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Author Topic:   Bottom Paint: For What Purpose

goalie74 posted 05-04-2009 12:06 PM ET (US)
What is the purpose of [bottom paint]? [I] purchased 1967 Boston Whaler 13-footer last year and have been refurbishing the engine and the interior. [I put] a product called "Newglass" on the hull. [I plan] on docking the boat at a lake house in Kentucky, so it will spend the summer in the water. Do I need to put bottom paint on the boat?
certif658 posted 05-04-2009 01:09 PM ET (US)
If you're going to use the boat in fresh water or store it out of the water (i.e. on a lift or trailer) for salt water usage there is no reason for bottom paint in my opinion. Bottom paint for salt water usage is mainly to keep the barnacles from growing on the boat.
TransAm posted 05-04-2009 01:28 PM ET (US)
If you boat will be regularly sitting in the water for more than a week or 2, you should apply bottom paint regardless of whether it is in salt or fresh water. Although there may be less to worry about in fresh water, fiberglass is a porous material and when immersed in water for long periods of time you still need protection from things like osmotic blisters. If it is your intention to regularly store your boat wet, I would paint the bottom. Research the correct paint for your application as there are many formulations for different applications. Remediating blisters can be a very expensive exercise.
Tohsgib posted 05-04-2009 01:51 PM ET (US)
While what T/A says is very true I have kept many unpainted boats in salt water for entire seasons and never encountered any blisters. I would scrub the bottom every weekend at a sandbar to keep it clean. Yeah it would be a tad yellow but clean. Once a month or so I would yank it and acid wash it, clean the whole boat and wax it and drop it back in. Fresh water I believe you would just need to scrub the slime off every week or so.
jimh posted 05-04-2009 03:23 PM ET (US)
The topic of bottom paint is covered in your owner's manual. If you do not have a copy of your owner's manual you can look at mine:
http://continuouswave.com/whaler/reference/manual9-17/maintenance. html#bottom
certif658 posted 05-04-2009 07:06 PM ET (US)
Sorry, I should have been more clear in the first post: in my experience you shouldn't need bottom paint in fresh water unless the water has a significant amount of bacteria. I kept a boat with no bottom paint in the water for a couple of seasons in the Adirondacks, where the water is very clean, without any problems. The bottom didn't even need a good scrubbing at the end of the summer!
However, when we put the boat in the water in a lake in Northern NJ we had problems with the slime build up. Bacteria got into the gelcoat causing blistering resulting in a $1000 repair job. I didn't want to paint the bottom of the boat so we put it on a lift.
If you decide not to bottom paint but get some slime build up I would suggest using On Off. Be careful as it's a strong acid, but it will take everything off without damaging the fiberglass.
jimh posted 05-04-2009 08:03 PM ET (US)
Bottom paint is a general term for anti-fouling paint, that is, a paint whose composition is designed to prevent the growth of marine organisms.
A barrier coat is a coating applied with the intention of creating a waterproof barrier so that the resin of the fiberglass hull is not permeated with water. I think the Boston Whaler owner's manual is rather clear about what should be done. I would follow their recommendations.
jimh posted 05-04-2009 10:05 PM ET (US)
With the warm water temperatures that you will have in a lake in Kentucky, you will probably have plenty of marine growth. The best indicator of the need for anti-fouling paint is the practice and experience of other local boaters. If no one uses anti-fouling paint it is probably not needed.
pglein posted 05-05-2009 02:03 PM ET (US)
Fresh or salt, you will want anti-fouling bottom paint of one kind or another if you intend to keep the boat in the water for extended periods of time. Anecdotal reports of minimal growth in fresh water do not offset the mountain of evidence supporting the idea that you will experience growth of some sort in any environment. The idea of scrubbing the bottom of my boat weekly, and acid washing it every 30 days is not very appealing. Instead, the application of an abblative anti-fouling paint once every 2-3 years (which is all that should be necessary for a boat kept in the water only in the summer) sounds a lot more simple and effective.
And, contrary to popular belief, an ablative bottom paint can be removed relatively easily, leaving the original, undamaged gelcoat behind.
