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

[Louie da fly]

Mark,

 

Yes, the shields hang on the sides. If you look on the first page of this thread, there are a couple of diagrams I've drawn which show them. Unfortunately, I've just realised that hanging them by the enarmes the way I've shown is physically impossible - the enarmes should be slung over the upright, not threaded along the horizontal beam of the pavesade. You'd never get the shields on and off. I haven't yet worked out exactly I'll fix them in place, but I'm sure I'll come up with something.

 

I've never tried sculpy, but I believe without having to cram the cardboard into the boss in the middle, it's likely the dog biscuit card will do the job without crumpling. And the detail is surprisingly good. I've just made a flattish conical shield out of modelling clay and cast it in a plaster mould.

 

 

 

Once that's hard, I'll cast a new shield blank made of builder's bog. It's hard and stable enough that I can carve all the detail in it I want - particularly the raised shield rim and perhaps a line to show the (non-raised) boss. And then use it to make a mould out of of builder's bog so I can make all the cardboard shields I want.

 

I've been collecting contemporary pictures of Byzantine shields. At this time they were pretty equally divided between round shields and others which were  tear-drop shaped. I'm going for round shields on the dromon (a tear-drop shield wouldn't work on the side of a ship) and I've so far collected over 50 designs, though several of them seem to duplicate each other. I've probably got enough for all the shields to be different from each other.

 

During my shield research I began to notice other things, particularly about the oars shown in contemporary illustrations. I'd based my oar blades on the ones in Age of the Dromon, but on further investigation I believe they aren't a true reflection of the shape of oar-blades of the time.

 

Contemporary illustrations show oars tapered all the way from the handle to the end of the blade. I don't believe the whole loom took part in the taper, but the blade itself may have. This picture is contemporary with the ship I'm making, and I based the shapes of both the dromon's tail and the steering oars on it. I've just noticed, by the way, that the steering oar of the left hand ship appears to show a tiller (though the steersman's not using it). 

 

 

 Even taking into account the likelihood of error and carelessness on the part of the artists (and the possibility they may never have really looked at a dromon's oar-blade), I still feel it's the best representation we have. Lacking any definite evidence to the contrary I've decided to taper my oar blades. I'm changing the ones I've already made and will make the next ones to the new shape (only 82 to go!). Here's a pic of the old and new shape together.

 

Edited May 1, 2016 by Louie da fly

[Louie da fly]

Thanks everybody for all the 'likes'. It's good to get the feedback.

 

I'm currently in two minds about the shields. In Byzantine pictures of battles mostly (but not always) each fighter's shield seems to have a different device.

 

 

 

 

This was before heraldry became a subject in its own right, with the shield device being specifically "owned" by the person, and handed down from father to son. That didn't start till the mid-late 12th century, and even then only in Western Europe.

 

But there only two existing contemporary pictures of ships with shields along the sides, and in one of them all the shields on each ship are the same.

 

 

In the other, two shields are visible and they're different.

 

 

So what do I do? Make them all the same, on the basis that the shields "belonged" to the ship, or make them all different, as though each fighting man had his own?

 

I still don't know. I'm inclining to the "all the same" view - it makes it all consistent. But maybe adding a bit of variety is a better way to go.

 

Steven

[druxey]

Difficult decision. But you've a ship to complete first, so there's lots of time to make up your mind! Seriously, I find many decisions become clear if I stow the problem in my sub-conscious for a while.

[cog]

Steven,

 

I'm not up to date with the byzantian empire, but wouldn't the crew or soldiers belong to a house or group with an equal outfit like e.g. the romans ... that would explain the 'all the same' shields part ...

[Louie da fly]

Druxey, this is mainly something I get into while I wait for the opportunity to do other things. Making and bending the frames is taking considerably longer than I expected, and every time I bend a couple of frames to shape on the plug I have to wait 24 hours for them to dry into a stable shape. Leaves me with time on my hands. (Also, perhaps I'm a little too easily distracted).

 

Carl, the Byzantine military and naval establishment was formed of themes - regions of the Empire that provided contingents of men. The Cibyrrhaeot theme (southern coast of Asia Minor) was the main source of men for the navy. So there's a possibility that they'd all have shields the same. But on the other hand, there's no evidence that the pattern on a Byzantine shield had any significance at all, except to look good - certainly nothing to suggest anything organisational. My own opinion of the picture above with all the shields the same is that the artist was a bit lazy. And even then, one of the warriors on deck is carrying a shield with a different pattern.

