CONTINUOUSWAVE

I have a 1964 13-footer with spider cracks throughout the inside and bottom of the hull. I am working on my first restoration project and this is new to me. To get rid of all the cracks should I be:

--sanding and grinding through the gel coat , or
--using a dremel to widen them all and repair them (lots and lots of them), or
--prime over them?

I've seen varying opinions on this. I started grinding to the bare fiberglass on the inside of the bow, but I am have second thoughts now. I would rather fix holes and dents, prime and paint with the roll and tip method instead of re-gel coating the entire boat.

I also want to make sure [the hull] is watertight with the gel coat sanded off.

Any advice on how to proceed would be appreciated. I plan to use Interlux products.

On 53-year-old Boston Whaler boat hulls that have extensive cracking in the gel coat layer, I do not see any method of repair of individual cracks to be practical. It will be extraordinarily unlikely you could maintain the original gel coat layer and refurbish it, if there is extensive cracking.

You seem to have already decided to abandon the gel coat layer as the top coat of the hull and to repaint the hull with a new top coat. I don't see any reason to try to preserve the existing gel coat layer and repair the cracks individually. Grind and sand the cracks, and use some sort of fairing compound to smooth the surface. I don't have first hand experience with this, but based on being deluged with promotions from Jamestown Distributors for their TotalBoat TotalFair Epoxy Fairing Compound, that might be one choice to consider. See

TotalBoat TotalFair Epoxy Fairing Compound
http://www.totalboat.com/product/totalfair/

The gel coat layer was made from polyester resin and was not particularly impervious to water. However, if you sand most of it away, then the exposed laminate layers will certainly not be impervious to water, and some sort of protection must be added. You might consider using an epoxy paint to seal up the hull laminate, at least in the hull side and underwater portions.

In keeping with the TotalBoat line, you'd probably then use their TotalProtect Epoxy Barrier Coat Primer. See

TotalProtect Epoxy Barrier Coat Primer
http://www.totalboat.com/product/totalprotect/

At this point you would have a hull ready for the final top coats. There are many choices. TotalBoat has some paint to offer, too.

Wet Edge Topside Paint
http://www.totalboat.com/product/wet-edge/

There is a recorded presentation showing use of these products to refurbish a Boston Whaler boat at

Boston Whaler Crazing Repair
https://www.youtube.com/watch?v=pUOlWPvgLfQ

There are other options for fairing, primer, sealer, and top coat. For example, see SPECTRUM COLOR catalogue:

http://forum.spectrumcolor.com/mmspectrum/workingdocs/2015%20Catalog.pdf

Thank you for the information. I plan to grind the gel coat to either very thin or bare fiberglass on the inside of the hull. Then, use Interlux Epoxy Primer (several coats) followed by two coats of Interlux Perfection Epoxy Paint. Should this provide enough water resistance to the surface of if there a pre-primer step that I need to take? If so, what would that be? On the bottom I plan to follow the same process for the topside, but use anti-fouling bottom paint below the water line.

Epoxy resins are usually watertight.