New breed out there boguing and you don't need a case.
For boats can I point you towards the Olympus Tough TG-Tracker series?
No case down to 100 feet, 4K, five built-in sensors (GPS, compass, barometer, accelerometer, thermometer), real Olympus lenses and quality plus very, very tough. Comes in at the Go Pro 4/5 price with proper warranties and support. Haven't tested it in water so you must check if it is a waterproof sinking brick and needs some floatation on the strap.
In contrast the Go Pro Hero 5 and 5 Session will go in water without a case but are only 1ATM rated to 33 feet.
One price notch down is the Ricoh WG-M2 - super tough for all outdoor activities no matter how wet or cold. Water, snow, ice all covered but think batteries in cold conditions for all these action cams and especially cell replacement when wet. Cheaper cams are generally 900 mAh units, middling are 1200/1300 (GoPro) and they top out at around 1700 mAh.
All the Sony units from the cheapest at 168 USD come with external cases for water and the top line one at GoPro prices is is 4K, rated to 197 feet and, of course can be externally hull mounted and controlled with the wrist monitor/controller.
Finally, and in the real budget range I'd like to suggest pointing out a newcomer, the OLFI ONE.FIVE 4K HDR ACTION.
It's 4K, Sony sensored, waterproof housing to 90 metres blah, blah, blah: great mounting options for boating - think suction, tube mounting and chest harnesses. But the real reason for this being at the the top of my list is HDR.
That's high dynamic range shooting and I'm not going to go on about it. Just get to a shop that prides itself on good TV and ask to see an HDR model side by side with their best 1080p and 4k traditional models. The womenfolk in my family have never been truly excited by 720p, 1080p or 3d as they arrived. They really can't get excited about 4k either but when they were shown the Barrier Reef in HDR their index fingers went straight out to point - that one please.
Attenborough's team are just about to release Planet Earth 2 but they're already arranging to go HDR for everything following.
Rob