Foam Cored Fibreglass Boat Construction

We are all familiar with cored fibreglass construction as almost all decks in GRP boats are foam or balsa cored. Hence we will appreciate that they are pretty strong. Even when heavy objects get dropped on them they stand up pretty well in my experience. Also we know of the problems: delamination and absorption of moisture into some core materials where through fittings have not been adequately sealed.

In general there seems to have been resistance to using foam core construction methods in monohulls particularly below the waterline, which would appear to be largely unjustified.

A GRP foam cored hull construction of the same weight as a solid laminate is stronger and stiffer. Therefore a lighter hull of the same strength can be built using a foam core. Foam cored construction is reported to have better impact resistance than a solid laminate. Foam cored hulls also have better insulating and sound deadening properties.

Catamarans in particular benefit form the use of light weight construction methods. Catamaran and monohull builders alike are now building hulls that are entirely foam cored except in the way of keel fastenings and engine beds etc.

As with all construction methods, the quality of the construction goes a long way to ensuring the integrity and longevity of any given hull, along with using quality materials of the correct specification. Bonding between the skins and the core is crucial to success of this method. Increased use of building methods such as vacuum bagging have reduced construction costs and increased construction quality. Quality PVC core materials will not absorb moisture, however ingress of water due badly sealed skin fittings or minor hull damage would obviously be a problem, but is unlikely to be life threatening in the short term.

Any comments or experiences anyone.

References:-
David Pascoe

Foam Core Materials in the Marine Industry
by Trevor Gundberg, Composite Materials Engineer with DIAB Inc.