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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Gas > Atomic 4
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Old 12-03-2011
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A4 in larger boats

I'm in the market to buy a boat and get back into sailing after a long absence and one of the boats that I am looking at is a 38 footer that still has the original A4 with a 2:1 reduction gear. It seems that most of the discussion about these engines involve smaller boats with direct drive transmissions. I haven't be able to find much info on the use of A4's used in bigger boats, and I would like to get an idea of what performance can be expected along with recommendations on props, cruise rpms, fuel consumption etc...
Thanks
James
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Old 12-03-2011
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The reduction gear will make a big difference. The much more common direct drive versions require a small fine pitch prop that is very inefficient and doesn't allow the engine to get close to its rated power. With the 2:1 reduction you can use a larger more efficient prop. Powering performance should be similar to a diesel of similar power with the same reduction ratio, though fuel consumption will be much higher. I would guess over a gallon an hour at even reasonable cruising speeds.

Last edited by JimsCAL; 12-04-2011 at 10:20 AM. Reason: fixed typo
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Old 12-03-2011
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I have a 1974, 33 Morgan Out Island with an Atomic-4 and 2:1 reduction. The boat tips the scales at 12,500 pounds and at 2,000 RPM the boat cruises effortlessly at 6.5 to 7 knots. This is my second boat with an Atomic-4 and I love this engine. It's extremely reliable, easy to work on if the need ever arises and parts are readily available. I've calculated the gas mileage several times using the GPS trip-meter and on days when the weather's dead calm I'm averaging about 12 MPG. When the weather's nasty, the mileage drops to about 9 MPG. That gives me a pretty good cruising range with my 30-gallon fuel tank.

Good Luck,

Gary
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Old 12-03-2011
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http://l-36.com/Atomic4/a4manual2.pdf is the manual for the A4. They recommend an RPM of 2000, which is stated to be 80% power. At this RPM the horsepower is 15 to 16.2 depending on engine model. This is the horsepower needed for a boat weighing about 10,000 pounds if you figure 3 to 4 horsepower per ton.
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Old 12-03-2011
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In the Mid-Atlantic region the folks to talk with about Atomic-4 engines is Moyer Marine Atomic 4 Engine Rebuilding and Parts

And, if you do purchase a boat with an Atomic-4, there is a product that will dramatically extend the life of the engine--Marvel Mystery Oil. This stuff has been around since I was a kid and it really works.

Good Luck,

Gary
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