 

So now I'm coming to the opinion that the shields should be different after all. We'll see - by the time I get to the point of putting them on the ship, who knows what I'll have decided?

 

 

 

Steven 

[Louie da fly]

Here's the process I go through in making an oar. I drew the oar in AutoCad and copied it multiple times and printed it off, then glued the sheet of paper to a sheet of wood a little thicker than the thickest part of the oar. Then I sanded the sheet back so it tapered from handle end to blade. I've shown a photo of that in an earlier post. Then with a coping saw I cut the individual oars apart.

 

 

Next, I use the Stanley knife to carve it to the outline.

 

     

 

And then carve it from the back so the thickness tapers to match the taper in the width, and the oar blade is getting close to the right thickness.

 

     

 

Once that's done, I cut off the corners, changing from a square to an octagonal section.

 

 

 

And using a fairly coarse file turned the octagon to a circle.

 

 

 

 

Clean-up and tidy up with a finer file, and finishing off the blade to shape - note this is the new shape I decided on from looking at contemporary illustrations. There are a number of previously made oars that will have to have that done to them as well.

 

 

To be honest, I'm not all that happy with my consistency in making the oars - it's more whittling than proper cutting to shape. At least two of them will have to be discarded, and I might get rid of several more that I'm not happy with.

 

 

I think I need to get more professional, and finish them, not by eye, but by measurement with vernier calipers. I think I'm a little too slap-happy in my technique, and I need to correct that so I don't waste all the time I put into making the oars. I timed it this time - it takes something like two hours to make one of these things, and I shouldn't throw that time away on an inferior product that then has to go in the scrap bin. There may well have been variation in oars 'in the day', but that would have been so minimal that at 1:50 scale it would be invisible.

 

On a happier note, I've finally finished the first batch of frames - I'm putting in every fourth frame onto the plug and planking over it, and then I'll put the rest in afterward. It's very difficult to cut the frames thin enough (1mm) with a Stanley knife and I was worried that the frames were too thick and might get stuck in the grooves in the plug when I wanted to take the assembly out.  

 

So I've filed them all thinner so there's more clearance between the frames and the grooves. Rather difficult with frames only 1mm thick, but I managed to work out a technique which worked without imposing too much strain on them. I put a thin sheet of wood over most of the frame and press down, and just file down the bit that's sticking out. The sheet of wood holds the frame still and reduces random forces in the wrong directions that otherwise might deform or worse still, break the frame.

 

 

 

 

 

Edited May 8, 2016 by Louie da fly

[mtaylor]

You're doing some seriously excellent work, Steven.   

[Louie da fly]

Thanks, Mark. But I must say looking at other builds on this forum, including yours, makes me very conscious of my own shortcomings and how much I have to learn.

 

Still, I suppose even the best modellers were newbies once. I'm not completely new to modelling, but the learning curve is very steep when I look at what others are capable of. But I suppose each of us is his/her own worst critic, and perhaps we should give ourselves credit for what we can do well.

 

Steven

Edited May 9, 2016 by Louie da fly

[druxey]

Self-criticism is good - but only if it spurs one to better efforts, not if it brings one to a stand-still. It's also good to have a goal to strive for, as well as moveable goal-posts! 

[mtaylor]

Steven,

What Druxey said...  We're harder on ourselves than anyone else could ever be.  And movable goalposts... I have to remember that.  

[Louie da fly]

Well, I bit the bullet and threw out three oars which didn't come up to standard. And organized the rest into categories - 1. almost right, 2. needs a fair bit of work, and 3. Perfect as it is.

 

There were more in the first and third categories than I'd thought.

 

And good news - the most recent half dozen were the best. So maybe I'm getting better as I go along.

 

It's quite cleansing throwing out the unsatisfactory ones. Now they're not sitting there sneering at me every time I go to make another oar.

 

I've marked out the lines of the wales on the plug and also where the oarports will be. Id been wondering how to mark them accurately enough to miss the frames, which are 4mm apart.

 

But the tholes sit in the third wale from the keel, with the oarport plank immediately above. Once the wale is in place I can shape the plank to fit and mark the oarports on it. Then when the ship is fully planked I'll cut them out.

 

When I made the Great Harry I cut the arched gunports in the upper works directly into the planks before fixing them to the ship. I got away with it - barely - but it weakens the planks and it's a bad way to go.

 

Figuring out how to accurately mark out the oarports on the dromon has taken a load off my mind.

