There are several articles in the archives that explain the process of making a repair to damage to the Unibond hull of a Boston Whaler boat. I recommend reading these:
Repairing Hull Damage the Whaler Wayby Taylor Clark
INSTRUCTIONS -- HULL PATCH KITSby the Boston Whaler Company, c.1994
From your photo-image, it looks like there is an indentation in the hull surface surrounding the area where the keel extrusion has been broken. You should repair this indented area and make it fair with the rest of the hull. The small extrusion of the keel will be a straightforward repair. Because this area is on the hull bottom and will not be seen in most situations, you can forego the careful matching of the color of the final top coat resin (or gel coat) to the existing hull color. Typically a base white gel coat resin can be tinted with some acrylic paint pigments from an art supply shop and a reasonably close match made in this manner, instead of buying expensive gel coat in small quantities from a boutique supplier that offers OEM color matching.
For more on using acrylic pigments to tint gel coat resin, see a third article on Boston Whaler boat hull repair at
The Epoxy CureThe hull bottom of your project boat appears to have a very old coating of anti-fouling paint. If you don't plant to remove all the anti-fouling paint, and plan to apply a new top coat of anti-fouling paint to the hull bottom, then there really is no concern about color matching the repair area to the existing hull color, as it will all be under a new coat of anti-fouling paint.