clamp between the vice-grips and the material both to prevent them cutting into the aluminum and to keep the legs of the arches straight.
I then carefully pulled both legs around the mandrel. It was quite easy with vice-grips clamped to the legs to extend the leverage, but you can only bend so far before the vice-grips come together. I then squeezed the two sides further with just one vice grip until they were parallel with each other and formed a perfect arch. Then I sawed the legs of the arch off square 1 5/8-inch from the top of the arch. Using a round file and sandpaper, I also rounded the top inside edges of the arches a little to prevent the rope from chafing as it passes through. A Dremel with a round sanding drum would also be good for this purpose.
Each arch is now 7/8-inch wide, so two will be a perfect snug fit inside the channel that measures 1 3/4 inches inside the legs.
Drilling the rope-retaining arches
With both arches centered in the channel I now clamped the assembly in the vice and with an electric drill, carefully and dead level, drilled either side of the arches through the hole in the channel leg. (drilling-arches.jpg) I then reversed the arches, and making sure they were centered in exactly the same position, re-clamped them in the vise and drilled through the other side. Do not be tempted to try to drill straight through both arches—it is very unlikely you will be level using a hand drill.
At this point it’s possible to push a 2 1/2-inch long 1/4-inch bolt straight through the channel and both arches pinning them together. If your measuring or drilling has not been accurate enough to make it possible to push a bolt through, ream the holes level by carefully running a 1/4-inch drill through. I discovered some unevenness when assembling my row of three channels to make the six-sheave block, but I ran a 1/4-inch drill through the whole lot and they work perfectly when bolted together.
The sheaves and bushings
The Ronston sheave has a 5/16-inch center hole and no ball or roller bearings. I therefore bought some small 5/16-inch bronze bushings from Ace Hardware for $2.35 each. Lowes and Home Depot also sell them. These fit perfectly inside the sheaves and reduce the hole to 1/4 inch. Unfortunately, they’re only available in lengths of 3/4-inch, so I had to carefully saw and file 1/8 inch off one end to make them 5/8-inch long to fit snuggly inside the arches. The sheaves will then rotate on the bushings and the bushings will rotate on the bolt, giving an almost friction-free roller-bearing surface for the sheaves.
If the sheaves don't rotate completely freely, something is wrong. Perhaps the bushing was distorted in reducing its length or it needs to be deburred on the inside and maybe also the outside.
Assembly and attachment
The photo of the two-sheave assembly shows it with no lines running through. To fix the channels to my fiberglass deck, I used 3/4-inch long #12 flathead self-tapping screws that finished flush with the bottom of the channel in the countersunk hole. I screwed these directly into the deck and bedded them with 3M 4000 sealant. It does not seem necessary to bolt these blocks straight through a deck as you would for a deck eye because, when the ropes are under load, they press the assembly down to the deck, rather than pulling it upward. It is necessary to fix the channel to the deck before assembling the sheaves, then assemble the rest in-situ.
Just before this final assembly, I used a dab of winch grease on the bolt and bushings, but not on the bushing-to-sheave surface. The sheaves and bushings are positioned inside their arches and the arches are pushed into the channel. Then the bolt is passed through the whole lot and secured with a thin washer and nylock nut. I found it best not to tighten the bolt too much allowing some play in the bearing surfaces so everything rolls freely.
The photo of six sheaves shows how I joined three two-block assemblies to make a neat row of six. It was just a matter of using a 6-inch bolt through all three assemblies. To make a multi-sheave combination, it’s best to bolt them all together without the sheaves or arches, position them where you want them on the deck, mark the attachment hole centers, and then drill the holes for the fasteners.
To make the three-sheave block I cut one leg off a channel, then made a corresponding half channel to butt against it. A 3 1/2-inch bolt goes straight through all three sheaves locking them together. Then a fastener beneath each secures them to the deck.
The single sheave leads the jib furling line down to the foredeck so it can be routed up-and-over the forward coach-roof and the saloon coach-roof. This block was also made using half a channel, but it has a different shape so I could screw it to the toerail. I secured a small half channel with one of the screws to fix it to the toerail. A 1 1/4-inch bolt fastens the assembly together.
These combinations demonstrate the versatility of this method of making over-the-top blocks. There’s no reason why larger combinations could not be bolted together as needed.
Finally, if you want to make these blocks look really professional, polish all the individual pieces on a bench grinder with a large polishing wheel and graphite applicator. The aluminum will shine up like chrome.
My over-the-top blocks work marvelously and with considerably less friction than the bulls-eye fairleads I tried in my first experiment. The lines look very neat running close to the deck and there is much less chance of tripping over them.
The total cost in materials was about $120 for 12 sheave blocks, or $10 for each control line. This is quite a savings compared to buying commercial units for about $500. This does not count my labor of course, but on boats that’s supposed to be a pleasure