Reply
 
Thread Tools Search this Thread Display Modes
 
Old 11-28-2023, 06:06 PM   #1
Veteran Member
 
City: Monterey, CA
Vessel Name: Scrimshaw
Vessel Model: 1990 GB 42 Classic
Join Date: Jan 2020
Posts: 56
Swim platform bonding

We just got hauled (South Puget Sound) and the yard noticed that our swim platform supports had corrosion around where they attach to the transom - EXACTLY the same as another GB in the yard (both GB 42CL late Ď80sí). According to the yard - the large zincs mounted on the transom are precisely to help with this - inside the rear lazerette the zincs and platform mounts are all bonded (independent of any other system). But they have no explanation for the corrosion - both boats are same harbor, different marinas.
Anyone solved this? Thoughts?

Pictures attached.
Attached Thumbnails
IMG_2973.jpg   IMG_2974.jpg  
jwag956 is offline   Reply With Quote
Old 11-28-2023, 06:37 PM   #2
Guru
 
mvweebles's Avatar
 
City: Saint Petersburg
Vessel Name: Weebles
Vessel Model: 1970 Willard 36 Trawler
Join Date: Mar 2019
Posts: 7,109
Question: are your swim step brackets bonded to the zinc anode? Should be.....

Peter
__________________
_______________________________________
Cruising our 1970 Willard 36 trawler from California to Florida
Join our Instagram page @MVWeebles to follow along
mvweebles is online now   Reply With Quote
Old 11-28-2023, 08:24 PM   #3
Moderator Emeritus
 
Comodave's Avatar
 
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 21,048
Either bond the brackets to the hull anodes or add individual anodes on each bracket. If the brackets are through bolted then just add a heavy green wire from the bolts to the hull anodes. On my swim platform extension that I added I put an anode on each bracket.
__________________
Boat Nut:
If you are one there is no explanation necessary.
If you arenít one, there is no explanation possible.
Comodave is offline   Reply With Quote
Old 11-28-2023, 08:26 PM   #4
Veteran Member
 
City: Monterey, CA
Vessel Name: Scrimshaw
Vessel Model: 1990 GB 42 Classic
Join Date: Jan 2020
Posts: 56
Thanks - as I mentioned - all the brackets are tied together inside the boat with the zincs.. (and nothing else - i.e. completely separate system/bonding than any of the other thru-hulls)
jwag956 is offline   Reply With Quote
Old 11-28-2023, 08:31 PM   #5
Moderator Emeritus
 
Comodave's Avatar
 
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 21,048
Quote:
Originally Posted by jwag956 View Post
Thanks - as I mentioned - all the brackets are tied together inside the boat with the zincs.. (and nothing else - i.e. completely separate system/bonding than any of the other thru-hulls)
When you say tied together inside with zincs, they should be wired together and then to the anode on the outside of the hull. Do you have a bonding system in the boat? All underwater metal should be either bonded or unbonded. If you bond some then you should bond all metals. Are you having any other corrosion issues? I prefer to have everything bonded and have adequate anodes on the hull. I would check to make sure the brackets are indeed connected to the anodes and actually have a good connection if they are connected. Break out the ohm meter and it should be 1 ohm or less between the brackets and the anodes.
__________________
Boat Nut:
If you are one there is no explanation necessary.
If you arenít one, there is no explanation possible.
Comodave is offline   Reply With Quote
Old 11-28-2023, 08:35 PM   #6
Veteran Member
 
City: Monterey, CA
Vessel Name: Scrimshaw
Vessel Model: 1990 GB 42 Classic
Join Date: Jan 2020
Posts: 56
Yes - sorry - inside the rear lazerette the support bolts go through as do the anode bolts. Those are all connected together.
Yes - the boat has all engine, thru-hulls, shafts, etc, all bonded.
The most interesting thing here is that the identical corrosion pattern is on 2 boats - same design/era, same harbor...
jwag956 is offline   Reply With Quote
Old 11-28-2023, 10:31 PM   #7
Moderator Emeritus
 
Comodave's Avatar
 
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 21,048
Ok, so they are connected but are the connections actually good? Put an ohm meter and make sure that there isnít more than 1 ohm resistance between them. Also it is preferred to have each connection make a home run and not to have them daisy chained together.
__________________
Boat Nut:
If you are one there is no explanation necessary.
If you arenít one, there is no explanation possible.
Comodave is offline   Reply With Quote
Old 11-29-2023, 07:33 AM   #8
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,064
I have been told and researched that too much zing can cause copper bottom paint "burn" around underwater protected metals.

