Can epoxy get wet i need to fix rowboat?

Any of the good brand epoxy repair pastes designed for smaller holes and cracks in an exterior/marine situation will be fine - as long as the area is dried well to start with so moisture is not trapped within. Holes that you could pass a biro through and larger probably need some glass fibre to maintain the original hull strength, the big repairs require fairing out at an angle of 12:1 the depth of the repair, and a series of glass patches mounted to keep the hull at the same thickness and strength. In all cases epoxy is superior to polyester. A protective coating or two of flow coat or two pack finish is required to finish the repair, none of the resin groups are able to withstand UV or continuous immersion in water without degrading to some extent, and as any solvents used have molecules far larger than a water molecule water entry will slowly occur if no surface protection is applied. It is critical that any damage that gets through the gelcoat on a GRP boat be attended to immediately. The glass fibre material is extremely hydroscopic, and water will be pumped deep into the structure of the boat by capillary action - causing repairs that get left to multiply to affect many times the area of the initial damage.