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New Bottom paint from steel to top coat
BjornDB
Posted: Monday, April 26, 2010 7:03 PM
Joined: 13/02/2009
Posts: 23


We are going into the yard and are having the hull water blasted down to bare steel and repainted on a 200ft motor yacht. What factors should I be keeping in mind when I keep an eye on our sub contractor? What paint should I be looking at using? how many coats of each and what about curing times and inter compatibility in between different brands? better to stick with 1 name that can guarantee adhesion? Any help would be appreciated!

junior
Posted: Monday, April 26, 2010 8:14 PM
Joined: 14/01/2009
Posts: 1026


Bjorn , this a technical subject with many preferences and opinions. As you know ,after blasting, steel can be primed with different primers....some primer systems are formulated to cover "white "steel and some are formulated to cover " brown" steel. And as you know, over coating time windows are critical. The time frame to blast and prime bare steel is always variable and relates to the condition, shape of vessel ,blocking arrangement and work force of the yard. I would say that the best solution is to consider the paint system that the shipyard proposes and normally uses since they have obviously produced satisfactory results in the past. Take this proposed paint system and run it by the different paint company representatives for comment. Pay particular attention to the paint systems that are MilSpec. Ie..... used by US government contractors. Be aware that all the different paint companies seem to be owned by the same corporation these days. With both white and brown steel I have had good luck with Devoe Industrial Coating. http://www.devoecoatings.com/home.jsp but as you can see this is an AkzoNobel group company . Same group as International, Awlgrip........ so be aware when questioning, comparing specs of these paint suppliers. My experience is that the over coating of bare steel time window is easy to keep. Blast and prime as you go. The application of antifouling over this primer is the problem.....Or to put it simply, next year when you haulout you will see antifouling patches falling of in areas that were painted outside of the overcoat period.... the Steel to Primer always seems to hold tight..
English Andy
Posted: Tuesday, April 27, 2010 8:19 AM
Joined: 17/09/2008
Posts: 93


Antifouling systems all perform largely the same function, but how they do it is a technical matter for the engineers who design the chemical structure of the antifouling or paint. From my point of view do not listen to the yard - instead go directly to the antifouling suppliers and be armed with several of these questions: how far does the yacht travel on average per month, how fast does your yacht cruise at and what is maximum sprint speed (these will decide if a hard or soft compound is needed) where will the yacht travel and will your selected brand be available there, does the yard offer warranty on the application process, and lastly is a tin free certificate from class going to be provided? This is mandatory for cruising special areas such as the Med. Will many years in the industry I have found that International Micron 66 is the best for a yacht that cruises hard and fast. DO NOT USE JOTUN!! We have cruised at 28 knots over 40 000 miles this year and our bottom is still clean ..... even in the Persian Gulf! Be warned though, the yard will have to closely supervised to apply this antifouling ...... if it goes on to thick it will not cure evenly throughout which will cause it to peel back! With regard to paint selection, there can be only one ....... Awlgrip! What you choose to apply from the many types is obviously the owner's choice but questions must be asked: what type of engines will you be using and at what RPM, do you have above and below water exhausts or just below - either way my preferred choice is Blue to hide the exhaust stains. With below water exhausts white is possible, but not recommended! Also consider crusing areas. Somewhere like the persian gulf with 40 degrees C and air temp of 55 degrees C in the summer whould preclude a blue hull! Choices, choices ....... Hope this helps, but remember to talk directly to the material providers .... yards usually wack a hefty profit onto this type of materials!
BjornDB
Posted: Tuesday, April 27, 2010 12:29 PM
Joined: 13/02/2009
Posts: 23


Thanks junior! something to start with. Would love to hear more from anyone else who can contribute their 5c, especially on the priming stages

Henning
Posted: Tuesday, April 27, 2010 12:47 PM
Joined: 01/06/2008
Posts: 1049


We had a 3 part Jotun system applied a year ago and spent most of out time sitting in a basin known for heavy fouling and growth, I have been extremely impressed and pleased with it.

junior
Posted: Tuesday, April 27, 2010 4:06 PM
Joined: 14/01/2009
Posts: 1026


Jotun in black seems to be a very popular anti fouling. I have never heard a complaint about Jotun anti foul. Personally I Have Micron antifoul over an International Primer system. Ive been on this yacht since new, 16 years...Aluminium, with original primer system and have no complaints. The primer is 100 percent tight and I have minimum fouling with MICRON. The yacht goes thru a one year haulout schedule. The previous yacht was steel , with a Devoe primer system and I had no adhesion problems for the 5 years that I ran the yacht. That steel yacht was blasted , 5 meter section of bottom at a time then primed as "white steel " .... 5 meters blast tomorrow then primed " white steel" immediately. I have no experience with primer over brown steel. A very good detail to examine while you are out of the water is the effectiveness of your anode system...To much electrical field will damage the primer to steel bond. If you have an anode specialist nearby have him inspect before blasting. Another professional detail that I see is a three colour primer system.....say first red, second coating black them third red again. In this way, be visually observing the "second " or third coat colour clarity you are confident that the correct paint film thickness has been applied. The same colour coding holds true with antifouling....important to apply the correct film thickness.
BjornDB
Posted: Tuesday, April 27, 2010 6:01 PM
Joined: 13/02/2009
Posts: 23


I have been in touch with the guys that will be doing the job and they suggest 3 coats of primer, 2 of anti fouling and 1 more coat of AF at the waterline and running gear. they can airless spray or roll. We are Lloyd's certified so I have to use a certified paint. So there are no other paint types I have to use for the bottom? just primer and AF? Also, is there typically a 'need' to remove all paint down to bare steel every 10 years? what if our primer is still holding up fine? what is the maximum time you could go on 1 bottom paint job?