 

Oh, and I've made 5 shields. The production line is up and running.

 

Steven

Edited May 10, 2016 by Louie da fly

[Louie da fly]

I've come to the opinion that I was on the wrong tack (pun intended) putting the frames in grooves in the plug when I'm planking - I think it's just asking for trouble. I believe there's a very good chance the frames will get jammed in the grooves and refuse to come out when I try to remove the hull from the plug.

 

 

 

Also, having the outside surface of the frames flush with the edge of the plug multiplies the chances of accidentally gluing the frames or the planks to the plug, no matter how much wax or other kind of resist I put on the plug. My doubts were confirmed when I experimented with putting a wood strip the same size as a frame into a groove and dropping in some glue. I had to carve the strip out again - it stuck like dog poo to a shoe. It's a rather extreme experiment - worst case scenario - but finagle's (or Murphy's) law applies - if something can go wrong it will.  

 

I had been thinking of some way of using cling wrap as a back-up to keep things from sticking together, as some other modellers have done, but of course it would be difficult to get it to go into the grooves.

 

I finally decided the best thing to do is to shave the plug down level with the bottom of the grooves, so the frames sit proud of the plug. It also allows me to use cling wrap.

 

It's more work, but I think in the long run it's the best idea. I've made a start and the pine of the plug carves down surprisingly well, using my old mate the Stanley knife. I'll have to sand it smooth when I'm finished of course. The dark wood is the original plug (turned brown with shoe polish I used as a resist). The lighter bit is where I've shaved it down. And fortunately the brown shoe polish leaves a line in the wood which shows where the groove was, and where the frame needs to go.

 

 

I cut down between only one pair of grooves at a time. This allows me to re-draw the lines of the wales and the locations of the oarports bit by bit so I don't lose them. 

 

I think having the grooves helped when I was bending the frames to shape. It helped them stay in place on the plug. And I think for something like a longboat there probably wouldn't be any problems using this method. But for something with as many frames as the dromon (and with a complex shape as well, especially at the stern) they are likely to cause too many problems.

Edited May 14, 2016 by Louie da fly

[druxey]

Another possibility is to have a ledge above (below, when inverted!) the line of the gunwale, inset the by thickness of the frames. Then you can glue the frame extensions to the ledge's side and cut them off when the planking is completed. It would only not work if there is tumblehome to the hull.

[Louie da fly]

That might be worth considering, and though the dromon has no tumblehome, it has an equivalent in the fore-and-aft direction with the curve of the 'tail'.So I have to sort of rotate the hull fore and aft when I take the it off the plug. If there are grooves in the plug there's more chance of the frames jamming in the when I do that.

 

On the other hand, I'm thinking that I really have to get my wales shaped now  rather than after I've got rid of the grooves. They're thick enough and the frames are so thin that if the wales aren't properly shaped they'll force the sides of the hull inwards. And for the same reason maybe I need to make and position all my frames before I put the wales on.

 

This is one of the problems of being something of a newbie - not enough experience with the problems that are likely to crop up, and not enough experience with working out solutions to them beforehand. I get a bit terrified that I'll do something irretrievable that ruins everything and have to start all over again.

 

Still, that's part of the journey, isn't it?

 

Steven

[Louie da fly]

I've now cut and soaked and bent into place 30 new frames. Copying the technique Archjofo used for for La Créole's boats in his build log, I managed to do as many frames fixed with push-pins in an hour as I did previously in weeks with a pair of clamps. So, thanks for the inspiration, Johann!

 

 

 

 

One thing I particularly like about this forum is the helpfulness and ideas from other members, freely given. It means you don't have to keep re-inventing the wheel when a problem new to yourself comes up that someone else has already solved in their own build.

 

There are a total of 120 frames for this dromon. So I'm halfway there. I'm just waiting for these to dry into shape and I'll make another 30, and then 30 more. I'm much happier with this rate of progress.

 

Steven 

Edited May 28, 2016 by Louie da fly

[archjofo]

Hello Steven,
I am pleased that my build log was an inspiration for you.
An interesting project that you're doing here.
I'm always watching.

[Louie da fly]

It's been a while since I posted last. I've been working on frames, but life's been getting in the way as well (I came down with the dreaded Lurgi and was not able to work for a while).

 

I had already made 93 of the 124 frames needed. Here is a photographic record of making the last 31 frames, which are 1mm x 1mm (1/25 inch) in cross section. Cutting them accurately to such a small size is difficult, and I've found pretty much impossible in the real world.

