tube problem

hey. since around 2 weeks i have a speadboat with 50 hp 2 stroke. i bought a 2person tube. a friend had some wakeboard robe left he gave me. all went fine with 2 persons(only that the line broke all the time) so i thought lets buy a real tube robe. i bought a 1-3 person tube robe. 59 feet. but then when i give full power. it come out the water. and then going 2 take a little dive. then comes up again. the shorter i make the robe the less dive he takes. but i now have the robe at 19 feet and he stills do it

Have your rider lean back on the tube as far as they can. Should keep the nose out.