logo
Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error
2 Pages12>
Soda Blasted Hull + Minor Corrosion
Options View
Previous Topic Next Topic
pastelblack
#1 Posted : Thursday, January 06, 2011 5:27:56 AM(UTC)
pastelblack

Rank: Dedicated Tin Star

Groups: Member
Joined: 12/20/2007(UTC)
Posts: 49
Points: 147
Hey All – I have a question for the corrosion experts……sorry to be long here but wanted to include enough detail....Last spring we soda blasted the hull of our 26’ Marinette to bare aluminum and left it unpainted. When we pulled the boat there were several very specific and isolated areas where there were some of the white puffs indicating some corrosion. These areas were:

1) The point where the stainless shaft comes through the hull (phenolic bearing installed last year).
2) On the strut where the shaft goes thru the non-metallic bearing (phenolic bearing installed last year).
3) By the freshwater intake where there are bronze screens intake screens and bronze seacocks.

Although the corrosion is minor I would like to solve this once and for all. As I stated, the bearings that the rudder and prop shafts (both stainless) run through are phenolic. The engine is isolated completely. I have 8’ of mg anode on the boat, a mg anode on the rudder, but no anode on the prop shaft (never had one on there).
The two bronze intake screens (one is functional and the other was a smaller original equipment intake screen I kept in place if I decided to install a wash down pump in the future) are separated from the hull by rubber gasket, so I am not sure why there is corrosion around the screens. The bronze seacocks inside the hull are also isolated from the hull. I thought that they would have to touch the hull for there to be a problem.
As far as my home-made capac readings go, they were around 1.000 to 1.05 all summer. Then in the fall they really dropped for some reason to the mid 0.70s depending where you were in proximity to the anodes. There was a good bit of slim / growth accumulating on the anodes so I am thinking that may have been part of the issue. And the lake was cooling significantly.
My ideas to fix the problem around the intake would be to replace the seacocks and the strainers with Marelon. Good idea???
As far as the corrosion around the rudder shaft and the strut bearing I am not sure. Go to a stainless prop? I’d hate to go there. Do I need anodes on the shaft? Does the rudder shaft need to be grounded to something.
Overall the soda blasting was great. Easy, clean and looks really great. Kinda looks like a coast guard boat. Just hope someone can guide me with these last few corrosion issues.
Thanks Guys
Bob
Back to top
Sponsor
Please Register : To weed out spammers, new members may not post until approved. An email is usually sent after approval. This forum is for Marinette Owners and other aluminum boat boaters who wish to share boating information. Aluminum Roamer owners are also welcome. (Do not post content you do not have the right to post and mass (robots) posters are unwelcome. We also have a marine electronics page and lots of Chrysler Engine info. State by what permission you copy content and give credit properly.) The site is now fixed with some more Chrysler information. We have space for pictures on the new location. Use shinkpic to autochange size http://www.onthegosoft.com/sp_download.htm

Great Sites - http://www.marinette.com Marinette Company

http://web.me.com/dougmrose/Doug_Roses_Website/Welcome.html

http://fastjeff.tripod.com/ Repair Tricks and Techniques for Marinettes

http://www.greatlakesmarinetteclub.com/

PLEASE post in the appropriate folder. Please, do not post your actual email address in publicly readable websites. The first rule is be a class act.
Back to top  
jralbert
#2 Posted : Thursday, January 06, 2011 6:42:12 AM(UTC)
Rank: Administration

Groups: Admin, Administration
Joined: 12/4/2007(UTC)
Posts: 1,117
Points: 665

Was thanked: 12 time(s) in 12 post(s)
pastelblack wrote:
... Do I need anodes on the shaft? Does the rudder shaft need to be grounded to something.
Properly grounded, the shaft doesn't need an anode. Though some, me included, leave one on as a good luck charm. It has never shown wear.
On the marelon question, after reading all the stuff about it over the years, it's well-regarded and should hold up well over many years and certainly will not be part of any corrosion problems.
Joel Albert, Potomac MD
"Charlie B" - 1988 32' FBS
Twin 318's/FWC/16x15 nibral props
docked Deale, MD
Back to top
fastjeff
#3 Posted : Thursday, January 06, 2011 7:27:12 AM(UTC)
fastjeff

Rank: Administration

Medals: aluminum star: For Marinette Owners Everywhere above the call of duty

Groups: Admin2, Admin2, Admin, Administration, Member
Joined: 12/5/2007(UTC)
Posts: 3,133
Points: 5,732

Was thanked: 34 time(s) in 30 post(s)
I have to replace the shaft "zincs" on mine every few years, and that's in fresh water. Those bronze props need help!

