Hello the list. Thanks for all the previous good advice in the past, need a little bit more.
If I take a pipe flange, weld it good, inside and out, thread a piece of pipe on it, then drill holes in the hull, would that be acceptable for a shower drain? The boat's on the water, and I really don't want to have to pull it before next spring when it warms up enough to sandblast, paint and relaunch. I could finish up the hole and paint it good in the spring.
It's a pretty good distance to the kitchen sink drain, and that seems to be the only one. I'm not sure I can get enough rate of fall for good drainage if I go there. A better idea would be welcome, and I'm always open for suggestions to improve my idea.

Buy a shower sump pump and plumb the discharge out the side of your boat. Avoids another hole in the bottom. This is common practice in many houseboats and cruisers.

Many thanks OHB.  that makes a great deal more sense.  I have a lot to learn.