The Difference Between Boat & Cable Wakeboards
In most cases boat wakeboards will have a Polyurethane core construction and be considerably reinforced around the centre of the board to create stiffness. The reason for this is so the board can maintain its shape and 'pop' over time for longevity.
Why can't I use a boat board at the cable park?
There is nothing to stop you from doing it, though in most cases if you looking at tackling obstacles, this can significantly reduce the life of your board. Most boat boards aren't equipped with grind bases and so can wear through the base quite quick. Another issue is that boat boards are considerably stiffer than most cable models, this leads to harder impact on obstacles and tougher landings
Cable wakeboards are reinforced in a different way, with most cable boards have a wood or part wood core, to allow for natural flex and give on obstacles and kickers. Another key feature of Cable boards are sintered or 'grind' bases to protect them from hitting obstacles and urethane or ABS sidewalls to protect from any unwanted hits and reduce the chance of your board splitting.
Why can't i use a cable board behind the boat?
Once again there is nothing from stopping you and it is much more feasible than a boat board at the cable park. The reasons why it's not ideal is that wood cores in most cases create more flex and so don't generate the same amount of 'pop' or vertical height and carry as boat boards. Another effect is wood core boards tend to want to flatten out over time, with speeds being faster behind boat than cable this accelerates the process and can slightly reduce the life of your cable board
There is definitely models that fall mid way between the 2 categories, but over the years they have become less and less common with most major brands ruling them out as viable models. This isn't to make you buy 2 boards, but more so because you would be sacrificing something that would benefit your boat riding to gain a slightly better cable feel, whether it be stiffness, grind base or sidewalls.