I put a similar 1cm2 hole into my bow just below the waterline a few months back. I filled it with an underwater 2 part epoxy
(I always keep a few sticks of this onboard) and it has held in very well for the few months until I haul out
(actually tomorrow) for a proper repair. I occasionally dive down (well a quick breath hold!) for an inspection
to ensure its all holding together. When you apply the u/w epoxy
you need do it ASAP after the damaged has occurred, prior to any build up of marine
growth which will impede the bonding.
We have a Lagoon
450 with where the fwd hull
is poly resin/epoxy below the WL.