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
Back to top
tundrarules
#4 Posted : Thursday, January 06, 2011 8:14:34 AM(UTC)
tundrarules

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 11/11/2009(UTC)
Posts: 411
Points: 413

Thanks: 22 times
Was thanked: 8 time(s) in 7 post(s)
We sure would like to see pics of your boat Bob. No paint should look cool.



1985 Marinette 29 Sedan bridge
Twin 318s, 660 hours
New Edelbrock 1409 carbs (working like a charm)
Original Electronic Ignition, Blaster 2 coils, 90 deg plug wire universal kit cut to fit
Raw water system
Freshwater always
Located Pickwick Lake, TN,MS,AL

RETRO BOATS ARE COOL

If the guys on this forum take their time to help you, have the courtesy to update your thread with the resolution.
Back to top
pfhlaw
#5 Posted : Friday, January 07, 2011 4:58:54 AM(UTC)
pfhlaw

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/10/2007(UTC)
Posts: 538
Points: 1,353

Thanks: 2 times
Was thanked: 8 time(s) in 8 post(s)
Just before launch last year I used a continuity meter to check all my bronze through hulls. I found one engine intake that was starting to ground to the hull. Had to remove it and re-install with a new gasket. If I had the chance, I would have replaced them all with marelon.
Peter
1981 32' sedan bridge
twin Chrysler 360 cu. in. 250 hp engines
Raw water cooled
Nimbus II
Home port: New Buffalo, MI
Back to top
jimski2
#6 Posted : Sunday, January 09, 2011 1:13:06 AM(UTC)
Rank: Top Rank Aluminum Star

Groups: Member
Joined: 11/3/2008(UTC)
Posts: 147
Points: 71

Was thanked: 3 time(s) in 3 post(s)
The USCG boats have their hull underwater painted. Somewhere on the "net" is their paint schedule.
Back to top
jimski2
#7 Posted : Sunday, January 09, 2011 1:26:06 AM(UTC)
Rank: Top Rank Aluminum Star

Groups: Member
Joined: 11/3/2008(UTC)
Posts: 147
Points: 71

Was thanked: 3 time(s) in 3 post(s)
Here you go,if you have a lot of time to read this.

https://www.fbo.gov/inde...mp;tab=core&_cview=1
Back to top
dougrose
#8 Posted : Sunday, January 09, 2011 2:10:39 AM(UTC)
dougrose

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member, Administration, Admin
Joined: 12/7/2007(UTC)
Posts: 1,332
Points: 1,746

Was thanked: 25 time(s) in 21 post(s)
Both the props/shafts and the bronze thruhulls should be electrically isolated from the hull. You should check this with a reliable ohmmeter while out of the water, or, if in the water, by shorting each shaft or thruhull to the hull and verifying that the Capac meter moves each time. You can use a piece of wire with a sharp probe at each end, be sure to get through any corrosion and down to metal when checking. Please note that the meter movement for a thruhull is pretty small and may be tough to spot in fresh water.

When you say that the engine is isolated completely, I assume that you mean that the drive flange on the transmission is electrically isolated from the shaft. Usually, the engine block itself is grounded to the hull.

The zinc collar on the shaft is there to protect the bronze prop from the stainless shaft. I would definitely install one. Most sources say to put it a short distance ahead of the strut: close enough so that it helps streamline the hub, but far enough that there is a good flow of water to the rubber bearing.

When our boats were built, bronze was the standard material for thru-hulls. They were isolated from the hull to prevent electrolysis with inner and outer gaskets, a washer around the shank, and nonconducting short pipes on the inside. Mine have given no trouble in 35 years.

Still, Marelon is a better material, ABYC approved, and if I ever take mine out, I will put in the reinforced plastic ones, with stainless steel (or marelon) ball valves, if I can find them. Everyone carries Marelon mushroom heads with barbed end, but you cannot use those below the water line. For the engines, a slotted (scoop) strainer end is required, and the valve should screw right to the fitting, with a solid tail that rises above the waterline. You can get the parts from Forespar. The scoop strainer, seacock, and tail pieces all come with straight pipe threads to make a single solid assembly. Do not mix straight and tapered pipe threads!


