Why bottom paint?

M

mrsrobinson

Well-Known Member
Mar 9, 2006
7,704
Virginia
Boat Info
2001 380DA
Engines
Caterpillar 3126
Our boat has been in salt water for 7 weeks now (previous 2 seasons in fresh water). It's been scraped 2 times and we are running her almost every weekend.

Still, stuff is growing on her bottom like crazy and the running gear looks like a marsh. So I ask, what is the real purpose (#1) of bottom paint? To protect the fiberglass from blistering? And, reducing growth is just a secondary effect?

Just curious, I think "bottom paint, oh, keeps growth off the bottom"...doesn't seem to be the case.
 
There are different kinds of bottom (anti-fouling) paint for different types fouling challenges. You may not have the right paint for the job. Anit-fouling paint will not prevent blistering. Bottom paint sloughs off as the boat passes through the water. Taking with it the growth that has attached.

My anti-fouling paint has to be applied every year as it ceases to work after it has been out of the water over the winter layup.

Barrier paints can help with osmosis and blistering, but can't prevent it if damage is already there.

I have a copy of Intelux's boat painting guide.

http://www.yachtpaint.com

The guide writes about:
Safety - Fouling makes the boat less responsive and sits in the water lower. I guess due to the added weight.

Protection - Fouling can damage the substrate of the hull from the natural glues from the orgamisms that attach.

Speed and Efficiency - Fouling causes drag, etc.

Types of fouling - Shell, Weed, Slime
 
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So bottom paints # goal in life is to prevent growth, or help prevent it? If that's the case, why do we have to be scraped every 3-4 weeks?

We had 2 coats of hard put on our 6 months ago, while she was in fresh water. Now that she is in saltwater, all the boats around us use alblative. Honestly, per the diver, our boat looks better than theirs. And, from walking around the docks I have to agree.

So I go back to, what is bottom paint for?
 
330DA said:
There are different kinds of bottom (anti-fouling) paint for different types fouling challenges. Anit-fouling paint will not prevent blistering. Bottom paint sloughs off as the boat passes through the water. ......
Click to expand...

Not all bottom painst "slough off" The Ablative paints will slough....Modifyed epoxy paints will not.
 
osd9, My typo. Thanks for seeing it.

Greg, The bottom paints will not prevent it, but help remove it. The link I posted to Interlux has some quick to read and good explanations.
 
Also the amount of growth is inversely proportional to how much you use your boat. Boats that don’t get used and are wet slipped will see a lot of growth on the bottom while boats that get used regularly may not. This is why High-n-Dry’s and lifts are so popular in Salt water regions like FL. Very few people wet slip their boats in my next of the woods. If it’s to too big for the high-n-dry, then you put it on a lift like the one below.



deco4.gif
 
We had bottom paint on our last boat.

Things I did not like:

Scraping and re-painting was a dirty messy bad job that needed to be done about every 3 years. Having it done for me at a discount marina I was quoted $1,350.

The stuff, Micron Extra w/Boulex was expensive, about $200/gallon (more then that today) and I needed to touch up each year, using about a quart.

Even with the bottom paint we got a ring at the water line. If I used mur1atic acid on this ring so it comes right off it damaged the bottom paint below.

I’m in fresh northern, cooler water. Summer peak water temperature is low 70’s so growth is not as much as it would be in salt water our hot southern water.

Loss of top end speed and some economy bothered me.

I saw other boats going with out.

I talked to many others and discovered the biggest reason people bottom paint by us is to protect the barrier coat that prevents hull blisters. Also, modern fiberglass that is used on some builders including my boat is much less prone to hull blisters.

You can acid wash the bottom yourself or have the marina do it. I had the marina do it and they charged me $250. Less if you do it yourself.

I decided I would go without and see how it goes. This is the second summer and I’m happy I went this way.

We use our boat often and I do brush from the water line on down about 2 feet once about every three weeks. I do have some hull staining that will come off with the next acid wash when I have the boat pulled this fall.

I do not coat the hull with anything.