Buckda posted 05-05-2009 03:49 PM ET (US)
I find it difficult to accept a claim that bacteria caused blistering of a hull. It is most likely that the blistering is from osmosis.
Fresh or salt water, a barrier coat is needed to reliably protect a wet-slipped boat from blistering through the process of osmosis.
While an unpainted freshwater slipped boat will not grow barnacles, it will grow zebra mussels and an algae "beard". I've seen plenty of these even on boats with old bottom paint here in the rivers and bays of the Great Lakes region.
If you plan to keep your hull in the water, you want a barrier coat followed by a coat or two of ablative bottom paint. The barrier protects against osmotic blistering and the ablative bottom paint protects against marine growth - both plant and animal.
Don't let the ocean-going gents on this site fool you with their assumptions about fresh water. They will sometimes try to tell you that the Great Lakes aren't dangerous as well.

Tohsgib posted 05-06-2009 12:05 PM ET (US)
Again I disagree. I have NEVER gotten a blister in my entire boating career....except form sanding mahogany.
Buckda posted 05-06-2009 12:12 PM ET (US)
Nick -
Neither have ANY of our hulls, which sat in the water all summer on Lake Huron, unpainted.
That said, to RELIABLY protect your hull, a barrier coat and bottom paint are needed.
Since we don't live in the channel into which this individual will place his boat, saying anything else is irresponsible.
Tohsgib posted 05-06-2009 12:38 PM ET (US)
Since we don't know what "Newglass" is either than we should all just keep quiet. Maybe barrier coats and bottom paint won't stick to "newglass" and we telling him to do so is gonna be a nightmare. On a 1967 boat, anything is possible.
Buckda posted 05-06-2009 12:42 PM ET (US)
http://www.newglass2.com/cgi-bin/cp-app.cgi
Now we know what Newglass is.
I stand by my counsel that the only way to RELIABLY prevent osmotic blistering is to store the boat out of the water, or to put a bottom coat/barrier paint on.
Fresh or salt water.
Tohsgib posted 05-06-2009 02:37 PM ET (US)
Oh no...polymer junk that does not work 20% as well as what the bottle says.

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Author	Topic: Bottom Paint: For What Purpose
goalie74	posted 05-04-2009 12:06 PM ET (US) What is the purpose of [bottom paint]? [I] purchased 1967 Boston Whaler 13-footer last year and have been refurbishing the engine and the interior. [I put] a product called "Newglass" on the hull. [I plan] on docking the boat at a lake house in Kentucky, so it will spend the summer in the water. Do I need to put bottom paint on the boat?
certif658	posted 05-04-2009 01:09 PM ET (US) If you're going to use the boat in fresh water or store it out of the water (i.e. on a lift or trailer) for salt water usage there is no reason for bottom paint in my opinion. Bottom paint for salt water usage is mainly to keep the barnacles from growing on the boat.
TransAm	posted 05-04-2009 01:28 PM ET (US) If you boat will be regularly sitting in the water for more than a week or 2, you should apply bottom paint regardless of whether it is in salt or fresh water. Although there may be less to worry about in fresh water, fiberglass is a porous material and when immersed in water for long periods of time you still need protection from things like osmotic blisters. If it is your intention to regularly store your boat wet, I would paint the bottom. Research the correct paint for your application as there are many formulations for different applications. Remediating blisters can be a very expensive exercise.
Tohsgib	posted 05-04-2009 01:51 PM ET (US) While what T/A says is very true I have kept many unpainted boats in salt water for entire seasons and never encountered any blisters. I would scrub the bottom every weekend at a sandbar to keep it clean. Yeah it would be a tad yellow but clean. Once a month or so I would yank it and acid wash it, clean the whole boat and wax it and drop it back in. Fresh water I believe you would just need to scrub the slime off every week or so.
