Scrape, Sand, Or Chemical Strip: Anti-Fouling Paint Removal

Four linear feet of hull scraped

I know… lovely photo.  Could actually be mistaken for abstract art.  But no, there is nothing artistic about scraping bottom paint.  Nothing easy either.  What you are looking at represents the end of my scraping effort.  But, some background first:

When our boat was hauled this winter, I knew I had to address some paint and finish issues below the water line.  Here’s why: usually at spring launch, the boat easily achieves hull speed, with its nice smooth, clean bottom paint.  Not so last spring.  It started half a knot off normal at launch, and of course, didn’t improve through the season as the bottom fouled.  A bell went off in my head when I realized this was happening.  It was an ‘aha’ moment, as I connected the un-smooth finish I’d applied last spring at commissioning time to boat speed I was experiencing.  I wondered about this when painting the bottom – can the un-smooth finish slow the boat that much?  Now I knew the answer.  I also knew I needed to do something about it.

Since I am semi-retired, I have a fair amount of time to do things like this.  Boat work is especially convenient since the boat yard is a mile from my home on the creek.  I determined to strip the bottom and reapply a proper bottom paint that will remain smooth.  So the question was, scrape, sand, or chemical strip?  Soda blasting was never an option, as I’m not flush with cash now that I’m retired. For a similar reason, I was avoiding chemical stripping, though I could probably do it for about half the cost of soda blasting.  So, since I have more time than money, a labor-intensive solution was okay.  I thought.

Scraping: I discovered that this is an amazing amount of work, and takes a lot of strength to remove paint that is well stuck to the bottom.  Yes, I used the good carbide scraper, and it is effective, but very difficult.  Hmmm.  Well stuck, huh?  If it’s so well stuck, why am I taking it all off?   There aren’t that many layers of old paint on it yet.  The unintended consequences of scraping include opening up those tiny blisters at the waterline which otherwise don’t hurt anything.  However, If they are opened, they have to be fixed and sealed.  This generates more work for very, very little gain in boat speed, hull integrity, or fun.  Okay.  Stop scraping.

Sanding?  Is this practical?  Well, it is also tiring, but faster and easier than scraping.  Plus the result is a smooth surface.  Scraping was going to need a finish-up with sanding anyway.  A 50 grit disc takes the paint off pretty fast.  36 grit would go faster, but then I would need to smooth it out with another round of sanding at 80 grit.  Today I managed to sand almost as much area in an hour as I scraped in about three hours.  If the winter continues mild, I should be ready for paint in March.

While we wait for spring launch, here’s another piece of abstract art to ponder:

Bow-on View
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