10th-11th century Byzantine dromon by Louie da fly - FINISHED - 1:50

[Louie da fly]

Very interesting, Carl. I haven't come across this one before. Certainly lateen rigged, and the "wings" at the stern are thought to hold a crosspiece which supports the yard when it's not in use. The hull is very unusual.

 

I wonder where they got the design from? It doesn't look like anything I've seen in contemporary pictures. But there's plenty of stuff out there I've never seen.

 

Steven

Edited June 25, 2018 by Louie da fly

[Louie da fly]

Just learnt something. I'd thought than on all lateen sails  the halyard attached to the centre of the yard. Certainly a lot of them seem to be this way in contemporary pictures, but if you look at the link http://forum.woodenboat.com/showthread.php?156203-Lateen you can see lateens with what I'd have thought was a very unbalanced set-up. 

 

Oh, and some nice footage of lateeners under sail. Having the mast to leeward of the sail (so it's blown against the mast) doesn't seem to be such a problem after all.

 

A pity there isn't any footage of boats sailing under lateen alone, without headsails (or booms, as some modern so-called "lateens" are).

 

Steven

[Mark Pearse]

Very interesting. Also noted is the quite large lateen sails on hulls that don't look to have much righting moment - or even freeboard - & the wind isn't light (black & white photos at the start).

 

On the rig balance question, I would have thought it's adjustable by changing the spar angle. More horizontal & there is more sail forward, more vertical & the sail is further aft. It would mean multiple sheeting positions so the sail could set well at a range of spar angles, perhaps a line of cleats or pegs along the rail.

[cog]

5 hours ago, Louie da fly said:

Oh, and some nice footage of lateeners under sail. Having the mast to leeward of the sail (so it's blown against the mast) doesn't seem to be such a problem after all.

THe only reason to switch sides is to avoid chafing the sail and having either to repair, or replace it more often

[Louie da fly]

That makes sense, though I thought it might also affect the performance of the sail (messes with the aerofoil shape). I expect in large, state-owned ships they'd have taken the trouble to move the end of the yard to the other side of the mast whenever they tacked, as shown in the diagrams on the first page of this thread.

 

Sporting sailors probably don't have to worry about it so much because they don't use their boats much. However, the skipper of the caravel replica that sails around the coast in our region says he does it "the way the Arabs do" - without changing sides when he tacks. A lot less hassle, but it does have the downside of chafing.

 

Steven

[woodrat]

18 hours ago, Louie da fly said:

owever, the skipper of the caravel replica that sails around the coast in our region says he does it "the way the Arabs do" - without changing sides when he tacks. A lot less hassle, but it does have the downside of chafing.

 

Steven

This can only be done if the sail is inboard of the shrouds. In mediterranean vessels of the mediaeval period, which I suspect includes the dromon, the sail was outboard of the shrouds (Landstrom and Pryor)

Dick

 

[Louie da fly]

Good point, Dick. I hadn't thought of that.

 

Steven

[Louie da fly]

Here are the sail plans I've arrived at - I still haven't decided to go one or two-masted, but both look better than previous versions. The dimensions no longer tie in with those of Age of the Dromon - I've decided that a gap of 200-300 years and different shipbuilding traditions, plus the different form of the two types of ship are enough to discount the Sicilian ships as a source of information. Instead, I'm going with size and placement of sail(s) to achieve the position of Centre of Effort needed to make a lateener sail properly, based on the theory outlined on the previous page of this build log.

 

 

 

I've also made a prototype of the Byzantine mast step assembly shown in my reconstruction diagram above. I did this in a hurry and in a poor light, so it's a bit rough. To put in the model I'll do a better job and make it complete - cutting it to width and with side pieces to hold it on the keelson.

 

  

But it seems to work!

 

 

Steven  

[Mark Pearse]

Hi Steven

 

is the CoE for the 2 sail rig much lower than the single sail rig? The single sail looks to be significantly taller.

 

[Louie da fly]

Mark, the single mast cE is about 2.2 metres (7 feet) taller than the double  - the difference between 9.4 and 7.2 metres above the bottom of the ship - about 30% higher. Don't know how much difference that would make.

 

Steven

Edited June 28, 2018 by Louie da fly

[Mark Pearse]

We changed the rig on our boat, partly to lower the CoE. Without calculating it I would guess it was lowered between 5 & 10%, & the difference was noticeable. 30% higher would be a large difference, & if my geometry/physics is good, the same force higher up would have more effect on a hull because of it's distance from the pivot point. 

 

What are your thoughts on the role of the sails on these vessels - were they a pleasant respite from the oars or the preferred way of getting around?

