Following my original question, my boat will travel at max speed of 25 knots, the hull is made of Grp. My contact with your technical dept suggests a zinc phosphate undercoat, whilst this is for steel and timber. Is the latter appropriate for GRP ?. The fishing boat is used in salt water only. Please make a recommendation on my requirement for both primer and topcoat for below waterline, before I place my order direct with you. Thank you.