The San Marco mosaic ship c. 1150 by Louie da fly - FINISHED - 1:75

[woodrat]

The venetians, having laid the master frame on the keel, then fitted every fifth frame and trued them. The intermediate frames were then fitted. Yoy will need spacers to maintain the space between frames. Dont forget that the mast step supports were part of the floors.

Good luck. Have you got a disc sander or is that for next birthday?

Dick

[Louie da fly]

Thanks for the advice and information, Dick. Interestingly, on my dromon I installed every second frame then filled in the gaps, but that was because of structural problems fitting all those frames in at once with the way I was building the dromon. 

 

I've certainly taken into account the need for spacers. I'd been intending to put in the master frame first and then progressively move forward and backward, frame by frame, but I'll look at the method you suggested. I can see the advantages - particularly in avoiding additive errors in maintaining trueness.

 

And yes, I hadn't thought about the mast steps. Thanks for that.

 

Finally, I do have a disc sander, but given how small the frames are, I might be better just using a file to bring them to shape.

 

I'm still in the experimental stage - working out how the frames fit together (or even if they do) and whether my jig pictured above will really work.

 

Steven

[botra288]

Louie

Your project is very interesting and a significant challenge, I will continue to follow with great curiosity and learn from you 😀

[woodrat]

Steven I notice that you are building your round ship with a straight keel. The keels on mediaeval round ships and galleys in the mediterrranean were slightly rockered. They did this by using a catenary curve made by a rope suspended between two stakes at each end of the ship.

Its not much of a curve but it will make a difference to the end result.

Dick

[Louie da fly]

Dick,

 

You had to post this just after I cut the keel, didn't you?  Like the Famous Eccles shouting 'Ahoy! Land Ahead!' CRASH - (I should have said that sooner, shouldn't I?)

 

(Actually, it's ok - I've only cut it roughly to shape - I still have to trim it and I'm pretty sure I have enough leeway to get a catenary curve into it.)

 

Steven

[woodrat]

Sorry, but could be worse. The keel could be already attached to the frames😬

[Mark Pearse]

12 hours ago, woodrat said:

Its not much of a curve but it will make a difference to the end result.

it's interesting with boats how a straight line can look curved (the wrong way), & a curved line...just looks right. 

[Louie da fly]

Dick, I was just checking your Venetian Round Ship build log (which I'm shamelessly copying) - there's no specific mention of adding the mast steps, but it seems to me that you used a rectangular piece of wood each side of the keelson plus "blocking pieces" between these to make a slot for the bottom of the mast. Am I correct in thinking this?

 

Best wishes,

 

Steven 

[woodrat]

I followed the Contarina 1 wreck which indicates  the floors are carved in such a way as to support two short planks. the mast is held between these planks and blocks fore and aft which may well be part of the keelson. In other words, the mast  sits on the keelson but the side planks are held by the floor and against the keelson. Weird, eh!

Dick

[BANYAN]

Some great research and discussion here - following with interest.  Thanks guys.

 

cheers

 

Pat

[Louie da fly]

Thanks, Dick. That's what I'd thought I'd seen on your model, but I wasn't sure. I agree - it does seem a bit of a strange way to do things.

 

Steven

[woodrat]

If you look very carefully at the photo of the Contarina mast-step, you can actually see the wooden wedge blocks that fell out when the mast was removed.

Dick

[Louie da fly]

Yes, I see them now you point them out! Naturally my question was prompted by wanting to do the floor timbers and get them right.

 

BTW, as far as strange ways of fitting mast steps, at least one of the Yenikapi ships had a mast step that was totally free-floating - not fixed to the hull at all! No idea how they made that work.

 

Now some progress on the model.

 

On coming back to it after several weeks, I decided the hull was too tubby and re-calculated the shape using the Mezza Luna method. You can see the new outline offset somewhat from the original. (sorry, it's a really rubbish photo).

Using My Precious, I cut a bunch of futtocks and then smoothed them off, as being very inexperienced with my new toy I cut well outside the lines:

 

Then I cut out the parts of the keel and stem and sternposts. And courtesy of the local Men's Shed I was able to smooth them down with their nice disc sander. (When you asked me earlier if I had one, I thought you meant a sanding disc, such as you'd attach to an electric drill. I've certainly got one of those, but the disc sander is so much better.) And yes, there's a very mild catenary to the keel.

And I cut and smoothed off all the rest of the futtocks. 

That still leaves the floor timbers, and the frames for the bow and stern to do, but it's good having finished this part of the project. It means I'm now free to go ahead with the next steps.

 

Steven

 

 

 

Steven

Edited June 3, 2023 by Louie da fly

[Cathead]

On 5/31/2023 at 4:42 AM, woodrat said:

The keels on mediaeval round ships and galleys in the mediterrranean were slightly rockered. They did this by using a catenary curve made by a rope suspended between two stakes at each end of the ship.

