I just noticed adjacent to my starboard engine bracket some bubbling which I know must be corrosion. What should I do? I have an '01 Gulfstream.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Gil Bracket Corrosion
- Thread starter BobKat
- Start date
richie rich
Well-Known Member
I assume you mean the bubbling is in the metal bracket? This needs to be sanded out, epoxied over and then painted with the right engine paint. The epoxy will keep moisture and air from continuing the corrosion. Check you zincs and any potential electrical loss....you may have an electrolysis issue.
Strikezone
GreatGrady Captain
I've got the same problem that has started at the engine mounting holes. I'll check my zincs but since I'm drystacked I'm not sure that's the cause of the problem.
I plan on taking care of it this winter.
I plan on taking care of it this winter.
richie rich
Well-Known Member
yeah, sometimes it doesn't take a boat to be sitting in the water all the time for things to happen....if you have moisture in the area of any kind and you have 2 different metals touching each other, you are going to have a potential problem. SS bolts and aluminum bracket or backing plate and things can start happening. Sometimes its good to isolate the 2 metals with either a plastic shim under the washer or bolt head or even a thick double faced tape to keep them from contacting each other. Making sure the sealant is in good shape helps as well.
BobP
GreatGrady Captain
- Joined
- Apr 27, 2005
- Messages
- 4,744
- Reaction score
- 6
- Points
- 38
- Location
- Long Island, NY
- Model
- Sailfish
The coating on the alum is not the same as gelcoat on glass, it will eventually loose adhesion, irrespective of claims to the contrary by manufacturers of these products like powdercoat.
You have corrosion, plain and simple, aluminum oxide, what you need to find out is if it's galvanic or not, if not galvanic, it is strictly a cosmetic issue, not structural.
Scrap off the coating and what do you see?
white powder
no pits
No white powder
pits
The latter two are a real problem to be attended to, soon, not the former.
Check continuity between each motor zinc and drive zinc, use your multimeter ringer function. Then check the same between battery neg term.
If you don't have a digital multimeter, get one. Get the $20 one on sale at Sears when it sells for 10 or 15 bucks, seems like every week another model is on sale.
You don't need a $150 meter, results will be the same.
You have corrosion, plain and simple, aluminum oxide, what you need to find out is if it's galvanic or not, if not galvanic, it is strictly a cosmetic issue, not structural.
Scrap off the coating and what do you see?
white powder
no pits
No white powder
pits
The latter two are a real problem to be attended to, soon, not the former.
Check continuity between each motor zinc and drive zinc, use your multimeter ringer function. Then check the same between battery neg term.
If you don't have a digital multimeter, get one. Get the $20 one on sale at Sears when it sells for 10 or 15 bucks, seems like every week another model is on sale.
You don't need a $150 meter, results will be the same.
richie rich
Well-Known Member
BobP,
why would the two types of corrosion result in one oxidizing and one not oxidizing, just pitting? That's an interesting scenario. You'd figure regardless of reason, if the aluminum gives it up, you'll have visible oxidation.
why would the two types of corrosion result in one oxidizing and one not oxidizing, just pitting? That's an interesting scenario. You'd figure regardless of reason, if the aluminum gives it up, you'll have visible oxidation.
BobP
GreatGrady Captain
- Joined
- Apr 27, 2005
- Messages
- 4,744
- Reaction score
- 6
- Points
- 38
- Location
- Long Island, NY
- Model
- Sailfish
Richie, they are both oxidizing, but the oxide is being displaced from the boat to another place, perhaps another boat following the current path that is now gaining the lost metal.
Pits or gouging are the key indicators of galvanic damage. There will be may be some powder too, way less, particularly below the water line.
Aluminum oxide doesn't look good, but it protects the alloy from further corrosion, not from galvanic destruction however.
Galvanic damage is the equivalent of drilling holes into the metal (just like what happens to zincs sometimes in agreesive environments)
The drive is made of the same alloy as your motors and I/O, inspect and treat both the same and the metals will last forever and never need to be replaced, they don't wear out.
Trying to maintain the metal surface condition (fairing) of the drive as it ages, equal to the glass hull, is a challenge, should that be your goal.
But you will never encounter one osmotic blisters on drive or motors !
And don't use copper bottom paint on it irrespectve of what marina does, use bottom paint compatible with metals, only.
Such paints can extend well onto the glass hull, then continue on with regular bottom paint, over or under the former, they can overlap each other - won't notice anything if using same color on both. No need to do tape line from one to another.
Pits or gouging are the key indicators of galvanic damage. There will be may be some powder too, way less, particularly below the water line.
Aluminum oxide doesn't look good, but it protects the alloy from further corrosion, not from galvanic destruction however.
