I would doubt that the tongue weight of a boat the size and weight of the Zip with a 40 HP outboard would be more than 40 to 50lbs. Your total rig will most likely weigh about 800 to 850 lbs depending on your motor weight and gear. A class 1 hitch calls for a maximum tongue weight of 100 lbs. My 17 ft Larson with a 65 HP Sport Four has a tongue weight of about 55 lbs. Of course the total weight of boat motor and trailer is somewhere around 1500 lbs. BTW my Squirt has a tongue weight of about 25 lbs and I have trailered it at 60 MPH through parts of the Adirondacks Mountains. It pulls straight and true with no noticeable sway or "fishtailing" even in a cross wind. The weight should be fairly balanced over the axle with a reasonable amount forward to rest on your hitch. Unless you plan to have a jack on your tongue you want it light enough to lift onto the hitch without getting a hernia.
Carpenter, I was stopped when I was about to post this to read your comment. I believe I guessed your total weight pretty close. I was also pretty close inmy calculation of your motor weight in my first comment. My Lark 35 is about 125 lbs.