junior: talking about overcoat-ability; we'll be out of the water for 3 months. what would be a good way to manage our bottom paint going on? start with 2 coats of primer at the start  followed by 1 more after a quick sand at the end before the AF goes on? 200ft is a lot of boat to sand...


junior
Posted: Tuesday, April 27, 2010 7:30 PM
Joined: 14/01/2009
Posts: 1026


Personally Ive never seen a shipyard physically sand between coats of primer. Imagine sanding a huge steel ship !.the yard would go bankrupt !!!! .The normal procedure is called wet on wet. One coat of primer, then the second coat applied on top during the first coats "green " wet stage.. When you overcoat during the green stage you achieve a chemical bond between layers...If you cant achieve this chemical bond because the paint has fully cured you must sand the surface to create a mechanical bond.....very difficult and prone to contamination. I normally see the yachts blasted and primed and antifouled all in the same phase...all coats of paint wet on wet. even the antifouling is applied wet on wet according to a schedule. . I would be amazed if any paint contractor told you differently. The secret to quality bottom jobs is to keep the paint surfaces sterile while you work.....put a coat of primer on today with the overcoat scheduled for tommorow morning and that night it rains or you have a very heavy morning dew... water runs down down the deck scuppers and contanimates the freshly primed sterile underwater paint surface.... Walk thru any shipyard and look at the bottom of yachts and you will see the paint adhesion problems formed by drain water....these contanimated areas are so easy to spot because they are in straight lines mimicking the fall of the water stream directly under drains. I have one myself on the port bow. . PLUG or pipe the water away from the bottom . I have actually seen Gutters...like on a house, duct taped to waterlines to keep the bottom sterile. Insist that the yard is super clean. By the way, airless spray is superior for bottom work...the paint film thickness is greater and more even. For instance Micron technical data sheet calls for 4 coats by roller or 2 coat by airless spray to achieve the film thickness required . As far as how long the interval between sandblasting routines > Hmmm good question. 10 years sounds a bit short...Ill ask around. Not good to sandblast a boat often ...each time you blast you erode the thickness of the steel hullplate. Very good idea to gather the technical data sheets on the products you propose to use. Your on a big yacht...perhaps the paints you will use carry unfamiliar Industrial names.
BjornDB
Posted: Tuesday, April 27, 2010 7:39 PM
Joined: 13/02/2009
Posts: 23


Thanks junior! I am aware of the wet on wet procedure. I was thinking more about the AF; i thought it could only sit dry for so long before it starts to deteriorate? If 3 months is acceptable then we can do all wet on wet right at the beginning.

also we are not sand blasting; we are hydro blasting at 40'000 psi. the obvious advantage that there is no erosion of any kind. We will be doing this in Mexico where labor and products are cheaper, making it a perfect moment to do something as expensive as this project.

Apart from looking at your usual yacht solution, I am also looking at the commercial paint system Ameron. 2 coats of primer and 2-3 coats of AF and you don't have to come out again for 5 years. I am still waiting on pricing...

junior
Posted: Tuesday, April 27, 2010 8:52 PM
Joined: 14/01/2009
Posts: 1026


Hydro blasting is the wave of the future...Ive never been involved with a project. Neither shipyard that I use offers it....Soon they will in order to conform to Environmental regs. American Bureau of Shipping doc. http://www.scribd.com/doc/24689452/Marine-Application-Maintenance-of-Marine-Coatings My understanding is that hydro blasting uses " Surface tolerant " primers. Exactly what that means ????? http://ppgamercoatus.ppgpmc.com/ http://www.airblast.com/Tech%20Tips%20Hydroblasting%20Standards.pdf
junior
Posted: Tuesday, April 27, 2010 9:02 PM
Joined: 14/01/2009
Posts: 1026


Oh and five years sounds like wishful thinking !!!!!!!!! Are you the owner or something ??????????? Ive never been able to stay in the water more than two years...always some bow thruster shaft seal eaten by monofilament fishing line, dinged prop, frozen thru hull or dead transducer. As a result I apply less than the recommended "full" anti foul coating....one coat and come out of the water often . Not sure what antifouling would look like on a yacht at after 5 years...let alone the anodes, props ....
aaurquhart
Posted: Tuesday, April 27, 2010 9:34 PM
Joined: 04/03/2010
Posts: 2


Bjorn, Andy here from Ocean Marine. I would suggest that you go to my best source on matters like these. Joe Purtell from Interlux, 954 494 0841
BjornDB
Posted: Tuesday, April 27, 2010 10:30 PM
Joined: 13/02/2009
Posts: 23


Wouldn't that be nice hey, not having to come out for 5 years?! I have to admit you're right; quickly putting another coat on is easily and quickly done whenever you're out of the water so no need to try and find AF that would triple outlast the break in between haul-outs. I also have comprehensive information on the hydroblast procedures that say exactly what's in the pdf you posted so we're on the right track.

Andy Ocean Marine: I'm getting prices and specs from all the big names incl Interlux. Joe's next on my list - thanks for his number!

junior
Posted: Wednesday, April 28, 2010 12:16 PM
Joined: 14/01/2009
Posts: 1026


Commercial shipping gets long periods between antifouling because the ships are in motion and this movement erodes the spent surface layer of toxin to expose fresh toxin. Yachts sitting still dont erode the antifouling. I regularly see totally fouled 2 years bottoms on stationary yachts with first class paint. Be wise with what what a salesman tells you
 
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