Every dog can be taught. Actually, it's the owners that need to be taught. We've done it with puppies and with older dogs. We just switched boats. One dog absolutely refused to go in the new area we designated on the new boat. So we backed up, realized the issue, and worked slowly, consistently, and with lots of praise for about a week. Now she happily runs to the new area on the new boat and does her businesses. We're now able to leave doors on the boat open again (you'll understand once you read the technique).
We wrote about the technique 8 years ago. Hundreds of dogs and people have gone through it with fabulous results. The time it doesn't work is when the people give up and stop working the technique.
When we adopted a 9 year old dog, she wouldn't consider going on the boat. It took running through the technique over a couple of weeks. Yes, weeks (that doesn't mean making them hold it - never do that but they can be uncomfortable for a day at a time). Finally, she did it. She died in our pilothouse at 15 loving every minute of the cruising she did over the 6 years (and pee'ing and poop'ing on the boat every day).
Even today at a dock, before the dogs go for a walk off the boat, they go to their spot on the boat to do their businesses. We'll often take them for a walk right after and they surely prefer to go off the boat but they'd rather be comfortable too. It's all about knowing where it's OK to go.
I can't imagine a situation where I'd have to lower a dinghy in bad weather to take a dog to shore. Or how about overnight passages? Or Superstorm Sandy where the dogs didn't get off the boat for 4 days?
Every dog can be taught to do it. You just can't give up. Again, it's not the dog's fault when the owners throw up their hands. It's the people's fault it doesn't work.
The technique:
https://activecaptain.com/articles/dogs/canineCrew.php