Quick Keel Bolt Question

I am calculating the number and size of keel bolts I will need for a boat i'm designing. What i'm wondering is if I use say 3/4in bronze and I have threads cut into it on both ends, can I still consider it a 3/4 in bolt or should I calculate the area remaining at the valleys of the threads. I am using Nevins rule of 1 sq. in per 1500 lbs of ballast.

Thanks for the help.

 

Use the minor thread diameter. It's not so much the reduction in area, but the stress concentration at the thread root. So for 3/4-10 UNC 2A, minor dia is 0.6255; for 3/4-16 UNF 2A, minor dia is 0.6718.

Remember to have at least 5 threads or 1 diameter engaged. Torque depends on what the internal thread material is. Also you should figure out the SM of the bolting pattern and look at the moment; really important for narrow fin keels without flanges.

 

Thanks, thats what I suspected, but its good to be reassured. Well written reply, thanks so much.

Cody

 

this is normal to use the minor dia, plus a safety factor for the stress concetration, for bolts in tension. if the bolt is in shear than you use the full diameter assuming the full diameter is at the mating/shear interface. On a keel you possibly have both shear and tension, the one that dominates determines the size and number of bolts.