How To Make Rope Stropped Blocks

How To Make Rope Stropped Blocks

Making Rope Stropped Blocks

Mortised Rope Stropped Block

Have you ever secretly yearned for some of the pictuesque gear of the old squareriggers, deadeyes and lanyards, tarred hemp and canvas buckets, salt horse casks and handy billies?

Have you ever tossed in your bunk on a windy night, cussing away as the noisy deck block clattered and banged away just above your ear?

If so, you need some rope stropped blocks. There was a time when all blocks were rope stropped. They were made in endless variety, each designed for a specific job, tested and proved through the years by hard usage. They were handmade by men who were masters and took pride in their craft.

A block is a single or multiple pulley. In use, a block is fixed to the end of a line, to a spar, or to a surface. A line (rope) is reeved through the (pulley) sheaves, and maybe through one or more matching blocks at some far end, to make up a tackle. Blocks are made for guiding rope, to control forces and to help with hoisting. Blocks are made using a different number of sheaves (or pulleys): single-sheave, double-sheave and triple-sheave (even up to a maximum of 7-sheaves). 

A block was originally a block of wood with a hole in it for a rope to reeve through. To save friction the hole was enlarged to take a pully-wheel or sheave. Then the surplus wood was cut away from the outside of the block, leaving a wooden shell. This was grooved to take a rope strop spliced round the block to secure it in place as required. When the wooden shell split the block was useless. The next improvement was the 'iron-bound block' in which the strop or hook was rivetted to an iron case carrying the sheave and its pin, the wooden shell serving to stiffen the case. Today the larger modern blocks are made of metal, and friction is further reduced by roller-bearings between the sheave and its pin.
There are various types of blocks that are used in sailing. Some blocks are used to increase mechanical advantage and others are used simply to change the direction of a line.

There are basically  two sorts of block construction: mortised blocks, and made or built blocks.
A mortised block is made from a single piece of wood, that is mortised or hollowed out to fit a sheave, some of the largest morticed bloacks are 28 inches in size, or over two feet! However, typically for small boat use, a mortised block is about 3 inches in size.
A made or built block can be constructed to any size, and is used on both small and large blocks. Some of the largest made blocks are up to fifty inches in size! The number of pieces it is composed of depends upon the number of sheaves; as the partition between each sheave is a separate piece, they are bolted together by four bolts or rivets, two at the top, and two at the bottom, and are typically  fitted with metal sheaves, and a shoulder to one side of the shell.
The size of a block is denoted by the length, and its classification by the flatness or thickness of the shell, the number of sheaves, the number of scores, and the quality of the stropping.
For instance - if a shell of a block is 6 ins. in length, it is called a 6-in. block ; if it is 10 ins., 15 ins., or 20 ins., it is called a 10-in., 15-in., or 20-in. block, according to whatever length the shell might be.
A block, if one sheave, is called a single block; two sheaves, a double block; three sheaves, a treble; four sheaves, a fourfold block, and so on, according to the number of sheaves.
If one score, it is termed a single score block; if two scores, a double scored block.
There are rope strops and iron strop-blocks,  can be both double and single. The rope stropping is fitted in various ways: for instance, single strops, double strops, and two single strops, according to the stand the block is required to have to establish a fair lead with any given point. 
A block is supposed to carry a rope one-third its length in circumference : that is to say, a 6-in. block a 2-in. rope, an 8-in. block a 2½-in. rope, a 9-in. block a 3-in. rope, and so on.
Types of sailing bloacks 
Various types of sailing blocks - including the stropped block
Parts Of A Rope Stropped Block
Parts Of A Block
Parts of a rope stropped block
1. Shell
The shell is the outer housing for the block. The shell holds the sheave (pulley) and pin in place and is surrounded by the rope strop. A shell can be made of wood or iron. Commonly used woods are : ash and elm.
2. Sheave
Is the wheel on which the rope travels, and can be ade of plastic, metal, lignum-vitae, or iron. In some cases the sheave can contain roller bearings to reduce friction. In small boats, a variety of manufacturers make sheaves with delrin ball bearings, for example the Harkin 160, bullet sheave.
3. Pin
Is the axle on which the sheave sits. It usually has a head on one end, and passes through the centre of the shell. The pin is typically made of metal, either stainless steel, iron or brass. However, in older times, lignum-vitae or hardwood might be used on smaller blocks.
4. Crown & Tail 
The ends of the shell, the crown is at the top of the shell, and the tail at the bottom, usually the score in the tail is slightly longer and wider than the crown.
5. Swallow
Is the open part between the sheave and shell.
6. Score
Is the groove in the outside part of the shell to take the strops either single or double scores, according to what the blocks are required for. Double-scored are always double-stropped.
7. Strop
A strap, especially a short rope whose ends are spliced together to make a ring known as a gasket, that serves as a band to support the block. Strops can also be made of metal or iron.



Nylon Sheeve


The Sheave:  The first step in making the block is actually to select the size and type of sheave you want to use. The sheave is a solid cylindrical wheel, and round its circumference is a groove one-third of the thickness of the sheave deep, in which the rope works.

Historically, it is commonly made of lignum-vitae; but when used for very laborious purposes, it is coaked in the middle with metal.

Today, the best type of sheave is a commercially made self-contained ball-bearing sheave. The ball bearings will minimize friction, and give you a very long life. There are several manufacturers including Harken, and Ronstan.  The Harken #160 bullet sheave is a good choice for small boat/yachting use and can handle a line of up to 5/16", in comparison a Harken #265 "big bullet" can handle a line up to 3/8".

Alternatively, you could also buy commerically made metal or plastic (nylon) sheaves. The better sheaves usually have as stainless steel bushing which prevents the plastic from deforming. You can get these from a variety of sources, at a fairly low cost. A very good economical choice is Duckworks Boat Building supplies.

