What is the cruising RPM for the Atomic 4 that is married to a C&C 33

[Orion C&C 33]

Hello everyone...

I am new to the world of Atomic 4's....
Can anyone tell me what their cruising rpm is? I see on the home page it says that the new and rebuilt Atomic 4 is rated to cruising at 2,000 rpm

I know that the boat, prop all play into this... But I am curious to know what others are cruising at...

Thanks

Mel

[CajunSpike]

On the one time(so far) I had my boat out, throttle wide open in fwd gear resulted in a tach reading of 2000 rpm.

Wasn't sure if this is normal but from your document, it appears to be.
Have a 2 blade folding prop on the boat, 12x8.

[Dave Neptune]

It's prop load

I had an E35-MkII direct drive and cruised between 2100 (12") & 2300(8"). If in a hurry I'd bump her up to 2500 @ 4" of vac.

It is more important to be concerned about the "load" on the engine due to prop "choice". That is why I listed my "manifold vacuum" which is a measure of the load on the engine. The vac gage is sort of like a "gas millage gage" in a car.

There are many with the reduction units that cruise at 3000 very comfortably.

My engine was very old and a bit tired, however with a good prop the performance and fuel usage really improved as I could reach an "efficient RPM range" for a direct drive.

Dave Neptune

[Mo]

It will depend on what you call cruising speed. I will try help you out here.

1. Bottom Clean
2. 2 or 3 blade prop.
3. Wind Conditions
4. Current.

I would expect the C&C 33 to cruise at about 6 to 6.2 knots on a calm day with fairly flat water, no wind on the nose. Usually, from my experience on my C&C 30, I'm at half throttle to get 6 knts with a clean bottom, flat calm, and holding my tongue just right I might get 6.2. Mine has a 3 blade prop.

To put this in perspective, if I go above 1/2 throttle the prop just causes cavitation and the boat doesn't go any faster...just burns more fuel.

Lets talk chop and wind. I can hold 4 knts in 5 to 6 foot swells with 20 kts on the nose...still at 1/2 throttle. Increasing throttle doesn't make it go any faster in these conditions either. Don't get me wrong, every now and then you will get hit with a huge wave that may literally stop the boat.

With a 2 blade prop the performance in moderate to heavy weather will drop off and significantly. We have a place around here called Sambro Channel...always swell, chop and big waves more often than not. I walk away from 2 bladed propped boats heading into that...diesel and gas engines alike.

[YOUTUBE]www.youtube.com/watch?v=WS6ZTAm-nDY[/YOUTUBE] The U tube video is just here in Halifax Hbr, not Sambro Channel...on my way back to the dock as a blow came up.

[Mo]

Dave Neptune...on the ball! Awesome reply! I rarely look at the tach

[MLW]

I'm at 1800 RPM and will be replacing with less prop.

[Al Schober]

Cruise RPM? Depends on how fast you want to go - and if there is some favorable wind, you can get a push from the sails.
Just did a crossing from the CC Canal to Rockland, ME in a Tartan 30. We'd filled up in Marion, so had 20 gal in the tank at that time. Left Marion at 1630 and motored through the canal, stopping at the marina in Sandwich. Underway at 0600 for Maine with light wind, keeping the engine running to maintain 5 knots SOG. 0600 the next day we were abeam Monhegan and at 1200 in Rockland on the mooring. Engine had been running for 30 hours. Checked the tank - still 10 gal left!
EDIT: 2 blade CDI prop (plastic). No idea of RPM (no tach). Did notice that the throttle setting seemed to keep slipping back towards idle. Snug up the screw on the Marmac control?

[ndutton]

Did we determine if you have a direct drive or reduction gear? Depending on your prop it affects cruising RPM quite a bit.

[Boat]

I "Cruise" at 2000 RPM. Max RPM is 2400. Newport 30. Full fuel (18 gal). In Lake Washington I'm doing 6.5kn. My prop is a fixed three blade 11x6

[edwardc]

With my 2:1 reduction V-drive, and a 15x8 three-bladed fixed prop, I normally cruise our 12,800 lb 32 ft Pearson between 2000 and 2400, depending on how much of a hurry I'm in. This gets me between 5 and 6 knots in calm conditions.

With a clean bottom and prop, at WOT I run 3100-3200 RPM; however, I've found that oil consumption goes up dramatically above 2600 RPM. Don't know where it goes. No noticable smoke or blow by.

[joe_db]

The redline of an A4 is 3600 RPM. No one with direct drive is getting anywhere near that. I am not 100% sure my tach is exact, but depending on how hard I push my cruise RPM is around 2000-2300 or so. When not in a hurry or trying to bash upwind, I find 5 inches manifold a good relaxed cruise power setting.

[Orion C&C 33]

Thanks everyone for responding... My apologies for not responding sooner to everyones input for that I'm very grateful for the responses.

I've been madly sanding and painting the bottom and changed out a badly corroded prop shaft these last few weeks... Honestly I thought I was in purgatory!

I'm running a 2 to 1 reduction on my drive unit... married to a 16" x 12 pitch.

I cruise comfortably at 5.5 to 6 knots @ 1800 rpm... engine temp stays around 140 F.

If I push it to 7 knots trying to navigate out a little quicker busy shipping lanes, my rpms climbs to 2000 rpms and the temperature climbs to 160F...

So I am assuming with the responses from everyone, that I am within my range of performance for my 16 x 12 folding two blade prop.

Again thank you all..

[Dave Neptune]

Orion, at 2000 RPM's you are on the very low side of the RPM scale and way up on the load side. You should be able to easily reach 3000 with a reduction unit or you are loading things up a bit.

Dave Neptune

[ndutton]

Orion, the specification I have from Robert Hess suggests your prop is ever so slightly aggressive. The specification is:

Propeller Size
Note: propeller fitted must allow the engine to reach at least 1,800 rpm during hull speed / full throttle testing

2 Blade
2:1 Reduction Drive: 12 x 11, 12 x 12, 13 x 10, 13 x 12, 15 x 8, 15 x 10

Your prop diameter is only 1" greater than the maximum recommendation, pitch is 2" over max. . . . but your hull speed RPM is still within spec. Corresponding vacuum numbers would be helpful if you have a gauge installed.

[Orion C&C 33]

Forward pressure plate cracked with missing pin

Hello

I find myself back on the forum again for sound advice and help....

This weekend I took a little cruise to celebrate Canada Day as I was coming to dock I found my forward and revers shifting becoming more vague with hardly any neutral.

Explored previous posts on this forum regarding the gearbox issues... and how to adjust the gearbox for the correct set for forward and reverse.

Adjusting the forward / reverse set in the gearbox was easy enough to understand and do... Upon opening my gear box low and behold a big surprise! A cracked forward pressure plate with the set screw missing along with a piece of the collar. Please see the picture

My issue is has anyone changed out a forward gear pressure plate on their Atomic 4... and how hard is it to do???

I plan to do some extended cruising up the remote coast... So learning all about my Atomic 4 and how to service it in cases of emergency is not a bad thing.

Would appreciate any input from fellow members