Don't do ANYTHING before getting a copy of Rob Napier's " Caring For Ship Models"
www.SeaWatchBooks.com!!! ( I have no skin in their game.)
It will set you back 75 bucks U.S. but it IS the bible for the much-overlooked art of ship model restoration.
I've done a lot of this work over the last twenty years or so and professionally restored historic period antique furniture for another twenty years prior to that.
I have sixteen or seventeen in restoration at the US Naval Academy. I would advise against using soapy water or water rinses or leaving it in the sun for any length of time at all.
I do not question what success has been achieved by Robert B. or anyone else who has taken this approach and do not, by any means, presume to criticize, or suggest it is wrong. But I would advise against it until you have a LOT more information from several reliable sources, such as the afore mentioned book.
Looking at the picture I see deteriorating rigging which is likely VERY fragile. If it is, it and the sail cloth got that way from prolonged exposure to U.V. light (daylight). The brown color is likely as much oxidation as it is dirt. If it is the sails which appear to be largely intact will tear easily with very little pressure.
If you feel you must start, start by making a cleaning hood out of a cardboard box large enough to accommodate the model. Cut the back out of the box put a paper furnace filter in the opening with a box fan behind that set to drawing air through the box and the filter and out the back. Use soft artist brushes to GENTLY dust the model from the top down. There are methods of using water-based solvents the strength of which can be controlled, and sparingly as well as judiciously applied, which is a discussion too lengthy and detailed to go into here.
This model is now your patient, First DO NO HARM!
This is the best considered advice I have at my disposal.
Pete