If Steven doesn't mind the distraction, why was this done vs. choosing a straight keel?

[Ferrus Manus]

I love how this one little ship facilitated the most underrated, history-altering heist in world history. 

[Reggiemon]

Very interesting!

Keep up the good research and work.

[woodrat]

This is a photo of the 14th century galley found in San Marco di Boccalama in the venetian lagoon. Note the coffer dam around it. The lower third of the hull is intact and beautifully demonstrates the carved mast-step supports in the floors. I think the central three supports are integral with the floors but the others may be separate from the floors

these are the mast step supports for the flat bottomed rascona found near the galley with separate knees to buttress the mast-steps

(INA Quarterly spring 2003 D'agostino and Medas)

So this type of mast-step was widespread at least in Venice and the Adriatic.

Dick

[mtaylor]

19 hours ago, woodrat said:

I dont think anyone knows for sure! I suspect this is a relict from thedays when most vessels were galleys and episodically needed to be dragged out of the water. Any other ideas?

Dick

It may have also been done to keep the keel from hogging.   

[Mark Pearse]

47 minutes ago, mtaylor said:

It may have also been done to keep the keel from hogging.

Yes, even a slight curve in the keel would make the hull much more resistant to hogging, or just generally changing its shape. The curved hull planking meeting a curved keel is a 3D curved surface rather than an 'extruded' curved shape.

 

[Louie da fly]

Dick, where do you keep on getting these amazing pictures? Absolutely wonderful! Thanks very much for them. Greatly appreciated.

 

Yes, I'd thought of hogging myself. Rather like (in reverse) the way the bed of a large flat-bed truck is curved upwards, so when it is under load it straightens out. But not . . .

 

Steven

[BANYAN]

Perhaps also worth considering this design for 'rocking' the vessel of sandbars or the mud in ports?  (Many ships in shallow ports sat on the mud when the tide went out.)  By shifting weight/cargo fore or aft would perhaps raise the keel sufficiently to get her off?  But, I think this would have been an addition or complimentary outcome, rather than a design feature?

 

cheers

 

Pat

[Ferrus Manus]

Or maybe, the extant shipwrecks simply show the keel having bent under the stress of almost a thousand years of existence. It could be a common deformation of the wood as it gets eroded away and buried in silt and dirt. 

[GrandpaPhil]

Could be for structural integrity reasons, too.  

I seem to remember something, from some classes I took twenty years ago, about the inherent strength of an arch.

 

The keel may have been curved just to strengthen the hull.

Plus, assuming that these boats were made for beaching, a slightly curved keel and hull would take the beaching better than a flat keel.

 

The curved keel would glide up onto the beach, instead of digging in, much like a sled gliding over snow.

 

It would also reduce surface contact with the ground, thereby reducing static friction, and thus making it easier to put the boat back in the water.

Edited June 8, 2023 by GrandpaPhil

[GrandpaPhil]

I asked Google’s AI about the catenary curve in the keel.

 

This is the response:

 

“The Venetians had a catenary curve in the keels of their round boats because it made them more stable and maneuverable. The catenary curve is the shape that a chain or cable takes when it is suspended between two points. It is a very strong and efficient shape, and it helps to distribute the weight of the boat evenly. This makes the boat less likely to tip over, and it also makes it easier to turn.

The Venetians were very skilled boat builders, and they were always looking for ways to improve their boats. The catenary curve was one of their most important innovations, and it helped to make their boats some of the best in the world.

Here are some of the advantages of having a catenary curve in the keel of a boat:

• Increased stability: The catenary curve helps to distribute the weight of the boat evenly, which makes it less likely to tip over.
• Improved maneuverability: The catenary curve makes it easier to turn the boat, which is important for navigating in narrow canals or through rough seas.
• Increased speed: The catenary curve helps to reduce drag, which can improve the boat's speed.
• Reduced stress on the hull: The catenary curve helps to distribute the weight of the boat evenly, which can reduce stress on the hull and improve its lifespan.

The catenary curve is a very important design feature for boats, and it has been used by boat builders for centuries. The Venetians were one of the first cultures to use the catenary curve in their boats, and they were able to achieve great success with this design.”

 

And here are the sources:

 

“Sure, here are some sources that I used to research this topic:

• Boats, Ships and Shipyards: Proceedings of the Ninth International Symposium on Boat and Ship Archaeology, Venice 2000 by Carlo Beltrame
• The History of Boatbuilding by Robert Gardiner
• The Venetians: Merchants of the Sea by David Nicolle

I also used a variety of online sources, including Wikipedia, the History Channel website, and the National Geographic website.

