Your “head” or bathroom on the boat, is a wet room o shower. There is no separate shower stall. The sink faucet pulls out and becomes a handheld shower head. If you book one cabin, and there are guests in the other cabin, you will share a head with the other guests.
The skipper and crew have a separate shower in their head.
There is also a shower head on the back of the boat for washing off after being in the salty seawater.
At some ports, there will also be showers at a hotel or public bath house, which cost about 2 Euro.