Sorry for the late response and sorry to hear of your keel bolt issue too, but... Why not find out how bad the leak is first before imagining the worst?
Which keel bolt is it? Is the water rusty? Do we assume it is salt water? Let's do some more investigation first.
I know it sounds obvious, and I'm sure you've tasted that it's salt water. But with a grid system like our Benny's use, the rare fresh water leak just might find its way into anything down there, like maybe inside the sealed grid down to the bilge and slowly leak out near the square bolt washer? In fact a couple of my keel bolts are actually bolted thru the grid's lip that is bonded to the hull. So with that out of the way (Ok, it's salt)... "IF" it is fresh let me know if you have those pesky leaky integral fresh water tanks like I have on my 473 -- BOTH of mine leak fresh water into the bilge! (I've been putting off cutting one open to have a look).
IF it is the forward keel bolt or the aft most keel bolt it might mean at some point in time the keel hit something, but not so much as to effect all the bolts or maybe not enough to damage the grid. If it's a middle keel bolt, my bet is it's a flaw in the bedding process during assembly. I'd pull the offending keel bolt first to get an idea whether the leak is a gusher, or a simple weeping. Also look to see if there is even slight crevice pitting of the stainless bolt caused over time from oxygen starvation and the salt water. That might give you a clue how long this has been going on.
If it is simply weeping, I'd dry out the hole as best as possible and using some easy to remove bedding compound (that cures underwater, like BoatLife), put a heavy dab over the leak and the bolt in the same area, and re-torque the keel bolt -- buying you some time for the next haul out -- but we're not taking years here -- okay? (check the torque on the rest of the bolts as long as you've got your hands on that huge torque wrench). Also, I would do a serious and very close up inspection of the grid frame under the floorboards that is bonded to your hull -- even looking for the most minute hairline cracks along the hull to grid joints. You can get to a lot of the grid's bonded area around the keel but not all of it up the sides -- I tend to think less important up the sides anyway. If here are ANY hairline cracks this becomes a whole new issue.
If it turns out to be a gusher have a small tube of BoatLIfe ready, apply a bead around the bolt and put it back in. This will need to be addressed with a haul out. It could be anything from a serious flaw in the cast iron to a crack or somehow a flaw in the hulls fiberglass keel stub -- or even something minor that isn't even visible and might be solved just by grinding the "smile" line a wee bit deeper around the keel stub and laying in a heavy bead of 5200 . This may be the result of something as simple as not enough bedding used in that top area of the keel when the keel was first attached.
MAYBE SOMETHING ELSE BEFORE YOU PUT THAT BOLT BACK IN? SOME MAY LAUGH:
This last trick I have never used. But here it is. While I had the keel bolt out, I'd get a pipe fitting with a hose barb on it (with tapered pipe threads) that was sized so it would cut its own threads into the fiberglass keel bolt hole but not so oversize as to damage the the glass -- just a nice tight fit so the threads did not go below the keel to hull joint. (We are going to be testing that hull to keel "seam"). So I'd thread the pipe fitting into the hole very tight and connecting my bicycle pump with a hose barb adaptor I'd pump 30 or 40 PSI of air into the hole, while my dear friend Luis, who owns an excellent dive service, would be swimming around the keel stub with his GoPro making a video of where the air bubbles were coming out. Pretty funny huh? Don't laugh... Also note: If you can push air out that hole in the keel stub? You just might be able to push, or better a term -- inject -- some thinned epoxy out that hole too, which your diver could also verify.
At any rate I would do some easy investigating topside before heading to the boat yard and dropping 4 digits of cash on any haul out or keel dropping. And a little investigation will only cost you the rental of that monstrous torque wrench and socket which maybe the boat yard might loan you anyway. Plus the cost of some BoatLife, a pipe fitting, and your local dive service to at least 'see' where the water is coming in.
However this ends up, good luck to you and please let us all know how it goes
Martin
s/v Lucky Spin
2006 B473