Like Smac999 said, any 3-wire cable will do. However, there are some advantages on using 'real' Seatalk1 cable. First, the Seatalk1 cable is shielded, which helps to avoid data loss due to external noise
. Second, is is very hard to obtain a 3-wire cable with the right color coding of te wires:
red-12 Volt plus
Blank shielding-common minus
There comes a day when you are glad you used the correct wire colors!