I’m not sure if this would work in a warmer climate.

Hope his helps.
 
Dumb question....

If a boat bottom has alblative on it and a diver is scraping it regularly, I assume the paint is getting removed during the scraping?
 
The quick answer to your question is that bottom paints (called "antifouling" paints) are designed to do just that- keep marine growth off of your boat.
There are two main types- "hard" paints, or modified epoxies, and "ablative" paints. The modified epoxy paints do not "wash-off" the hull; the copper is contained in a slow release compound within the paint and is gradually released into the water. Ablative paints, on the other hand, are formulated/designed to gradually wear away (slough) as the boat moves through the water, constantly exposing a "fresh" surface containing the antifouling.

With that said, the primary ingredient in both types of paints is copper (in differing formulations), and the bottom line is this- the more copper content, the better the antifouling properties. Some "cheap" brands contain far less copper which may be suitable for colder, northern waters. The "top shelf" brands, like Petit Trinidad, contain up to 76% or so copper- which makes them both expensive, and heavy...

Ablative paints have the advantage of not building-up over the years (I just had to sandblast twenty years worth of paint off my bottom) but work best on boats that get used regularly. Ablative paints are also "multi-season", meaning the boat can be hauled and relaunched the following season and the paint will still be effective; this can't be done with modified epoxies.
Modified epoxies are best suited for boats that are used less frequently (like mine).

You say your running gear "looks like a marsh". The running gear requires special prep, primers and careful application to last. There is often a lot of debate about painting props- some do, some don't. There may be a small loss of performance from painting, but if I leave my props unpainted in the summer I've got growth in less than two weeks.

Bottom line is this- I'd check with the yard to see what paint they used. I'm assuming you had it painted just prior to splashing it seven weeks ago, right?
Actually, cleaning the bottom twice in seven weeks is about right. In case you didn't know, thoroughly scrubbing the hull bottom and gear is required once a month- sometimes more during the summer months (my water temp is 88 degrees), somewhat less (maybe 6 or 7 weeks) during the winter. But, it is scheduled maintenance and has to be done. If you don't dive, you'll need to hire a diver to do it for you. I made up a 50 ft. hookah rig so I can do mine without having to strap the tank on my back.

The problem you're experiencing desn't seem right to me (and I've had boats in the water for over twenty years). With a fresh bottom job-done properly with a quality paint (BTW- two coats with a third at the waterline is the "standard") you shouldn't have that much growth in such a short period.

I'd contact the yard that did the work for you.
 
Presentation said:
We had bottom paint on our last boat.

Things I did not like:

Scraping and re-painting was a dirty messy bad job that needed to be done about every 3 years. Having it done for me at a discount marina I was quoted $1,350.

The stuff, Micron Extra w/Boulex was expensive, about $200/gallon (more then that today) and I needed to touch up each year, using about a quart.

Even with the bottom paint we got a ring at the water line. If I used mur1atic acid on this ring so it comes right off it damaged the bottom paint below.

I’m in fresh northern, cooler water. Summer peak water temperature is low 70’s so growth is not as much as it would be in salt water our hot southern water.

Loss of top end speed and some economy bothered me.

I saw other boats going with out.

I talked to many others and discovered the biggest reason people bottom paint by us is to protect the barrier coat that prevents hull blisters. Also, modern fiberglass that is used on some builders including my boat is much less prone to hull blisters.

You can acid wash the bottom yourself or have the marina do it. I had the marina do it and they charged me $250. Less if you do it yourself.

I decided I would go without and see how it goes. This is the second summer and I’m happy I went this way.

We use our boat often and I do brush from the water line on down about 2 feet once about every three weeks. I do have some hull staining that will come off with the next acid wash when I have the boat pulled this fall.

I do not coat the hull with anything.

I’m not sure if this would work in a warmer climate.

Hope his helps.
Click to expand...

