The first time your dog sees a boat should not be the moment it pulls away from the dock. A moving, slippery surface can be strange even to a dog who loves water. Start by deciding whether the trip can wait until you've seen how your dog feels on a boat that is still.
Practise on land before leaving shore
Let your dog explore the boat while it is secured and not moving, if the owner or operator permits it. Reward a voluntary approach or step aboard. Give them a way to step off again. If they freeze, try to leave or will not take their usual reward, don't push them into a ride. You can make the next attempt easier or choose a day on shore instead.
Arrange a properly fitting canine life jacket before the trip, including for a dog who swims well. Check that your dog can move and breathe comfortably in it while on land. Have fresh drinking water, shade and a plan for getting back to shore. Keep your dog under close supervision. Don't tether the dog to the boat: if it capsizes, a tether can trap them.
Keep the first ride optional
If the dog remains relaxed on the still boat and the operator confirms a safe plan, choose the calmest, shortest outing that lets you return early. Watch for distress or overheating, end the trip if your dog is struggling. Don't assume a dog who can swim wants to be in open water. Lakes and rivers may contain currents, hidden hazards or unsafe water quality, so keep the dog out unless you have assessed the conditions.
Tonight, try on the life jacket calmly on land and make a note of how your dog responds. If the fit or the boat itself worries them, postpone the ride. Staying ashore is a sound decision.
Sources: AKC on boating with dogs. Dogs Trust on open-water hazards.