There are laminate trimmers (small routers) with multiple bases and one of the bases can be angled. My laminate trimmer kit is a DeWalt, about 10 years old. It has a 7/8 hp motor and takes 1/4" shank bits only. There are 4 different bases in the kit that I have, a standard fixed base with adjustable bit depth. An offset base for getting into tight corners, a seaming base for precisely joining two pieces of laminate, and an angle base that lets you angle the bit up to about 45 deg. Laminate trimmers are designed small in diameter but are quite powerful and can handle cbhores like this if you don't expect them to remove a lot of material. Trimming the edge of plywood should be easy for them if you take your time and don't push it along too fast.
This link is a newer model kit than mine and it only contains three bases. The seaming base is not included, but the rest of the bases are, including the angle base.Each base slides onto the end of the motor and locks in place with a lever to tighten it to the motor. https://www.carid.com/dewalt/laminat...ent=4181287608
This kit has the identical bases to mine, but the motor has a rounded top and mine is more flat. It's the model that they came out with after I bought mine and the seaming base is not included ( I have only used my seaming base once in 10 years.)
Other brands may be available too, but I'm only familiar with the DeWalt.
Without a router, You could do the beveling with a flexible blade carpenters hand saw following the side of the boat carefully and trimming off the edge of the bottom at the angle of the side. Then use a rasp and sanding block to clean the cut up.
I can remember that my dad did it this way back when I was very young. But if I had to do it today I would go with a laminate trimmer and angle base using a bottom bearing flush trim bit and working with the boat upside down so the trimmer could ride the flat bottom and the bearing on the angled bit could ride along the boat side. An extension board on the router base would make the router more stable as it slid along the boat bottom.