[Louie da fly]

That's a good reason to go two-masted, Mark. Galleys in general are not too stable.

 

I think sail would be preferable while journeying - assuming the wind was in the right direction, so the ship wouldn't heel over too much.

 

Oars definitely under battle conditions - in fact the masts were lowered and stowed. For maneuvrability and also to remove overhead hazards.

 

Steven 

[Louie da fly]

I've done a preliminary fitting for the support system I'll be using for the lower oars, to see if it will work. A number of cross-members hold at the correct height a frame with a series of lines all at the same angle, as guides for the oars. The oars go through the oarports with the inner end resting on the frame and the outer end resting on a raised plane (currently two thicknesses of balsa wood) to simulate water level.

 

  

I've done my best to get all the oars as close to identical as possible, so they'll all be at the same angle vertically when they rest on the frame. Also, they'll be interchangeable so it doesn't matter which one goes where. The other quantity that has to be kept constant is how far the oars poke out from the hull, which is done by simply drawing a pencil line around the circumference of each oar at the point it goes through the oarport.

 

I've only tried it with three pairs of oars so far, but it looks like it will work. Now to get it all done properly, with everything lined up and glued in place. As I mentioned before I won't be putting the oars in till later on in the build so they don't get damaged while I'm working on other parts of the ship.

 

The two mast steps are still in progress - I'm making them like the ones found in the Yenikapi ships. Though they're more complicated than my original version I think it's good to do it the way it was done back in the day if at all possible. The blocking piece is shown above the two mast steps. Sorry about the photo quality.

 

 

At some point I have to correct the line of the beam shelf - it's a bit wonky and has to be made into a smooth line, or the deck beams - and the deck itself - will also be wonky. As can be seen in the photos, the line wobbles very slightly all along its length.

 

 

As the beam shelf so narrow and flexible, I can probably correct it by cutting it away from the frames at the offending places and re-glueing it in the correct position. If not, I'll have to cut and fill till it's correct.

 

Steven

 

 

Edited July 6, 2018 by Louie da fly

[BANYAN]

Glad to hear that you have resolved (within yourself) which way top step the masts Steven; that will allow you to move on with other work.  The banking of the oars solution looks very workable with the mock-up looking very good - great idea.

 

cheers

 

Pat

[Mark Pearse]

I actually like the slight wobbles in the beam shelf, it looks ... old

[Louie da fly]

Thanks, Mark. But the shelf needs to follow a smooth curve to get the deck to be consistent, otherwise the deck itself will be all wobbly.

 

Steven

[Louie da fly]

Working on getting the beam shelf smooth.

 

 

 

To be honest, the amount of wobble is pretty tiny - maybe 1/2mm - but it does make a difference. To smooth out the curve I've used all three techniques I mentioned earlier - slicing off where it was too high, filling where it's too low, and relocating the beam shelf where it's too far off the line to slice or fill. Still a bit to do before it's all smooth.

 

Next time I do something like this I'll make sure I get it right first time so I don't have to get into this whole correction thing, which wastes time and effort. A lesson learnt (I hope!).

 

Steven 

 

 

[cog]

4 hours ago, Louie da fly said:

A lesson learnt (I hope!).

Many more to come, is my experience Steven. It does bear it's fruits though: I can't see a wobble

[Louie da fly]

I've made the mast steps and put them in. Here they are dry fitted:

 

The supports for the frame to hold the lower bank of oars are now glued in place:

And the frame has been glued to them.

  

Oops: I discovered that the pencilled guidelines I'd drawn to fix the angle of the oars faced 180 degrees the wrong way, so I had to erase them and redraw them. I still have a remnant of the wrong ones because I started with spirit pen at one end and couldn't get rid of it. As the pencil line around each oar where it goes through the oarport was getting faint I've also re-done the lines.  

 

And the mast steps are now glued in, along with the blocking pieces.

 

 

Still working on the new masts and then I'll make the wedges to hold them in place. I also have to make and insert the mast partners to hold them rigidly.

 

Steven

[BANYAN]

The hull is looking fantastic Steven; a testament to your search for accuracy and quality.

 

cheers

 

Pat

[Louie da fly]

Thanks everything for the likes.

 

Pat, thanks for the comment, though I'm afraid the frame to hold the oars is a modern fudge, as I'm not prepared to put in lower oar benches and oarsmen that will never be seen.

 

Steven

[Louie da fly]

I've made the foremast.

 

I'd cut a piece of walnut with a tapered thickness with my drop saw, and I marked out the two masts and cut them roughly to shape with a coping saw. I trimmed the foremast with a Stanley knife (see picture) as close as I could to the lines I'd marked, and made the faces flat and straight with a file. I left the top rough to start with, because it was going to hold the "blob" containing the sheaves.

