Removing old bottom paint

[moakie]

What's the best way to remove old bottom paint?

The paint is very chalky and thin enough to see the white gelcoat in places. I would like to just remove it if possible. The boat will not be moored and will be used in fresh water.

 

[jcastle]

If it's that thin it should be fairly easy with a Marine Paint Stripper. The key is to keep it moist so it keeps working through the layers (in your case doesn't sound like many). As long as you're seeing gelcoat under the paint so you know a high build primer wasn't used and you can restore the gelcoat easily.

 

[dpmulvey]

Fresh water and bottom paint are not mutually exclusive. I see you are in Northern MN. I realize you have a 5 to 8 hour boating season up there! BUT.... Is there anything in the water that could cause gunk to stick to the bottom (read more fuel burn). Also, I hope Frank chimes in here, is there a need to coat the boat with something to preclude blistering.

 

[fwebster]

With a 1973 model hull, that means you do not have vinyl ester resin so your boat is much more susceptible to osmotic blistering on the hull. Freshwater storage seems to be more prone to blisters than a boat slipped in salt water. Since you already have bottom paint and given how hard and expensive it is to remove old paint and end up with a pristine slick hull, I think it only makes sense to properly prepare the hull for bottom paint then paint it with a high quality (expensive!) bottom paint with a slime or algae resistant component like Interlux Ultra w/Biolux or Sea Hawk Tropikote Biocide Plus. Both are effective against zebra muscles, if you have them where you are.
If there is already evidence of blistering, then you need to prime the bottom with a barrier coat like Interlux Interprotect 2000E before bottom painting.

Without a bottom paint, you will have a performance problem as algae and scum form on the boats hull. With bottom paint, at least you can remove what little growth you get with a good pressure wash at the end of the season.

 

[Lazy Daze]

Moakie, if the bottom paint job was done correctly, the surface of the gelcoat would have been distressed (either physically or chemically). Meaning, it's not going to look good. In fact, it will look much worse than a fresh coat of bottom paint. To get it back to "nice looking" will take many, many hours or labor that, I'm sure most will agree, is not something you'd want to do. And if you paid someone to do it, it would cost much more than a bottom paint job. But, take note to where Frank is talking about blistering - bottom paint does NOT protect against blistering. However, if you're not going to keep it in the water for the season, I wouldn't worry too much about any blisters you find.

 

[Turkj40]

I just used Aqua-strip from west marine (I was willing to try anything after sanding half of the boat. 1 hr to put a nice thick coat about 1-1/2 gallons of the stuff on half of my 320 let it set for 8 hrs then used my pressure washer to remove it. In one day I had it stripped and sanded ( some of the paint does stick) compared to 3 days of sanding the other side.

 

[SkiPharmer]

I boat in MN too and I was under the impression that bottom paint was only for looks and keeping algae off your boat. I've always acid washed my boat at the end of the season.