Atomic 4 in a Catalina 38?

[Old Man Winter]

HI, New to this forum. Thank you for having me.
In the process of purchasing a 1979 S&S designed Catalina 38 that has the venerable Atomic 4 engine with a Maxprop 3 blade feathering prop. I have two concerns:
1) the 30 hp gas A-4 engine seems sorely underpowered for the 16000 lb Cat 38 -- any Cat 38 owners out there who can confirm or put this fear to rest for me? I'll be cruising in her with my family and do not want to get into a situation where we have to power against wind and wave and are unable to swing the bow around into the wind.
2) the present owner claims that the max motoring speed is about 4.5 kts. Could this be fixed by simply adjusting up the pitch of this prop - but not so high on the pitch as to cause cavitation?
Thanks!
Old Man Winter

[Jesse]

Your concern is well founded. The A-4 is and has been a great old engine but it lacks the power needed to propel a boat of that displacement in the conditions you describe. There are modern marine diesels designed to replace the A-4 and will bolt right into the same engine bed, with suficient power and torque to do the job. Universal comes to mind and I believe there are others as well.

[GordMay]

Greetings and welcome aboard the CF, Old Man Winter.

Boats between 14,000 and 18,000 pounds displacement generally require the 28 hp Beta Marine replacement engine. Beta Marine marinizes Kubota industrial diesel engines.
See ➥ http://www.betamarinenw.com/Applicat...tomicfour.html

[Mike OReilly]

We have an A4, 30hp in our 34-foot ketch. We displace 12,000# and can easily get to hull speed in most conditions, but it may be a challenge at 16,000#. The other thing about our A4 is, it is great in forward, but sucks in reverse. Thrust is cut in 1/2 (or worse).

I think the A4 is a great engine, but it has some obvious limitations. As with all considerations, it depends on how, and where, you plan to sail/cruise.

[cal40john]

I don't have experience with the Cat 38. Yes I believe the engine is too small for your stated requirements. That said I sailed for years on a friend's Cal 34, 10,000 lbs, with an Atomic 4. We once convinced the owner to take us out in 50-60 knots, we watched roofs being blown off. This was in a flat water area. The autopilot couldn't move the tiller far enough to hold us on course motoring upwind at times but we made progress.

I have brought this boat home in 40-50 knot winds in Puget Sound motorsailing. We had tried this once before sailing and the VMG was so bad we turned around and spent another day in the harbor we had been in. So this time we tried motor sailing. Double reefed main, bear off just enough to fill it, maybe 25-30 degrees and we were doing 5.5 knots or better.

I now have a Cal 40, 15,500 lbs, 3 blade Maxprop. These quite often came with Atomic 4s. The fuel filler on my boat says gasoline. I now have a Yanmar that one of the previous owners put in. A Yanmar 3GM30 is 27 hp max, 24hp continuous. Don't know if you actually get 30 hp out of an Atomic 4, but that's what it says for comparison. I've been in around 35 knots motoring with the reefed main up at around 4.5 knots. I don't think I had the engine at full power or even cruising revs as we were working on getting the 150% off the furler to put up a smaller flatter sail as we had a full day of upwind progress to be made.

Anyway the point of this rambling is if the wind picks up and you just want to drop sails and motor at close to hull speed I believe the engine is too small, but you might try experimenting a few times in higher wind conditions each time with motorsailing with the main up, maybe with some experienced sailors as crew for the experiments, to see if you really need to upgrade the engine right now.

John

[SabreKai]

have a chat with Stanley at Beta Marine US. They will manufacture a set of mounts for their diesels that will make them a drop in replacement. There are a couple of people in our club who have done so lately and they are quite pleased.

[S/V Alchemy]

I have a Beta "in process" and I have a rebuilt Atomic 4.

You need a Beta. The A4, besides being underpowered for that displacement (the usual limit is 35 feet/13,000 lb. before you start noticing that it's not up to the push).

The other thing to note, however, is that while you will find diesel more economical than gas, a full gas-to-diesel switch usually means a redo of tankage, hoses, exhaust and even may require a different seawater inlet and other tweaks. It's non-trivial and potentially expensive if you don't have skills or the determination to do most of your own work.

So while you could experiment with prop pitch, etc. to try to get every newton out of the equation, your choice is gutless but cheap, or properly powered but pricey.

If you are keeping the Catalina for another 10 years, it's probably a break-even "value proposition". Less than that? Stick with the A4 and give it a tune-up. You may not be running on all cylinders.

[cal40john]

Just to make it clear, my 27 hp engine works fine for me. I have no intention of upsizing it. I can do 6.8 knots at 2900 rpm in flat water. I might consider going a little bigger when the current engine cannot be repaired and has to be replaced, but unless I do something stupid that is many years in the future.

If your Cat 38 is the Congressional Cup boat based on the Yankee38, that's an easy to push through the water IOR design and shouldn't need a lot of horses in flat water.

