Hempel classic over international primocon

[fatsdoodah]

Hi,

I couldn't find much on compatibility of these two products. Any ideas if this is a good combination for preparing and antifouling once galvanised bilge plates? Primocon seems to have preferable anti-corrosion properties to hempel underwater primer. Is there any advantage to primocon over hempel underwater primer? I'm kind of hooked on hempel classic as antifoul, if going with primocon on the steel would it be worth applying tie coat of hempel underwater before antifouling?

These plates are a bout 1/4" thick steel with pretty heavy pitting. The plan was to blast / sand down to bare metal, treat with rust converter, prime with plenty of coats of primocon then a couple of coats of hempel classic.

Another thought was to coat in epoxy & chopped strands after rust treatment but I could imagine this may be problematic should rust blooms breakout under the resin?

The plates go through the Hull and are encapsulated and bolted under the berths so it seems there could be rust that has travelled up the plates some way which might cause corrosion to erupt around the joints.

 

[Tranona]

If you are going to the trouble and expense of blasting then suggest you coat with epoxy. This is what I did on my Golden Hind. When blasting try to get the boat supported so that it does not stand on the keels so that you can do the underside as well. You might also have the area around where the keels go into the hull blasted as well then epoxied to limit the likelihood of water getting into that joint.

If you do decide to go down the conventional route then suggest you use this primer. smlmarinepaints.co.uk/products/vinyguard Just as good as the more expensive Hempel and International. No compatibility problems with antifoul. I used this smlmarinepaints.co.uk/products/CU-PRO which seems more effective and longer lasting than Hempel Classic.

 

[fatsdoodah]

If you are going to the trouble and expense of blasting then suggest you coat with epoxy. This is what I did on my Golden Hind. When blasting try to get the boat supported so that it does not stand on the keels so that you can do the underside as well. You might also have the area around where the keels go into the hull blasted as well then epoxied to limit the likelihood of water getting into that joint.

If you do decide to go down the conventional route then suggest you use this primer. smlmarinepaints.co.uk/products/vinyguard Just as good as the more expensive Hempel and International. No compatibility problems with antifoul. I used this smlmarinepaints.co.uk/products/CU-PRO which seems more effective and longer lasting than Hempel Classic.

Thanks I'll have to get quote from yard for the blast. It shouldn't be too difficult proping her up on centre keel and rest of boat is pretty tidy for age so probably worth keeping the keel plates in good order.

Has the golden hind got similar arrangement for bilge keels?

 

[Tranona]

No. The keels are bolted through a flange to the hull so removable if required. It does have a long central keel and we blocked it up on that with props to the hull. What boat do you have? Where are you based?

 

[fatsdoodah]

No. The keels are bolted through a flange to the hull so removable if required. It does have a long central keel and we blocked it up on that with props to the hull. What boat do you have? Where are you based?

Ah OK Its a trident 24 in suffolk and the bilge plates are embedded through the hull so I definitely want to make sure they are protected from corrosion as best as possible. There was a survey done a year or two back recommending removal of bilge anodes which is advice i don't understand but guess it is something to do with the anodes driving excessive and unnecessary cathodic reaction under the painted surface or something like that and that it would be better to just make sure the steel which is as far as i know isolated from other metalic components is well coated.

 

[Tranona]

Correct advice to remove anodes as they are ineffective on mild steel where corrosion is simple old fashioned rust not from any galvanic action because as you say the plates are not connected to any other metals.
I asked where you are located because finding a good blaster can be tricky and there is a good one in Poole where I live - but no good to you in Suffolk!

 

[fatsdoodah]

Correct advice to remove anodes as they are ineffective on mild steel where corrosion is simple old fashioned rust not from any galvanic action because as you say the plates are not connected to any other metals.
I asked where you are located because finding a good blaster can be tricky and there is a good one in Poole where I live - but no good to you in Suffolk!

Ah ok thanks anyhow. Ill try the boat yard where she is laying but maybe this is a job for another year and will see how it goes with plenty of paint and no anodes.

 

[Bilgediver]

Be careful about acting on information action that might be incorrect . Ask your self why do all ships have numerous anodes placed around the underwater section. These anodes are replaced as required at every drydocking. Even steel canal boats have to have anodes to reduce corrosion.. Speak to McDuff

I would prefer Primocon in this case and have used it . The zinc rich property has to be paid for. I did cast iron keels on a Westerly Chieftain over 30 years ago as you propose and applied a few coats of Primocon before antifouling. Following that I applied Primicon as a tie coat prior to antifouling annualy. Ther was only minor touching up required about 30 years when it was considered time had come to take the Hull and keels back to bare surface and repeat.

One interesting g fact that puzzled me that I expected to see alternate layes of red and grey when I feathered th pai t on the keels with a sander. . This was not the case. No sign of the layers of Primocon. It certainly protected the keels.

A friend did likewise to the steel keels on a Hunnter channel with similar results.


UK's Industry Leader for Cathodic Protection Systems and Anodes

 

[Tranona]

Be careful about acting on information action that might be incorrect . Ask your self why do all ships have numerous anodes placed around the underwater section. These anodes are replaced as required at every drydocking. Even steel canal boats have to have anodes to reduce corrosion.. Speak to McDuff

I would prefer Primocon in this case and have used it . The zinc rich property has to be paid for. I did cast iron keels on a Westerly Chieftain over 30 years ago as you propose and applied a few coats of Primocon before antifouling. Following that I applied Primicon as a tie coat prior to antifouling annualy. Ther was only minor touching up required about 30 years when it was considered time had come to take the Hull and keels back to bare surface and repeat.

One interesting g fact that puzzled me that I expected to see alternate layes of red and grey when I feathered th pai t on the keels with a sander. . This was not the case. No sign of the layers of Primocon. It certainly protected the keels.