 

The sheet of wood I made them from was cut for me by the guy across the road with a bench saw not really suited to the job, so thickness varied from 1mm to 1.3mm. Then cutting a sliver 1mm wide with a Stanley knife is pretty hard to do without stuffing it up completely, so I erred on the conservative side figuring I can always take some wood off, but I can't put it back on.

 

 

 

 

 

You might notice there are actually more than 31 frames in the pile. I made extras in case of breakages while bending them to shape, which happens every now and then.

 

After I'd cut out the frames it was time to file them to size and shape, using a bastard (medium) file. Takes a while, and I had to quit at one point when I broke three frames one after the other. I came back after a bit of time off, and filed down the rest of them.  After filing, I used wet and dry sandpaper to smooth off the corners, which were a bit rough after the filing.

 

 

Here are two frames - one freshly cut and the other filed to size.

 

Next job is to soak them in water for at least a day, preferably longer, so they'll bend properly without breaking. A take-away food container is ideal for the job.

 

While they were soaking, I undid the previous 31 frames from the plug and labelled them with little slips of paper so I could tell them apart.

 

So here are all the frames - 62 I'd already made, 31 just taken off the plug, and the last 31 (plus extras) soaking.

 

Edited June 19, 2016 by Louie da fly

[druxey]

Certainly an exercise in patience, Louie! For not having the best equipment to cut small section wood, those look really good.

[ggrieco]

Hello Steven,

 

I've been looking forward to your return. It's good to see you back at it. Looking good!

[Louie da fly]

Thanks everybody for all the 'likes'.

 

Druxey - yes, I'm pretty happy with the finish on these. It would probably be nice to have all the equipment and do it faster, but I think after all that work I probably have more of a sense of achievement than I otherwise would have. Trouble is, most of each frame will be covered up by the deck anyway, so really I'm doing it because otherwise I'd always know I'd accepted second best.

 

Thanks for the comment, Glenn. I appreciate the feedback, especially from people whose work I respect, like you and Druxey. 

 

Steven

[woodrat]

Just a thought. With a long narrow hull like this would it be advised to put it into a jig during planking and applying longitudinal members so as to prevent torsion of the hull?

Dick

[Louie da fly]

Quite right, Dick. It's certainly an issue. The plug will act as the jig, and I'm hoping that the wales (there are five each side) will give the hull rigidity as I'm doing the planking. I think I'll have to put the wales on first (they're about 3mmx3mm) and then plank between them. I'm still trying to work out what will be the best sequence with frames, keel, keelson, wales and planks. At the moment, though, I'm back to square one with the frames. About half of them broke when I tried to bend them to shape. I think I chose the wrong wood. It's too coarse grained - I think the ones that broke are sapwood while the good ones are heartwood. I've got to make a bunch more frames and start again. But I'm off to Sydney tomorrow for a few days so there'll be another gap before the next instalment.

 

Steven

[Louie da fly]

It's a bit frustrating cutting and shaping all these frames, soaking them for days and then having half of them break the moment you try to bend them. But it looks as though I can tell the good wood from the bad. If it's light brown it's ok. If it's sort if greyish it's likely to break. So I have maybe another 15 new ones to make and shape and bend. Fortunately I have plenty of wood to work with. And anyway it'll all have to wait till I get home.

 

Steven

[woodrat]

Thanks Steven. I wasn't being very clear before. My concern is that torsion may occur AFTER the shell is removed from the plug. Is this something that others have seen with this type of construction? It has happened to me.

Dick

[druxey]

Torsion would only occur if there are unequal forces acting on both sides of the shell. I've not had any issues of this nature by spiling the planking properly and pre-bending them, so that the shell is stress-free.

[Louie da fly]

Dick I take on board your comments and to be frank I think I haven't previously given enough thought to this issue. Druxey, your advice seems to be the way to go. With such frail frames and planks, I think that unless I make very sure the wales are pre-formed exactly to shape they're likely to deform the rest of the hull, so I'll have to take vdry great care to get them right.

 

Steven

[Louie da fly]

After a delay due to various unavoidable factors I’ve finally completed the last set of frames and bent them to shape on the plug.

 

 

Unfortunately, now I’m not happy with some of the first ones I did – they’re not quite the right shape and I’ve got them soaking so I can re-bend them. Though I've replaced the water, it's gone a rather dark brown due to residue in the container from the tannin in all the wood I've been soaking.

