Therein's Ship Bond

You bond with a water vehicle you are presently on and within sight (This could be as simple as a makeshift raft to a war ship). While bonded in this way your ship gains temporary hp equal to the level of this spell × 5. This temporary hp reset whenever you have a long rest while touching the vehicle. Additionally you can make any spell you cast that targets only you can also target the vehicle. You must be touching the vehicle to utilize both of these traits and while using a concentration spell that also targets the vehicle any damage that the vehicle takes you will take half in psychic damage. This spell can be dismissed whenever (no action required), is temporary suspended if your not touching the vehicle and ends if the vehicle is destroyed.

It is up to the DM's discretion to how the spell interacts with the vehicle if the spell isn't clear. For example, the spell Shadow Blade normally needs someone to wield it, but the DM could have the vehicle's ballistas and/or cannons fire them instead of regular ammo.

At Higher Levels: When you cast this spell using a spell slot of 5th or higher the temporary hp given to the vehicle increases by 5 each slot level and the size of ship you can effect increase 10ft by 10ft each slot level.