A question for the engineers. Assuming a bulb weight of about 5 lbs., what would be the minimum size fasteners to use to hold the bulb to the keel and the keel to the boat?
Thanks
Don
Vancouver Island
Mine are about 3/16" stainless at the top and bottom of the keel. My bulb only weighs 4#. Most bulbs I have seen are not removable. Mine are.
Don
I have tried 4-40 SS hardware to hold IOM keels, but by the time you add the weight of the large washer it takes to keep the 4-40 nut from digging through the deck, you might as well go with something bigger. I now use whatever size threaded SS rod that I can fit into the keel head without breeching either keel skin. Drill the hole in the appropriate place on the top of the keel a bit large, and set the threaded rod in epoxy. Most of the keels I work on have a balsa core, and putting thin epoxy in the hole allows it to seep into the surrounding balsa core, creating a water tight solid point of anchor. Make sure the threaded rod is where you want it, because you will never get it out!
Precision Park West:
Higher Technology Racing Solutions
“Beyond Hyperbole”
Don
Sorry, a bit hasty on the posting button - I also use this technique for attaching the bulb to the fin. Drill a hole in the bottom of the bulb slot and put a countersink on the bottom to house a SS aircraft nut (nylock) for a secure fit that allows the bulb to be removed for travel. I recently did a bulb using Mike Eldred’s technique of drilling 2 hole athwartships across the bulb (through the bottom of the keel) and cross pinning them together with 0.25 Ti rods. Plug the holes with Bondo or clay. He says it works well, and also allows bulb removal.
I have broken a bunch of small drills trying to poke holes in bulbs. My solution is: 1) use large drills & fasteners. The weight savings are insignificant and the hassle factor is too high with small fasteners. 2) Clean the bit a lot. 3) Freeze the lead before you drill it - makes it a bit less gummy.
Precision Park West:
Higher Technology Racing Solutions
“Beyond Hyperbole”
One last note - before you set the threaded rod into the epoxy filled hole, file a bunch of abrasions into the threads that will be in the epoxy. This keeps the rod from unthreading.
Precision Park West:
Higher Technology Racing Solutions
“Beyond Hyperbole”
Thanks guys! I’ve been using #10 stainless ready rod and just ran out,so I thought I might try a little thinner. If you’ve have used #4 with no breakage problems I should be good for #6 or #8. The nut is not a problem as I make my own knurled aluminum knobs. I use much the same method as you except I bend the rod a bit and cut a slot in the keel to match. I then inlay some thin ply on either side just to add a little strength. Maybe a little overkill if you’ve had no problems with just roughing up the threads.
Thanks
Don
Vancouver Island