Hull Pitting / Flowering

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AK7Buck
Posts: 14
Joined: Thu Sep 17, 2015 10:48 pm

Hull Pitting / Flowering

#1

Post by AK7Buck » Wed May 16, 2018 11:17 pm

Need Assistance on a 2525 Kingfisher. Summary:

- Boat has always been stored at my home when not in use; limited use for a 10 year old boat (400 hrs on motor).

- Have extensive flowering and pitting on the bottom outside hull of the boat; no pitting on inside hull. Last Fall, I used scotchbrite pads (course) to buff out the pits on outside of hull with angle grinder; Afterward, I acid etched with Zep. Thought I did a decent job at the time but also recognized that I did not get all of them out.

- This Spring (6 months later) the pitting returned. Either I did a very poor job buffing or the hull is corroding further. See pictures.

- I contacted local boat repair shop and asked if this was somehow caused by electrolysis and they said no, it was caused by the salt water in contact with the aluminum, which is why I have the pitting on the outside of the hull only and not on the inside of the hull. They said I did not sand enough to remove the pittings and recommended a more aggressive re-sanding (again with scotchbrite) to entirely remove pitting, again using an angle grinder. When asked if I could just re-sand and leave the hull unpainted, the repair shop said “no and without a primer and paint job, the pitting will return. They also said to not acid etch after re-sanding as it would contaminate the hull before its painted. After re-sanding, they recommend 2 coats of Interlux underwater aluminum primer and 2 coats of Interlux Trilux 33 paint.

Questions:
1) Does the repair shop’s recommendation seem reasonable? I know I need to have the hull re-sanded, but do I need to prime and paint to avoid the pitting coming back? After removing the pitting, do I need to acid etch again?
2) How good is Interlux as a primer and Interlux Trilux 33 as a paint? Is 2 coats of each sufficient?
3) Any other recommendations or thoughts on the cause of the pitting? I did acid etch earlier (2 years ago) without sanding, and it really appears to not had any effect.

Any insight would be appreciated. Thanks.
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kmorin
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Re: Hull Pitting / Flowering

#2

Post by kmorin » Fri May 18, 2018 6:39 pm

AK7
the buff job seems to have left different colors of sheet? From the pictures, but not looking at the boat myself so I can't be sure- I'd say the buffing was not uniformly deep enough into the mill scale and that a good amount of it remained?

Zep works best in higher concentrations, warmer metal and hot water added to acid to help activate the reaction- since the bottom's coloration is so mixe/splotchy/mixed ??? I'd say neither the buff job or the acid etch were done at levels that completely cleaned the metal?

I'm totally relying on the color images on the screen- and they may not tell me enough to make such a determination?

Image

here is an image of buffed/sanded/mechanically prepared 5086 alloy aluminum, note the uniform color?

Image

Here is a comparison; the cabin has been buffed and then white metal etched with acid. The tank along the forward, lower cabin bulkhead has only been buffed and there are color variations- the tank was etched prior to use.

AK, I'm using the variations in color to base these remarks upon.... If the color, in your posted images, is exaggerated by the camera images - or lighting for example? - THEN my remarks are not applicable. The images I provide do show what clean aluminum looks like when it is buffed completely (and incompletely) AND when it is etched properly.

Hope this reference help your work planning and boat maintenance?

Cheers,
Kevin Morin
Kenai, AK
kmorin

Chaps
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Re: Hull Pitting / Flowering

#3

Post by Chaps » Fri May 18, 2018 11:07 pm

Is the pitting/flowering both above and below the waterline? Show a couple of close-up pics of your transom anodes, trim tabs and engine mount brackets.
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AK7Buck
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Joined: Thu Sep 17, 2015 10:48 pm

Re: Hull Pitting / Flowering

#4

Post by AK7Buck » Sun May 20, 2018 11:12 am

Thank you for your responses.

The pitting is both above and below the water line.

I have applied 2 applications of zep, once a few years ago (but did not sand) and then again last Fall after I sanded. I don't think there is any question that I did not sand enough - no way did my hull look as clean and uniform as the pictures you provided, not even close. I am (or was) concerned about taking too much off. Not sure if this is really valid when using a course scotchbrite pad.

Additional pictures below. Thnx.
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One of two anodes welded to hull. Painted by manufacturer. There is open space behind anode - does not appear anode itself touches much if any of the hull, but the weld does. These are the original anodes installed in 2007.
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I have a barrier (Tef Gel) between the stainless trim tabs and the aluminum hull.
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Pic 11a.jpg
Anode on motor
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AK7Buck
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Joined: Thu Sep 17, 2015 10:48 pm

Re: Hull Pitting / Flowering

#5

Post by AK7Buck » Sun May 20, 2018 12:09 pm

To add:
1) There is no ground from the negative terminal on the batteries to the hull of the boat. I keep hearing conflicting information on this - some say absolutely not, other say absolutely yes.

