Fiberglass Boat Construction Part 3 Cores

Back to our discussion of fiberglass boat construction. Last time we looked at the various materials used in cored hull and deck construction. We learned that the most common materials are End Grain Balsa Wood and various types of Closed Cell Foam. The next question is, that since these materials are rigid and do not bend, how do boat builders manage to shape them into the compound curves necessary for hull and deck construction. Core materials are supplied in various configurations other than standard sheets. It can be supplied in narrow strips and small blocks attached to a scrim which is a thin flexible material that hold the blocks together and the small gaps between the blocks, called Kerfs allow the material to be shaped into both single and compound curves. Below is a diagram of core material showing the blocks, scrim and kerfs.

Core Close up1_Layout2

Here we can see a Balsa core material laminated into a boat hull. The kerfs are easily visible between the blocks.

This is a side view diagram of sandwich core construction as used in boat hull.

Cored GRP Hull2_Layout4

When performed correctly sandwich core construction can provide strong light structures but the trick here is to ensure that core materials are installed correctly. As we’ll see in future posts this has been somewhat of a problem for boat builders over the years.