Some sailors bathe in the ocean. They take their soap, shampoo, and conditioner and plunge in. This, however, can be rough on the skin if done too frequently (salt water is abrasive). Once a week is almost too frequent.
Some sailors do a towel bath. They jump in the ocean, get wet, jump out and take a towel soaked in fresh water and clean off. This one you almost get anyway each time you go for a swim in the sea. Just be sure to focus more on the washing part than drying.
Some sailors do a region wipe down. They take a soapy towel and simply wash the parts of their body that require a good scrub. I employed this technique a lot when I was in the Army.
Some sailors take a rain bath. Each day that it rains, they go out on the deck of the boat with shampoo and soap and shower in the rain. This is a favorite of mine and I look for excuses to do this. There is something exhilarating about showering in the rain.
Some sailors take baby baths. This technique isn't eco friendly, but it works well. Buy packs of baby wipes, and wash up using them. This one makes me feel refreshed.
While talking about showering, most folks don't think about it but there is a "best practice" when showering. Always do your wipe downs starting from your head, and end at your feet. That is, wash your head first, then neck, then chest, then upper back, then arms (and arm pits), then stomach, then lower back, then frontal stuff, then rear stuff, then thighs, then calves, and finally feet. This keeps moving the germs/filth away from your head where ingestion of such things can be detrimental.