2) I only charge the batteries when the boat is on the trailer and do not use a galvonic isolator.

kmorin
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Re: Hull Pitting / Flowering

#6

Post by kmorin » Mon May 21, 2018 12:44 am

AK7,
just a few notes from the images.
#1 the zincs (don't know alloy? might be a better alloy out there?) don't show excessive wear if they're original.
#2 the trim tabs don't show too much galvanic reaction to the surrounding transom mount- the edges of these would be reactive even if the flats are bedded- they could be passivated and have an anode - won't take a four pounder to help eliminate them from the equation
#3 the flowers aren't often stray current but can be a galvanic 'sign' if there are active trim tabs (SS is galvanic to aluminum) but you're don't show lots of action around their base/mounts
#4 With maroon 3M Scotchbrite (tm) you'd have to work pretty hard to get much metal off the hull with a rotary 4" grinder!
#5 the welding on this hull is nothing to write home about!! (Sheesh! I'm pushing 70 and cold manage that zinc tab weld a little cleaner than shown!)
#6 if there is mill scale remaining on the boat- regardless of what you've done to it (sand, buff, etch, sand blast, anything) then you will get flowers!
#7 there is no debate (conflicting opinions; Yes- but serious logical reasoned debate of the physics; No) about single point bonding DC Neg Bus to the hull. There is wide spread ignorance as there is about several points of building and maintaining- like mill scale! I say it has to go, none of any of my boats has the "flowering" but there are name builders- who's work shows on this Forum new, used and abused where the builder won't/didn't take off the mill scale. So you can "lead them to water but you can't make 'em drink." and their boats all show surface deterioration- even those with shark hide or Nyalac clear coats.

I guess the ABYC is not the 'last word' in boat electrical systems but for what its worth they do specify that all DC electrical systems' Neg Bus SHALL be connected to the metal hull in one location only.

I'd suggest you start with real clean up- mechanical or chemical, then see about cleaning the anodes' faces- there's lots of material left but they're somewhat covered in oxidation that could reduce their usefulness. I'd suggest you bond the engines starters Neg lug to the hull via a pencil sized copper lead, crush/crimped to the lugs, and soldered;then shrink wrapped and bolted with galvanized hot dip fasteners to the aluminum- the lugs can be silver or cadmium plated - over copper: this will bond the DC neg. Other wise you can bond at the DC neg terminals of the Neg Bus?

NOt sure if all that is useful info, but IMO it would all help- especially the details added to one another to eliminate potential problems as you use the boat.

Cheers,
Kevin Morin
Kenai, AK
kmorin

Chaps
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Re: Hull Pitting / Flowering

#7

Post by Chaps » Mon May 21, 2018 6:13 am

Strongly suggest you replace those zinc hull anodes with aluminum equivalents plus add aluminum rudder anodes to the stainless tabs. Also be sure the main engine anode is aluminum. Agree with Kevin the flowering and pitting has other factors encouraging the problem but getting your anode situation straightened out will help a lot. Your zinc hull anodes have been doing next to nothing for years because their galvanic potential is too close to the gp of your hull. Aluminum anodes are a little lower on the scale than zinc thus they will be more willing to sacrifice themselves. Additionally the stainless tabs attached to the hull are the other bad guys in all this, give them their own anodes so they have something else to satisfy their galvanic demand from besides your hull.
Last edited by Chaps on Tue May 22, 2018 2:36 am, edited 1 time in total.
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AK7Buck
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Re: Hull Pitting / Flowering

#8

Post by AK7Buck » Tue May 22, 2018 12:04 am

Thanks, your comments / input is much appreciated.

* Trim tabs have Tef Gel applied between tabs and hull. I also have zinc anodes on the trim tabs (see picture).

* I sanded last Sept (to a shiny aluminum) but the flowering came back after sitting all winter outside. Today, I re-sanded a small section to see how it would look – to a shiny aluminum color, but how do I know if I am sanding enough to get the mill scale off? The aluminum shines quickly and looks good, but if I inspect closely I will see very small pits left over.

* On grounding, is there an advantage to grounding the engine starter to the hull vs. from the negative battery terminal directly to the hull?

Plan of attack:
1) Will replace all anodes with aluminum;
2) Will create single ground to hull (battery or engine starter);
3) I will re-sand (scotchbrite) the hull in sections to see if it solves the problem. I have no problem being aggressive, but how do I know if I am getting the mill scale off?
4) When I re-sanded a small section this evening, I noticed deeper pitting – unlikely from mill scale (perhaps stray current)? Can I sand these pits out or do they need to be filled? There are not many of these. Thanks.
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Chaps
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Re: Hull Pitting / Flowering

#9

Post by Chaps » Tue May 22, 2018 9:14 am

Its an older aluminum boat that is showing the cosmetic effects of being setup wrong from the beginning though it appears that no significant damage has been done so why all the worry? Pitting due to galvanics will likely stop when you fix the anode situation. The ultimate solution if you want to go there (at least for the bottom) is to sandblast, prime with epoxy and apply non-copper bottom paint. Click on the link below my signature picture to see how that gets done.
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AK7Buck
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Re: Hull Pitting / Flowering

#10

Post by AK7Buck » Wed May 23, 2018 9:05 am

Thanks Chaps - and outstanding work on the hull painting!

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