blacking the base?

[DHutch]

Electrolitic action does not work round corners, it only works by "Line of sight". so although anodes on the bottom will protect the baseplate I'me afraid they will do nothing for the sides.

[rog guiver]

While talking about blacking, why not, as we have done each time the boat is blacked, take action along the area of most concern.

 

Following the high pressure wash, and once it is dry, treat the area along the waterline with Curerust (spelling?) or an equivalent. It normal only takes a short while to dry so should not delay the bitumen application by much.

 

The success of this procedure could be seen each subsequent blacking where there was almost no rust along the waterline.

Edited September 8, 2006 by rog guiver

[ChrisPy]

While talking about blacking, why not, as we have done each time the boat is blacked, take action along the area of most concern.

 

Following the high pressure wash, and once it is dry, treat the area along the waterline with Curerust (spelling?) or an equivalent. It normal only takes a short while to dry so should not delay the bitumen application by much.

 

The success of this procedure could be seen each subsequent blacking where there was almost no rust along the waterline.

which is why I will use Vactan (everywhere initially) before blacking.

 

It would be possible to galvanise a boat in large sections anyway. I do not forsee a problem with this. I have not yet done a search of platers.

 

It might then fall apart only at the final seams. Of course if the seams were perforated like toilet paper it would be guaranteed not to come apart at the seams either.

[blackrose]

Electrolitic action does not work round corners, it only works by "Line of sight". so although anodes on the bottom will protect the baseplate I'me afraid they will do nothing for the sides.

 

Line of sight? You obviously know more about this than me. Surely it works on annode/cathode proximity? Doesn't a galvanic isolator protect the whole hull (corners & all) by stopping galvanic action? Anyway at least the annodes I put on are protecting the baseplate!

[Yoda]

which is why I will use Vactan (everywhere initially) before blacking.

It might then fall apart only at the final seams. Of course if the seams were perforated like toilet paper it would be guaranteed not to come apart at the seams either.

 

I think that it would be possible to galvanise a whole 70 foot hull. The setup cost for the first off would be high but after that, quite cheap.

 

Another form of protection that I will investigate is powder coating. The limitation is how to bake it on. Like all things, if there is a market someone will respond.

 

The difference to not coating is always having to pull the boat out and clean/repair it. I know where I want to spend my time and money and its not servicing steel work.

[ChrisPy]

Line of sight? You obviously know more about this than me. Surely it works on annode/cathode proximity? Doesn't a galvanic isolator protect the whole hull (corners & all) by stopping galvanic action? Anyway at least the annodes I put on are protecting the baseplate!

I was surprised, so I googled for it. there are several references to home made electroplating where it is made quite clear that electrolysis works mainly on line of sight.

 

I think that it would be possible to galvanise a whole 70 foot hull. The setup cost for the first off would be high but after that, quite cheap.

 

it would be great if someone could set it up, I grant you.

[blackrose]

I was surprised, so I googled for it. there are several references to home made electroplating where it is made quite clear that electrolysis works mainly on line of sight.

it would be great if someone could set it up, I grant you.

 

Electrolysis might be slightly different. The terms galvanic corrosion and electrolysis are often used interchangeably. In galvanic corrosion there is a flow of current generated because of the potential difference between dissimilar metals causing the least noble one to corrode. In electrolysis a stray (or intended) current is involved - for example a DC current, from an external source flowing into the water from the metal & carrying metal ions with it.

 

I'm open minded about whether galvanic corrosion/protection can occur around corners - I'm looking into it, so watch this space!

[ChrisPy]

Electrolysis might be slightly different. The terms galvanic corrosion and electrolysis are often used interchangeably. In galvanic corrosion there is a flow of current generated because of the potential difference between dissimilar metals causing the least noble one to corrode. In electrolysis a stray (or intended) current is involved - for example a DC current, from an external source flowing into the water from the metal & carrying metal ions with it.

