A life jacket is the first rule, however well he swims
A strong swimmer can still be knocked overboard by a wake, slip on a wet deck, or panic in cold water far from a ladder he cannot climb. Choose a canine life jacket that fits snugly around the chest and neck, lifts the head clear of the water, and has a sturdy top handle so you can haul your dog back aboard without grabbing at a collar. Let him wear it around the house and garden first, paired with treats, so the jacket predicts good things instead of a strange day. Test the fit in shallow water before a real trip: he should paddle level, not tip forward or slip out backwards when lifted by the handle.
Make the first boarding boring
Introduce the boat while it is tied up and still. Let your dog step on and off at his own pace, scatter treats on the deck, and settle him on the non-slip surface where he will ride — a mat gives claws something to grip when the boat moves. Practise the engine starting while you feed him, so the noise links to food rather than alarm. Only when he can lie down calmly at the dock should you take a short, slow trip, watching for drooling, lip-licking, whining, or a hunched posture that suggest nausea or stress; several short outings build a sailor far better than one long voyage.
On board: edges, heat, hooks, and harbour water
Keep your dog leashed or in a settled spot away from open transoms and boarding gates, and stow the hazards boats accumulate: baited hooks, knives, fuel containers, cleaning chemicals, and loose lines that tangle legs. Decks become paw-burning hot in sun just like pavements, so provide a shaded, wetted mat and check the surface with your hand. Offer fresh water from your own supply regularly and discourage drinking from the marina or sea — salt water and harbour water carrying fuel or algae can both make a dog seriously ill. Plan toilet stops ashore every few hours, because a dog holding on uncomfortably is a dog who may leap for the dock at the worst moment.
Around the marina itself
Pontoons are slippery, narrow, and full of gaps a paw or a whole small dog can fall through, so walk your dog slowly on a short lead and lift him across the gap between dock and boat rather than letting him jump until he knows the step well. Scan for spilled fuel, discarded fishing line, bait, and fish scraps before letting him sniff freely, and keep him clear of other boats' dogs until owners confirm a greeting is welcome. At night, a light on his harness makes him visible among the masts and mooring lines.
If he goes in or goes missing
If your dog falls overboard, keep eyes on him, throw flotation toward him, manoeuvre to lift him by the jacket handle, and watch afterwards for coughing, exhaustion, or shivering that warrant a prompt veterinary call. A frightened dog who reaches shore may run, so searching with his photo and details ready matters as much as the rescue itself. Should a marina mishap ever leave your dog loose among the pontoons, KinsLe's Lost Pet Alert System sends a free alert to nearby Circle of Love members, and the person who finds him can message you directly through his alert.