Hey Doug - being a former Michigan boater and now a Florida boater, I'd have say that there is a difference. The worse thing in MI were zebra mussels. I'm guessing they've probably made their way to WI by now. Down in Florida, there is constant junk that wants to grow on the boats. Bottom paint is pretty much a must if you have to keep your boat in the water. We do the rack storage thing, which is great - your zincs stay in once piece and you don't have to worry about getting the boat scraped. I've talked to a few people at our marina who have to get their boat scraped monthly - they say that bottom paint makes it easier to get the barnacles off. That's just a handful of people that I've spoken to around the dock, so it's a pretty unscientific survey.

I'm glad that I don't have to bottom paint down here, but that just means that it's more to wax , LOL! ;)
 
Ablative paints offer the advantage of minimizing the build up of paint on the bottom. But you have to keep in mind that if you do use ablative paint you will have to go easy when you have your bottom scrubed. Otherwise, you will prematurely remove the paint from the hull.
 
The other thing to keep in mind is that once you paint ablative, you can never switch to hard paint unless you remove all of the ablative. You can however paint hard and then switch to ablative without removing the hard paint.

Doug
 
The growth on ours is not bad. I hit WOT every time I run her. In 7 weeks she has been dived on one time, scheduled for 2nd time this week.

She was painted with Interlux BottomKote with Irgarol in January, when in fresh water, prior ot us deciding to go to salt for the summer.

This weekend the Mrs and I both noticed how awful looking the trim tabs look, tons of growth. That's when I was informed by locals the running gear needs to be scraped too. So now we are on a monthly scraping schedule for the bottom and running gear.
 
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The BottomKote is 42% copper, Trinidad is 70% (I incorrectly said 76%).
If you have problems with growth, you should consider switching at the next bottom job.
 
water rat said:
Actually, we don't get the bottom of the boat, but we do get the entire side, so yes, part is under the water line. Why? Just because it's there and it's a layer of protection.
Click to expand...


If only the sides it’s likely no big deal.

The reason why I asked is I see other people at our marina wax the bottom of their boat. They need to lie on their back and get in all sorts of funky positions to get it all done. Arms get soar, junk gets in their eyes.

What are the benefits of waxing the bottom? None that I can think of.

What are the drawbacks? Slower boat and more fuel consumption due to greater water adhesion. People who race boats will gladly wax the bottom of their competitor’s boat, sometimes with out asking and in the middle of the night.
 
You might want to look into getting a boat bunker (boatbunkers.com). I'm on my 2nd boat with one, my last being a 25' Doral without any bottom paint and keeping it in the water in the bunker was great...no growth and never had any problems other than cleaning the scum line. With my 320, the bottom is painted, but I won't have to repaint for a long time since again nothing grows on it. Yes a lift would be awesome, but for the weight of the boat, the price of the lift was way too expensive.. You can send me a PM if you want more info or photos of it.

Barry
 
Bottom coat is a hard, non-ablative paint. As soon as you get a little slime on the paint from non-use, Bottom coat is almost useless because the antifouling particles are covered up and cannot do their job. Every geographical location is different so I can't say how long a boat can sit in Va, but down here, commercial boats that are used daily or every few days all use hard paint with great success. Pleasure boaters who will let a boat sit for a couple of weeks have terrible luck with hard paints and all use ablatives.
 
In australia, we have this new product, that to me it appears like lanoline with fine copper powder mixed in it.. Lanoline is a well known protector for trailers etc.. As its winter here i have not tried it yet, but have got 2 jars of the stuff to test very soon. Its very cheap, and you can put it on and take it of at home in 1 or 2 hours. The great thing about this is once you put it on.. you finished for the summer, you can take it completely off with a pressure washer and/or citric acid (so resale value is high because looks as though you never had bottom paint). It goes on paper thin, and can be used on fiberglass aluminium stainless etc. From comments i have heard it works great.. only thing i am not sure of, is how well it holds when you go 40knts.. on slower boats i think would be perfect. I have put some on a knife blade, then put it under the tap fully opened, and it seems to hold very well. Should find out in a few months when putting the new boat in the water (sydney harbour - salt water)
 
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