Why paint bottom?

[Skip K]

I have painted the bottom of my boats forever, but now that I own a small boat, 19 feet, I wonder if it is worth it? I keep the boat on a mooring in the Caribbean, true. And growth does accumulate. But I clean it off once a month, use a plastic scraper on the hard stuff, and can even clean the full keel. I use scuba to get under the bottom in those hard to reach places. Is there some reason, other than growth, to paint the bottom? If I keep it clean why paint?

 

[JamesG161]

Most boats paint for protection of Fiberglass and keeping it smooth for faster sailing.

Your Boat, Your Choice.
Jim...

 

[Alan Gomes]

I have painted the bottom of my boats forever, but now that I own a small boat, 19 feet, I wonder if it is worth it? I keep the boat on a mooring in the Caribbean, true. And growth does accumulate. But I clean it off once a month, use a plastic scraper on the hard stuff, and can even clean the full keel. I use scuba to get under the bottom in those hard to reach places. Is there some reason, other than growth, to paint the bottom? If I keep it clean why paint?

If you don’t mind more frequent cleanings there is no reason I can see.

 

[Rich Stidger]

I *think* that if there is even a slim residue of fouling, it will be conducive to promoting faster attachment of new fouling.
But give it a try. If it doesn't work to your satisfaction, then paint.

 

[LakeShark]

The lack of paint with the proper primer on a boat left in the water may also lead to an increased number of blisters in the gelcoat because the gelcoat is porous.

 

[Ralph Johnstone]

The lack of paint with the proper primer on a boat left in the water may also lead to an increased number of blisters in the gelcoat because the gelcoat is porous.

Could you please supply your source for that information ? Thanks.

 

[Alan Gomes]

The lack of paint with the proper primer on a boat left in the water may also lead to an increased number of blisters in the gelcoat because the gelcoat is porous.

Bottom paint does not prevent blisters. For that a barrier coat is needed.

 

[LakeShark]

Could you please supply your source for that information ? Thanks.

Most of my knowledge is from many years of experience and working in Marine yards, owning many vessels, and the teachings of the "Old Salts" I have met along the way. However the porous properties of Gelcoats are well documented and can be found through an easy google search.

"Is the gel coat what causes the blisters on your boat? Nope. It’s unable to prevent them either, though. The surface moisture that causes the blisters will be absorbed right through the gelcoat. After that it goes to the lower layers."

(How to Repair Boat Hull Blisters AKA Chicken Pox | Boat Safe | Water Sports, Product Reviews, and Nautical News)

Some boats are naturally more prone to blistering than others. For instance Hunters made in the late 90s and early 2000 had a very soft gelcoat that needed to be sanded with 60 grit to expose voids in the gelcoat layup so that they could be faired before painting. Other manufactures has a harder gelcoat with Jeanneau and Catalina being on the harder side in the same years. I am no chemist, just was a yard rat who prepped a bunch of brand new boats as they came from the factory to the yard before being first launched. Boats at the time I could only dream of owning one day.

Now I trailer sail my boat now and would actually prefer gelcoat as the hull has plenty of time to dry between outings. However over the years I have had both large and small boats (even lived onboard for over 11 years) and generally those boats with no bottom paint tended to gain more blisters than others. Its not a guarantee but the OP asked for opinions as to the potential issues of leaving a small boat on a mooring in the warm tropical salt waters of the Caribbean.

Painting a properly prepped gelcoat surface with the proper epoxy primer "seals" somewhat the porous nature of the gelcoat to prevent water intrusion to the underlying layers. If it were not necessary or needed then it would not be such a big part of the marine industry today. However were only talking about a 19 foot boat here so even blisters will be less of a big deal than they would be on a larger 60+ footer that requires lifting equipment and yard time to repair.

 

[LakeShark]

Bottom paint does not prevent blisters. For that a barrier coat is needed.

Looks like I was replying at the same time. But my statement is clear that it requires the proper "primer" albeit a barrier coat, Zink oxide, etc.. depending on hull material and sailing waters (salt or fresh).