A friend did likewise to the steel keels on a Hunnter channel with similar results.


UK's Industry Leader for Cathodic Protection Systems and Anodes

There is nothing incorrect about advice that anodes are not required on sheet metal bilge plates on a GRP boat. Anodes are required where there is a possibility of a galvanic cell - and a steel plate is just a single metal. Any corrosion which occurs is simply rust and arises because of a breakdown of the protective coating exposing the steel to seawater. Not surprising to find this on a boat getting on for 50 years old like the OPs. adding an anode will not make any difference. Originally the plates were probably galvanised and this has broken down . Once rust starts it spreads under the zinc coating. The remedy is to clean the metal back and apply a waterproof coating. Conventional primers like Primocon or Vinygard are commonly used because they are more tolerant of less than perfect preparation, but blasting and immediate epoxy coating is potentially superior. However that is an expensive solution. I have just had my bilge plates blasted and epoxy applied at a cost of £700, although DIY application of the epoxy would have reduced that by about £200.

I learned all this the hard way. One of my previous boats to a similar design had some corrosion on the bottom of the plates from grounding on a drying mooring. The advice was to clean and repaint the affected area and add anodes. This was a big mistake. Not only did the anodes show no sign of depletion but created a new source of corrosion starting from the mounting of the anode. There were anodes on the current boat when I bought it and the previous owner said they had been there when he bought the boat. They were like new - no depletion so clearly not doing anything.

 

[fatsdoodah]

Be careful about acting on information action that might be incorrect . Ask your self why do all ships have numerous anodes placed around the underwater section. These anodes are replaced as required at every drydocking. Even steel canal boats have to have anodes to reduce corrosion.. Speak to McDuff

I would prefer Primocon in this case and have used it . The zinc rich property has to be paid for. I did cast iron keels on a Westerly Chieftain over 30 years ago as you propose and applied a few coats of Primocon before antifouling. Following that I applied Primicon as a tie coat prior to antifouling annualy. Ther was only minor touching up required about 30 years when it was considered time had come to take the Hull and keels back to bare surface and repeat.

One interesting g fact that puzzled me that I expected to see alternate layes of red and grey when I feathered th pai t on the keels with a sander. . This was not the case. No sign of the layers of Primocon. It certainly protected the keels.

A friend did likewise to the steel keels on a Hunnter channel with similar results.


UK's Industry Leader for Cathodic Protection Systems and Anodes

Be careful about acting on information action that might be incorrect . Ask your self why do all ships have numerous anodes placed around the underwater section. These anodes are replaced as required at every drydocking. Even steel canal boats have to have anodes to reduce corrosion.. Speak to McDuff

I would prefer Primocon in this case and have used it . The zinc rich property has to be paid for. I did cast iron keels on a Westerly Chieftain over 30 years ago as you propose and applied a few coats of Primocon before antifouling. Following that I applied Primicon as a tie coat prior to antifouling annualy. Ther was only minor touching up required about 30 years when it was considered time had come to take the Hull and keels back to bare surface and repeat.

One interesting g fact that puzzled me that I expected to see alternate layes of red and grey when I feathered th pai t on the keels with a sander. . This was not the case. No sign of the layers of Primocon. It certainly protected the keels.

A friend did likewise to the steel keels on a Hunnter channel with similar results.


UK's Industry Leader for Cathodic Protection Systems and Anodes

Thanks bilgediver,

Though I'm getting quite confused at this juncture. The bilge keel anodes are quite heavily corroded so must be doing something. Could this be caused by stainless bolts or some galvanic activity occurring through localised positive and negatively charged areas of the each keel plate?

It is curious the surveyor specifically advised to remove them and additionally the one on the rudder which I find particularly strange since there is at least mild steel stainless steel and probably some brass on the assembly and ive read reports out there of another trident where anodes placed on each keel caused problems with the paint around them which improved after removal.

I'll definitely go with primocon then with either hempel or international antifoul and might try contacting surveyor to find out reasoning behind the advice!

 

[fatsdoodah]

There is nothing incorrect about advice that anodes are not required on sheet metal bilge plates on a GRP boat. Anodes are required where there is a possibility of a galvanic cell - and a steel plate is just a single metal. Any corrosion which occurs is simply rust and arises because of a breakdown of the protective coating exposing the steel to seawater. Not surprising to find this on a boat getting on for 50 years old like the OPs. adding an anode will not make any difference. Originally the plates were probably galvanised and this has broken down . Once rust starts it spreads under the zinc coating. The remedy is to clean the metal back and apply a waterproof coating. Conventional primers like Primocon or Vinygard are commonly used because they are more tolerant of less than perfect preparation, but blasting and immediate epoxy coating is potentially superior. However that is an expensive solution. I have just had my bilge plates blasted and epoxy applied at a cost of £700, although DIY application of the epoxy would have reduced that by about £200.

I learned all this the hard way. One of my previous boats to a similar design had some corrosion on the bottom of the plates from grounding on a drying mooring. The advice was to clean and repaint the affected area and add anodes. This was a big mistake. Not only did the anodes show no sign of depletion but created a new source of corrosion starting from the mounting of the anode. There were anodes on the current boat when I bought it and the previous owner said they had been there when he bought the boat. They were like new - no depletion so clearly not doing anything.

It's interesting that the anode was really quite depleted on the starboard plate (at least half mass has gone). If having anodes would at worst be ineffective I'd rather leave them on but from your experience and others it seems they can actually cause problems. Could this be due to lack of paint under anode?

Anyhow i might have a probe around with continuity tester it seems there must be some galvanic reaction occurring to have reduced anodes so heavily.