Hull Area Below the Waterline?

[KeelsonGraham]

Does anyone know the approximate wetted area of the hull? I'm trying to figure out how much epoxy and antifoul I need to buy!

[glennd3]

Sorry but I failed calculus. : shock: When I paint the bottom, I use 1 gallon plus a little, however there are variables.IE. paint, thickness of application..

PS I really did not fail calculus, but it was a long time ago and I may have inhaled during college.

[waughoo]

I used two gallons on my boat and didn't get a full coat on.  Maybe it was really dry and took more paint?  Next time I plan to buy three gallons and hope for the best.

[Holger Dieske]

... I needed 3 liters for one layer of antifouling (Seajet 039 Platinum).

Holger

[KeelsonGraham]

Anyone got any experience of how much epoxy primer you need? At £200 per gallon it's going to be an incredibly expensive job putting on the recommended 5 coats 😯

[scgunner]

Alex,

Two gallons for one coat, that is really strange. I've been painting the bottom myself since I got my boat in '88, around 7 or 8 times. I've found one gallon will almost give me two coats. I use two gallons which gives me two good coats then I go back and hit the waterline, the keel, and the rudder with two or three more coats. I'll even put a couple more coats on the rudder. After all this I usually wind up with about a 1/3 to a 1/4 of a gallon left.

What brand of paint are you using?

[PaulJacobs]

Calculating the C-34 total wetted surface is not trivial!  I did this about 10 years ago using the Newton-Raphson method, and determined that the total wetted hull surface area was approximately 230 sq. ft.  (+/- about 2 sq. ft.) Both sides of the keel add another 36 sq. ft., and both sides of the rudder yet another roughly 14 sq. ft. for a grand total of very nearly 280 sq. ft.

"In principle" a gallon of bottom paint should cover about 400 sq. ft.  However, some paint inevitably adheres to the inside of the can, some stays adhered to brushes and rollers, and unless replenished some of the volatile components evaporate while one is painting.  Thus, actual bottom paint coverage is probably somewhere between 330 and 350 sq. ft. per gallon.

In painting Pleiades bottom myself for the past ten years I find that if I add about 10% thinner, I can cover everything with one coat, and still just barely have just enough to apply a second coat to the rudder, and from the waterline down about one foot, which is the area that tends to accumulate the most slime during the season.  I typically swim / scrub just below the waterline about 10 times during the sailing season.  Using Interlux ACT ablative bottom paint I have found from experience sailing in NE waters it can "just barely" withstand that much scrubbing before I start to see a bit of the signal coat (e.g. blue just visible through green)showing through.

I hope this was helpful.

Dr. Paul F. Jacobs
Pleiades, TR-FK
1990 C-34 MK1.5
Wickford, RI 

[waughoo]

Now that I am reading others' posts, I must have started with a smaller amount as I was planning to touch up the waterline.  Please disregard my earlier comment about the number of gallons used.

[KeelsonGraham]

Thank you Paul. V useful info. And thanks to everyone else for some great inputs.

[Breakin Away]

Anyone got any experience of how much epoxy primer you need? At £200 per gallon it's going to be an incredibly expensive job putting on the recommended 5 coats 😯

A MkII should have vinyl ester resin and other blister resistant FRP layup features, which IMO should eliminate the need for any epoxy primer. My boat has no epoxy primer and has never had any blisters.

[KeelsonGraham]

I've decided to use Coppercoat. 6 gallons for four coats.

[Jim Hardesty]

I've decided to use Coppercoat. 6 gallons for four coats.

Please write up the installation and the performance.  It looks like a very good idea. 
Hope it works out well,
Jim

[scgunner]

Graham,

Six gallons, WOW! I could paint the bottoms of three maybe four Cat 34s with that much paint. Also I'm puzzled by the four coat strategy unless you're planning to leave the boat in the water for a very long time. I normally get four years between haul outs with two coats with additional coats on the hot spots. If that's how you are going to proceed I'd suggest buying two gallons to start and then a gallon at a time as required, that bottom paint ain't cheap.

[Noah]

Kevin- Coppercoat has its own exacting application regime, which involves multiple coats, applied semi-wet upon wet. It provides (allegedly) 10-years of antifouling protection.

[scgunner]

Noah,

An exacting regime indeed! Three pages of instructions for stripping and six for application. Also I found the claim of ten years between bottom painting interesting but that requires "touch ups". If I hauled my boat every couple of years and just painted the bare spots I could go ten years between bottom painting too!

It seems too overly complex and maintenance intensive for my taste but as we say your boat, your choice.