How much bottom paint

[unbusted67]

Hey all, I've got a 31 foot Contest I am refitting. I've taken the bottom back to gel coat and I am trying to figure out how much paint to order. All of the product data is in Sq feet but my friggin boat is anything but square.

Also, anyone able to weigh in on Petit Protect vs Interprotect?

[Nicholson58]

We ground, filled and repaired our 1984 bottom and then applied six coats of Interprotect 2000E about ten years ago. Absolutely no new blisters including four years in the Caribbean. I’m a believer.

A reasonable area estimate for fin keel might be about 1/2 x length x beam. With a big full keel probably 2/3 x length x beam. Use waterline length, beam.

We used just a little less than three gallons Interprotect per coat on Roxy. 47 WLL, 15 WLB, 7 draft, modified full keel.

[rbk]

First consider a barrier coat then consider a primer then 2 gallons should just about do it for 3 coats and a quart for the boot stipe (assuming a different colour). When you’re done the boot stripe mix the remaining quart into the base coat as a tell tale for coverage. You can try for 1.25-1.5 gallons but they’ll be light coats. Try and keep using the same tray and roller (if rolling) each time you use a new one they soak up a ton of paint, also the nap lays flatter and you’ll end up with a flatter finish. No comment on brands, them’s fighting words.

[sailorboy1]

2 gals

Expoy Primer is expoy primer as long as you follow the directions

Your aren’t doing till Spring right

[unbusted67]

Originally Posted by sailorboy1

2 gals

Expoy Primer is expoy primer as long as you follow the directions

Your aren’t doing till Spring right

Not sure I might try to get it done this season. I think I have a couple more weeks of 50 degree weather.

[sailorboy1]

You need to check the time before launching the boat for the paint, not all can set out so long

[Orion Jim]

Originally Posted by unbusted67

Hey all, I've got a 31 foot Contest I am refitting. I've taken the bottom back to gel coat and I am trying to figure out how much paint to order. All of the product data is in Sq feet but my friggin boat is anything but square.

Also, anyone able to weigh in on Petit Protect vs Interprotect?

I stripped my bottom down to the gel coat four years ago. On the advice of the local pro I let the boat sit out the winter and used Interprotect as my barrier coat in the spring. I used West System epoxy rollers, they are perfect for this application, and put five coats on in one day. For my 31 foot full keel it took 3 gallons. As an undercoat over the last barrier coat I applied my choice of ablative antifouling but in a contrasting color to the top coats so I could easily see when it was wearing thin.

[SVTatia]

Originally Posted by unbusted67

...All of the product data is in Sq feet but my friggin boat is anything but square....

There is always a way, you do the math:

For a rough estimate, LOA (Ft) x Beam(Ft) x 0.85 = the squre feet of below waterline area.

[GordMay]

There are five ways of finding the Wetted Surface Area (WSA):
A formula
Girthing
The secant method
Using a CAD system
Integration of a known mathematical function.
Much more ➥ https://www.boatdesign.net/threads/w...-formulas.930/

[jmschmidt]

Over-Kill?

[Carver Power]

Sand well, Primer a must , Paint three coats, Do no skimp on paint heavy coats, 1/2 lambswool cover or 3/8 synthetic roller cover, Let dry between coats. 2 gals paint maybe, I would buy three and not open third.. Do not dry roll. Prep is super important.

[bkrizmanic]

I have always taken LWL x Beam x .785 it is a formula for the area of a pad, it has worked for me on my last three boats with just a little to spare. First coat is usually really close.

[billdre]

Petit has a calculator right on their website for both anti-fouling and barrier coat paints.
I took my bottom right down to the gel coat 7 years ago. Washed it down and put two coats of ablative paint on it. First one black, second one blue. I use Petit's Hydrocoat and I have consistently gotten 3 years out of each full repaint of the top coat. In between I simply touch up where the black layer shows through.
I understand most people want to play it safe and put a barrier coat over the gel coat once they have taken all the layers of paint off. However, and I get ridiculed for this, if once you are looking at bare gel coat on an older boat and there isn't any osmosis then I don't see why a barrier coat is necessary. It may be needed in the south or if your boat stays in the water all year round. But you're in New England like me and I suspect you will pull it each fall. My boat was built in 1979 if it didn't develop hull issues in 33 years, in my opinion it's not going to. So far I have 7 years direct experience. If you're looking at blisters in the gel coat then barrier coat it.

[David B]

Originally Posted by unbusted67

Hey all, I've got a 31 foot Contest I am refitting. I've taken the bottom back to gel coat and I am trying to figure out how much paint to order. All of the product data is in Sq feet but my friggin boat is anything but square.

Also, anyone able to weigh in on Petit Protect vs Interprotect?

If you've gone to all that trouble, why repeat the process only to have to remove it all again in a few years time? We put Coppercoat on ours 8 years ago - never touched since other that a pressure wash or scrub. Saved us thousands, plus a lot of hassle.

[Maka]

I agree on the need of a barrier coat.