Mallo,
Sorry not to have responded earlier re: your antenna question. Have been busy.
I agree with the advice re: grounds, and think you have that covered. You're lucky with a steel hull...great RF ground system!
RE: antenna material, virtually anything will work, but I tend to favor insulated s/s lifeline because it is robust and will stand up to the marine environment, whereas bare copper wire won't last very long, and other materials are sort of "in-between".
RE: length, it depends a bit on your boat's configuration and, especially, on which bands you wish to favor. Longer lengths favor the lower bands (e.g., the 4, 6, and 8 mHz marine bands), while shorter lengths favor the 12, 16 and 22 mHz marine bands). The antenna should be at least 23' in length, counting the distance from the tuner to the top of the antenna. Forty feet or so is often a good compromise.
RE: placement, this is a bit of a quandry in your case. While the mast and spreaders are wood -- and, therefore, won't radiate or have much affect on the radiation pattern -- all the other standing
rigging will. In general, it's good to get the antenna as far away from other
rigging as possible. On some ketches, the triatic stay works well. On some, it's possible to run the antenna from the truck of the mainmast to one rail just forward of the mizzen, in such way as to ensure clearance of the main boom.
Assuming your mizzen mast is also wood, and remembering that the radiating part of the antenna
begins at the tuner, it might be possible to mount the tuner under the mizzen mast and run the antenna up the mizzen -- either inside or outside -- to a triatic stay. With wooden masts, you wouldn't need
insulators on that stay....just connect to the stay itself in a secure manner.
Lots of possibilities. Don't be afraid to experiment, including with temporary lashups before you make them permanent. For example, once you've connected a good ground to the hull, get yourself a roll of insulated wire and use that as the antenna. Experiment with it in different locations. When you find something which works well, go ahead and make the investment in a more substantial antenna material, such as s/s lifeline.
Be sure to do the experimentation when at
anchor or at sea, since marinas can be very noisy and will confuse your results.
Good luck. Let us know how it works out.
Bill