If your wires are in good condition, you don't need those spreader bars. They don't do anything other than make the wires routed neatly. If you are really worried about your spark plug wires arcing, run the engine at night sometime and look in the engine compartment and see if you see anything. If you don't, you don't have a problem. Autos have way more of a problem because the heat destroys the insulation. You don't have that problem with a boat.