Go Back  The Hull Truth - Boating and Fishing Forum > BOATING FORUMS > The Boating Forum
Reload this Page >

Aluminum boat and dissimilar metals.

Notices
The Boating Forum

Aluminum boat and dissimilar metals.

Old 03-09-2017, 03:30 PM
  #1  
Senior Member
Thread Starter
 
Join Date: Feb 2016
Posts: 192
Received 9 Likes on 9 Posts
Default Aluminum boat and dissimilar metals.

So I recently purchased a new Xpress H24 Bay. Now, once I got it home and used it I found out the thru hull for the livewell was leaking. Took it to my local Xpress dealer and they changed it out to a brass thru hull. Now, I know some about metals but not a lot nor enough to know whether that is right or wrong. Any help?

Next question, when mounting/installing anything onto the boat do I need to use stainless hardware or track down aluminum?
Old 03-09-2017, 03:52 PM
  #2  
Admirals Club
 
ol guide's Avatar
 
Join Date: Mar 2012
Location: Baja Sur
Posts: 6,959
Received 1,189 Likes on 404 Posts
Default

The two metals are just too far apart on the galvanic scale. The farther apart metals are from one another on this scale, the more dissimilar they are and the more likely they are to corrode if connected. One will become anodic and the other cathodic. In this case, the aluminum will become the anode, and as most boaters understand, anodes dissolve in seawater. At least this is my understanding. If they are not in direct contact it should be fine i think
Old 03-09-2017, 03:54 PM
  #3  
Senior Member
 
trimnyc's Avatar
 
Join Date: Jul 2015
Location: Queens, NY
Posts: 3,347
Likes: 0
Received 130 Likes on 85 Posts
Default

http://www.clihouston.com/knowledge-...corrosion.html
Old 03-09-2017, 04:05 PM
  #4  
Senior Member
Thread Starter
 
Join Date: Feb 2016
Posts: 192
Received 9 Likes on 9 Posts
Default

Ok, so the thru hull that was just put in needs to be replaced if my understanding is correct. Just don't want to chance anything with a brand new boat. Would a stainless thru hull be better? Or should I stick with a plastic one. (Got away from plastic due to a brand new one already leaking)
Old 03-09-2017, 04:23 PM
  #5  
Admirals Club
 
ol guide's Avatar
 
Join Date: Mar 2012
Location: Baja Sur
Posts: 6,959
Received 1,189 Likes on 404 Posts
Default

Originally Posted by NCoutdoorsman90 View Post
Ok, so the thru hull that was just put in needs to be replaced if my understanding is correct. Just don't want to chance anything with a brand new boat. Would a stainless thru hull be better? Or should I stick with a plastic one. (Got away from plastic due to a brand new one already leaking)
i think if it is "isolated" from direct contact by some kind of other fitting it would be fine. id ask the guys who installed it. im betting they will shoot you straight
Old 03-09-2017, 04:29 PM
  #6  
Senior Member
 
Join Date: Jan 2011
Location: Pgh Pa
Posts: 16,210
Received 1,341 Likes on 1,011 Posts
Default

Forespar Marelon
http://www.forespar.com/
I don't think you will be able to isolate the bronze from the aluminum even with a gasket. You would need inserts for the bolts that secure it
Old 03-09-2017, 05:16 PM
  #7  
Senior Member
Thread Starter
 
Join Date: Feb 2016
Posts: 192
Received 9 Likes on 9 Posts
Default

I will have to give them a call tomorrow. Looking at what I can see is there is no gasket, but some 4200 or 5200 if I had to guess. Really just don't want trouble down the road with corrosion. What about mounting items inside the boat. Will stainless screws be ok for that?
Old 03-09-2017, 05:48 PM
  #8  
Senior Member
 
Join Date: Jan 2011
Location: Pgh Pa
Posts: 16,210
Received 1,341 Likes on 1,011 Posts
Default

