Rope diameters for Block attachment

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RegW

RegW

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I have just completed the wood construction phase of my first ship build and
now getting prepared for the Rigging Phase...

Is there a chart out there that indicates correct rope size for rigging the various blocks (seized to eyebolts etc) - looking for rope diameter specifically? I'm able to convert full scale size to this model (which is 1/48th scale).

I have great references for the actual rigging lines. Some involve circumference and a few discuss diameter. I am specifically looking for the rope that actually secures the block - not the rope that runs through the sheaves.

I'll be using the following block sizes and want to ensure that I select the correct diameter rope for each block :

3.0mm - single sheave
3.5mm- single sheave
4.5mm - single sheave
5.0mm - single sheave
5.0mm- double sheave
5.0mm - triple sheave
7.0mm - double sheave
8.0mm - triple sheave

Build Log: https://shipsofscale.com/sosforums/...-artesania-latina-build-log.13917/post-441407
 
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Here are a couple of spreadsheets that have been passed around the forums a few times. :)
I believe the more complex of the two is from HiS Models. I don't know the origin of the other one.
Hope they help you!
 

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Corsair said:
Here are a couple of spreadsheets that have been passed around the forums a few times. :)
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I've seen one of those spreadsheets before and have used it for some of the steps early in the build. The "Rigging - size of rope and blocks - Final.xls" is going to be useful with a bit of interpolation. I think that Zoltan's proposed chart (mentioned above) will be a wonderful solution. Thank you both for your rapid responses!
 
Bob Cleek said:
David Steel's Elements and Practice of Rigging and Seamanship, online at https://maritime.org/doc/steel/ will provide you with the sizes of all rigging on most any period ship of the type you are modeling. Prototype line sizes are given in inches of circumference, not diameter.
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I have a few documents that detail the rope size for rigging but that's not my issue. The rope that actually secures the block to the yard, mast, eyebolt or sail is what I need. I've been using my "eyeball" technique to decide on the various blocks that i have already secured to the hull, but I'd like to get a more precise reference for this. Thank you for your response as all info is appreciated.
 
As mentioned by Bob in post #5, Steel is a wealth of information. Regarding rope strapping/stropping Steel wrote:
A seventeen-inch block has a five-inch rope strap, and every inch in length above or under, to a 12 inch block, has half an inch more or less fixed rope allowed for the strap; an 11-inch block has a 3-inch strap; a 10 and 9 inch block, 2 inches and a half; an 8 and 7 inch block, 2 inches; a 6-inch block, one inch and a half; a 5-inch block, 1 inch; and a 4-inch block, three-quarters of an inch.

But, if my math is correct, this does not seem quite right. If taking a 12 inch block, that is 5 inches in length less than a 17 inch block. Therefor the strop would be
5"-(5X0.5) = 2.5". But, he states that an 11 inch block would have a 3 inch strap, which is more than a 12 inch block. I suppose the numbers are approximate, and at our scales 1/2" circumference difference would not be very noticeable to the human eye. 1/2"/3.14=0.16" At 1:48 which is probably our largest most common scale that is a diameter of 0.003" (0.08mm)

Overall, this formula seems to be the best I have seen so far.

Allan
 
AllanKP69 said:
As mentioned by Bob in post #5, Steel is a wealth of information. Regarding rope strapping/stropping Steel wrote:
A seventeen-inch block has a five-inch rope strap, and every inch in length above or under, to a 12 inch block, has half an inch more or less fixed rope allowed for the strap; an 11-inch block has a 3-inch strap; a 10 and 9 inch block, 2 inches and a half; an 8 and 7 inch block, 2 inches; a 6-inch block, one inch and a half; a 5-inch block, 1 inch; and a 4-inch block, three-quarters of an inch.

But, if my math is correct, this does not seem quite right. If taking a 12 inch block, that is 5 inches in length less than a 17 inch block. Therefor the strop would be
5"-(5X0.5) = 2.5". But, he states that an 11 inch block would have a 3 inch strap, which is more than a 12 inch block. I suppose the numbers are approximate, and at our scales 1/2" circumference difference would not be very noticeable to the human eye. 1/2"/3.14=0.16" At 1:48 which is probably our largest most common scale that is a diameter of 0.003" (0.08mm)

Overall, this formula seems to be the best I have seen so far.

Allan
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Reg mentioned above that is not his issue,what he needs is the rope diameters for certain block sizes from Dry Dock Models and Parts
 
Hi Zoly,

Shouldn't the size of the strop around the outside of the block be the same for blocks from anyone, including Drydock? When Reg wrote I am specifically looking for the rope that actually secures the block - not the rope that runs through the sheaves it seemed like he is looking for stropping sizes which is what I posted above.
IF the stropping is what is needed a quick calculation for approximate strop rope sizes at 1:48 scale on the blocks Reg listed above:
3.0mm - single sheave approximately a 6" block so strop with 1.5" circumference = 0.25mm diameter at 1:48
3.5mm- single sheave 0.25mm diameter
4.5mm - single sheave 0.34mm
5.0mm - single sheave 0.34mm
5.0mm- double sheave 0.34mm
5.0mm - triple sheave 0.34mm
7.0mm - double sheave 0.5mm
8.0mm - triple sheave 0.65mm

Hope this is making some sense.