 

 

As I mentioned before, over half the last batch of frames snapped in two as I tried to bend them and I had to start over. Since then I’ve noticed three on the plug that hadn’t snapped completely in two but had partially broken at the bend.

 

Following the technique of another modeller on this forum (forgotten who it was, but thank you!) I managed to plug up the break with a mix of PVA glue and sawdust (fortunately I had a LOT of sawdust from filing the frames down to shape). The frames were still in the plug when I did this and I was worried the glue would make them stick in the grooves and I’d have to chisel them out, wasting them. But all went well, and I’m happy to have retrieved 3 frames that would otherwise have been thrown away. Here’s a photo of one, as good as new.

 

 

I’ve put to one side the strips that I’d trimmed down to make into frames but broke or were made out of ‘snappy’ wood. I might be able to use them when I build the light wooden superstructure.

 

 

 

 The man across the road with the bench saw kindly cut all my wales for me from 3mm planetree timber he’d earlier cut from some tree loppings I picked up on the side of the road. So now I have about 16 wales 3mmx3mm (1/8” square) which I now have to bend to shape.

 

 

 

Now I have to make a steamer for myself to bend the wales. I’ve been looking up how to steam and bend timber. The steam box seems very simple, but I have to scout around for a source of steam. The most likely is an old tea urn, if I can lay my hands on one. Fortunately I’m only going to need 10 wales, so I have 6 to experiment on and waste if things don’t go well as I’m learning how to do it.

 

The admiral has very kindly given me an old white pillow case which has reached the end of its usable life – as a pillow case. The fabric is very thin now, and is ideal for sails, so I’ve got enough fabric to equip a dromon flotilla!

 

Steven

 

 

  

Edited July 10, 2016 by Louie da fly

[Louie da fly]

I’ve now finished all the frames – 124 of them, each with its little paper tag to tell me where it goes.

 

 

And I’ve so far carved 30 oars of the 50 needed for the upper bank. This means I’ve got enough upper deck oars for one whole side of the ship, with some left over. I'm a lot happier with their consistency - they all look very much the same now, instead of having differences that were obvious to the naked eye. Maybe I'm getting better at this stuff!

 

 

 I’ve had my first experiment with bending the wales. I don’t have a steamer so I soaked each wale in water and fixed it in place using large headed screws as clamps, and then ran a heat gun over it. It worked after a fashion – the wale took the shape of the plug reasonably well, but not completely. Particularly at the ends the curve wasn’t tight enough – it sprang back a bit. The one I worked with was one of my “throwaway” wales – if I stuff it up it doesn’t matter – and it’s a little shorter than the others - too short to get a good purchase on the ends to bend them properly. However, even the longer ones will have the same problem.

 

 

 

 

I needed a way of putting bending force on the ends and clamping them there. So I put together a simple jig to tighten the curve after the initial bending, just using a bit of wood and some nails. And it works!

 

 

So now I’ve started using my ‘good’ wales, and I’ve done the initial curving on two of them. There’s still some adjustment and tweaking to be done, but it looks like I’ve got a workable technique.

 

While I’ve been working on shaping the frames and wales I’ve also been looking at how the superstructure will work. According to the 10^th century treatise “On Sea Warfare” by Emperor Leo VI:

 

The dromon should have a siphon (flamethrower) in front at the prow . . . . Above this siphon there should be a kind of floor of planks fortified all around with planks, so that marines can stand on it to fight the enemy attacking from the prow . . .                          

 

So dromons had a forecastle raised above the siphon for marines to stand and fight from.

 

Moreover, they should set up xylokastra [wooden castles], fortified with planks, on the large dromons  ‘towards the middle of the mast’, so that men can stand on them and throw into the middle of the enemy [ship] great millstones or heavy iron [weights] like sword-shaped blooms . . ..

 

The statement ‘towards the middle of the mast’ implies some sort of fighting top halfway up the mast.  But it was usual practice for dromons to lower their masts before going into battle, as ships of the time had weapons designed to cut shrouds so the mast came crashing down on deck. A fighting top would be a liability.

 

Professor Pryor in Age of the Dromon proposes that the passage above has been incorrectly copied by a mediaeval scribe, and that the original Greek is more likely to have read “around the middle mast” or “around the middle [i.e. halfway between] of the masts”, or even “around the mast of the middle” (i.e. a mast stepped midships).

