Don't dismiss this so rapidly. You can easily find SS 316 theaded coupling with design loads of over 1100lbs each. In my case the keel is 4100lbs and has 6 or 7 bolts, plus the epoxy filling in the keel to hull joint, plus the fiberglass seal on the outside. Both of these reducing the stress on the bolts. I think that it can be a simple and elegant solution if implemented correctly.
For me it remains a viable option if the original bolt is not corroded at the base.
At 1100 lbs strength (is that max tensile or yield strength?) that would give you a total strength of either 6600 or 7700 lbs, depending on 6 or 7 bolts total. That is less than 2 to 1 safety margin at best and only 1.5 to 1 on the low end.
For comparison, when I redid the keel fastenings on my 43, I thought the 10 X 3/4" bolts looked a little skimpy so I did some research to reassure myself - even though the 1/2 corroded originals held it on with no leaks.
Here are the numbers for my boat;
- Keel weighs 10,200 lbs
- Static load on each bolt - 1020 lbs
- Total tensile strength of 10 bolts - 289,000 lbs- a 28 to 1 safety margin
- Yield strength - 136,000 lbs - a 13 to 1 safety margin
- Max loading at 90 degrees of heel (knockdown) 3 times the keel weight or 30,000 lbs in this case. Dynamic loadings are not calculable as far as I know but are well in excess of the highest of these numbers - falling off a wave for example.
These figures are FAR in excess of the safety margins provided by your figures and they are for a set of bolts that looked skimpy to my eye and are smaller than would be spec'd for a comparable boat now - I've seen lots of 35 footers with 1" bolts.
I'd strongly recommend you do some more research before going out in deep water with your life depending on those couplings.