Originally Posted by erickbou
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.