The only way to tell for sure is to do a bonding system survey with a silver-chloride electrode or other methos to make sure you have not overzinced certain underwater fittings.

Research/Google silver-chloride electrode use/measurement.
psneeld is online now   Reply With Quote
Old 11-29-2023, 07:36 AM   #9
Veteran Member
 
Fleming's Avatar
 
City: Ft. Lauderdale
Join Date: Apr 2023
Posts: 48
You're overprotected, too much zinc for those small supports. That's not corrosion, that's "haloing" of the paint.

https://www.practical-sailor.com/blo...too-many-zincs

Edit: I was writing at the same time as psneeld
Fleming is offline   Reply With Quote
Old 11-29-2023, 07:53 AM   #10
Guru
 
mvweebles's Avatar
 
City: Saint Petersburg
Vessel Name: Weebles
Vessel Model: 1970 Willard 36 Trawler
Join Date: Mar 2019
Posts: 7,109
Will leave diagnosis to Fleming and Psneeld, but here is a silver-oxide reference electrode for $139 plus shipping from BoatZincs.com. not a lot of money but since it won't get used much, seems like something best purchases by a group of friends or a yacht club.

https://boatzincs.com/categories/too...electrode.html

Peter
__________________
_______________________________________
Cruising our 1970 Willard 36 trawler from California to Florida
Join our Instagram page @MVWeebles to follow along
mvweebles is online now   Reply With Quote
Old 11-29-2023, 09:43 AM   #11
Guru
 
Portage_Bay's Avatar
 
City: Coupeville Wa.
Vessel Name: Pacific Myst
Vessel Model: West Bay 4500
Join Date: Oct 2015
Posts: 2,380
Suggest starting with Comodave's test. Easy to do and hopefully solves the problem. Given that your problem seems to be limited to the swim step supports it's a good chance he's right. A bonding system like any system on the boat requires maintenance.

Then if corrosion is still a problem as psneeld suggests a full bonding survey. That's the only way to really figure out what's happening.

Flemming may be correct you are over zinced burning the bottom paint. It happens. On my last boat at survey several areas showed looking like yours. The surveyor called out over zinced. The problem continued and turned out to be a near complete failure of the bonding system.
Quote:
Originally Posted by Comodave View Post
Ok, so they are connected but are the connections actually good? Put an ohm meter and make sure that there isnít more than 1 ohm resistance between them. Also it is preferred to have each connection make a home run and not to have them daisy chained together.
Quote:
Originally Posted by psneeld View Post
I have been told and researched that too much zing can cause copper bottom paint "burn" around underwater protected metals.

The only way to tell for sure is to do a bonding system survey with a silver-chloride electrode or other methos to make sure you have not overzinced certain underwater fittings.

Research/Google silver-chloride electrode use/measurement.
Quote:
Originally Posted by Fleming View Post
You're overprotected, too much zinc for those small supports. That's not corrosion, that's "haloing" of the paint.

https://www.practical-sailor.com/blo...too-many-zincs

Edit: I was writing at the same time as psneeld
__________________
Some things are worth doing simply because they are worth doing.
Portage_Bay is online now   Reply With Quote
Old 11-29-2023, 10:43 AM   #12
Guru
 
