Armond Perretta wrote (on 25 April 2009):
I have been using Pettit Trinidad on my 28 foot sloop for many years
(1981 boat purchased new). When we haul, the boat is
pressure-washed, and then in the Spring the loose stuff is scraped
off and the entire bottom wet-sanded with 80 wet-dry. I use a foam
roller and about 3 quarts per coat on this full keel boat with a 22
foot waterline. At this rate every 3 years I've had enough paint on
hand to avoid buying a new gallon. This routine has worked for many
years, and even though the boat has never been taken down to bare
glass, the buildup is not an apparent problem. In recent years the
boat has been kept on the Jersey Shore in brackish water.
This year I have decided to honor the titans of Wall Street and what
remains of the financial system by "going cheap." I took a new
gallon of Trinidad, split it in half into a new empty gallon can,
added what appeared to be about one half quart of last year's paint,
and then thinned each can to bring the volume to about three quarts
in each one gallon can. This means the paint was thinned about 25 to
27 percent, which is well in excess of the manufacturer
recommendations. In fact just about any source I can find would
disagree with my approach and advise that I will end up with less
than adequate protection. The only advantage to me is, of course,
cutting my paint cost by half.
I suppose I will find out in the Fall if this plan is practical, but I
thought I'd throw it out there to see if anyone else does it this way
or has similar experience.

Last April I posted the above looking for comments and similar experiences.
We hauled the boat yesterday and were able to determine how the highly
thinned bottom paint performed. The short answer is: "Very well."

This past summer we did an "average" amount of sailing based from New
Jersey. We spent 3 weeks in southern New England and otherwise sailed
approximately 2 to 3 times a week daysailing in and around Barnegat Bay.
The boat is usually moored on the Toms River in what I would call brackish
conditions, although we do have ocean access through several inlets quite
nearby. I did not dive on or clean the hull during the season.

When we pulled the boat we had a bit of slime but not much and certainly not
more than on previous occasions using the same paint straight from the can.
We had no barnacles on the paint, but they are out there as I had a few on
the prop (which has pretty much always been the case since I don't make any
effort to treat the prop).

I would have to say that this thinning method works for me, as I am now
going to get 2 paint jobs from one gallon on this 28 foot full keel
sailboat.

--
Good luck and good sailing.
s/v Kerry Deare of Barnegat
http://home.comcast.net/~kerrydeare