View Full Version : bronze screws and 316 bolts
08-12-2001, 08:14 AM
I am reframing a 30' schooner. White Oak 1 1/2" x 2 " ribs, 1 " pitch pine planking, what diameter should the screws be and how long. The screws will be silicon bronze. To fasten the frames to the floor timbers I need 8" bolts, Bronze is to expensive in this application. As these bolts will be on the inside of the hull will 316 stainless be ok, or will the electrolysis demon attack. Also stainless fastners to thru bolt the rudder? would these be alright in the water with the bronze? If I am way off course please steer me back. Thanks
08-12-2001, 09:15 AM
If the job is worth doing she deserves the bronze.....
08-12-2001, 09:25 AM
Buy bronze rod and thread it yourself, or copper and rivit. Stay away from stainless as it will severely limit the lifespan of your work. False economy.
08-12-2001, 10:46 AM
The rule is roughly, "No stainless anywhere under the waterline." It's likely to develop crevice corrosion (rust) in short order. Okay for internal work, except in the bilges.
Also, don't mistake brass for bronze. Brass is okay for things like locker hinges or door handles or cabin lamps, but can dezincify quite quickly, resulting in complete loss of integrity.
[This message has been edited by Mike Field (edited 08-12-2001).]
Check out Dave Gerr's book "The Elements of Boat Strength" or Kinney's "Skene's Elements of Yacht Design" for info on what size of fasteners to use. I agree with paladinsfo and Mike Field re: material, but if silicon bronze floor bolts are too pricey (and the schooner is a "worky" not a "yachty" type), consider using hot-dip galvanized bolts a la older working schooners - they will have a 20-year lifespan if properly bedded and seated.
Because of price I make bronze bolts by putting thread on rod stock and running nuts and washers on both ends, alternately copper rod peened over washers/burrs forms a superior bolt.
Sorry Dale, I see you already said that.
Go with bronze, make your own bolts from round stock like Dale suggests. Get a copy of Stewarts Boat Building Manual if you don't already have one. Lots of good basic information in it, including fasteners. Good luck.
08-12-2001, 04:41 PM
Go with the bronze, even if it hurts. I'm currently reframing a 37 footer that had an interesting mix of stainless, bronze, and galvanized fastenings used below the waterline over the years. The damage from electrolosis is amazing. I'm having to replace strut and rudder blocking, many floors and ribs and much of the transom.
Although I'd only read about it and never seen it, the crevice corrosion in the stainless bolts, etc. is very real, 1/4" bolts hollowed out like straws and screws that look like they were dipped in acid. So much for stainless being the fastener of choice!
Considering how much work is required to make it all right again, and the major disruption it has caused in my using and enjoying the boat, I'll never skimp on materials for any thing I build or repair again, and I've been known to be a bit cheap. It ain't worth it.
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