I have calf-length hair and find it to be relatively easy to manage while I'm travelling or having an active lifestyle. One important tip is to not wash it every single day with shampoo. If you do that you will end up with straw-like dry hair. When you wash your hair too much, it just dries out the ends and encourages your roots to produce even more oil. As you start getting used to a more extended (every 2-3 days) washing interval, it may take a few weeks but eventually your scalp will adjust and produce less oil.

On the days that you don't wash, you can either keep it dry while you wash your body, or simply rinse it with fresh water can get the sweat and salt out of it. When you do wash it, let the conditioner sit for a while on the ends. I usually slather on the conditioner and let it soak in while I'm busy shaving my legs to be time-efficient.

Also, consider that you probably will not always be able to wear it down and flowing every single day. Sometimes it's more convenient to just braid it back neatly, or coil it up into an elegant bun/twist. Even dirty hair looks great in a bun.

Lastly, make sure that you're getting proper nutrients (especially enough protein, iron, and B vitamins). Heavy exercise can require a lot of resources, and the body considers hair/skin/nails more of a luxury item. So if you are deficient in anything it's likely to affect those areas first.