I cruised for a couple of years with a blind English Setter ... with a quite steep companionway ladder into a deep salon.

Yup, I had to 'steer' the dog by the dog collar but real good non-skid on the companionway steps was the 'secret' to get this all to work. If youre 'confident' (important) in doing this, the dog will be confident.
Eventually the dog had all the intricacies of the boat memorized (but we couldn't ever leave a door or locker drawer open), including using a 'potty patch' on the foredeck.

To get the dog on and off the boat I tried sloping ladders, ramps and other PITA 'devices' and simply taught the dog to (blindly and with implicit trust in me) jump off the boat into the dinghy and I simply steered her by the collar and a hand under her butt. All the 'devices' simply took tooo long for the dog to 'get it over with' and allowed too much 'dwell time' for dog to become nervous while we 'futzed around' with the (usually shakey) 'device'. Getting back on (high freeboard) I trained her to first put her front legs up and onto/close to the cap rail ("ready-up") and on the command 'jump-up', she would and I would 'boost' her hind end onboard.

If the dog is old and wobbly due to dysplasia or neuro hind-quarter atrophy this wont work so well; but, if the dogs 'hind end' is still healthy, 'training' that is heavily rewarded will work especially if the dog already 'wants' to please you.

For any dog on a boat, Id strongly recommend training the dog to 'go on command' ... and then use a 'potty patch' (and a deck wash down pump) as that will save a lot of on/off, especially when its 'dark and stormy'. Do websearch for 'go on command' or 'pee on command'; even an old dog will/can learn to 'do' it, just takes time and patience.