Allan
 
RegW said:
I have a few documents that detail the rope size for rigging but that's not my issue. The rope that actually secures the block to the yard, mast, eyebolt or sail is what I need. I've been using my "eyeball" technique to decide on the various blocks that i have already secured to the hull, but I'd like to get a more precise reference for this. Thank you for your response as all info is appreciated.
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A block strop should be at least the same diameter of the line running over the sheave. A strop with a diameter smaller than the line running over the sheave would make the strop the "weakest link" in terms of maximum breaking strength and render the larger diameter of the running line simply waste in terms of the overall strength of the tackle. This assumes that the cordage is otherwise identical. (Strengths differ given the material, lay-up details, and so on.) On larger blocks, the two strops are doubled, each being half the diameter of the line running over the sheave, if it is desired to "flatten" the stropping on the sides of the shell as pictured below.
A block with a strop forming an eye may then be simply lashed to the spar or other point of attachment through the eye. If a pendant is desired, the strop may be spliced around the shell with the desired end of the pendant at the length desired, which can then be secured as required.
If lashing two attachment points together, the lashing can be made out of however many turns of smaller cordage are necessary to build up a breaking strength equal to the two points being lashed together.

Consult your Lees' Masting and Rigging English Ships of War specific details in various applications.


1746479508264.png
1746479599782.png

In the picture below, block (#12) is a metal-stropped block which has a hook attached to the block (which could also be secured by a strop.) The hook is attached to a pendant with a thimble spliced in the end to receive the block hook.
The lower block in the picture below (#13) is a "pendant block." It has the pendant spliced around the block to serve as its strop.

1746480709865.png

Whenever hooks are used in rigging applications, as in the hooked block (#12) above, the hook should be "moused," as indicated in the picture below. (The slight reverse curve at the tip end of a rigging hook is intended to secure the mousing as pictured below.

1746481028355.png

These pictures illustrate the various options for stropping blocks and attaching pendants to blocks. There are many variations on the theme. What should be considered when rigging is 1.) the appropriate diameter of the cordage (as indicated by Steel's or some other recognized authority, 2) the avoidance of "weakest links" in the capacity of the cordage elements that make up the rigging element, and 3) the simplicity of the rigging element in terms of its overall design.

While the design and purposes of rigging elements are relatively the same over time, the methods of attaching blocks to eyebolts or other points of attachment can vary widely from period to period and from ship to ship. Depending on the period and/or the ship, attachment may be made by lashing the block thimble to an eyebolt, taking sufficient turns to provide a strength equal to or greater than the running line, or by tying the block pendant to the lashing point. In later periods, where possible, connections were made with shackles which were stronger and more secure. Securing with a shackle should be "right side up" as indicated by the drawings below. This is very important. An improper upside-down shackle (second illustration from the left below) can create a significant reduction in the rated strength of the shackle. Note on the left-hand side, the shackle is hung over a hook. For anything other than a temporary connection, the example at the left side below should have a hook that is "deeper" than the one illustrated with the point coming sufficiently high above the shackle pin to allow for a proper mousing of the hook.

1746482134718.png

As I
 
Bob Cleek said:
A block strop should be at least the same diameter of the line running over the sheave. A strop with a diameter smaller than the line running over the sheave would make the strop the "weakest link" in terms of maximum breaking strength and render the larger diameter of the running line simply waste in terms of the overall strength of the tackle.
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My head hurts from trying to get through this. If there is a double block in the setup the main rope can carry double the weight. Does that mean the strop needs to be larger than, not the same as, the rope being run through the block? For example if I have a double block set up with 1 inch manilla rope it has a safe load of about 1300 pounds. But for a single manilla rope to have a safe load of 1300 pounds it needs to be 1.5 inches in diameter, 50% larger than the working rope. Hope this is making sense.
Allan
 
AllanKP69 said:
My head hurts from trying to get through this. If there is a double block in the setup the main rope can carry double the weight. Does that mean the strop needs to be larger than, not the same as, the rope being run through the block? For example if I have a double block set up with 1 inch manilla rope it has a safe load of about 1300 pounds. But for a single manilla rope to have a safe load of 1300 pounds it needs to be 1.5 inches in diameter, 50% larger than the working rope. Hope this is making sense.
Allan
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If there is a double block instead of a single, it does NOT mean that the line can carry more load. If a single block tackle and a tackle using a double block use the same size rope for both the running line and strops, then the tackle with the double block can lift the SAME load with less force by the sailor, and the sailor has to haul more length of line to perform the same amount of work. More sheaves = less force required to move the load, but more line to heave. Work is the same. If you want to lift a heavier load, a tackle containing larger blocks, larger size running rope, and larger strops will be required no matter how many sheaves are in the block.
 