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
Back to top
 |  Edit by user
ComputerJoe
#9 Posted : Sunday, January 09, 2011 6:57:53 AM(UTC)
ComputerJoe

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/7/2007(UTC)
Posts: 603
Points: 1,119

Thanks: 2 times
Was thanked: 1 time(s) in 1 post(s)
dougrose wrote:
Both the props/shafts and the bronze thruhulls should be electrically isolated from the hull.


While going thru the State charter boat inspection and the marine surveyor for insurance they wanted every thru-hull bonded to the hull.
Back to top
Barkleydave
#10 Posted : Sunday, January 09, 2011 7:48:21 AM(UTC)
Barkleydave

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/4/2007(UTC)
Posts: 460
Points: -618

Thanks: 3 times
Was thanked: 7 time(s) in 6 post(s)
Many years ago I went through the Michigan Charter Boat inspection training and was certified to do MI inspections even though I never did any since I worked for Illinois not Michigan.

Anyway you still can ground your thru-hulls to satisfy the inspection and still keep them isolated.

1. First your current thru-hulls are isolated by an insolator preventing the actual thru-hull from touching your hull...
2. You can install a grounding wire to the thru-hull valve. Since your lower fitting is isolated it will not ground with a wire on the actual valve. It will appear to be grounded while in fact it an't..Eh?

Naturally a plastic fitting would require no grounding.

dave
None
Back to top
ComputerJoe
#11 Posted : Sunday, January 09, 2011 9:29:29 AM(UTC)
ComputerJoe

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/7/2007(UTC)
Posts: 603
Points: 1,119

Thanks: 2 times
Was thanked: 1 time(s) in 1 post(s)
This is what I've done but all the wires are commonly bonded to the hull. No dissimliar metals touching but they are anything but isolated from the hull.
Back to top
dougrose
#12 Posted : Monday, January 10, 2011 12:40:04 AM(UTC)
dougrose

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member, Administration, Admin
Joined: 12/7/2007(UTC)
Posts: 1,332
Points: 1,746

Was thanked: 25 time(s) in 21 post(s)
Dissimilar metals underwater that are electrically connected will form a battery, and one of the metals will eventually be destroyed. The loser is the one further toward the active end of those lists that are ordered by chemical activity. I believe that if you wire your fittings directly to the hull, you defeat the purpose of insulating them in the first place.

Any such effect will be quite slow in cold fresh water, but would go very fast in warm salt water (chemical reactions double in speed about every fourteen degrees). You might not notice it in Michigan, or perhaps your entire hull is insulated from the water, so no problem. We need an expert....

It was once the practice (with non-metallic hulls) to tie all of the underwater fittings together with a bonding system, that was in turn connected to zincs. Fittings used to be ordered in boat sets from the foundry, and all the fittings were cast from the same pot. Today, however, they are bought from different sources, and everyone calls their fittings "bronze" whether they are made of bronze or not. It might not be a good idea to connect them all together until their alloy has been determined. A factory engineer will look at this, but not end users like us. The plastic is looking better and better.....


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
Back to top
pastelblack
#13 Posted : Monday, January 10, 2011 2:17:40 AM(UTC)
pastelblack

Rank: Dedicated Tin Star

Groups: Member
Joined: 12/20/2007(UTC)
Posts: 49
Points: 147
Wow, thanks for all the great responses and recommendations. I will try and post a few photos but need to get back up to the marina to take them, so hang tight.

Well, as far as the seacocks and strainers go, it really looks like just going with the marelon is the way to go....simple and tough.

I am still wondering however about the corrosion at the point where the rudder comes through the bottom of the boat, and around the strut. Very localized corrosion. Please note we installed phenolic brgs in both of these locations a while back, so I am confused why we are still getting corrosion there. Has anyone else experienced this?

Thank you all for the great and detailed help. You guys are the deal.
Back to top
ComputerJoe
#14 Posted : Monday, January 10, 2011 11:13:27 AM(UTC)
ComputerJoe

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/7/2007(UTC)
Posts: 603
Points: 1,119

Thanks: 2 times
Was thanked: 1 time(s) in 1 post(s)
A battery or capasitor is two conductors seperated by an insulator (dielectric) is it not?
By electrically connecting (bonding wire) the two conductors (hull & fitting) would not you short out any potiential voltages between them?