Unfortunately I got it wrong with the after-mast. Somehow I'd missed the lines and the thing ended up with a bow in it.

 

Fortunately I'd left myself enough wriggle room to straighten it out - barely enough. After it was straight I put it to one side and went on with the foremast.

 

I marked the correct taper for the other two faces of the foremast, and trimmed them so I had a square-section mast tapering from the base to the top, then filed it flat and straight. I cut faces at 45 degrees, to create an octagonal section. Then with the file I turned that into a round section, rotating the mast in my fingers to get the "feel" (which I've found gives a pretty reliable circular section when you don't have a lathe). Cut the "blob" to shape and cut the tenon at the lower end of the mast

 

   

 

and dry fitted it into the mast step,

 

adding a wedge to hold it tight against the blocking piece.

 

 

More to follow.

 

Steven

Edited July 21, 2018 by Louie da fly

[Louie da fly]

I promised a step by step outline of making a lower bench oar, so here it is. Two of the oars had turned out to be unsatisfactory - one was bowed and the other had a dark blemish in just the wrong place - so I had to replace them.

 

Here's the first oar blank with the outline on paper glued onto a piece of 2mm thick planetree wood.

 

 

I trimmed it with a No. 11 scalpel till the wood was almost cut back to the outline - leaving a little overlap in case of Murphy. Then I cut faces at 45 degrees to give it an octagonal section and started trimming the thickness to make the oarblade.

 

   

 

Comparing it with a "standard" oar - it's quite a bit too thick.

 

 

Trimmed down further to get the shape closer to the desired one. (Sorry, the new one's on the right this time).

 

 

More to follow.

 

Steven

  

[Louie da fly]

Trimming down with the scalpel to get closer to the standard oar.

 

 

And further still

 

 

Side view

Shaped the blade - using the file now, as I did on the mast, rotating the oar in my fingers to check for roundness and filing down any lumps and bumps.

Cleaned-up with the file and then sanded to finish. Note the pencil line near the base - this is to mark where the oar goes through the oarport.

The finished oar side-on.

 

 

Steven

[druxey]

With the pivot point so near the loom end, those oars must have been beasts to row!

[Louie da fly]

Oh no, these oars are only correct from the oarport outwards, Druxey. I've built a framework of my own invention to support the lower oars rather than have to make 50 lower deck oarsmen (who will be invisible anyway), and reduced and bodged the inboard section of the oars to go on the framework. See my post of 6 July above. Sorry if I gave the wrong impression!

 

Prof Pryor's reconstruction has the outboard length as 3.395 metres (including the blades) and the inboard as 1.265 metres (including the handles). Though I'm not following his reconstruction completely as I believe the Yenikapi finds have invalidated some of his conclusions, I have followed it in regard to oar lengths (well, the bits you can see, anyway).

 

Steven    

[druxey]

Ah, thanks for the clarification, Steven.

[Louie da fly]

Here's my theoretical midship section, to give some idea of the oars.

 

 

Sorry, I wasn't holding the camera quite straight so it looks like the ship has developed a list.

 

It was very difficult getting enough headroom for the lower oarsmen while keeping the ship low enough in the water to allow a workable angle for the upper bank of oars - the deck beams are only the equivalent of 100mm (4") deep, which won't span from side to side of the ship without bowing, so there are a pair of beams running the length of the ship to support them, held up in their turn by a series of posts - positioned so a person can walk between them but allowing the oarsmen enough room to row.

 

None of this lower stuff appears on the model, but I had to work it out to my own satisfaction to see if it would work in the real world. Probably not the way they actually did it, but it is workable.

 

Steven

[Louie da fly]

The "blob" at the top of the mast that holds the sheaves for the halyard is a bit too small to match the one in the picture I based it on.

 

 

So I'm making two new ones, one for each mast.

 

 

 

Also they'll have two sheaves instead of the single one in the original one I made, as the forces involved in hauling up the yard are pretty large.

  

The drill bit in the hole is to ensure the tenon for the blob is at the correct angle, as I don't have the luxury of a drill press to drill the hole exactly in line with the axis of the blob. Had I thought of it earlier, I could have used the drill bit as a guide in carving the blob itself and not have to adjust the tenon on the mast.

I expect I'll have to re-drill the holes for the sheaves through the tenon once the blob is in place, so the halyard can pass through the sheaves.

 

Steven

Edited July 23, 2018 by Louie da fly

[woodrat]

Steven, what angle is the foremast from the vertical?

Dick