View Full Version : Rotten screws
05-16-2005, 08:15 AM
The brass screws that held the brass rub strip on my Cat'spaw disolved below the waterline. Just the screws, not the strip. Not above the waterline.... The stupid "How to build a cat'spaw dinghy" book said to use brass... So now that this is reality, and I'm going to have to shift the rub strip a bit so the new screws don't bump into the chunks of old screw... what to use? Is it just because they were soft hardware store brass? Should I use bronze instead? Can I find #2 bronze screws? Should I use bronze nails?
05-16-2005, 09:02 AM
How many of these screws are below the waterline in your stem nosing? Can't be many and you can't generally see them, tight?
#2 seems jewelry-box tiny to me. Rather than unbed and move the strip, I'd be looking to drill the bad ones out in place for #4 bronze. My smallest tapered pilot is a #6, so I'd use whatever wiregage I had below an 8th drilled along side your broken shafts followed by a 45-degree countersink just enough to get the screw head flush. Dipped in poly sealant before driving, they shouldn't leak water into your stem.
05-16-2005, 09:07 AM
What Bob said. Number 2 is teeny-weeny. Was that a typo? Number 8 or 10 seems more likely.
Common brass cannot be used in saltwater. It's an alloy of copper and zinc, which sets up internal galvanic action, causing the zinc to rapidly disintegrate. Silicon bronze is a good choice.
It doesn't matter where you bought the screws, the brass screws did what brass does around salt water. It dezincifies. Brass has two kinds of crystals, zinc rich and copper rich, and they have different electromotive potential. In other words, electrolysis.
Intime the zinc rich crystals will be corroded away leaving the copper rich. The wood screw will look red and will be full of little tiny holes where the zinc rich crystals used to be. Sometimes you can snap the screws in your fingers.
Use bronze. That said, massive brass fittings like cleats, or bullet blocks don't seem to be affected.
05-16-2005, 05:20 PM
If you take the strip off and turn it end for end the new screw holes might not interfere with the old ones.
05-17-2005, 08:51 AM
The plans called for #2 brass screws in a 1/2" wide brass half oval rub strip. That's what I used. I didn't use bedding compound in this application because the instruction manual didn't say it needed doing. (actually, the only place it said to use bedding compound was in the keel rabbet, and between the rubrail and sheer strake. I used it in a few other places, like the plank/transom connection...) I guess I'll get out the flat bar, and mini-pry, and try to pull the rest of the strip off. Those ring shank babies don't like to budge, and the above waterline screws are so crusty they'll strip out before I get a quarter turn...
05-17-2005, 09:09 AM
...didn't use bedding compound in this application... Bingo. I don't think it woulda saved pissant #2's....but it didn't help.
I'd still drill them out for #4's or even #6's. Using a jeweler's screwdriver to remove a nosing sounds too sissy for me. ;)
05-17-2005, 09:14 AM
OK..... Where do I find 16 #4x5/8" bronze screws? I really don't want to buy a box of 100 if I don't need to..... :rolleyes:
05-17-2005, 09:18 AM
Why not a box, as you'll use them again I'm sure? 12 bucks?
Won't Jamestown break down a box for ya?
Fisheries Supply in Seattle will, and I use them for ones and twos like that, although that's an expensive way to go. So will Tacoma Screw, although they only have square drive. Tacoma carries excellent screws, probably from Pacific Fastener....I've never had a bad one with them.
Am sure there's plenty of East Coast sources.
[ 05-17-2005, 09:22 AM: Message edited by: Bob Smalser ]
05-17-2005, 09:32 AM
As usual, you're right. I will eventually use them all for something. It's just my Yankee stinginess rearing it's ugly head...
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