Questions About Bottom Paint

[cousineddy]

I can read technical data sheets on bottom paints. They tell you the what, but not the why. I got questions.
1. Why is there a maximum dry time before launch with some paints?
2. Why do you need 5 coats of barrier primer, instead of 2?
3. If the techsheet says paint is dry to touch in a half hour, recoat in 4 hours, launch in 8 hrs. What happens if you recoat in 1 hour, launch in 4 hours? Whats the trade off? People do this all the time and say no issues. Boatyards too.
4. If your old paint wipes off with brushing thinner, why do you need to sand it with 80 grit before applying new paint. Wont the old paint dissolve into the new paint?
5. If racing paint like VC-17 provides a slick and hard racing finish, what good is it if its fouled with algae? Would you want the strongest antifouling performance on a race boat?

 

[dlochner]

I can read technical data sheets on bottom paints. They tell you the what, but not the why. I got questions.
1. Why is there a maximum dry time before launch with some paints?
2. Why do you need 5 coats of barrier primer, instead of 2?
3. If the techsheet says paint is dry to touch in a half hour, recoat in 4 hours, launch in 8 hrs. What happens if you recoat in 1 hour, launch in 4 hours? Whats the trade off? People do this all the time and say no issues. Boatyards too.
4. If your old paint wipes off with brushing thinner, why do you need to sand it with 80 grit before applying new paint. Wont the old paint dissolve into the new paint?
5. If racing paint like VC-17 provides a slick and hard racing finish, what good is it if its fouled with algae? Would you want the strongest antifouling performance on a race boat?

1) Ablative paints lose their effectiveness if allowed to dry too much. The paint hardens and it won't ablate as well. It may prevent the pesticide in the paint from leaching out and doing its job.

3) With solvent based paints, it is important to let the solvents evaporate. Allowing the extra time makes sure the solvent has fully evaporated. Overcoating too soon can trap the solvent in the first coat preventing it from fully curing.

4) Sanding increases the surface area increasing the paints ability to bond to the surface. A solvent wash does not increase the surface area. The new coat of paint does not chemically bond to the old surface, it is an adhesive bond. The solvent in the new paint may actually make the surface smoother.

5) Serious racers clean their bottoms before important races. Racers like VC-17 because it forms a very smooth and slick surface that is easy to clean and maintain. Some believe the coating reduces friction between the hull and the water.

 

[cousineddy]

1) The ablative paint I just used didn’t have a max dry time, but the bottom kote hard paint had a 60 day max out time.
3) How do solvents evaporate after the paint is dry? Seems like they wouldn’t be able to escape.
4) I sanded the bottom as instructed, but then it instructed to wipe with brushing thinner before applying new paint. The bushing thinner disolved the old paint and it wiped off on the rag. The 80 grit finish was replaced by wipe marks from the rag. The new paint solvent is the same as brushing thinner. So, it should have blended with the old paint, no mechanical adhesive bond is possible. Seems like if the recommended brushing thinner dissolved the old paint, whats the point of sanding all day long.
5) My old paint was “racing paint”. Bottom Kote Racing Bronze. Had a slick hard finish when fresh. I brushed the bottom before every race. Pulled the boat after 2 years and it was caked with growth. Shocking.

 

[Davidasailor26]

2) Barrier coats need to be a specific thickness to effectively block water intrusion. If you’re just using the barrier coat as a primer to prep the surface and ensure paint adhesion then the thickness doesn’t matter. But if you’re using it to prevent osmosis you need to reach that minimum thickness, which is often many coats. It’s also valuable to overcoat the final coat with paint before the barrier fully cures, so you get a relatively strong chemical bond between those layers.

 

[dlochner]

How do solvents evaporate after the paint is dry? Seems like they wouldn’t be able to escape.

The solvents in paint will continue to evaporate even after the paint feels dry. This may take a couple of days. It really depends on the particular coating.

1) The ablative paint I just used didn’t have a max dry time, but the bottom kote hard paint had a 60 day max out time.

The pesticide in the paint may also react with oxygen in the air which adversely affects it effectiveness.

5) My old paint was “racing paint”. Bottom Kote Racing Bronze. Had a slick hard finish when fresh. I brushed the bottom before every race. Pulled the boat after 2 years and it was caked with growth. Shocking.

Cleaning the bottom is a mixed blessing. It removes the growth, but it also removes some paint. I'm not familiar with Bottom Kote, I used VC 17 for about 30 years. VC 17 is pretty good at preventing animal growth, i.e, zebra mussels and ok with heavy growths of algae, but no paint is perfect. There are lots of factors that contribute to growth, water temperature, sunlight, and nutrients in the water are part of the equation. Although many paints advertise as multi-season paints and they are under ideal conditions for the paint, in reality 2 years of continual submersion is really pushing the limits.

 

[rgranger]

I rolled my eyes when I saw the title of this post but those were actually interesting questions.

 

[cousineddy]

I rolled my eyes when reading other threads on this subject. Most replies just say follow the instructions, but they don’t say why. Thanks! New question:

6) How long does ablative paint last?

 

[dlochner]

I rolled my eyes when reading other threads on this subject. Most replies just say follow the instructions, but they don’t say why. Thanks! New question:

6) How long does ablative paint last?

That depends. There are different kinds and qualities of ablative paints, soft paints wear off faster than hard, better quality paints last longer.