 

He proposes two castles, one either side of the ship, with a catwalk between allowing easy access between bow and stern. This would also allow room for the lateen yard, which would have been obstructed by a single central castle. This idea is supported by Leo’s reference not to a castle, but to castles.

 

I took the forecastle and xylokastra from the illustrations in Age of the Dromon, but I had to make some adjustments. Their floors are higher off the deck – the forecastle needed room below it for access to the siphon apparatus, and the xylokastra had to be high enough for the oarsmen below to row without hitting their heads. And their sides had to be higher to properly protect the marines standing on them, so I placed the bulwarks at chest height, with battlements on top.

 

In my original drawings it sort of looked ok, but once I made up cardboard mock-ups and put them on the hull, it looked totally wrong. The forecastle was too big and too high, and the castles were too high and too far forward. And all that superstructure so far forward would weigh the ship down by the bow.

 

 

I started by removing the battlements – after all a dromon’s primary purpose is attack, and the battlements would have interfered with the marines lifting their “millstones and heavy iron weights” high enough to drop them onto the enemy ships.

 

I made the forecastle shorter – it still left plenty of room for the fighters. I also angled the forepart of the triangle forward, in line with a dromon illustration found in Malaga in Spain. It started looking better.

 

The floor of each xylokastron will be about a metre (3’3”) above deck level. they can’t be too long because galleys are notoriously unstable, and too many marines standing above decks along one side, as they would be when fighting another ship, would make it even more unstable. (a galley can only heel about 10 degrees before the oarports are under water).

 

I shortened the castles moved them aft, half way down the ship. It looked better still, while allowing enough room for 5 or 6 marines to stand and fight from it (any more might capsize the ship).

 

 

At the prymne (poop) - though this may or may not be an actual raised deck – there is a krabbatos (berth) for the captain, probably with an arched awning over it, as both earlier and later galleys had. There’s still enough room either side for the steersmen to stand. 

 

 

 

 

 

You can see the little guy standing on the castle. I've worked up designs for two more crewmen - the helmsman and the man who gives the oarsmen the time with a flute/trumpet thingy, plus a lion's head for the siphon to look out of and scare the enemy. But that will take a while to do.

 

The word used for the captain's berth is one usually used for beds, so perhaps it was some kind of day-bed the captain could either sleep in or sit on for councils of war. An 11th century Byzantine picture of refugees shows two people carrying beds (and one with a table). Perhaps it was like this?

 

 

 

 

 

I’ve made the castles about 1.3 metres (4’3”) wide, which should give enough standing room on top as well as space on deck to walk between them and enough room for the oarsmen to row. They’ll be open at the back with a railing to stop the marines falling off backwards. There’ll be an opening at one end of the railing with rungs to climb up.

 

The forecastle is about 0.9 metres (3 feet) above the deck to give space for the siphon and its equipment. Access from the deck will be the same as with the xylokastra.

 

 

The mid-12^th century copy of the Chronicle of John Skylitzes held in the Biblioteca Nacional in Madrid contains many illustrations of warships, and one illustration shows a ship with a xylokastron. I’m using that as a model as well.

 

Edited August 11, 2016 by Louie da fly

[druxey]

This is interesting stuff, Louie! Would the bulwarks on the xylocastra be closed? I'm thinking of windage. Professor Pryor's interpretation of their location and your mock-up seem logical.

[Louie da fly]

Druxey, the cardboard mockups are a bit misleading.  I don't think the bulwarks themselves would be closed - the castles would be up above the decks, supported by columns. I've drawn the columns (and arches) on the cardboard mockups, but I wasn't prepared to go to all the work of cutting out the gaps when I was just trying to work out shapes and proportions.

 

But they are fortifications - as Leo wrote; "fortified with planks", to protect the marines inside. I agree about the windage issue, but if the castles aren't too large it shouldn't be too big a problem. And they were only used on the largest dromons, so they shouldn't be too large in proportion to the size of the ship itself. 

 

Ancient Greek biremes appear to have had something like latticework screening as protection for the lower oarsmen, but I believe the problem being solved in that case was to let them get enough air. And it's possible that in battle the screens were covered in leather. 

 

Speaking of which, according to Professor Pryor the problem of sufficient air for the lower oarsmen on a dromon still hasn't been satisfactorily solved. The evidence all points to their having been fully decked, but if that's the case, airflow wouldn't have been sufficient for men working as hard as these. It's currently just one of those mysteries. There's no evidence, written or pictorial, to suggest an answer.