 

seems to me there is no difference, except either: the current is generated by the condition, or an electric current creates the condition. I'm sure for the ions it feels much the same either way - they are being pushed along lines of sight.

[blackrose]

seems to me there is no difference, except either: the current is generated by the condition, or an electric current creates the condition. I'm sure for the ions it feels much the same either way - they are being pushed along lines of sight.

 

I think the potential difference is much greater with electrolysis.

 

Anyway, let me get this straight, we are saying that ions cannot move from a magnesium anode in relation to cathodic steel which is not visible from the anode?

 

So by this rule of thumb anodes placed on the sides of a boat will do nothing for the baseplate even if they are welded to the bottom of the sides?

 

Well, if that's true at least my baseplate is protected. I know it's usually a thick sheet of steel but coming back to the original topic, why would anyone leave their baseplate unpainted AND without any sacrificial protection?

Edited September 13, 2006 by blackrose

[Yoda]

I think the potential difference is much greater with electrolysis.

 

Anyway, let me get this straight, we are saying that ions cannot move from a magnesium anode in relation to cathodic steel which is not visible from the anode?

 

So by this rule of thumb anodes placed on the sides of a boat will do nothing for the baseplate even if they are welded to the bottom of the sides?

 

 

If all of the steel sheeting is at the same potential, ie bonded together, then it matters not where the anodes are placed. It is only where there is a difference to the potential that will require a local anode.

[ChrisPy]

If all of the steel sheeting is at the same potential, ie bonded together, then it matters not where the anodes are placed. It is only where there is a difference to the potential that will require a local anode.

I don't think so.

If there is a mechanism causing corrosion of steel in some part of the hull, then the anodes will corrode, in preference to steel in their locality.

The steel will tend to be more liable to corrode if it is more distant from the anode, and if the anode is not in line of sight of the offending 'cathode' (which might be your own bronze propellor or some foreign object).

[DHutch]

Another form of protection that I will investigate is powder coating. The limitation is how to bake it on. Like all things, if there is a market someone will respond.

Powder coating is good stuff, several part of our engine and boat are powder caoted, as are 99% of all "white goods"

- However, it wouldnt really be very suitable for hull protection, the size of part would make it prohibtably expensive both to set up and run, and its very much doubtfull the finshed job would be better than that of currently used two-pack solutions such as the paints we use on emilyanne.

 

 

Daniel

[blackrose]

Electrolitic action does not work round corners, it only works by "Line of sight". so although anodes on the bottom will protect the baseplate I'me afraid they will do nothing for the sides.

 

I don't know where you got that information, but according to a US based website (Finishing.com, homepage of the metal finishing industry), this "line of sight" theory is not true. Please see links to their letters page and my enquiry which was answered by the main man.

 

http://www.finishing.com/Letters/

 

http://www.finishing.com/422/29.shtml

Edited September 14, 2006 by blackrose

[ChrisPy]

I don't know where you got that information, but according to a US based website (Finishing.com, homepage of the metal finishing industry), this "line of sight" theory is not true.

there are many other references giving the opposite message.

 

I know it's usually a thick sheet of steel but coming back to the original topic, why would anyone leave their baseplate unpainted AND without any sacrificial protection?

because you shouldn't expect much corrosion at a depth of 1.5 ft or more. It is much much worse at the waterline because of more oxygen in the water, turbulence, wet/dry cycling etc.

[Guest]

there are many other references giving the opposite message.

because you shouldn't expect much corrosion at a depth of 1.5 ft or more. It is much much worse at the waterline because of more oxygen in the water, turbulence, wet/dry cycling etc.

Must admit our previous boat showed hardly any corrosion on unpainted baseplate after 10 years. When it was hauled out for blacking I got the guy to weld new anodes on it, on which of course he made a profit, but I got the impression that he didn't believe anodes did a great lot of good. I wouldn't risk it without anodes personally, but quite a few don't seem to bother with them.

