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Zinc anode on TC255 aluminum motor bracket

 
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NoCats



Joined: 09 Dec 2021
Posts: 9
City/Region: Whidbey Island
State or Province: WA
C-Dory Year: 2019
C-Dory Model: 255 Tomcat
Vessel Name: No Cats
PostPosted: Mon Jan 17, 2022 3:33 pm    Post subject: Zinc anode on TC255 aluminum motor bracket Reply with quote

New to us TC255 with Honda 150s. The boat has been in CA for the past 18 months and during the survey before we brought it back up to WA we found some electrolysis of the sponson drain plug screws (as in gone) and the transducer screws. The external anodes on the outboards also show marked wear and need replacing. There is also some bubbling of the paint on the aluminum bracket near the waterline. There is some bottom paint left, but it definitely needs replacing. I don't know what was applied and the PO didn't know as he only owned the boat a short while before re-selling it.

Is electrolysis with these aluminum brackets an issue? Should I have a zinc anode on that bracket in addition to the outboard anodes? The boat is going to mostly live in salt water (Puget Sound). I am going to be applying a copper-free bottom paint (Interlux Micron CF. Too cold right now for Pettit Hydrocoat) so that should remove one metal from the mix. If folks are putting an anode on this bracket where is the best place for it?

Thanks as always for the great information the group provides.

J.M. Kiel
No Cats 2019 TC255

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2019 TomCat 255 No Cats
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gulfcoast john



Joined: 14 Dec 2012
Posts: 989
City/Region: PENSACOLA
State or Province: FL
C-Dory Year: 2010
C-Dory Model: 255 Tomcat
Vessel Name: Cat O' Mine
Photos: CAT O' MINE
PostPosted: Mon Jan 17, 2022 7:35 pm    Post subject: Reply with quote

Greetings J.M.

As you know, it’s a boat, so it’s ALWAYS something! But nothing worrisome.

I recently decided to replace the bottompaint on the aluminum bracket since it never lasts as long as that on the sponsons. I’m told that’s because copper is much more effective but of course can’t be used on an aluminum bracket. I had some spots with paint flaking off and tiny starburst zigzags of bare aluminum. I scraped the paint off with a pro scraper down to what was left of the barrier coat of Interlux 2000 (PO had the cans from the dealer). Sanded, cleaned then immediately applied self etching aluminum primer. Here’s the pic after that:



Then two coats Interprotect 2000 epoxy then 2 coats Pettitt Eco.

Starting at the bottom of the sponson (not bracket), note the drain and ducer screws are just drilled into the fiberglass hull (at least mine were). This is another ‘re-bedding’ job; note the length of the old screws, drill out an oversize hole, dental pick out any wet foam (likely none) and fill with x. My x is West Systems Six10 thickened epoxy cartridges, because it self mixes, can be ‘squirted’ in there, no waste (another self mix tube is $2) and it’s the easiest and most expensive. You’ll find many other x choices if you search ‘re bedding hardware.’

I’ve been told SS should not be used underwater (but what’s your propshaft made of?) and if the drain housing is bronze the screws should be bronze. Even Jamestown Distributors might not have that. Hope Bob will weigh in here. I used SS and check or replace them every season.

The external anodes on the engines, if like mine, are drilled into the engine and have an upside down handle appearance. I replace them with every annual service no matter how they ‘look.’ To check the remaining ‘mass’ (think bones with osteoporosis) you’d have to remove and weigh them, not wait until they look ‘half as big’ as when new. If I wait more than one season, the SS bolts get frozen in there and break off. Although the engine is bolted onto the bracket, there will be plastic spacers there as well as where the underwater portions of the bracket are bolted to the transom with big SS bolts. Bottom line, those engine anodes provide zero protection for the aluminum bracket.

If you don’t know the history for sure, I’d go ahead and replace the engine cavitation plate anodes as well.

So yes, the engine bracket should have it’s own anode protection. Mine is a Pooder (cheaper than Armstrong). It came with a 3 inch round CM-3 that fits in the hole pictured to the right. Put a bead of your fav adhesive sealant (I like Boatlife) in a circle on the top and bottom parts to keep water out of the hole and tighten the hex nut. This is much easier with two people with vinyl gloves…one sticks the bolt end up through the hole, the other spins down the other half of the clam shell from the upper access plate. This is another annual change out so don’t use 3M5200. I called the Pooder factory for this advice.

I also had some paint bubbling and flaking on the upper part of the bracket about five years ago. The experts pronounced it not galvanic corrosion, just normal paint behavior. Especially for paint that had behavioral issues to begin with. I had it stripped and re-done with a primer and non-slip paint for $800.

I recently noted minimal paint bubbling around the screw-on deck plates. I just chiseled off the bubbles, sanded, cleaned and immediately touched up with Rustoleum gloss white for metal (mixing up small batches of Interprotect 2000 epoxy is a pain). I just ordered Beckson replacement deck plates, since I don’t expect any O-ring to last 12 years when it gets submerged under 2 inches of saltwater while coming off plane. Here again we have SS screws into the aluminum in salt air and often under salt water. What could possibly go wrong?

Also, the aluminum boarding rail will not be the exact composition of the aluminum bracket and is secured with more SS bolts into the aluminum.

Lastly, the bracket drain plug was a ⅛” NPT iron pipe plug. I put Tufgel on all these and hope for the best. I just found ⅛ NPT aluminum plugs on Amazon but at $30 I doubt it’s worth it.

Hope this is helpful!

