I would have read this around 1978 or so in my gradeschool. It had a aqua and black cover – with a dog standing on the porch of a houseboat? In a storm. I thought it was called Sea Dog, but none of those titles give me the right story. The dog rescues the kids uncle in a hurricane?
Could be Scuppers the Sailor Dog, by Margaret Wise Brown. (It has its own Wikipedia page.)
Maybe Clarence the Sea Dog by Patricia Lauber?
Could it be “the Sea Dog” by Morgan Dennis. The dustcover shows a girl and a spaniel in front of a houseboat (the cover underneath has a completely different illustration). set in Key West. Splash is an Irish water spaniel who lives in Key West with his mistress, Heather, and her father and mother. Heather’s mother wanted a house, her father a boat; but everyone was satisfied when they built a house-boat. They called it The Sea Dog. Splash was especially happy because there was plenty of water all around and even some dog friends nearby. One day when it was very rough, and small-craft warnings went up, everyone hurried to get ready for the hurricane
There’s some interior pictures here
https://flic.kr/p/ddGCh