BLIND BOLTS HOLDING RUDDER TO TRANSOM

[skip1930]

bronze bushings, bronze bolts.
Aluminum gudgeon is a non-player as their ought to be zero influence on the bronze on bronze hardware.
The bronze just sits in the aluminum. Nothing moving.

skip.

[Shawn]

bronze bushings, bronze bolts, aluminum gudgeon....

Shawn

[Bob23]

A bit off topic, but a great book on corrosion is "The Boatowners Guide to Corrosion" by Everett Collier. Wow! Sounds really interesting, right? It is, if you really want to understand galvanic corrosion, stray current, dissimilar metals, etc. This is something that us salt water guys need to understand.  If you're an amateur engineering geek like me, you'll eat this stuff up. But then again, I enjoy reading my Tundra technical manuals, too. Weird, huh.
Bob23

[Shawn]

"Aluminum gudgeon is a non-player as their ought to be zero influence on the bronze on bronze hardware."

No, it won't effect the bronze on bronze. What will happen is the aluminum surrounding the bronze will slowly corrode away and turn to dust as it is the loser in that combination. The reason I didn't reuse my old gudgeon is because on the bottom leg the aluminum had corroded away to the point that you could see the outside of the bronze bushing. It was bad, maybe 1/4 of the material gone working its way up from the bottom. I'll see if I have any pictures saved of it, I chucked the gudgeon itself.

In fresh water what you are suggesting is fine, not in salt water.

Shawn

[Bob23]

I had the same exact problem, Shawn. I ordered and installed a new one which now is showing signs of the same corrosion. I've installed 3 small zincs this year to try and slow the corrosion down...We'll see how well it works.
Bob23

[skip1930]

OK, as the aluminum 'powders away' over twenty years so every couple of years re~drill out and insert a larger bronze bushing.
Eventually a new aluminum casting will be needed.
Or weld up a new one out of black iron or ss steel, or a phenolic.

"Water is the universal solvent", given enough time water dissolves everything, including rock, leaving 'salt' behind, glass, and plastic.

skip.

[Bob23]

Skip:
   The aluminum can deteriorate in as little as 2 years...if it was 20 years, that would be no problem. Forget the problem of dissimilar metals, even just the salt water vs aluminum battle is a tough one to win. Factor in bronze, stainless and aluminum and salt water, and you have a corrosion war of epic proportions! Ok, maybe not quite that bad, but I've seen my brand new gudgeon deteriorate in less than 2 years...that's why I use zincs now.
Bob23

[CADMAN]

The hatch on my cp d16cb looks like this: http://www.defender.com/product.jsp?path=-1|118|48504&id=49161 -- I'm not certain of the size. I would think you could check Hutchins parts list for size (or for that matter, possibly order them from Hutchins if the shipping wouldn't kill the pricing). If you interested, at a minimum, I'm certain Hutchins would provide the size and mounting location.

If you go to http://www.com-pacyachts.com/trailerable-sloops/legacy-photogallery.html and look closely at the transom photo, under the tiller you can see where Hutchins installs them.

Hi doug,
Unfortunately my ISP (British Telecom) cannot locate either the Hutchins website or your own, so I have not been able to see how others have done the hatch. I am considering two approaches: 1. Drill four holes through the cockpit inner skin to correspond with the four screws through the rudder bracket. These would give access for a socket spanner with extension bar to the nuts, and 2. cut a 6" dia round hole with a trapanneing cutter through the cockpit inner skin then to blank this off with a varnished wooden blanking plate secured with say four self tapping screws into the grp.
I am not keen on ctting holes through the skin so would welcome any comments or advice before I start
Thanks in advance, Barrie

[CADMAN]

Further to my previous post, I was browsing the shelves at my local Chandler and came across the ideal screw off access hatch for access to the the transom bolts. Amazingly it was only £3.25 ( about $7) but it did require cutting a 4.5" dia hole through the cockpit skin. Luckily I have a trepanning tool for cutting large holes and this worked superbly-a very clean cut with no chipping of the gel coat. It only took about 15mins to cut the hole and install the hatch.It took anothe 15mins to remove the self lock nuts from the Rudder Bracket screws and bingo, the bracket came off very easily- Job done !
Thank you all very much for your helpfull suggestions. Im sure I will be back as I continue the restoration of my CP 16 Raven. Barrie

[doug]

great -- glad it worked

[skip1930]

So I'm reading in the BOAT US Magazine about galvanic action between two metals and here is a link to the galvanic series table, www.engineersedge.com/galvanic_capatability.htm depicting Anodic Index [ V ]. The two metals should be NO FURTHER APART 0.15v.

For example a Brass & Bronze fixture with a Stainless type 316 screw in it.  The Brass Bronze 0.40 and the 316 ss is 0.50 so 0.10 apart. Close enough.

Everything is hunky dory.  But the ss is harder then the soft brass, not a good idea to preserve the threads.

skip.

[Shawn]

"NO FURTHER APART 0.15v.

The Brass Bronze 0.40 and the 316 ss is 0.50 so 0.10 apart.

Everything is hunky dory. "

No further apart doesn't mean no corrosion, just that it will be slower.

Per your own link bronze and aluminum will be up to 0.6 apart. According to that link that is too far apart even in a controlled environment let along a salt environment.

The way to completely avoid corrosion is to not have dissimilar metals in electrical contact. A Delrin bushing gets rid of the aluminum on brass on stainless combo and has aluminum in isolation and stainless in isolation.

Shawn