SteveK's Avatar
 
City: Gulf Islands, BC Canada
Vessel Name: Sea Sanctuary
Vessel Model: Bayliner 4588
Join Date: Jul 2019
Posts: 4,915
Is this the first year this has occurred to your boat and to the others. All things being the same over the years then I would look for another reason this occurred like stray AC current.
__________________
SteveK
You only need one working engine. That is why I have two.
Sea Sanctuary-new to me 1992 Bayliner 4588
SteveK is offline   Reply With Quote
Old 11-29-2023, 11:41 AM   #13
Guru
 
tiltrider1's Avatar
 
City: Seattle
Vessel Name: AZZURRA
Vessel Model: Ocean Alexander 54
Join Date: Aug 2017
Posts: 4,245
What was the bottom paint? 70% copper paints have a tendency to halo when over zinced. 55% copper paints are much less likely to halo.
tiltrider1 is offline   Reply With Quote
Old 11-29-2023, 12:47 PM   #14
Guru
 
porman's Avatar
 
City: Duvall, Wa. USA
Vessel Name: Beach Music II
Vessel Model: 2003 Mainship 430 Trawler
Join Date: Aug 2014
Posts: 1,039
The way I read post 4, he has two separate systems. One for the supports and anode, and another for the rest of the underwater metals. Shouldn't they all be bonded together?
porman is offline   Reply With Quote
Old 11-29-2023, 04:57 PM   #15
Veteran Member
 
Fleming's Avatar
 
City: Ft. Lauderdale
Join Date: Apr 2023
Posts: 48
Quote:
Originally Posted by porman View Post
The way I read post 4, he has two separate systems. One for the supports and anode, and another for the rest of the underwater metals. Shouldn't they all be bonded together?
That's the way I read it, and yes it should all be tied together to that big hull zinc. It's too much zinc for just the supports. It's not hurting anything to be overprotected except the paint.

What is protecting the through hulls if not that zinc?
Fleming is offline   Reply With Quote
Old 11-29-2023, 10:23 PM   #16
Guru
 
fgarriso's Avatar
 
City: .
Vessel Name: GOTCHA
Vessel Model: Hatteras 58 LRC
Join Date: Jun 2019
Posts: 1,097
Bond everything to everything! Add more zincs everywhere!
__________________
Captain F. Lee - R.P.E.
USCG 200 GT Master
fgarriso is offline   Reply With Quote
Old 11-29-2023, 11:34 PM   #17
Guru
 
tiltrider1's Avatar
 
City: Seattle
Vessel Name: AZZURRA
Vessel Model: Ocean Alexander 54
Join Date: Aug 2017
Posts: 4,245
I make a point to test continuity of all items that are bonded. You would be surprised how often you will find no continuity.
tiltrider1 is offline   Reply With Quote
Old 11-29-2023, 11:35 PM   #18
Veteran Member
 
City: Monterey, CA
Vessel Name: Scrimshaw
Vessel Model: 1990 GB 42 Classic
Join Date: Jan 2020
Posts: 56
Thanks for all the input - looking back at the GB Bible - it implies that all the thru-hulls, engines, etc should all bond back to the transom zincs... so I got some bad info...

I have checked the transom zincs to swim platform resistance and all were at or around 0 - so those all seem to be bonded together - next up - start from first principles and check from engines to transom...
jwag956 is offline   Reply With Quote
Old 11-30-2023, 12:10 AM   #19
Guru
 
SteveK's Avatar
 
City: Gulf Islands, BC Canada
Vessel Name: Sea Sanctuary
Vessel Model: Bayliner 4588
Join Date: Jul 2019
Posts: 4,915
with boat out of water you can also check continuity from the outside since bonding should complete circuit. Zinc to all metal parts. Then last check zinc to engine block.
__________________
SteveK
You only need one working engine. That is why I have two.
Sea Sanctuary-new to me 1992 Bayliner 4588
SteveK is offline   Reply With Quote
Old 12-04-2023, 01:50 PM   #20
Senior Member
 
Duvie's Avatar
 
Join Date: Nov 2011
Posts: 339
I am of the do not bond camp. Galvanic corrosion requires two dissimilar metals to be connected together and submersed in the water. I don't see it being very likely that any other under water metal will be electrically connected to your swim step brackets unless they used stainless bolts to fasten a bronze bracket or vice versa.

When you bond you set up exactly what is needed for galvanic corrosion to occur and then use the zinc to protect it. Then if you have failures in your bonding system you can have set things up for galvanic corrosion to occur.

My guess on the current issue, as others mentioned above, is that it is over zinced. I think on wooden boats this can cause deterioration of the wood around under water metals also!
Duvie is offline   Reply With Quote
Reply

Tags
corrosion

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 06:34 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012