What is the purpose of these holes in this block?

[Louie da fly]

I'm working away at my dromon model and have hit a question that has me stumped. Here are drawings of a three sheave block (the block as found and a reconstruction drawing) found on the c. 1025 AD Serce Limani wreck off the southern coast of what is now Turkey.

 

Most of it makes sense, but what are the holes at the bottom for? I made a model of the block, but three holes instead of two as I believe that for symmetry the original must have had them,

but I really can't figure out what they do. Can anybody enlighten me?

 

Steven

[mtaylor]

Somethings missing here. I can't quite put my finger on it (mentally speaking).     Is it possible that the lower block is missing and that they were used similar to dead eyes where you'd need two?   Then a set of the holes could for knots....  Or maybe this block is upside down?   Anyway, that's my guess....  

 

[Louie da fly]

Certainly there's got to be another half to this block system - whether it's another three-sheave block or perhaps a calcet (the integral block at the top of the mast). No problem there. But those holes are like a fifth wheel - they don't seem to have a function.

 

However, one thing that has occurred to me is that they are in a "tenon" (see the reconstruction drawing). Maybe the block slots into a mortise and the holes are for fixing the two structures together? But the large through-hole is so obviously for a rope as in my model, which would suggest the ropes in the sheaves would run in the direction opposite to that. Which leaves another question - what does the tenon slot into? And why?

 

Still confused . . .

 

Steven

Edited June 15, 2019 by Louie da fly

[thibaultron]

If the "bottom" holes are used for a tenon, perhaps the upper hole is an upper eye, for securing the other end of the rope used in the pulley system.

[lehmann]

12 hours ago, Louie da fly said:

There are a lot of features that don't make sense for this to be a regular block.

1. The top lateral through-hole would not be able to take much load as the end-grain would easily pull out.  For this to take a tension load there would have to be an iron band around the block.  This is a large block, so it's not for small rope or small loads.  Also, if the outer corners are relatively square, so chaffing would soon cut the rope.   To me, this means a pin, wooden or metal, went through the through-hole.    
2. The tops of the pulley mortises appear to intersect with the bottom of the lateral through-hole. 
3. The pulley pin is not centered in the block.  It's more towards the left in the side view.  It's too far off to think it wasn't made that way  This may indicate that the back of the block is against a surface.  However, the rounded ends of the rope mortises indicates that the rope should only go over the top of the pulleys. 
4. Based on the location of the pulley hole and the diameter of the pulley, the rope just run down across the "front" face, but could not run down the "back" face.   This means the rope turned through and angle of, say 90 degrees, certainly not 180.
5. The large opening above the pulley will also make it easier to run the rope through the pulley, which may indicate that the block was used frequently, but the rigging was temporary or changed often.  Since these blocks were made by hand, no one is going to dig out  a mortise larger than necessary,  Based on the tight opening around the bottom of the pulley, it doesn't look like the pulley was worn down.
6. There is more asymmetries:

• in the side view, the top right corner is relatively sharp, the top is sloped and the left corner is very rounded.
• in the side view, the shoulder for the tenon seems to be only on the back side.  I don't know how a shoulder on the front side can be justified. To me it looks like a rabbet on the "back" side only.
• the top of the mortise for the middle pulley is slightly higher, and appears to intersect with the bottom of the lateral through-hole. 

Overall, I think the block is intended for the corner of a deck or railing where ropes need to turn roughly 90 degrees.  The flat back and the rabbet take the horizontal and vertical compression sload, and the three holes on the bottom are possibly for trunnels to hold the block in place and take the tension load that would develop there.   Consider that the block may mounted horizontally, not vertically.   

 

I realize that this doesn't explain the lateral through-hole, but I suspect a pin or bar went there, not a rope.

[BANYAN]

Hi Steven,  Lehmann has raised some interesting points worth some further investigation.

 

My 'tuppence' worth - I would really like to know the purpose or position of the block.  Was it part of a tackle, fixed to the hull/deck or a running block.  This would help to determine the block's shape and construction as some of the features have been lost to 'rot' - how much we do not know I assume.  Fore example, if the block was used as part of a tackle, it also may only have needed one or two holes.  But if fixed to the hull or deck, the holes may only have been needed for securing other ropes as well?

 

Do you have some information, even a hint, as to what it was used for?

 

cheers

 

Pat

[Louie da fly]

Thanks Ron, Bruce and Pat. I'm going to have to sit and ponder all this, particularly all the points in Bruce's reply, which I've only had time to skim over briefly so far. I'm not very good with visualising pulley systems, and I have to go forward one step at a time, with halts in between to digest the information. 

 

Ron, that occurred to me last night. I hadn't realised that was a "thing" in combining blocks into a system until I did an image search for blocks and tackle.

 

Pat, the archaeological report says "This block was found concreted to the downslope arm of the ship's forward port bower anchor." That's it, I'm afraid. Doesn't tell all that much, does it?

 

Steven

[mtaylor]

 

Pat, the archaeological report says "This block was found concreted to the downslope arm of the ship's forward port bower anchor." That's it, I'm afraid. Doesn't tell all that much, does it?

 

Interesting.  Possibly then it was for working the anchor?

[BANYAN]

Thanks Steven,  I am with Mark based on the initial feedback, possibly something to do with working or recovering the anchor? (or possibly he ram?)

 

When I get a chance I will look back through some of my early stuff and see if I uncover anything.

 

cheers

 

Pat

[druxey]

Another theory! The upper hole was used for a strop to secure the block to something else (assuming that the illustration shows the block right way up!). The lower hole was for securing the standing end of the fall to the system. Does this make sense?

 

Another factor is how much the holes may have been scoured out larger than originally made.

Edited June 16, 2019 by druxey

[Louie da fly]

Thanks again everybody for all the input. Lehmann, I take your comments on board, and they certainly provide food for thought. regarding your points above, 

 

1. However, lacking a metal reinforcement I can't see how the end grain pulling out could be avoided. Certainly there's no evidence of grooves for a rope strop running around the end, either.

2. It certainly seems that way, doesn't it?

3. Both points taken and they certainly look valid.

4. Yes.

5. Possible, but I'll have to give that one some more thought.

6. Yes.

It's quite possible that the theoretical reconstruction is incorrect in several ways, particularly in assuming symmetry where the evidence for it is at the very least equivocal. 

 

Further speculation may be served by adding the opposite side view and the end view of the block, including a black mass I take to  be a cross section about halfway along, perhaps level with the hole for the sheave axle (I'm finding it difficult to get my head around that bit, I have to admit).

I think overall that I should leave this block off my model, at least till I can work out better what if any function it might serve. Fascinating stuff, though.

 

Steven