Galvanic damage is the equivalent of drilling holes into the metal (just like what happens to zincs sometimes in agreesive environments)
The drive is made of the same alloy as your motors and I/O, inspect and treat both the same and the metals will last forever and never need to be replaced, they don't wear out.
Trying to maintain the metal surface condition (fairing) of the drive as it ages, equal to the glass hull, is a challenge, should that be your goal.
But you will never encounter one osmotic blisters on drive or motors !
And don't use copper bottom paint on it irrespectve of what marina does, use bottom paint compatible with metals, only.
Such paints can extend well onto the glass hull, then continue on with regular bottom paint, over or under the former, they can overlap each other - won't notice anything if using same color on both. No need to do tape line from one to another.
richie rich
Well-Known Member
Thanks for the info Bob....
my zincs on my engines never get powder but scallop badly..they are gone after 2 seasons. But the Grady bracket does get powdery (at least above the waterline), as it should to protect itself like you said...same goes for the gas tanks....I simply assumed that the zincs and the bracket stay "clean" simply because they're in the water.....I didn't know the two types of corrosion actually looked different on the metal....keep that on file!
I re-did my bracket last year...had it blasted, etched and barrier coated within 30 minutes to stay ahead of aluminum oxidation.....then used Trilux on the lower half and Perfection above the waterline......see how that holds up...I see a ton of people painting regular copper bottom paint on everything including transducers...what are ya gonna do?
One funny thing though, the horizontal zinc on the bracket...NEVER wears out....I never removed it after blasting...I wonder if there's paint in between it and the bracket not allowing the zinc to give up?
my zincs on my engines never get powder but scallop badly..they are gone after 2 seasons. But the Grady bracket does get powdery (at least above the waterline), as it should to protect itself like you said...same goes for the gas tanks....I simply assumed that the zincs and the bracket stay "clean" simply because they're in the water.....I didn't know the two types of corrosion actually looked different on the metal....keep that on file!
I re-did my bracket last year...had it blasted, etched and barrier coated within 30 minutes to stay ahead of aluminum oxidation.....then used Trilux on the lower half and Perfection above the waterline......see how that holds up...I see a ton of people painting regular copper bottom paint on everything including transducers...what are ya gonna do?
One funny thing though, the horizontal zinc on the bracket...NEVER wears out....I never removed it after blasting...I wonder if there's paint in between it and the bracket not allowing the zinc to give up?
BobP
GreatGrady Captain
- Joined
- Apr 27, 2005
- Messages
- 4,744
- Reaction score
- 6
- Points
- 38
- Location
- Long Island, NY
- Model
- Sailfish
Take your multimeter and check continuity between the bracket and zinc, I bet it does.
If you don't want to pin prick the bracket metal for the test, run a lead inside the back of the transom to a bolt/nut head.
If continuity is good, and the drive zinc is not freeting away or doing so at a lesser rate, it's OK, it only means the other zincs are taking care of the drive too.
When I added trim tab zincs, the drive zinc slowed it's fretting rate in half.
There you have it.
Be sure your zincs never run down (not even one of them), get it out when it's no less than about half weight if original, presuming you get multiseasons out of it. Since zincs can retain their shape but be sucked out as they erode, comparing outer dimensions doesn't always work.
Marina's have many agendas, other than doing the job right.
It's easier and faster to use one paint type (and open can) to do a boat than tow. Less time = more profit and more quantity of boats can be painted in same time. And what do most people know anyway!
You have everyting under control, just stay up with periodic inspections looking for any changes, a new neighbor in the marina may appear and bring along some things than can effect your boat's ability to protect the underwater metals.
Inspect screws on FF transducers, metal thruhulls, and any other underwater metals too, not just motors and drive.
If you don't want to pin prick the bracket metal for the test, run a lead inside the back of the transom to a bolt/nut head.
If continuity is good, and the drive zinc is not freeting away or doing so at a lesser rate, it's OK, it only means the other zincs are taking care of the drive too.
When I added trim tab zincs, the drive zinc slowed it's fretting rate in half.
There you have it.
Be sure your zincs never run down (not even one of them), get it out when it's no less than about half weight if original, presuming you get multiseasons out of it. Since zincs can retain their shape but be sucked out as they erode, comparing outer dimensions doesn't always work.
Marina's have many agendas, other than doing the job right.
It's easier and faster to use one paint type (and open can) to do a boat than tow. Less time = more profit and more quantity of boats can be painted in same time. And what do most people know anyway!
You have everyting under control, just stay up with periodic inspections looking for any changes, a new neighbor in the marina may appear and bring along some things than can effect your boat's ability to protect the underwater metals.
Inspect screws on FF transducers, metal thruhulls, and any other underwater metals too, not just motors and drive.
richie rich
Well-Known Member
yeah, there are a lot of people around me with their power plugged in and A/C running 24/7 in the summer....lot of stray current around
thanks for the input!!
thanks for the input!!