If you want to move something in Dungeons & Dragons, there’s rules for it. Whether you want to grab and shove someone around, shift heavy objects to and for, carry too much in your pack, the game has you covered. There are various magical means for moving things, though their are weight limits on these abilities. The point is, everything can be moved, one way or another.
Even the ‘Immovable Rod’ can be moved. It takes 4 tonnes of pressure to do so, but you can shift it, even if the names suggests otherwise.
I mention this, to emphasis how powerful the Ramora is. To simply ‘anchor’ a massive ship out at see, or steer that ship to safety, requires some serious physical or magical force.
Ramora

In the end, I went with magical. All sorts of large, sea beasts can grab a ship and drag it around, but to hold a ship fast and then effortlessly steer it seems more extraordinary than a physical grab or giant suction cup. I also preferred the image of the great fish swimming near the ship it is guarding, rather than a tangible connection between creature and hull.
One change you might want to make to these stats is the creature type. Making this a ‘beast’ means that anyone level 6+ character with polymorph can become this mighty creature with its magical tether. ‘Monstrosity’ might be a better creature type. For once though, I liked the idea of the group having this option. Polymorph is an hour long, enough to avoid a dangerous storm but not enough to totally spoil your seafaring adventure.
And the Ramora is a rare creature, so no one is changing into this unless they have seen it in your adventure.
Besides, if your spellcasters can conjure the Ramora, so can the villains… cue maniacal laugh.
Thank You For Reading.
I have made all the Fantastic Beasts into D&D monsters. Find them here!