John

Originally Posted by cal40john

I don't have experience with the Cat 38. Yes I believe the engine is too small for your stated requirements. That said I sailed for years on a friend's Cal 34, 10,000 lbs, with an Atomic 4. We once convinced the owner to take us out in 50-60 knots, we watched roofs being blown off. This was in a flat water area. The autopilot couldn't move the tiller far enough to hold us on course motoring upwind at times but we made progress.

I have brought this boat home in 40-50 knot winds in Puget Sound motorsailing. We had tried this once before sailing and the VMG was so bad we turned around and spent another day in the harbor we had been in. So this time we tried motor sailing. Double reefed main, bear off just enough to fill it, maybe 25-30 degrees and we were doing 5.5 knots or better.

I now have a Cal 40, 15,500 lbs, 3 blade Maxprop. These quite often came with Atomic 4s. The fuel filler on my boat says gasoline. I now have a Yanmar that one of the previous owners put in. A Yanmar 3GM30 is 27 hp max, 24hp continuous. Don't know if you actually get 30 hp out of an Atomic 4, but that's what it says for comparison. I've been in around 35 knots motoring with the reefed main up at around 4.5 knots. I don't think I had the engine at full power or even cruising revs as we were working on getting the 150% off the furler to put up a smaller flatter sail as we had a full day of upwind progress to be made.

Anyway the point of this rambling is if the wind picks up and you just want to drop sails and motor at close to hull speed I believe the engine is too small, but you might try experimenting a few times in higher wind conditions each time with motorsailing with the main up, maybe with some experienced sailors as crew for the experiments, to see if you really need to upgrade the engine right now.

John

[Jim Cate]

Another thing to consider is the size of your Max Prop and the reduction ratio (if any) in the tranny. From distant memory, many A-4's (like the one in my Yankee-30) were 1:1... ie no reduction. this meant that the prop had to be fairly small and turn pretty fast... not a good setup for a displacement vessel and possibly the reason for your poor motoring performance.

Finally, again from memory, the A-4 had but two main bearings and didn't really like to run at max hp rpms, so in practice was not really a 30 hp engine.

Good luck with it.

Jim

[Old Man Winter]

Wow! Thank you to all who responded to my questions about the A-4 in a Catalina 38. I really appreciate your info, advice and time! I am going to have to think long and hard about purchasing this boat as I do not have the money to buy it AND replace the engine.

[S/V Alchemy]

Originally Posted by Jim Cate

Another thing to consider is the size of your Max Prop and the reduction ratio (if any) in the tranny. From distant memory, many A-4's (like the one in my Yankee-30) were 1:1... ie no reduction. this meant that the prop had to be fairly small and turn pretty fast... not a good setup for a displacement vessel and possibly the reason for your poor motoring performance.

Finally, again from memory, the A-4 had but two main bearings and didn't really like to run at max hp rpms, so in practice was not really a 30 hp engine.

Good luck with it.

Jim

This is true, Jim. The 1:1 version, known as a "direct drive" is effectively more like a 18 hp engine and will rev up differently than one with a reduction gear. On the other hand, you can reverse like the dickens!

I have an 11.5 x 8 Gori two-bladed folder on my direct drive pushing a 9,500 lb. 33 footer. It replaced a 12 x 6 Michigan Wheel fixed two-blader. I lost about half a knot "top speed", but gained a slower "dead slow" (down from 2.2 to 1.7 knots) and noticeably greater acceleration under sail. I much prefer having the folder, because, after all, it's a sailboat.

[Bash]

I have a friend who has the old Catalina 38 with an Atomic 4. He has difficulty motoring the boat into choppy seas any time he has wind on the nose. In conditions that will only slow my boat down a knot, he'll be unable to make more than a knot.

[Old Man Winter]

Bash, That's exactly what I anticipate happening with this setup. Would hate to have my back to some rocks and have to rely on that engine to power us out of harms way!

GordMay, Thanks for the link to Beta. I guess I'll have to try to find a used diesel with 28+ Hp.

[scubascooter]

Another replacement for the Atomic 4 is Universal B series. I think that the parent company is Westerbeke.

Check the attached PDF

UNIVENG, M-35B.pdf

[neilsailingrn]

OldManWinter...I had an A-4 in a 1968 Columbia 36. It was 12000lbs per the specs. With all our stuff probably close to 13500lbs. Add water....maybe 14000lbs. I went from Chula Vista Marina to the mouth of San Diego bay at 6 knts by GPS. I wasn't close to full thottle. It was a newly rebulit A4 and had a 3 blade prop. Backing up? No problem. I even towed a 26' sailboat back to the dock because his outboard gave up on him. Not a problem. Maybe you have some performance issues...tune up, poor compression, etc. Just my 2 cents. All that said. I too would replace the A4 if it is old and you have any misgivings. A diesel is piece of mind! As other's have said, Beta Marine is the way to go! I have met the guy who sells them and he's a no BS kinda guy. He won't steer you wrong and he stands behind his product. They are Kubota engines...I guess that says it all. I had those too. Excellent engines!