jimh	posted 05-04-2009 03:23 PM ET (US) The topic of bottom paint is covered in your owner's manual. If you do not have a copy of your owner's manual you can look at mine: http://continuouswave.com/whaler/reference/manual9-17/maintenance. html#bottom
certif658	posted 05-04-2009 07:06 PM ET (US) Sorry, I should have been more clear in the first post: in my experience you shouldn't need bottom paint in fresh water unless the water has a significant amount of bacteria. I kept a boat with no bottom paint in the water for a couple of seasons in the Adirondacks, where the water is very clean, without any problems. The bottom didn't even need a good scrubbing at the end of the summer! However, when we put the boat in the water in a lake in Northern NJ we had problems with the slime build up. Bacteria got into the gelcoat causing blistering resulting in a $1000 repair job. I didn't want to paint the bottom of the boat so we put it on a lift. If you decide not to bottom paint but get some slime build up I would suggest using On Off. Be careful as it's a strong acid, but it will take everything off without damaging the fiberglass.
jimh	posted 05-04-2009 08:03 PM ET (US) Bottom paint is a general term for anti-fouling paint, that is, a paint whose composition is designed to prevent the growth of marine organisms. A barrier coat is a coating applied with the intention of creating a waterproof barrier so that the resin of the fiberglass hull is not permeated with water. I think the Boston Whaler owner's manual is rather clear about what should be done. I would follow their recommendations.
jimh	posted 05-04-2009 10:05 PM ET (US) With the warm water temperatures that you will have in a lake in Kentucky, you will probably have plenty of marine growth. The best indicator of the need for anti-fouling paint is the practice and experience of other local boaters. If no one uses anti-fouling paint it is probably not needed.
pglein	posted 05-05-2009 02:03 PM ET (US) Fresh or salt, you will want anti-fouling bottom paint of one kind or another if you intend to keep the boat in the water for extended periods of time. Anecdotal reports of minimal growth in fresh water do not offset the mountain of evidence supporting the idea that you will experience growth of some sort in any environment. The idea of scrubbing the bottom of my boat weekly, and acid washing it every 30 days is not very appealing. Instead, the application of an abblative anti-fouling paint once every 2-3 years (which is all that should be necessary for a boat kept in the water only in the summer) sounds a lot more simple and effective. And, contrary to popular belief, an ablative bottom paint can be removed relatively easily, leaving the original, undamaged gelcoat behind.
Buckda	posted 05-05-2009 03:49 PM ET (US) I find it difficult to accept a claim that bacteria caused blistering of a hull. It is most likely that the blistering is from osmosis. Fresh or salt water, a barrier coat is needed to reliably protect a wet-slipped boat from blistering through the process of osmosis. While an unpainted freshwater slipped boat will not grow barnacles, it will grow zebra mussels and an algae "beard". I've seen plenty of these even on boats with old bottom paint here in the rivers and bays of the Great Lakes region. If you plan to keep your hull in the water, you want a barrier coat followed by a coat or two of ablative bottom paint. The barrier protects against osmotic blistering and the ablative bottom paint protects against marine growth - both plant and animal. Don't let the ocean-going gents on this site fool you with their assumptions about fresh water. They will sometimes try to tell you that the Great Lakes aren't dangerous as well.
Tohsgib	posted 05-06-2009 12:05 PM ET (US) Again I disagree. I have NEVER gotten a blister in my entire boating career....except form sanding mahogany.
Buckda	posted 05-06-2009 12:12 PM ET (US) Nick - Neither have ANY of our hulls, which sat in the water all summer on Lake Huron, unpainted. That said, to RELIABLY protect your hull, a barrier coat and bottom paint are needed. Since we don't live in the channel into which this individual will place his boat, saying anything else is irresponsible.
Tohsgib	posted 05-06-2009 12:38 PM ET (US) Since we don't know what "Newglass" is either than we should all just keep quiet. Maybe barrier coats and bottom paint won't stick to "newglass" and we telling him to do so is gonna be a nightmare. On a 1967 boat, anything is possible.
Buckda	posted 05-06-2009 12:42 PM ET (US) http://www.newglass2.com/cgi-bin/cp-app.cgi Now we know what Newglass is. I stand by my counsel that the only way to RELIABLY prevent osmotic blistering is to store the boat out of the water, or to put a bottom coat/barrier paint on. Fresh or salt water.
Tohsgib	posted 05-06-2009 02:37 PM ET (US) Oh no...polymer junk that does not work 20% as well as what the bottle says.