I have a lab who goes everywhere with me. He was born for the water and loves riding in the boat. He's a trained waterfowl hunting dog so he's been riding in boats since he was a puppy.
A word of warning - when the boat is under power he should be inside the boat in a secure position. Riding on the back part of the boat like in your pictures made me cringe, is just plain dangerous. Good way for your dog to get injured or killed. You say he only fell off once, he shouldn't fall overboard at all. In over 30 years of boating and hunter from boats with dogs ive never had a dog fall out of the boat. Another thing never let him ride in the bow of the boat while under power. If they fall in they are either dead or will be missing a leg or two. Treat dogs in your boat like they are your 2 year old child. You need to keep them close, secure, safe and under control. Holding her leash is good but won't prevent her from going overboard while riding in an unsafe position.