How would I connect the bonding wires to negative without having a conductive circuit to the hull?
The battery negative is connected to the engine block which is bolted to the hulls frames.
Back to top
Barkleydave
#15 Posted : Monday, January 10, 2011 11:18:51 AM(UTC)
Barkleydave

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/4/2007(UTC)
Posts: 460
Points: -618

Thanks: 3 times
Was thanked: 7 time(s) in 6 post(s)
Great job of explaining this stuff guys!

1. The hull is part of the negative 12V ground.

2. The trick is to isolate dissimilar metals from the ground circuit (hull,engine) ie, shafts, thru-hulls, etc.


dave
None
Back to top
 |  Edit by user
ComputerJoe
#16 Posted : Monday, January 10, 2011 11:31:19 AM(UTC)
ComputerJoe

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/7/2007(UTC)
Posts: 603
Points: 1,119

Thanks: 2 times
Was thanked: 1 time(s) in 1 post(s)
But I am required to bond the thru hulls to the hull through seperate wires. And would any potiential (voltage) between them be neutralized by this bonding wire. Without a potiential difference there can be no electrallisys.
Back to top
 |  Edit by user
Jack Marchand
#17 Posted : Monday, January 10, 2011 2:20:54 PM(UTC)
Jack Marchand

Rank: Upper Crust Bronze Star

Groups: Member
Joined: 4/30/2010(UTC)
Posts: 162
Points: 398

Thanks: 1 times
Was thanked: 13 time(s) in 13 post(s)
Computer Joe wrote: By electrically connecting (bonding wire) the two conductors (hull & fitting) would not you short out any potiential voltages between them?

Yes! Followed by rotting (coroding) out your hull! Isolate! Read dougroses link above.

75 FB express, "Big Enough II" twin 318s, 950hrs, raw water cooling, 1 to 1 transmisions, Beautiful Lake Charlevoix, MI
Back to top
Roger2
#18 Posted : Monday, January 10, 2011 2:36:48 PM(UTC)
Roger2

Rank: Marinette Royal Aluminum Poster (300+) posts

Groups: Member
Joined: 12/16/2007(UTC)
Posts: 567
Points: 879

Thanks: 3 times
Was thanked: 5 time(s) in 5 post(s)
Joe,
I have marlon fittings in my boat. If I had brass I would run a ground wire to all the thru hulls. I would not jumper to the hull at each location. If they are all connected together, they will probably never catch that they are not connected to the hull, ie grounded.
When a brass fitting, thruhull, is grounded to the hull the voltage potential is reduced to near "0" and the curent flow increases. It's pure ohms law. The dissimilar metals produce about 1 1/2 volts when grounded to near "0" the current gets very high! You can do your own calculations.

Plumbing code requires insulated unions in copper water lines entering into the hot water heater. Electrolysis
is caused by current flow, not by voltage potential.

I would guess that the electrolysis is caused by grounded rudders, possible steering cylinder, or cables.

My 2 cents.

Sea Jay
1983 37 double cabin, twin 230hp Volvo diesels, twin disk 1.5-1 20X 23 4 blade props
Back to top
pastelblack
#19 Posted : Tuesday, January 18, 2011 9:26:19 AM(UTC)
pastelblack

Rank: Dedicated Tin Star

Groups: Member
Joined: 12/20/2007(UTC)
Posts: 49
Points: 147
I am still wondering however about the corrosion at the point where the rudder comes through the bottom of the boat, and around the strut. Very localized corrosion. Please note we installed phenolic brgs in both of these locations a while back, so I am confused why we are still getting corrosion there. Has anyone else experienced this??
THANKS!!!
Back to top
fastjeff
#20 Posted : Tuesday, January 18, 2011 11:35:49 PM(UTC)
fastjeff

Rank: Administration

Medals: aluminum star: For Marinette Owners Everywhere above the call of duty

Groups: Admin2, Admin2, Admin, Administration, Member
Joined: 12/5/2007(UTC)
Posts: 3,133
Points: 5,732

Was thanked: 34 time(s) in 30 post(s)
Have you checked the rudders with an ohm meter to see if they are isolated? It's possible someone (the previous owner, of course) left out an isolating part in the complex rudder mechanism.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
Back to top
Users browsing this topic
guest
2 Pages12>
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Powered by YAF 1.9.5.5 | YAF © 2003-2011, Yet Another Forum.NET
This page was generated in 0.270 seconds.