TOPIC: redfish shark floor

i need some help with my redfish shark what thickness of balsa core should i put in. Also how do you fiberglass over it what type of mat needs to be used. And how should i repair the cracks and splits in the gelcoat one spot is about 3 or 4 ft long and about 1/2 to 3/4 inch high
thanks thad

Hi Tbergh,

I don't know what was originally in the Redfish floor, but typically 1/2" balsa core thickness will give a good amount of rigidity to a wide expanse like a hull bottom.

Make sure the bottom skin of the sandwich is prepped meticulously; remove 100% of all traces of the previous core and give the fiberglass surface some "tooth" with 60 grit paper.

Vacuum the surface and clean it with Acetone or denatured alcohol.

When bedding the new core, thicken the resin with a structural additive (cabosil, microballoons, etc..) until you get a spreadable paste.

Coat the hull and the balsa and lay it in place. When the core is fully in place, cover the surface with waxed paper and add evenly distributed weight over the whole surface. Let it cure for 24 hours.

Once cured, mix up more thickened resin and coat the top of the end grain balsa. Then wet out enough layers of glass to build the appropriate thickness.

With balsa as a core material, water intrusion is your biggest enemy. Balsa must be protected at all costs.

Use 1.5 oz mat for the first TWO layers, then add a layer of 6 oz cloth, then another layer of mat, then another layer of cloth, then TWO more layers of mat.

The mat isn't very strong by itself, but it's much more waterproof than the open weave of cloth. The cloth is the strength, the mat is the waterproof part.

You can use woven roving instead of cloth, but it adds a lot of weight which defeats the purpose of having a strong but lightweight cored hull, and woven roving won't conform to any but the most gradual of curves.

Use a resin roller to make sure there are no air bubbles and make sure the balsa is entirely encapsulated. Done well and methodically, it will last for a very long time if you don't start drilling holes into it.

Another option is a synthetic core material like rigid urethane foam or a honeycombed core like airex. Both are rot resistant, lightweight, and perfectly compatible with all resins.

The lay up procedure is the same regardless of the core material.

You can find more info here:

glassclownboats.com/CoredFiberglass.aspx