[blackrose]

there are many other references giving the opposite message.

 

I would tend to trust someone from industry who's actually using the electrolytic process in their business.

 

Anyway, I've also found some references for electroplating and line of sight (not sure how relevant it is but it does use an electrolytic process). However, some references also go on to mention applications which are line of sight dependent or non-dependent. The question then is whether magnesium anodic protection of steel is line of sight dependent.

Edited September 14, 2006 by blackrose

[ChrisPy]

I would tend to trust someone from industry who's actually using the electrolytic process in their business.

 

Anyway, I've also found some references for electroplating and line of sight (not sure how relevant it is but it does use an electrolytic process). However, some references also go on to mention applications which are line of sight dependent or non-dependent. The question then is whether magnesium anodic protection of steel is line of sight dependent.

it's probably a matter of degree but, for sure, anodes that are out of sight will be less effective than if they are L-o-S. Maybe the compromise answer is to fit lots of them at the edge of the bottom of the baseplate?

[Yoda]

Just found a boat that is galvanised on Apollo Duck.

 

Fassifern, 69 feet long and fully galvanised, built 1999 and for sale. So someone is galvanising boats.

[DHutch]

Just found a boat that is galvanised on Apollo Duck.

- Fassifern, 69 feet long and fully galvanised, built 1999 and for sale. So someone is galvanising boats.

Very interesting, i wonder if we can find out more about it.

 

 

Daniel

[steaming floater]

I`ve noticed that there seems to be more boats having anodes fitted to the bottom of the boat,would this save painting it?

 

 

Anodes will wear out quicker the more electical charge builds up in your hull. More gizmos more wear to anodes and therefore the shell.

 

I met an "anorak" who knew about these things, its his idea not mine. Sounds reasonable though.

[blackrose]

Anodes will wear out quicker the more electical charge builds up in your hull. More gizmos more wear to anodes and therefore the shell.

 

I met an "anorak" who knew about these things, its his idea not mine. Sounds reasonable though.

 

Only if you've got stray currents from those gizmos

[DHutch]

Yeah, there no reason why electical items onboard should cause any negative affect of the hull.

- 99% of boats run a two wire system, with (hopfully) only one earth point to the hull.

 

 

 

Daniel

[ChrisPy]

Just found a boat that is galvanised on Apollo Duck.

 

Fassifern, 69 feet long and fully galvanised, built 1999 and for sale. So someone is galvanising boats.

69 feet - yow!!

but was the boat galvanised after fabrication? if so, I'd love to know how and where.

[frangar]

To get back to the topic.......I had my boat grit blasted and the baseplate painted with Comastic as the hull which was bulit in 1982 is 6/6/4 on the advice of the surveyor and the base had some pitting......That was in 1991 and I have docked the boat every 2 years since and made sure it is dock where I can get to the base plate and on a full hull survey last year no further pitting or corroision had occured. My boat draws 2 foot 6 inches and I only lose some paint right on the skeg with a few front to back scratches where we have gone over something so for the slight cost of the paint plus finding a good dock or crane out its well worth it esp. if you have a hull made of thinner plate than is used now

[DHutch]

To get back to the topic.......I had my boat grit blasted and the baseplate painted with Comastic as the hull which was bulit in 1982 is 6/6/4 on the advice of the surveyor and the base had some pitting......That was in 1991 and I have docked the boat every 2 years since and made sure it is dock where I can get to the base plate and on a full hull survey last year no further pitting or corroision had occured. My boat draws 2 foot 6 inches and I only lose some paint right on the skeg with a few front to back scratches where we have gone over something so for the slight cost of the paint plus finding a good dock or crane out its well worth it esp. if you have a hull made of thinner plate than is used now

Yeah, sounds very simular to what we did with emilyanne from the start, only we used twopart paint.

- As you say, its suprissing how very little paint you actally loose, we draw 2ft8-9ish and find the same.

 

 

Daniel