One is sufficient in all but rare cases. Though it definitely pays to find a boat with one that's properly configured, & that's useable when you have 5 layers of
clothing on.
Specifically, ones set up so that you face either forward or aft when sitting on them are far superior. As you get the feeling of needing a seatbelt far, far less when using them underway. Also there needs to be room in the head compartment for you to reasonably manuver while in foulies, boots, & a few layers of polar
gear. Though not so much that you can't easily brace yourself in place without using your hands. Both when sitting on the head, & when in the compartment proper.
This may sound like a small thing. Trust me, it ain't.
Having a seperate
shower (compartment) onboard can be really nice if you've got the room. Especially if you sail anywhere outside of the tropics much. Including from the perspective that you then don't keep anything in such a
head that's not used when taking a shower. Which helps a lot for keeping TP, & other toiletries dry. Plus it makes for fairly easy cleaning/cleanup of said shower/head.
Here are some premium features of an onboard shower:
- Shower head. Which, a hand held sprayer is great. So the original unit in most ensuite showers found in OEM showers is fine.
- Properly sealed
wood, & finished walls. To include 2-part
epoxy paint with anti-mildew agent. And multiple coats of your fav
sealant on the
wood;
varnish, clear
epoxy, or both.
- Floor grate, with nonskid. Skateboard tape's fine in a pinch.
- Sump with included
pump, possibly the macerating type.
- Seat that drains, & isn't slippery. And on the luxurient side, a foot bench/rest so that the ladies can shave while seated.
- Ventillation system. Anything from an overhead
hatch, or Dorade, to something having a blower system with a timer.
- Towel rack nearby, preferably heated.
-
Storage for soap, shampoo, lotions & such. AKA a "shower caddy".
-
Heating unit or vent near the shower, though this is one of those luxurient items.
EDIT: I almost forgot. Definitely ensure that all guests know how to properly use the head, including doing a demonstration if you're so inclined. And that they know what goes into it, & what doesn't. Along with
posting instructions on both of these things prominently in the head (instructions sheets). With the warning that if a guest clogs it, they'll be fixing it under the Captain's supervision.
Also, make sure that there are lots, & lots of convenient, stout handrails in a head or shower. Little things like that make a real difference.