Weathering is a must in plastic sailing ship modeling?

Drybrushing is one technique to use to weather, however, due to the small nature of parts, will tend to make the weathering look heavy and out of scale. Another technique is to look up and learn to do washes. ( and make sure to open up to using enamel, acrylic, oils, and inks) This is by thinning the paint and going over the base many times until the hue that you want is obtained. My rule is to look up the grayscale (as referred by printers and photographers) to see what the base color will do when adding a lighter tone to it. Colors fade due to the elements such as salt, wind, UV and moisture, but are also tuned to the fact that ships are kept ship shape, so don't go overboard by showing a lot of rust, peeling paint, or exposed wood since a ship in that condition would not be floating long.
I use weathering not so show actual age, but to be able to blend the colors so that there is no abstract or clash to the model. I like to see my model as how a woman dresses with all the colors complementing themselves, and this can be done through washes. Washes are a must when aging sails, whether made of cloth or plastic, since it is really easy to make the sails look out of scale if the colors are not blended right.
I find that weathering varnished surfaces work well with diluted Future floor wax. By mixing too much water in it and then putting on heavy layers over a brown surface, makes the floor wax turn opaque and crack and peel, like weathered varnish. But be careful, because it could look out of scale.

Another thing to keep in mind to as why you do not see a lot of model sailing ships weathered is that the market doesn't allow it. Most sailing ship models are built for museums, collections, or interior decoration, and that these markets do not want a model that shows the stresses of time, they usually want "showroom" quality. However, that is kind of turning with the popularity of "antique" appeals in the current home interiors fashions. Then again, some go to extremes and I have been seeing "reproduction" models that look like garbage scowels.

Scott

Scottrc has given some excellent suggestions. I would add one point: there are NO "requirements" for historic plastic sailing ship modeling.

That said, I'll offer one suggestion: be sure to paint everything. Unpainted plastic looks like unpainted plastic - and therefore like nothing that appears on a real sailing ship. That's the only hard-and-fast "rule" I follow myself, and it's a personal one.

We're living in an age of great sophistication in the world of model building. Standards of quality and accuracy have never been higher. The range of products, materials, tools, and references for modelers in all fields is the greatest it's ever been. One unfortunate byproduct of all this, however, is the emergence of some individuals who feel obliged (and qualified) to judge every model by some sort of allegedly universal standard. Even in this forum about ship modeling, which hasn't been infected as badly as the aircraft and armor fields, I occasionally see references to "the color police." And at least one international ship model organization has "officially condemned" weathering of all sorts. I suppose if those people want to act like that, they have the right to do so. But it seems to me that such behavior only damages the hobby.

For my plastic sailing ships I use mostly wood stains on them. Then I use washes of either India ink.As I have just wrote about on the other topic.Or oil washes with burnt umber.Than I use the oils to dry brush after everthing has dried.I agree with Scott. Sailing ships to me look better weathered than showroom clean.
Rod