Boat structures 101

[Bushwacker]

Great thread, Dave! I agree it definitely deserves to be a "sticky" because of the valuable info it contains!

I also bought Dave Gerr's book based on your recommendations, and I agree it's a very comprehensive book. I'm still wading through it, but I've run a few calculations on his recommended Scantling Numbers and compared them to what SeaCraft used in the early 4-stringer 20' hulls. Although I believe Moesly arrived at his structure by trial and error, including some very creative use of thin laminates and brittle resin in prototypes to find the high stress locations, he ended up with laminate thicknesses that are very close to Gerr's recommendations! The tall stringers are probably even more massive than needed, but he certainly did plenty of proof testing in the extremely rough offshore powerboat races, and none of his boats ever broke up, so I'd be very careful about changing anything he designed!

Friz, thanks for adding the material property info on the various core materials! Many people are quick to condemn balsa, but it actually has better shear strength than most of the foams, and better water resistance than plywood, so I consider it one of the best core materials in terms of strength/weight ratio! You just have to know how to use it and properly seal and backfill any holes you put in it! It also tends to absorb resin better than most foams, so getting a good bond between it and the outer skins should be a bit easier than with most other core materials.

One good reference I'd like to add to the discussion of cores are the extensive articles on "Cores and Structural Issues" by Dave Pascoe. As an experienced surveyor, he's seen first hand what works and what doesn't, and his articles provide some dramatic examples of problems with poor laminate bonds and water intrusion that can occur when cores are not properly installed!