 

[Skip K]

Thanks for the insights. I did paint the bottom with some kind of antifouling bottom paint two years ago, and now get grass and seaweed growing at the water line, barnacles and soft slimy stuff on the bottom. The first year I used a sponge to clean the bottom, once every three months. I now use a plastic paint scrapper and most of the stuff comes right off, a few hard barnacles seem to take an extra bit of scrapping, and I am doing it monthly. I see bottom paint and a barrier coat in the future and a hard look at the bottom for blisters. It looked good two years ago, and I don’t feel any blisters ( or see any)…but I think for peace of mind I will have look out of the water!

 

[Ralph Johnstone]

Most of my knowledge is from many years of experience and working in Marine yards, owning many vessels, and the teachings of the "Old Salts" I have met along the way.

Working in marine yards and the teachings of "Old Salts" are two of the most unreliable sources of crap you will come across. Do some reading from respected authors such as Nigel Calder and other published authors in order to deal in facts.

For instance Hunters made in the late 90s and early 2000 had a very soft gelcoat that needed to be sanded with 60 grit to expose voids in the gelcoat layup so that they could be faired before painting.

Where do you get this rubbish from ? I have never heard that one before. My Hunter is a 1999 with no soft gel coat problems, deck or hull.

Please do not post these unfounded statements unless you can produce a reliable source for your claims. There is a real danger that someone may believe you.

 

[LakeShark]

Where do you get this rubbish from ? I have never heard that one before. My Hunter is a 1999 with no soft gel coat problems, deck or hull.

Please do not post these unfounded statements unless you can produce a reliable source for your claims. There is a real danger that someone may believe you.

Wow man this is a public forum not a how to book. How do I know about hunters because I have personally sanded them by hand and watched the sanders sink through the gelcoat into to the glass layers. I have watched a brand new boat be covered in filler just to get a fair bottom due to all the divots created by bad gelcoat application while prepping for barrier coat. If you don't have anything to say regarding the original question and are just looking for an argument well. Go somewhere else

Oh and by the way

Boats are supposed to be fun!

 

[jon hansen]

nigel calder has a collage degree in philosophy. not an engineer, not an electrician.

he is not a trained seaman, not from an academy, prolly not even an able bodied seaman.

why would anybody listen to what he wrote? he's an "OLD SALT" he was/is curious, figured a few things out. was willing to share for a price.

here we share for free. it's only worth what you paid for it.

 

[stickinthemud57]

I bought my boat without any bottom paint (never kept in the water), but because I would be keeping it in a slip (freshwater) I asked around regarding bottom paint. The advice I got from those I spoke with recommended VC17M, and instructions with that product recommended the application of multiple coats of Interprotect, an epoxy paint, to prevent blistering. One person I spoke with said that all of that was unnecessary if the gel coat was applied properly and the bottom was cleaned regularly. I went ahead with the process just to be on the safe side. It was quite a chore. If I had it to do over I might approach it as the OP is doing and keep a close eye out for blistering.

 

[rgranger]

An experiment that I would like to see (for a boat treated the boatway you were treating yours) would be to take a block of hard paraffin wax in between scrapings and rub it over the bottom of the boat after a cleaning. see if that Discourages aor encourages growth. Maybe just rub it over a small area and then compare it later to see if it’s any better or worse than the Raw hull.

 

[rgranger]

Sorry that last post was done with voice command and it’s a little goofy

 

[stickinthemud57]

Sorry that last post was done with voice command and it’s a little goofy

LOL. I use voice-to-text a lot in my work. It's great boon and a fiendish imp all at the same time.

Regarding your proposed "experiment", give it a try and let us know how it goes!

 

[Ralph Johnstone]

As long as no one believes this disinformation :

The lack of paint with the proper primer on a boat left in the water may also lead to an increased number of blisters in the gelcoat because the gelcoat is porous.

............................... no harm done.

 

[stickinthemud57]

As long as no one believes this disinformation :



............................... no harm done.

"Disinformation" is a strong word, indicating a deliberate attempt to mislead.

I would be curious as to what part of that statement you consider to be incorrect. Also, what causes pitting, if not water infiltrating the gel coat?

 

[Davidasailor26]

Also, what causes pitting, if not water infiltrating the gel coat?

Osmotic blistering is by definition water penetrating the gel coat. The problem is that antifouling paint and many primers do not effectively prevent that osmosis. The ways to prevent it are either vinylester (rather than polyester) gel coat, or an epoxy barrier coat built up to the specified thickness (which is more than just one or two primer coats).