Now I understand how you are launching your boat(s). For some reason I had it in my head you were "sliding" the boats down the embanckment, guiding it with the wires and unhooking them once in the water. [X(] I've seen similar using two 1" pieces of webbing with lead weights sewn in at the half way point to make them sink below the boat. Either way, it's a lot of weight to hold up.
BTW, have you ever tried working with Sintra? it's a
PVC Foam board and glues very well with CA glue. It comes in 1, 2, 3 and 6 mm thicknesses and is flexible enough to work with around curves. I've used it once and like it well enough to use it on some other projects.
I like Mack products. Pricy but well worth it. Q-tips, why didn't I think of that? I just used twisted up paper towel. Learn something new every day.
Bob