The other big variable is boat use. The more the boat is used, the faster the paint wears off. The more the bottom is cleaned, the faster the paint wears away. Boats in nutrient rich waters will have their bottoms cleaned more often than those moored in stagnant water. Boats moored in high current areas will also lose bottom paint faster.

Last year I applied an ablative paint in June, by February it was gone, but that included about 2,000 miles of travel, 2 pressure washings, and 2 aggressive boat cleanings.

Periodically Practical Sailor runs bottom paint tests. These tests are good for relative longevity in a specific area. Typically PS paints a bunch of coupons with different paints and suspends them in a marina, every few months they pull them up and inspect them for growth. These tests are good for understanding relative strengths between paints, but can not factor in boat use.

Jamestown distributors surveys it customers about their bottom paint experience in different areas. All useful information, but hardly definitive.

Ask local sailors about what they use and how it is working for them.

 

[RoyS]

The maintenance manager in my marina told me he has been studying bottom paint effectiveness for decades while he hauls and pressure washes all of the boats in our marina. Intrigued, I asked him what bottom paint he recommends. He said he had not yet reached any conclusions. I had to laugh. I use a water based, multi-season ablative. I never sand. Total recoat every four years with just chip touch ups every year. This system results in no paint build up and prevents hard growth, but fails to halt slime and eventual grass growth from accumulating. I have determined that monthly in water bottom cleaning is required and will engage a diver starting next season. Boston harbor water is full of suspended mud. Visibility is about four feet at best. Nothing grows on the seabed due to lack of sunlight down there. I do not think any paint alone will keep your bottom clean around here.

 

[jssailem]

6) How long does ablative paint last?

Until it wears off.
Being on a boat this will occur in different spots and at different rates.
Where your paint has worn thin you will notice undersea growth take hold.

Typically it is the leading edges of the rudder, bow, and keel that wear off first. The turbulence and cavitation of the water bubbles are to blame.

Your environmental conditions and the application of the paint also factor into your limits on time between repainting or not.

 

[JBP-PA]

6) How long does ablative paint last?

Not all ablative paints are the same. I found that Interlux ACT is so soft it will ablate with just a stern look. TotalBoat JD Select (water based) seems much more durable. TotalBoat Krypton seems somewhere in the middle. Note that none of these three have a max limit on the amount of time before launch. The traditional method is to make your first coats a different color than your final coats so you can see when it needs more.

 

[cousineddy]

Good information. I good visually see slime growth 1 month after the last bottom job with the bottom kote racing bronze. I was horrified. But it was on the hard 30 days before launch. So brushed every two weeks. I would brush it until I couldn’t see debris coming loose. But, when I pulled it 2 years later after continuous brushing, I couldn’t believe what I saw. So, needed to do something different, switched to ablative. I sail about 15 times a year, about 4 hours each time. I think I will pull it this summer again and check it.

 

[dlochner]

Sunlight is your enemy. Transom hung rudders are the worst for bottom growth because they get lots of sun. There is no bottom paint that will prevent this. The side of the boat away from the dock will always have more growth than the dock side. On my boat, the top of the wings on the keel will get growth even when the rest of the keel is pretty clean. Likewise there is usually more growth right at the waterline.

 

[jssailem]

Only way I have combated this issue is to call up the diver and ask for a scrub before I go out sailing.

It has worked for the past several years. When I can sail the boat, the movement helps to keep the buggers at bay... A little less need for the diver's intervention.

Going to paint the bottom as soon as the temps are friendly to the paint drying.

 

[cousineddy]

Here is a photo of the hull. Eeek!

 

[dlochner]

Here is a photo of the hull. Eeek!

yep, time to redo the bottom!

 

[JamesG161]

You should note you sail in Fresh Water, In Iuka, Mississippi.

Different bottom paints needed.
_________

Sunlight is your enemy.

Nope. Water Temperatures are cold there. Slime loves to grow any where.

Without Sunlight, no winds. Sailing often is your friend.

Ask houseboat owners on the Pickwick Lake what they use.
Jim...

PS: You bottom does not look too bad.

 

[cousineddy]

My sailor friends said ablative is what I need. I used Pettit Odyssey Triton, triple biocide, and ablative. Will see if it slimes up after 1 month like the bottom kote did.

 

[capta]

If any of you finds an antifouling paint that actually works in New England waters, please, please let me know. Every sailor in the GGR is having major problems with barnacles.
It may be that the ecological rules will soon make bottom paint useless. Perhaps there will be a black market where we can get antifouling paint that actually works.

 

[rgranger]

I rolled my eyes when reading other threads on this subject. Most replies just say follow the instructions, but they don’t say why. Thanks! New question:

6) How long does ablative paint last?

I think @dlochner summed it up. I have had my boat slipped in a cold water lake in the Mountains of Virginia, a warm water lake in a lake in Alabama and now I am in a salt water tidal river. In Virginia my bottom paint held up and I basically pressure washed the bottom a few times a year with minimal algea growth. In the warm water lake of Alabama, I had to snorkle with a bursh on a handle about once a month or I would get a salad growing on the bottom. Where I am now I have a diver scrape barnacles off once a month. They grow fast and will cover the bottom in 6 weeks if I let them get a foot hold. The more I use the boat, the less problems I have.

I use ablative. In the lakes I would recoat each season but now I put on three coats at the start of the season.

My diver told me "bottom paint does not stop growth, it just makes it easier for me to scrape it off".