Originally Posted by NCoutdoorsman90 View Post
I will have to give them a call tomorrow. Looking at what I can see is there is no gasket, but some 4200 or 5200 if I had to guess. Really just don't want trouble down the road with corrosion. What about mounting items inside the boat. Will stainless screws be ok for that?
Stainless against aluminum will cause corrosion also
Old 03-09-2017, 06:03 PM
  #9  
Senior Member
 
trimnyc's Avatar
 
Join Date: Jul 2015
Location: Queens, NY
Posts: 3,347
Likes: 0
Received 130 Likes on 85 Posts
Default

http://www.forespar.com/marelon-mari...plumbing.shtml
Old 03-09-2017, 06:39 PM
  #10  
Senior MemberCaptains Club Member
 
Join Date: Jun 2002
Location: Seattle, WA
Posts: 3,074
Likes: 0
Received 74 Likes on 55 Posts
Default

Xpress dealer should be drawn and quartered if they are installing bronze fittings
Old 03-09-2017, 07:04 PM
  #11  
Senior Member
Thread Starter
 
Join Date: Feb 2016
Posts: 192
Received 9 Likes on 9 Posts
Default

Originally Posted by Chaps View Post
Xpress dealer should be drawn and quartered if they are installing bronze fittings

I did ask for something better then plastic. (Cheap one that was installed) and came back with brass, didn't think about it much until I had it out the last time.
Old 03-09-2017, 07:24 PM
  #12  
Senior Member
 
Join Date: Mar 2016
Posts: 1,095
Received 97 Likes on 70 Posts
Default

Originally Posted by NCoutdoorsman90 View Post
I did ask for something better then plastic. (Cheap one that was installed) and came back with brass, didn't think about it much until I had it out the last time.
You were right to do so. Marelon is not plastic and it is the only through hull fitting that should be in an alloy boat. Its also not cheap, though it is a little cheaper than silicone bronze I think so incompetence is the reason not greed.

Either way tell them to get it swapped out. Bronze is going to rot to boat, just a matter of how fast.
Old 03-09-2017, 07:34 PM
  #13  
Senior Member
Thread Starter
 
Join Date: Feb 2016
Posts: 192
Received 9 Likes on 9 Posts
Default

I will definitely call them tomorrow and get it back in to get changed out. Can anyone recommend what fasteners to use to mount items to the boat? In example, battery switch, float switch for bilge, onboard charger? (Everything is being mounted to starboard then the starboard mounted to the boat)


Originally Posted by textured captain View Post
You were right to do so. Marelon is not plastic and it is the only through hull fitting that should be in an alloy boat. Its also not cheap, though it is a little cheaper than silicone bronze I think so incompetence is the reason not greed.

Either way tell them to get it swapped out. Bronze is going to rot to boat, just a matter of how fast.
Old 03-09-2017, 08:11 PM
  #14  
Senior Member
 
Join Date: Nov 2009
Location: Australia
Posts: 4,807
Received 534 Likes on 412 Posts
Default

Yes, get that bronze out of there ASAP! What idiots they were for even contemplating putting it in......

Alloy boats are incredibly popular here in Australia. Would outnumber GRP boats 3-1.

Ive only ever had alloy boats, starting in 1978. Current boat is an 18 footer.

Anything you need to attach with screws or bolts - only use high grade stainless steel (316 at least) and use a light coating of either tef-gel or lanoline grease between the alloy and the bolt/screw.

If you can, use a nylon washer under the head and nut on bolts as well.

An alternative fixing is alloy or monel rivets. Again, a little lanoline grease on them before they go in is advisable.

The above rules are burnt into everyones heads here who buy alloy boats.

Never ever let anything made of brass, copper, lead, mild steel or low grade stainless steel come into contact with the alloy.also be careul with some black rubber - high carbon rubber products are also BAD. Such as the black rubber gaskets often used under deck mounted rod holders.
Old 03-09-2017, 08:32 PM
  #15  
Senior Member
 
Join Date: Dec 2003
Location: NorCal
Posts: 3,144
Received 242 Likes on 162 Posts
Default

Unless they isolated the Bronze thru hull fitting from your hull it will cause galvanic corrosion of the aluminum. The bronze will act as the cathode and your boats bottom will be the anode and will suffer severe corrosion in short order.

