The sailing ship in question is a major 'character' in the plot, so I want to get everything right if possible. My intentions for the ship are as follows:

1) Not particularly large - Crew of approx 70

2) One large main-mast, with square-rigged sails (one to three).

3) Possibly a pair of mizzen-masts situated horizontally towards the stern, fitted with smaller sails - if there's a reason why this won't work, please let me know!

4) Built for speed, not really a cargo ship.

5) Eight pairs of oars (two men to an oar, I'm presuming) for precision movements/windless days.

6) Strengthened bulwarks to prevent buckling under storm conditions.

7) Two or three decks below - one for crew quarters, one for oarsmen, poss. hold for storage of supplies, etc.

Level of technology is certainly pre-gunpowder, possibly considerably earlier. Pulleys and capstans etc would be fine, but no real high-technology.

Now my questions: Does the above make sense? Are there any gaping holes in these plans that would be blatantly obvious to a sailing type? What sort of dimensions would the ship have to be able to be crewed by 70 men, often in shifts?

What about rigging (or cordage, if my research leads me right)? I take it you'd need ropes from the masts to front and back along the centerline, then probably others to the sides of the ship to hold the masts in place, and more via pulleys to assist raising and lowering sails. Anything I'm clearly not thinking about?

Finally, what about supplies of food and water? Would a ship of such a size be able to carry enough food and water for 70 crewmen for a month's voyage without resupplying?

Any wisdom on this topic would be gratefully received.

Cheers,

Most Oared ships have dozens of pairs of oars.

Look up in Wikipedia the following:

Sloop
Viking Longship
Trireme

You'll not see masts anywhere other than along the keel. No other part of the boat is structurally strong enough to support a mast. So two masts horizontal is not possible.

Oars were not used for open sea travel. Their only purpose was Ramming Speed, really. Sometimes for fine manuvering into and out of the tradewinds. But for long travel, no.

Many thanks.

Those links are the sort of thing I was looking for. Many thanks.

The main mast should generally be footed at the deepest point in the keel (for obvious structural reasons). With square rigging, the sails carried by the main mast transfer most of the wind-force collected into the mast itself. Because the deepest part of the keel tends to be near the centerpoint of lateral hydraulic drag (again for obvious reasons), that means that any masts aft of the main mast should be balanced by equivalent masts to the fore.

Sweeps are possible, but it would probably be more effective to have an oared launch which could tow the ship for limited distances. This could serve other purposes and wouldn't compromise the internal structure of the ship. You could even have two.

You never make it clear how large the ship is. But a month's supplies for a man doesn't take that much space, if you keep it to the bare essentials. Say 50 liters of water per man (112 pounds or so), and twenty pounds of food. That would require pretty strict discipline to get through the month. You can cut back on food and slightly reduce needed water if your men are willing to eat raw fish, though few low-tech navies have been so lucky. Over the course of a month, you can count on losing a good deal of the water one way or another, so 100 liters per man would be safer. And if you need to break out the sweeps, you're going to need several liters per man per day. So reserve that for real emergencies, or there simply isn't going to be any way to carry the water you'll need.

Say we have three watches with two on and on off for the hands. One in ten are officers or warrant officers. Three guys minimum to handle each set of sails, lookouts, helm, watch, supernumeraries (cook, doctor, steward, whatever) and you've got ten to twenty guys on duty at a minimum, depending on how big a ship it is. So you've got double the guys I think you'd need, which is fine if this ship goes into battle even occasionally (land exploration counts as combat, for our purposes). Of course I'm assuming no more than four masts.

You should also note that a pre-gunpowder ship isn't going to like straying far out of sight of land, even if they intend to go without landing for a month.

One thing to note, these notes on design aren't conclusive or anything. The Chinese super-junks had dual keels and internal bulkheads, and thus could (and did) mount off-set masts. They were also up to 400 feet long. Multiple hull designs also predate modern materials, as do sailing ships that didn't have conventional keels at all. Depending on your fishing technology (both catching the fish and knowing how to use them), you can eliminate some or all of the supply requirements. Vikings were physically different from Greeks or Japanese, storms differ in intensity and duration from one sea to another, gun-powder is a "unique" technological development (that is, you can imagine a history where it wasn't discovered or refined until later than was the case in our own history).

Another option is that the oarsmen aren't needed but that this is just a good way for the penal system to keep prisoners occupied. They sail when they need to get somewhere but row in the meantime. (Or to go upwind. Square riggers can't go up wind).

http://www.theshipslist.com/accounts/index.htm

Cheers,