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AllanKP69 said:
My head hurts from trying to get through this. If there is a double block in the setup the main rope can carry double the weight. Does that mean the strop needs to be larger than, not the same as, the rope being run through the block? For example if I have a double block set up with 1 inch manilla rope it has a safe load of about 1300 pounds. But for a single manilla rope to have a safe load of 1300 pounds it needs to be 1.5 inches in diameter, 50% larger than the working rope. Hope this is making sense.
Allan
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I'm not sure that's completely correct, but it shows you're thinking! Actually, I didn't address multiple purchases, at all and probably should have. The simplest statement of the principle is that the strop must be strong enough to carry the load placed upon the block. A block purchase merely distributes the work of lifting over a longer distance, or, as might be said, it makes the grade less steep. Given the "weakest link" principle, the strop should be at least equal to, or greater than the greatest strain placed upon the block, i.e. the breaking strength of the line that's running through it, which is presumably greater than the weight to be lifted. A multiple purchase tackle distributes the effort necessary to life a given weight, but it doesn't reduce the weight itself. If a line is run through blocks at either end to hoist a weight, the strain of that weight is still completely borne by the uppermost block's strop. Mechanically, the "purchase" only "distributes" the energy required to lift the weight, just as an incline "extends" the work necessary to lift a given weight to a given height.

When we're talking about wooden blocks and fiber cordage in the Age of Sail, it's really not an exact science. There are the established standards which dictate the proper size block for each size of running line as well as the size of the sheaves and strops (e.g. Steele's Elements.) For both modeling and real-life purposes, following those should suffice. (And I expect the Admiralty in its wisdom required the strops to be a bit stronger than the running line, because it's always preferable to have a running line break if it's going to before a strop breaks and sends a deadly missile hurtling down from aloft onto the heads of a deck crew.) For modeling purposes, "If it looks right, it is right." but that assumes the modeler has an "educated eye."

In actual practice, rope block strops were wormed, parceled, and served "quoits" made up of unlaid strands which were re-laid upon themselves to make up a three-strand rope worked up out of a single strand. I expect that a strop made up of the same size strand as the running line for the block might be considerably stronger than the running rope alone. I don't believe I've ever seen anybody try to depict served strops at a scale smaller than 1:48, though! :D

See: https://www.engineeringtoolbox.com/pulleys-d_1297.html for an explanation of how, theoretically, the motive effort expended can be distributed, but how at the same time, the load weight remains a constant.
 
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AllanKP69 said:
Kurt, You can see why I went engine not deck and certainly not dualie back at school.:)

No worries Bob, I get it now and thank you and Kurt. :)
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I was actually Systems Engineer for 2nd Class Year, but had to drop back to straight Engine when grades fell as a result of the academic load. That allowed me to make it to graduation, the lone survivor from Minnesota. My classes were thus unique, with the addition of differential equations, refrigeration, statics, and dynamics above and beyond the straight Engine curriculum. Statics and dynamics was where you learned how tackles work.
 
So I'm going to throw another little fly into the ointment here regarding the relationship of strop size vs. running line size. I posit that the strop must (in certain cases) be twice as strong as the running length.

Consider, for example, a single block fixed to a mast top through which the yard lift is run. Obviously, the weight of the yard itself is placed on the block (and strop), but many people don't realize that the other end of the lift must have an equal amount of weight on it in order to balance the weight of the yard (regardless of whether this "weight" is provided by crew or pinrail). Therefore, even though the lift line itself never sees more than the weight of the yard in tension, the strop sees twice as much and must therefore be twice as strong.

This all assumes, of course, a straight up and down pull. If the running end of the lift is belayed (or hauled upon) at an angle to the mast, the values decrease slightly, but for most purposes, you can figure twice the weight. Even with multiple blocks in a block & tackle arrangement, the running end trades distance for load, but the outermost block and strop still sees twice the static load.
 
The photo below shows stropped blocks for a rigged longboat that I built. The blocks were sculpted from pear wood by me.

I’ll leave the question of strop diameter to others, but once you’ve solved my question here’s my system for stropping blocks; served as Allan points out.

1. Measure the length of the strop by my measuring the length of a piece of thread wrapped around the block. Divide this number by three.

2 Pick out a dowel with a diameter close to that calculated in 1. above. Using a razor saw, cut a thin slot in the end of the dowel. Also drive a very small nail part way into the side.

3. Using thread much thinner than the finished strop, secure one end of the thread in the slot, pull the thread down and make an half turn around the nail. The nail holds the resulting coil in position. Wrap several turns around the dowel. The last turn should be “sewed” around the previous turns. With the coil still on the dowel do this by threading the thread in a needle and alternatively passing the needle under and over the coil. Secure both ends of the coil in itself.

4. Without removing the coil serve it by passing a needle and thread around the coil with each loop close to its neighbor and drawn tight.

The result; a seamless served strop. As shown in the photo it’s also possible to incorporate a hook in the strop as part of this same process.

RogerIMG_2766.jpeg
 
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