I didn’t either, but it’s apparently a boating term that means to raise the bow of the boat by adjusting the boats trim.

I guess this can also be done by overloading the rear of the boat? I know some boats have bladders on either side of the rear of the boat, called ballasts, that do this.

This is from a comment on this cartoon, in the farside archive:

“Trim is simply the running angle of the boat as it makes way in the water; when we adjust the trim, we raise or lower the bow (the front of the boat).”