It was too late for my brain last night. If you want to wire yourself, buy a 50A 125/250 plug
50A 125/250V Male Plug | Marinco
The green wire gets connected to the green screw (that should also be labeled "G")
The white wire gets connected to the silver screw (that should be labeled "W")
The black wire gets wired to either of the gold screws (should be labeled "X" and "Y"). Doesn't really matter which one.
Then you'll have a 50A 125V cord able to plug into a 50A 125/250 outlet. If for some reason the cable you got is European coded then green or green/yellow is the same as green above, blue = white, brown = black.
That all presumes your boat is laid out for a 50A 125V connection and that is was the plug on the cord that was damaged. If it was the receptacle end then you'll need to replace both, and if your boat was intended for 125/250 then...
[Edit] we crossed typing paths. Buy both a 125/250 male plug end, a 50A 125V female end (if that was damaged) and a 50A 125V boat end plug and wire as above. [/Edit]