So you have a Euro Powered Boat so you only require a 3 core
connection, the next thing to determine is what amps your boat is pulling with the 220Vac connection.
the standard euro amps are 16amps 220Vac which equates to a standard 30amp 125Vac USA connection. Your Cat is not small so i would say it runs on a 32A 220Vac system so this can run a 50amp 125Vac USA connection but you would need to check how much load you are pulling as you could make the dock
breaker trip by using too many amps.
You would need to confirm the size of cables
on the back of your shorepower inlet to confirm they are rated to carry the 125V rating, the cable connecting your shorepower inlet to your isolation transformer inside the boat should be 6AWG, if it is below this then you are leaving yourself open to a fire hazard.
The cable used for shorepower cords have a special PVC jacket on the outside which is UV, temperature, oil
, salt water
resistant to name a few, this is why shorepower cables
are so expensive. if you use normal cable for marine
purposes then you will see the cable will degrade over time and the PVC will start to crack and crumble which creates a safety
Saying that your price
quoted for marine
cable seems extremely expensive for what you need. Depending if the cable is for mounting as a permanent fixture or must be removable will determine your best and cheapest solution.