why not external keel attachment?

[themotorman]

MY Columbia 28 keel bolts are dust or actually rust what were steel bolts and nuts. I am considering not adding more new bolts but adding external keel straps that will connect the lead to the main hull. It will look odd but I think effective, may be even add some hydrodynamic feature to the craft.
Opinions very welcomed. My calcs. show that 4 straps 316 stainless 3 inches wide and 1/8 thick will work using 4 bolts and nuts at each end. The ends that attach to the lead will be by bolts that go through the lead just above the bulge. Easy to examine unlike regular keel bolts !
If anyone is interested in this idea I am open to a direct email.

 

[Davidasailor26]

I’m no naval architect, but I’d be concerned about whether the hull could handle the weight and the other forces from a bouncing keel if it’s attached somewhere other than the original location. The bilge around the original bolts was probably designed to be strong enough for those forces, but the rest of the keel stub may not be.

The original bolts lasted what, 40 years? I’d replace them and put the design in the “not broken, don’t fix it” category.

 

[themotorman]

There is not much space to put new bolts in on a C28. I'd like to do this but drilling into lead is not easy and making sure the new bolts are really fixed into lead is not proven. The upper end of the straps were going to the upper part the hull near the deck attachment. This is at least 3/8 thick fiberglass so with backing plates should be plenty strong in shear. At the moment there is no gap as the rusted bolts and original glue are holding the lead on.

 

[dlochner]

The hull is not a uniform thickness. At the sheer the hull laminate will be fairly thin, maybe ¼" to ⅜" at the keel the hull will be as thick as the keel bolts. If you do as you propose, the bolts will rip out of the hull, the keel will fall off and you'll go swimming.

Replacing keel bolts is tricky, but it can be done. A new vertical hole has to be drilled then a horizontal hole is drilled to intercept the vertical hole. The bolt is replaced with a large washer and nut in the horizontal hole and tightened. Then the hole is fill with thickened epoxy and the keel faired. Doable, but requires a lot of precision work.

On a 50 year old boat that has little cash value, it may not be worth the time and effort.

 

[jssailem]

Welcome @themotorman. I found this site which tells us you have one of the 553 built and that there is detail about the keel bolts, their construction etc.

Columbia 28 Specifications

www.columbia-yachts.com

“553 C-28's were built from 1967 to 1975. There is no mention of any change from a C-28 to a C-28 MkII is indicated on the sheet.”​

​

I’m not a nautical engineer but I have some experiential knowledge about boat design and the types of stresses applied to the hull and keel sections. It is no simple thing to process the vectors and levels of force applied to a boats hull by water and the sail. what is easy to observe is the concentration of those forces at the point of junction between the mast base and the keel. You identify the shear force and conjecture or have calculated the ability of the hull to handle this force. But consider the addition of the thrusting force on the hull connections as the hull moves through the water over/through/beneath the waves. Add the complexity of the lift forces of the hull and keel simultaneously applied and the downward forces from the sails on the keel to enable the boat to move through the water.

The inquisitive mind in me says on a boat that could be 54 years old it might be an interesting experiment with many ways to fail. The practical side tells me that likely hood of failure is great.

If I am interested in sailing with this boat the most efficient path is to follow a way that bolts the keel to the stub that was designed to address the forces and stresses on the boat. @dlochner ’s suggested solution is a practical one utilizing average skills possessed by many sailors. This is not to say it will be an inexpensive endeavor and one that will require a fair number of hours. In the end I think it is a method likely to have success.

I will watch with interest which path you choose. Please share your experiences.

 

[themotorman]

thank you for your input. i know that the original steel bolts are no longer holding or at least making her unseaworthy. my choices are either do pocketed new bolts or lag bolts.
the pockected bolts have to staggered to avoid weakening the lead and the lag bolts might not adequately hold in the lead. I am getting a boatyard quote since she is in the yard. If not excessive for my budget ill let them proceed. if not i like the lagbolts combined with a structural 3M adhesive. This might prevent creep with the lead.
Putting out my idea for external support was to get your much valued input. FWI she is a 1968 build. Original bolts were galvanized steel AFAIK. It has been suggested that 316 stainless might last longer but some claim due to electrolytic action the galvanized might be better. There are alloys that are much better but finding bolts made with these alloys has proven impossible. Its an interesting challenge but otherwise the boat is great!

 

[jssailem]

Challenges are what makes sailors.

Try McMasters-Carr they have a large inventory. You might find what you seek.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[dlochner]

Putting out my idea for external support was to get your much valued input. FWI she is a 1968 build. Original bolts were galvanized steel AFAIK. It has been suggested that 316 stainless might last longer but some claim due to electrolytic action the galvanized might be better. There are alloys that are much better but finding bolts made with these alloys has proven impossible. Its an interesting challenge but otherwise the boat is great!

Lead is pretty inert and 316 bolts are pretty common in modern keels. The one issue with SS is crevice corrosion this occurs with SS when it is in oxygen depleted water. The SS needs oxygen to maintain its protective coating. Once oxygen is no longer available, the SS starts to corrode and pit. Often there visual inspection is the only way to know if it has started as there may not be any tell tale rust staining.

Monel Steel is less prone to crevice corrosion, however, it is considerably more expensive. Some folks have replaced SS nuts on the keelboats with Monel to prevent corrosion and because Monel is less prone to galling and cold welding which SS is prone to.

The problem with using lag bolts is the inability to tighten them as needed. Given that lead is soft it would be easy to over torque the bolts and strip the threads in the lead. Sooner or later the keel bolts will need to be re-torqued.

Another option, and this doesn't get cheaper, is to drop the keel, cut the bolts out, add the J-bolts, and fill with lead. Then reinstall the keel with lots of 5200 to hold it in place.

 

[Hunter216]

This is from the link @jssailem made above

So if the original bolts were lagged into the lead would it be feasible to drop the keel, exposing enough of the existing bolts to “unscrew” them from the lead?

 

[themotorman]

i tried to find hanger bolts as then i would have a threaded end to put a tightening nut on. they make hanger bolts but cant find any in long ones in 1/2" size. could thread the end of a standard lag bolt i guess ?
thanks guys for yr help.

 

[capta]

I'm sorry, but thanks for the laugh, I needed one today. You can take your straps to the top of the mast, but they won't be nearly as strong as the place that is designed and reinforced to hold the keel. No shortcuts here.