Before you take your pet out on the seas, there are several initial preparations that should be taken.
In case your pet finds himself or herself in the water, make sure they know how to swim and get back on board. Practice or make sure you have devised a rescue plan or a method to getting them back safely aboard. You may have to teach your dog how to use a ramp or swim platform. Most every boating store will sell life preservers for both cats and dogs.
If your pet is new to the boating life, it may be smart to take them on board your boat while it is docked to help them grow accustomed to the space, feel and sounds of being at sea. Start the engine of the boat so they begin to get acclimated with the loud noises.
Toilet issues may arise in which case a piece of astro turf or a liter box will solve the problem. Make sure you bring enough food for your pet, and constantly provide them with water, as it can be hot on board. Along those lines, make sure there is a shaded area in which your pet can lay during the day, and be aware of potential sunburn or seasickness that may occur.