John

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2010 Tom Cat 255, Cat O' Mine
Yamaha F150, LXF150
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rogerbum



Joined: 21 Nov 2004
Posts: 5922
City/Region: Kenmore
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 255 Tomcat
Vessel Name: Meant to be
Photos: SeaDNA
PostPosted: Mon Jan 17, 2022 9:49 pm    Post subject: Re: Zinc anode on TC255 aluminum motor bracket Reply with quote

NoCats wrote:
New to us TC255 with Honda 150s. The boat has been in CA for the past 18 months and during the survey before we brought it back up to WA we found some electrolysis of the sponson drain plug screws (as in gone) and the transducer screws. The external anodes on the outboards also show marked wear and need replacing. There is also some bubbling of the paint on the aluminum bracket near the waterline. There is some bottom paint left, but it definitely needs replacing. I don't know what was applied and the PO didn't know as he only owned the boat a short while before re-selling it.

Is electrolysis with these aluminum brackets an issue? Should I have a zinc anode on that bracket in addition to the outboard anodes? The boat is going to mostly live in salt water (Puget Sound). I am going to be applying a copper-free bottom paint (Interlux Micron CF. Too cold right now for Pettit Hydrocoat) so that should remove one metal from the mix. If folks are putting an anode on this bracket where is the best place for it?

Thanks as always for the great information the group provides.

J.M. Kiel
No Cats 2019 TC255

You should have anodes (the zincs appropriate for aluminum) on the bracket. My TC255 has had them since I bought it and they get regularly replaced. Last year (or maybe the year before - I forget with COVID as it's all a blur), I also dealt with some corrosion where the SS rails were bolted to the bracket. I wound up taking the rails off, sanding the bracket down to fresh aluminum, painting it with an appropriate primer and then painting it white (with sand for the non-skid). I then isolated the rails from the bracket with silicone gaskets and I isolated the SS bolts with nylon inserts and delrin washers. Also, if I recall, the plugs on my bracket are PCV plugs as it's a standard pipe thread. I definitely wouldn't use brass plugs in the aluminum bracket.

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thataway



Joined: 02 Nov 2003
Posts: 20778
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Tue Jan 18, 2022 12:28 pm    Post subject: Reply with quote

The reality is that the Tom Cat 255 is going to have mixed metals on the motor bracket. You have the aluminum of the bracket/tank. (The bracket on each side behind the twin hulls had a tank, where the engine is bolted to the bracket and the bracket is bolted thru the transom of each hull.) The aluminum alloy on the outboard motor is likely different than the bracket's aluminum alloy. There are going to be SS (316 probably) which hold the motor onto the bracket. The props are often a different alloy of SS. There is a SS shaft on the lower unit, and bronze is used for thrust washers and prop nuts. Then you have the SS hand rails attach to the bracket.

As for prop shafts they are often a SS alloy. Aquamet 22 is a very common inboard shaft which is high in chromium and nickel. But most inboard props are bronze, and there are "zincs" on the shaft.

"Zincs" can run a number of types of alloys: Real zinc alloys, Aluminum alloys and Magnesium alloys. The magnesium are for fresh water only. Aluminum can be used in brackish and salt water. Zinc alloys for salt water. Each of these alloys should be formulated to specific Military specs. These specs keep the "zinc" from becoming "Passivated" where the surface film blocks the effectiveness of the zinc.

Zincs must be in full metal contact with the metal they are protecting. This metal should be clean and bright in the area of contact.
Outboards and I/O drives should be out of the water when in the slip. There should be a large anode on the outboard bracket (which will still be in the water, even though the lower unit/leg is out of the water.

Also remember many of our outboards have internal zincs. I would want all of my "zincs" to match if possible.

Quote:
I’ve been told SS should not be used underwater (but what’s your propshaft made of?) and if the drain housing is bronze the screws should be bronze. Even Jamestown Distributors might not have that. Hope Bob will weigh in here. I used SS and check or replace them every season.


The reality is that there will be many metals, including SS under water. Many rudder shafts are SS. You want to have as resistant allow as possible for the SS. 316 or 316L are the most commonly used alloys of SS for salt water resistance. If possible when you source any SS on the boat 316 is advisable. Although 304 is also corrosion resistant, the 316 is best for our uses. Thru hulls should be bronze, especially below the water line. (I know that some use Marelon plastic [Dupont Zytel 70G13L – BK 13% glass-filled carbon blacked 6/6 nylon] and in recent years it has held up well. Early on there were some failures.). Also all thru hulls should have a backing plate, and under certain circumstances should also be bolted thru the hull, backing plate and fitting--typical 3 bolts--which should be metal which is comparable with the thru hull.

Another metal which one rarely hears of is Monel metal; Screws, bolts, and even sheets is available in both 400 and 500 alloys. For the most part on our recreational boats the Cu/Ni alloy of the 400 works well. The "brass" screws have a lot of tin and are to be avoided. There are alloys of bronze which which are also fairly corrosion resistant. I know of boats which had Monel metal fuel tanks, and fastenings which are over 80 years old.

John gives excellent advice. The reality is that our boats come from the factory without sealing of the core--and potential issues. I'll have to admit that any moisture in the cores of the boats where I have replaced the drain plug, and then removed any core, the water intrusion has been minimal. I would think that if you use Monel metal for the screws, and epoxy plugs for the screws (as part of the plug for the drain) that you will have very long life from the screws and the drain fittings.

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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL
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NoCats



Joined: 09 Dec 2021
Posts: 9
City/Region: Whidbey Island
State or Province: WA
C-Dory Year: 2019
C-Dory Model: 255 Tomcat
Vessel Name: No Cats
PostPosted: Tue Jan 18, 2022 7:59 pm    Post subject: Reply with quote

As always thanks for the great advice. Looks like my worklist prior to splash just got a bit longer. I also think the call that I planned to make to Pooder just got higher on my list.

J.M.
No Cats 2019 TC255
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