Lastly, you can make your own sheaves, the traditional method is to make them out of lignum vitae, a hardwood which is self-lubricating. Lignum vitae is very rare and hard to source nowadays,  - but it can be had from specialty wood working supply stores, such as Lee Valley Tools, Woodcraft,  Rockler Woodworking and Hardware, or Exotic Woods USA.  In lieu, you could also  use other suitable hardwoods such as walnut or locust. In terms of cutting the sheaves, the traditional method is to either turn a dowel on a lathe, and then part-off the sheaves. If you dont have a lathe, a hole saw can work just as nearly well, and then the groove can be made by running a bolt through the middle to make a mandrel, so it can be turned and scored.

Other materials for making sheaves include UHMW (Ultra High Molecular Weight) polyethylene, which  is soft enough to be worked with wood working tools, self lubricating, and impervious to moisture. It can be obtained in small quantities from wood working suppliers such as Lee Valley Tools. Alternatively, you could also use those cheap plastic cutting boards, the white ones, which would be suitable enough for smaller sheaves.

In terms of making your own sheave, the formula for the traditional dimensions are given in The Elements and Practice of Rigging And Seamanship, 1794, by David Steel as:

"the thickness of the sheave is one-tenth more than the diameter of the rope it is intended for, and the diameter of the sheave is five times the thickness."

So basically, this means a 1/2" rope should have a sheave about 5/8" wide, and a diameter of about 3 1/8" according to the traditional means. In comparison, a 1/4" line would have a sheave width of about 3/8", and a diameter of 1 1/2" to 1 5/8" in.  In terms of the depth of the groove, according to David Steel, "the outer circumference hollowed one-third of its thickness, that the rope may embrace it closely".

In our blocks, we used commercially manufactured sheaves, the cost can range from $3-30, but knowing that we have a long-life well working sheave with minimal chance of failure is nice piece of mind.

Block Mill
In 1794, a block mill was used to create large sized sheaves.


rope block shell

Block Diagram
Basic Block Diagram from
The Marlinspike Sailor, by Hervey Garrett Smith

STEP 1: To make a mortised block, the first step is to find a nice solid piece of wood to cut your block from. Traditionally, the best woods to use are hardwoods with an interlocking grain that resist splitting and cracking but are easy to carve and won't dull chisels. Elm or Ash is preferred for creating blocks, and has been the choice for centuries. However, today, many exotic woods are available that not only have great properties, but also an awesome estethic appeal, examples include: canary wood, rosewood, sycamore and black walnut. You can order these species through mail-order suppliers, such as Lee Valley Tools.

However, our preference is to use local species whenever possible, such as a re-purposed old walnut plank, or wood cut from a  tree. If you are going to use wood cut from "your own backyard" make sure that it is throughly dried and seasoned. If you don't, the "green" wood may split and crack during the drying process ruining your blocks. 

In our case, we used wild cherry. Cherry wood is very hard, and can definitely be difficult to work with hand tools, but it has a very nice grain, and is readily available in our area. The heartwood of cherry is also very durable to rot and decay.

cherry wood
A nice well seasoned piece of wild cherry
that we plan to use for our wooden blocks

STEP 2.: Once you have selected the wood, you will need to cut it to the size of your block. A good rule of thumb is that the block width should be three times the width of your rope, for example, if you have a 1/2" rope, your block should be at least 1 1/2". In terms of height, a general measure is twice the diameter of your sheave. You can always trim and shave down excess bits of wood, but you can't add wood back

cherry wood
We cut the cherry to the size we needed for our mortised blocks.

As far as the general shape, the first blocks used in ships were simply a square block, but by forming the block, the improved shape not only reduces weight, but prevents marring of the deck and spars and will not be as prone to getting fouled up in the rigging. The traditional shape of wooden rope blocks is similar to an egg, with an oval appearance, however you can use your own discretion to determine your own shape.

We drew out the rough oval shape of our block to be
cut out of the "blank" with a bandsaw. 

STEP 3.: Cut the block to your desired shape, an egg shape is traditional, but it doesn't hurt to be a little creative - and you may want distinctive looking blocks. A "clump block" is nearly circular. The diagram below of a tradition block  is from the Marlinspike Sailor, by Hervey Smith. 

Rope Stropped block diagram
An example of a "traditional rope stropped single block"


cutting to shape
We rough cut the shape of our block with the bandsaw, we will further finish
by using hand tools such as a rasp  and sandpaper.

STEP 4.:  Now that the block is cut to shape, it is time to mark the location of the mortise. In a typical block the swallow (the space above the pulley) is usual larger at the top than the bottom. In sizing the mortise, you want to make sure then length is at least 1 1/2 times the diameter of your sheeve. The mortise should only be as wide as the sheave can spin freely, too much play in the sheave will create wobble, and require the use of shims. 

mark mortise
Mark the shape of the mortise
it should be longer than the sheave.

The mortis is marked and ready to be hollowed out.


The traditional method of hollowing out a mortise is to use an auger,  or a hammer and chisel. In the early 1800's in England that had a special machine in the dockyards in Portsmouth. Today, we can also use a fixed router and table or a plunge router with a jig.

Mallet and Chisel 
Master woodworker Ian Kirby still makes mortises with a hammer and chisel.
Click hereTo find out more on this method from Rockler.

mortise and chisel
Here is another method: Lumberjocks


hand brace and bit mortise
The brace and bit method of making a mortise

Of course there are other methods, one could use a brace and a bit, or a drill press, and finally a router. In our case, we opted to use a router jig for a plunge router since we planned on making a number of blocks. While less traditional, even with the router jig, we required fine tuning the mortise by hand with a rasp and file.

A simple plunge router jig
makes block mortises quick and easy