Here are some specific quotes from these sources that I used to answer your question:

• Boats, Ships and Shipyards: "The curve of the keel (colomba) is defined by the catenary of a slack cord fixed at its two extremities."
• The History of Boatbuilding: "The catenary curve is a very efficient shape for a keel, as it helps to distribute the weight of the boat evenly and reduce drag."
• The Venetians: "The Venetians were the first to use the catenary curve in their boats, and they were able to achieve great success with this design."

I hope this helps!”

Edited June 8, 2023 by GrandpaPhil

[Louie da fly]

Thanks very much for this information, mate, and the thorough research involved in obtaining it.

 

Steven

[Roger Pellett]

Increased Stability:  I assume that this refers to Transverse Stability- resistance to capsize.  This is a complex and often confusing subject.

 

Transverse stability involves the action of two equal and opposite forces- gravity pushing down and buoyancy pushing up.  The gravity force acts from the vessel’s center of mass, aka center of gravity.  The buoyancy force acts from the center of buoyancy.  Complicating this is the fact that for floating objects the center of gravity is usually ABOVE the center of buoyancy.  Something else must therefore be in play or most ships would capsize.

 

That something else is the underwater shape of the hull.  When the vessel heels, the submerged shape of the hull changes, shifting the center buoyancy, causing its upward force to right the vessel.  The amount of this “shift” determines whether the hull will be tippy or stable.  Determining the “shift” requires calculus.  The theory of hull stability and the mathematics to evaluate it were not discovered until the mid 1700’s, 600 years after the Venetians built the San Marco Ship.  It is by no means obvious without elaborate calculations unknown in 1150 if longitudinal curvature of the keel had any effect on the transverse stability of the San Marco Ship.

 

Roger

[Louie da fly]

So, the keel is now complete.

 

Due to its complex shape the stempost had to be built up, using scarph joints to join the individual elements.

 

   

And here it is all assembled and glued together. Starboard side:

Port side:

And starboard side with the paper sanded off.

 

Next step is to assemble the frames. I have yet to determine the shape of the frames which attach to the stem and sternposts, as the hull rises and narrows at bow and stern. That'll take a little while to work out.

 

Steven

Edited June 10, 2023 by Louie da fly

[Cathead]

19 hours ago, Roger Pellett said:

It is by no means obvious without elaborate calculations unknown in 1150 if longitudinal curvature of the keel had any effect on the transverse stability of the San Marco Ship.

Great explanation, Roger. But I'd suggest that there are plenty of examples of historic people figuring out, through trial and error and accumulated knowledge/experience, things that until only recently could actually be explained through science. For example, any Middle Ages peasant who slaughtered a beast had an instinctive understanding that blood circulated through an animal and that the heart was related to it, but it took ages for "science" to catch up, stuck as they were on whatever an ancient Greek wrote without checking for themselves. Medicinal characteristics of plants are another example. To me, it doesn't seem hard to imagine that centuries of maritime experimentation led to Venetian builders (and buyers) learning that they liked such a design, whether or not they had any idea how or why it worked. 

 

What makes me really curious is how/why different cultures settled on different designs, when in theory many of the background conditions are the same. Water acts the same way on vessels in the Med as it does along the Chinese coast, for example (with the possible exception of subtle differences in salinity). 

[Roger Pellett]

Eric,

 

Yes, these vessels were designed empirically.  These people apparently had powers of observation that far exceed ours.  They incorporated features in their designs that they believed improved performance.

 

However, my post is about Modern sources not ancient peoples.  We don’t know that the builders of the San Marco believed that a curved keel improved transverse stability.  Instead, this conclusion comes from modern sources, who are apparently unfamiliar with the theory of transverse stability.  The only way to verify the effect of the curved keel would be to design two hulls, straight and curved keel and to run the calculations.

 

BTW, my son-in-law works for Google on some sort of AI related project.  I would not get into a boat that he designed!  😆

 

Roger 

 

[Louie da fly]

I've made all the floor timbers that incorporate the knees to take the mast steps. Twelve in all (plus one for luck!) Here's a typical one.

To get the distance between the knees correct, I made a jig (made of the keelson plus a piece either side that will eventually form the sides of a mast step, plus a top spacer to duplicate the blocks fore and aft of the mast itself), and shaved away till the jig fitted in the gap.

And I shamelessly copied Woodrat's jig for assembling the frames. 

Master frame:

The first three frames. Of course I'm labelling each one so I don't get them mixed up.

The tolerances are pretty tight to fit within the jig, and there was a certain amount of swearing when, despite all my care, one of the frames got glued to the jig. (I got it out eventually, but not a lot of fun).

 

More to come soon.

 

Steven

Edited June 14, 2023 by Louie da fly