Strength Exercises for Sailing

I am currently writing a strength and conditioning program for a varsity sailing team. It is the first time I have ever worked with this type of “strength” sport. Sailors have to hold isometric contractions of the quads while hanging over the side of the boat for long periods of time. We are currently using wall squats, slow eccentric dbell squats, isometric abdominal holds and some shoulder work.
However bodyweight must be carefully controlled to make weight classes.Anyone have any ideas or exercises for not only increasing isometric hip flexor and abdominal strength with the body reclined horizontally (approx knee angle of 180* and hip angle 180*).
Thanks y’all.