Its not common to bother trying to isolate a bronze fitting on an aluminum hull, especially on a smaller boat. If this is what they did they should have discussed it with you first.
Old 03-09-2017, 08:43 PM
  #16  
Senior Member
 
Join Date: Feb 2015
Posts: 3,465
Likes: 0
Received 135 Likes on 111 Posts
Default Fittings on aluminum boat

Ol guide and Thalasso are correct that aluminum will corrode when in contact with most corrosion resistant metals but there are options. Forespar marelon non metallic through hulls rated for use below the water line work fine without fasteners when aluminum is prepped and fitting is properly bedded in high grade sealant. West Marine and other chandleries have good assortments of nylon cleats, plastic through hulls for both above and below water line use and other miscellaneous non metallic fittings that eliminate the potential for galvanic corrosion and you can source aluminum bolts, screws, nuts, rivets and washers from Fastenal and other specialty fastener suppliers.

Aluminum fasteners can break relatively easily under tension and especially shear force and sometimes stainless fittings and fasteners are the only/best corrosion resistant option to provide the strength required for the application (e.g. bow cleat, bow eye, etc.). I had a 1969 aluminum center console that required replacement of virtually all fittings after years of use in saltwater. I installed stainless bolts, washers and nylock nuts to mount nylon bow and stern cleats that replaced badly corroded chrome plated zinc types but I used neoprene and nylon washers to isolate the stainless washer from the aluminum hull and prevent galvanic corrosion. I also used stainless steel through bolts, nuts and washers with nylon and neoprene washers against the aluminum hull to replace failed 1/2" diameter structural aluminum rivets that joined the motor well to the stern. I could find only stainless through bolt bow eyes when the OEM aluminum eye failed so I installled a wood backer block inside the hull and bedded the outside eye plate in 5200 and waited 7 days for sealant to cure before tightening bow eye bolts to isolate stainless washers and plate from aluminum bow stem.

Nothing lasts forever in saltwater of course but all the fittings above were installed 15+ years ago and both the fittings and hull they are attached to still provide good service and show no serious signs of galvanic corrosion. Aluminum hulls are really no more difficult to fasten than fiberglass or wood (aluminum rivets are actually a lot easier where applicable) but require a little more planning and imagination and different hardware and techniques.

Last edited by LeakinLena; 03-10-2017 at 03:59 AM.
Old 03-09-2017, 09:26 PM
  #17  
Senior Member
 
Join Date: Oct 2006
Location: 46 N 125 W
Posts: 100
Received 3 Likes on 3 Posts
Default

Weld in a stand pipe and aluminum scoop, why worry about dissimilar metals at all?
Old 03-09-2017, 10:43 PM
  #18  
Admirals Club Admiral's Club Member
 
Join Date: Sep 2011
Posts: 3,071
Received 316 Likes on 181 Posts
Default

Originally Posted by textured captain View Post
You were right to do so. Marelon is not plastic and it is the only through hull fitting that should be in an alloy boat. Its also not cheap, though it is a little cheaper than silicone bronze I think so incompetence is the reason not greed.

Either way tell them to get it swapped out. Bronze is going to rot to boat, just a matter of how fast.
Stainless with marelon/plastic isolator
Old 03-10-2017, 08:17 AM
  #19  
Senior Member
Thread Starter
 
Join Date: Feb 2016
Posts: 192
Received 9 Likes on 9 Posts
Default

Wow, never knew all of the things that a aluminum boat needed different. Thank you all a ton for the information!
Old 03-10-2017, 09:21 AM
  #20  
Senior Member
 
Join Date: Feb 2015
Posts: 3,465
Likes: 0
Received 135 Likes on 111 Posts
Default Aluminum and dissimilar metals

Originally Posted by BadgerS View Post
Stainless with marelon/plastic isolator
Aluminum will act as anode to stainless and corrode through. Marelon through hull fittings are best option below the waterline.

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.