New rudder needed

[McKee]

I've owned Pendragon for 11 years, and have been fighting electrolysis and corrosion on the rudder hardware the most recent 5 years. The rudder was coupled to the rudder post by a flange with 4 bolts, which now looks like a steel sponge. It's been less than 2 years since I had the bad steel cut out and replaced. I would have gone for bronze strapping and the like but the pocket book couldn't take it.

I'm running into trouble posting pics here so I'll just link them in...
http://picasaweb.google.com/mckeeb/Rudder#

The blue tape is the rough position for the straps, the thin vertical strap is for bonding purposes.

[willmarsh3]

http://lh6.ggpht.com/_810XQK5Hyao/SldI1KBeFII/AAAAAAAABJM/QDMdyhWxZsg/s512/IMG_0970.JPG Nice boat! I notice the multiple chines. Is she made of steel?

Is the rudder post steel? Bronze is much higher on the galvanic scale than steel. What is the rudder itself made of? You might be better off making the straps of steel. Then sandblast and coat with epoxy. Attach a zinc somewhere and you should be fine.

[McKee]

Apparently the other pics didn't make it. The boat is a Cornish Trader, the hull was built by Cornish Crabbers, and the rest was finished out by the previous owner. I converted the boat to a cutter, as the mizzen only existed to cause weather helm, and fouled sheets. She's glass, not steel, and I'm told that the designer built the first one out of ply.

The new rudder is fir. I chose to use stainless as the only corrosion problems were on the steel , not on either the stainless or the bronze. The rudder post is stainless and has been since the beginning. I intend to zinc the rudder straps. I completely agree that bronze would be better but I almost can't afford the repair as is, and its not optional. I could feel how loose the coupling was every time I put the helm down.

I did have a variety of professional come out and make a bunch of suggestions over the years, and I tried all of them, and no luck.

[willmarsh3]

Cornish crabbers are quite nice boats. I once looked at a 24 foot one that had quite a bit of room.

I think bronze would eat up stainless steel as it's higher than stainless on the galvanic scale. But then again there are countless propellers made of bronze on stainless shafts (including mine) that do fine with a zinc. My best guess is to weld stainless straps on quite stoutly of course and that should be the end of it.

Others may come along soon to offer other suggestions.

[McKee]

Welding everything together is the plan. The rudder will get it's own zinc, and I hope that's the end of the story.

[donald branscom]

You HAVE to have a zinks on your steel rudder.

Weld a rudder together with steel plate.
DO NOT USE BRONZE bolts! You cannot have copper or bronze next to steel because there is a 30 point difference between the two metals.

Use grade 8 steel bolts. I would not use stainless. That has other problems.
Anytime you use dissimilar metals you set up a battery so to speak.

Hope you have zinks on that boat.

BTW you can make a steel rudder by welding two steel plates together the shape you want. Just tack weld the two edges together untill you get the pipe between the two sheets. Then drive a steel pipe in between the two sheets to create a foil shape. Then fully weld the edges. Flatten the pipe to a wedge to get it started. Position the pipe near the leading edge of the rudder. About a 4th of the way back from the leading edge.
Use like a 1.5 inch diameter pipe . The rudder will lighter and less force on the fittings.
The just set the rudder on a large cardboard and trace the shape onto a steel plate to make the foil shape end pieces. Make sure there is good welding so no holes allow water or oxygen to get inside the rudder. If you want the correct NACA foil do not worry because water is 12 times more viscous than air, so the chart will not help that much. It will not be too fat.

The steel plates can be 1/8 to 3/16 inch thickness. For a 36 ft. boat the rudder would be 3/16 thickness with that foil shape.

Check out the book STEELAWAY.

[McKee]

I've always zinced the shaft, and in the last 5 years I've tried a variety of zinc/bonding options on the old rudder. I intend to zinc the rudder straps, the prop shaft and probably the shoe (as it will be insolated from the rudder shaft by a bushing) Perhaps I should better describe the new rudder...

I'm using doug fir for the blade, stainless steel for the shaft (same as the old shaft which had no evidence of carrosion), and stainless steel external straps welded to the shaft to connect the blade and shaft. The rudder is hung under the counter, and pivots at the upper end on a gland, and in a shoe at the base of the keel.

[donald branscom]

I've always zinced the shaft, and in the last 5 years I've tried a variety of zinc/bonding options on the old rudder. I intend to zinc the rudder straps, the prop shaft and probably the shoe (as it will be insolated from the rudder shaft by a bushing) Perhaps I should better describe the new rudder...

I'm using doug fir for the blade, stainless steel for the shaft (same as the old shaft which had no evidence of carrosion), and stainless steel external straps welded to the shaft to connect the blade and shaft. The rudder is hung under the counter, and pivots at the upper end on a gland, and in a shoe at the base of the keel.

Wait till you see what happens when you put steel or stainless next to wood!

BAD IDEA.

You need to make the entire rudder out of steel. Make sure you do not use too many zinks because you can end up making a battery.
On a boat like that just put one round or flat or teardrop shape zink on each side about 2 inches in diameter.

There are many great steel boatbuilders in the area that you live in.
Google Brent Swain and get excellent advice.

Do not use wood for a rudder on a steel boat.

[donald branscom]

OK...Now I see on your previous post that the boat is fiberglass NOT steel.

You could use almost any material for the rudder. BUT stainless does have corrosion problems ALSO.

Use 316 stainless below the waterline.

If the rudder has a metal pivot post do not weld transverse around that pipe.