From what I can determine, once a boat is on plane, it is primarily
the weight that determines fuel efficiency so a lighter weight boat
should give much better fuel economy.
BUT, as I have found with my Tolman which is very light for her size,
a lightweight boat is easily pushed around by a wave due to less
momentum. So, although you might consider a boat made from new
lightweight composites, would it be as seaworthy as a heavier one?
This is actually a practical consideration for me if I build a Tolman
Jumbo with slightly gretaer deadrise than the design. More deadrise
will make her pound less but will the lightweight make her less
seaworthy than similar heavier boats?