from under the boat seat?
Can you dismantle the seat and the underseat compartment as a unit and remove it from the boat? If so, then you can then move the assembly to your desired location and then work on removing the bees from the seat/compartment assembly.
A bee vaccume would be good to have.
If the above is not an option you will have to get under the seat in the compartment and start cutting the comb loose from it's attachment points.
The comb will be attached, hopefully only at the top, or, hanging down and free from other attaching points on the side of the comb. If the comb is hanging in rows that would be ideal.
Things to consider about the comb. There should be some comb with possibly all honey. Some comb could be empty or partially empty. Some of the comb should have brood, honey and pollen and there you should encounter the most bees. If there are the number of bees that you state there should be lotsa comb for sure. I doubt that a novice can accurately judge bee numbers in feral colonies though. Furthermore once the comb cutting begins the honey smell will waft in the air and there will be more bees than you can imagine buzzin around from other feral or kept hives nearby.
The empty comb is easy, cut it away and place in a bucket for melting later.
The comb filled and capped with honey should be carefully handled and placed in some sort of pan high enough for the comb to stand against the side for your consumption or feeding the bees later. Avoid crushing the honey filled combs as much as posible and keep the container covered or robbing and bees feeding will drive you nuts
Once you are at the point of cutting out the comb the bees will be really really a-buzzin round ya. Those bees will fly around like in a swarm if they are as numerous as you state, and, if you have never done this before you will probably be distracted and uncomfortable with your situation. Believe me, it will be distracting if you are not well protected and stung.
If you think you can master the technique then you must take some of the comb with brood, pollen and honey and place same into an open frame and somehow make it stand up and stay in place with heavy duty rubber bands slid around the frame. If the comb is long a deep frame is recommended and you cut and trim to fit snug. If the comb is short a medium frame will serve better.
As you cut the comb away the bees will travel away and towards the remaining comb or into some hiding places, if available, to get away. Some, or, maybe many of the bees will stay with the brood comb and
if you are careful, they can be placed in the box with the comb you have inserted in the open frames.
You have to cut ALL the comb and fill as many frames as possible with it, preferably brood, pollen and honey filled.
Now for trapping the bees and placing them into the box??? after all the comb is cut out. That will depend on the working area and the under the seat location you describe does not appear to be very roomy, but a combination of brushing some of the bees into a container or scooping them with a wide scraper and pouring them into the hive box will start the tranfer. If you can place the box, with bottom and cover, near the colony area more than likely the remainding bees will march in the box if you knock the bees down to a floor or flat surface. Probably hard to do in a boat in my minds eye. Failing that. just leave the box overnite in the boat and see what happens. The bees will congregate/cluster around the queen so be careful when brushing. If you can find and capture the queen, place her in the box and your bee removal will more than likely succeed.
I have, I hope, provided some techniques that I have used that have worked for me. I do know boats but have not done any removals from them. I have removed bees from pop-up campers though.
As far as stings go, well you and/or your clothes will be stung and that cannot be avoided IMO. You could try spraying a light spritz of sugar water on the area, comb and bees which could help calm things. Smoke has not always worked for me when busting up a feral colony.
You will kill seemingly many bees and that can't be avoided so
If you are squeamish about killin bees then this project is not for you.