Well, I'll take a stab at this...in my non-technical way..and then let other more knowledgeable...technical folks weigh in.
Yes, lightness has to do with displacement
and ballast, but I think it also refers to methods of construction. ( you can have heavy boats that are not built well and visa versa )
Are the bulkheads fitted into a mold
or are they glassed in supported and act as a stiffner to the hull
. How is the deck
attached to the hull
..are the ends turned down and in glued and bolted through? There are many people here that can speak to the best construction methods. What is the deck core
material? other material selections....Steel vs Plastic ports
My simplified thought process..(open to criticism ) is that there are 3 main types of vessels that I see in say the 35-37 foot range..And I think they are designed and built to the markets they serve
Those that are coastal cruisers but that are not best suited to long offshore
passages. I might include Catalinas and Hunters in this category. Those that are good coastal cruisers and may also be well suited to some offshore
passages....I might include Sabres, Tartans et al. in this group...then there are those that are worthy blue water
boats..I might incude Gozzards, Shannons, Passports, Island Packets...et al. in this group...
I know I've only named a few in each category and there are dozens more in each category..others will weigh in on ....but what distinguishes each group in my mind has more to do with methods of construction and material/hardware selections ..than weight, though granted they often seem to go hand in hand.
Does that mean that All Passport owners go offshore...or that no Catalina
has ever made it to Bermuda
...or that a Tartan can't circumnavigate ..no...But ...I've been in 10 foot seas in a Catalina
and watched the water
out of it's mount and nearly bust out of it's locker...I've been in 12-14 foot seas for 2 days in my boat and someone pulled the interior
overhead grab rail loose other than that..things held together well..still I wasn't thrilled at that development..
Other things to consider offshore, tankage, cockpit
designs..etc. Comfort for living aboard
at the dock
, is different from comfort at sea...often we make some compromises...
Hope that helps a little..