Strength Training Without Weights?

[MiddleMike]

Well maybe I'm just daft, but if you're on a sailboat you have a wide variety of "things" to exercise with as opposed to bringing along 100+ pounds of kettlebells instead of food and other provisions. First, any sailboat suitable for ocean sailing has more than a few blocks arranged for putting those funny sail things up. Viola, you can work on your beach body lifting sails, buckets, etc. and many other items, no bands needed. As for the one legged bosu calf contractions, simply go stand on the bow of the boat underway and try to hold progressively larger sails (all folded up of course) and work to your hearts content. Then of course there are the myriad of places to do pullups and chins.
Sufficed to say you can pretty quickly come up with a wide array of exercise elements onboard. Granted I am assuming said sailboat is at least a reasonable size. If you're going anywhere actually offshore, there's a simple principle to go by, "nothing under 50ft after 5pm."

Enjoy the sailing, lift some sails, do a few chins and you'll have the adventure of a lifetime!

[Cheesepuff]

I'd consider that rope, water and buckets are available.
Water is heavy.
Decent light handles can be made from pvc.

But most buckets would not be sufficient weight for most lifters.
A 30 gallon water barrel filled with sea water is 249 pounds. (maybe coolers could be used)

I'd guess that a trap bar type arrangement could be possible using coolers or water barrels.
Your footing might need to be raised to get to an appropriate height.

Plus your inevitable mishap will make for an entertaining video.
Suspended barrels of water swaying on an uneven / pitching deck is sure to be fun, and dangerous.

So maybe just keep a weather eye on the horizon and make sure the boat is on course.