Wednesday 18 December 2013

Modelling the ships

Yes, really I have been working on the novel today, but the actual text is not much further forward. I'm now up to 20,500 words, which is progress but not fast. However, I've been doing a lot of background research on speeds of camel caravans, speeds of iron age sailing ships, and other details; and I've been working on my calendar, to make sure all the right characters can plausibly be where I need them to be at the right dates, given the transport they have available to them.

Interestingly, this exercise has brought back to mind (and validated) my previous essay, 'The spread of knowledge in a large game world'. Because of the speed of the ships (more below) my protagonist sails from the northern city where he's spent the early summer thirty five days after his home city has been conquered - but he does not know of it, because there's no plausible way for news to reach him. On his way he visits The City at Her Gates, and there he may plausibly pick up news of the conquest of his home - but it's equally possible that he won't, since although the news could have reached there if a convenient ship has happened to make the passage, it's possible that it hasn't.

The Ship

But most importantly, I've been modelling the ship.

The plot driver for Merchant is the arrival of a disruptive technology: new ships which are seaworthy enough to circumnavigate the continent, and thus bypass the bottlenecks of the caravan road which has been the main trade route for hundreds of years. So, I need a ship. But since this world is not based on real history, it has to be an ahistoric ship: a plausible, effective type of ship which would work and could have been developed in the real world, but wasn't.


So what I've gone for is a semi-elliptical squaresail. That is to say, a fully battened sail which hoists and reefs like a Chinese junk sail, but which tacks like a square sail: it has no specific luff or leach. This actually has some advantages. A junk mast cannot effectively be stayed, because when tacking the sail sweeps through the area where useful stays would have to be. Consequently, junks have unstayed masts. With a semi-elliptical  squaresail, you would be able to have stays on the mast, provided they allowed the yards to be braced round to 45 degrees. Also, with a semi-eliptical squaresail, you can set the aerodynamic curve of the sail to a considerable extent by using curved battens (semi-elliptical battens, hence the name). So this sail would be very much more effective upwind than a conventional square-sailed ship. Also, as the sail is reefed by lowering it, it's not necessary to send men aloft to reef it.

Such a rig could only develop in a place with tall, straight trees - forest-grown conifers, probably, because although unlike junk rigs the mast can be stayed, it can only be stayed at the very top - you can't hoist the sails past the attachment point.

Of course, Shearwater would not be as effective upwind as a modern racing yacht. She could not lie closer than 45 degrees to the wind and in practice wouldn't lie closer than 50 degrees; she'd also make a certain amount of leeway, so 60 degrees off the wind is a likely most effective course. But downwind she'd be pretty good, and on a reach she would be very effective. As I'm positing a prevailing westerly coriolis airflow modified by strong convection over the steppe giving rise to reliable onshore winds all along the southern coast, a 'trade route' going east along the north coast, south along the east coast, west along the south coast and north along the west coast would involve very little if any beating to windward - for a ship which could lie a close reach, as this one could.

She has no staysails - she could have, but I'm assuming that either they haven't been invented or haven't been found advantageous - so she has no bowsprit and her bow is short and cobby. Her forecastle extends right to the stem, and is pretty broad at the front, with no front bulwark or rail. This is to make anchor handling easier (but, of course, more dangerous). She's a cargo ship, a beast of burden, and she's not slim or elegant; but on a 40 metre overall length she has a payload of at least 40 tons of cargo - possibly significantly more, her displacement will be more than twice that.


Not only does she carry at least as much as 160 camels, she can make two round trips from north to south in the time a camel caravan can make one. This surprised me. But camel caravan speed is about 32Km/day, whereas the speed of a classical period merchant ship was about 220Km/day. much greater. So even if (as I'm assuming) the sea route round the continent is three times as long as the caravan road, the ship, with seven times the speed, makes the journey in less than half the time. That in turn means - something I hadn't seen until I worked this out - that not only could she outperform the camel caravans on the cargoes they can carry, she could carry perishable cargoes - perhaps fruit, for example - that they couldn't carry. No wonder the cities which depend on the caravan trade feel threatened!

As a cargo ship she has a cargo derrick to aid loading and unloading positioned over the main hatchway.

She has some features which are there simply because I needed them in the story; for example the shore boat I mentioned in chapter one is visible stowed on the main hatch; the stair on which Dalwhiel stands to talk to Karakhan is visible, the companionway out from the after castle is there, and even has an arched roof to add headroom.

Building the model of the ship helps me to visualise it and consequently to be able to write more confidently about it; it's the same reason I have town plans of my cities. I can even visualise her in the context of them.

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