I am surprised that in such good wind, you had such little chop. That is a great video. You guys are good athletes, and that 1978 really flies.
1. Second the motion re a piece of bungee from one side of the dolphin striker (where it meets the hull) up through the lower parts of the diamond wires, across to the the other side of the dolphin striker. An upside down 'V', rigged in such a way that your jib sheets lie on TOP...then they won't get tangled in the base of the mast.
2. Tacking & the Jib - Teach your crew to kneel under the boom, facing forward, with one hand on the 'lazy' side of the jib sheet, the other hand on the 'busy' side of the jib sheet, spare jib sheet in front of him on the tramp. Keep the jib cleated until the H18 is through the eye of the wind, then release with one hand and pull to the new side with the other, such that the jib continues to 'draw' wind right across as it changes sides. Don't let it flap around like that. Takes practice.
Also, going upwind, you may want to 'scallop', depending on wind shifts. Read up on headers and lifters...
3. Downwind....work out if you want to sail 'wing on wing' or 'tack downwind'. The trick is to know the lake/river/ocean conditions where you are sailing. Often, broad reaching downwind, (the fastest point of sail), while it means that you travel further, you often travel faster so that your VMG is better. In other words, don't straight line your course, zig zag down, gybing at each zig or zag.
4. Weight distribution. As a general rule, sit as far forward as is safe for the conditions, so as to minimize drag on the stern of the hulls. You would also do better to 'focus' your/ your crew's weight in one spot. Not you at the back and him at front. Ask any H16 sailor about 'hobby horsing'. Ideal is you sitting on the lip of the hull, leaning back against the knees of the crew as they hike out.
5. The foot of your jib is fluttering a lot....how old is that jib?
6. Outhaul, downhaul and rotation adjustments are not critical....what you might find useful is a 5:1 downhaul, they are VERY nice to use.
Continue to sail like that and you'll win lots of trophies. Good winds!
1989 Hobie SX18 Sail # 1947
'Only two things are infinite, the universe, and human stupidity. But I'm not sure about the former.'