Cannot Achieve Maximum RPM's in Gear

[TedCant]

I have an Erickson 29 with a fresh water cooled A4. The engine runs great, however, I cannot achieve maximum rpm when it in gear. In neutral the engine can achieve 3,000 rpm but in gear the maximum I can get is around 2,000 rpm. I have put in an electronic ignition kit, new plug wires and coil wire, new plugs and I also replaced the prop with a smaller dia. and lower pitch. The only gain was in boat speed at 2,000 rpm, but the engine will not go over 2,000 rpm under load (unless it is in neutral). I also tried adjusting the timing while the boat was running in gear at 2,000 rpm with no success.
Any suggestions.

Ted

[ArtJ]

I suspect that 2K RPM is all you can get with your existing prop.
With a Indigo prop and tweaked timing you can sometiimes get to
24OO RPM. Having said that 2000 rpm is not that bad. The original
props on many Atomic 4's would only allow 1700 rpm.

Regards

art

PS no one gets 3000 rpm, nor should you try to.

[roadnsky]

In addition to Art's advice, somewhere I have read that you SHOULD NOT be revving your A4 up to 3K while in Neutral.

[sastanley]

Ted, Your engine is running perfectly...go sail!

You want to adjust the timing at whatever RPM you cruise at most of the time. There is a lockdown bolt under the distributor..loosen this bolt enough you so that you can slowly twist the distributor while the engine is running..lock it back down at max RPM for that throttle location. My max RPM is 2,050...I did my "power tune" at 1,800, since I cruise between 1,700 & 1,900 RPM.

Now, if every problem was this easy!

[TedCant]

I just purchased this boat a last year and not that familiar with this A4 engine. It appears by everyones comments that everything is ok, which is good news. Thank you for all your comments.

Ted

[dvd]

I keep seeing posts indicating that people are changing props and the ptich of props. My 30' cal 3-30 is a 2 to 1 drive and has a 16 10 martec folder on it. I removed a 16 10 2 blade fixed. My boat will easily get over 2000 rpms if I allow it. (dont usually do this for any length of time) What I am getting at is that your boat, according to weight and I suppose other factors, should only have a certain size prop with certain pitch. When I purchased the new martec couple of years ago I told martec, over the phone, what I had. They looked something up and told me what prop and what pitch this boat should have. I followed this advice and it works great. I would think that if your engine cannot achieve more than 2000 rpms flat out something is probably wrong. I suppose either the prop and pitch is wrong or maybe the motor is just tired. Is 2000 rpms all anyone gets flat out?

dvd

[Baltimore Sailor]

I have the Indigo 10" 3 blade 7.4 deg prop. and the best I can do is about 2000 rpm.

I'll add the caveat that when I first got the boat I lost control of the rudder while backing up and the prop beat against it (no stop for the rudder!), and a kindly mechanic pounded it back out for me. But we don't know if the geometry was properly restored or not -- it looked good, but who knows?

If I replaced the prop I might get another couple of hundred rpms out of it -- but with a clean bottom and prop I can do 6.3 mph in it, which is just a bit under my hull speed, so I figure I have better things to spend $300 on.

[High Hopes]

I have contemplated swapping my 1:1 for a 2:1 gear, but the cost is dear.

[dvd]

Maybe that's it. The 2 to 1 produces more power I suppose by the engine turning twice and the prop only once. I would think that the 2 to 1 should be in boats that weigh over a certain amount. My old cal 3-30, vintage 1974, is really built and, according to the specs I have read, weighs in at 10,500 lbs. when new. (who knows how much after 36 years in the water and all the gear) So I would assume that this would be nearing the top end, as far as weight, for the atomic 4 to perform well. I have heard of boats as big as 36 foot having A-4s and also old gas Palmers. Wonder how well they perform and if they all have 2 to 1s. So I guess if you have a relatively heavy boat with a 1 to 1 the max of 2000 rpms is probably fine.

How many of us out there have boats longer than 30 feet with A-4s and how do they perform in conditions??

dvd

[hanleyclifford]

If you are getting 2000 rpm at cruising speed you are at very near ideal conditions. What is your fuel consumption and vacuum at that rpm?

[High Hopes]

I am pretty sure what happens is that once you near hull speed, the drag get very big. More HP, more revs, size of prop doesn't matter. The A4 will either have to push the boat up the bow wave of cavitate the propeller. If the prop doesn't cavitate, the engine will lug. If the prop cavitates, the revs go up, but the boat doesn't go any faster.

The reason for the 2:1 reduction is to allow the engine to run at higher rpms where efficiency is best and wear is minimal. The boat will go the same speed, but the engine turns faster.

The Indigo prop and the details provided by the designer suggest that the 1:1 A4 is just too fast for sailboat application. Diesels are slower and preferred, prop speed-wise. But the A4's are cheaper to run and maintain, easy to repair, and more reliable.

A 5:3 reduction would probably be ideal. 1800 x 5/3 = 3000

I may explore this if I put an AC generator on the engine next year to keep the wife cool.

[ILikeRust]

I have very much the same issue with mine. My boat is a 1968 Pearson Wanderer 30. The engine, according to what the seller of the boat told me, and the paperwork that came with it, is a 1983 Atomic 4.

In forward with WOT, max RPM is about 1600. The surveyor said it should be able to go higher than that, but the seller said it's always been that way. He has had the engine gone over by mechanics, and within the past year or two he replaced the carburetor and electric fuel pump and a couple years back he put in electronic ignition. So the engine starts right up instantly - I mean immediately - and runs perfectly. It really is an impressive little engine - just purrs right along. But the RPM at idle does seem a little high to me, and pop it into gear and the RPM drop significantly. Throttle up to max speed, and I get about 5.5 knots at 1600 RPM and that's all she's got.

Hull speed is just under 6.5 knots, which I've seen often under sail.

According to the power curve, at 1600 RPM I'm getting only about 12 h.p. out of my 30 h.p. engine. I'm concerned that it's lugging the engine and not good for it to run it like that.

So I've been considering trying out the Indigo propeller, but of course it's about a $350 experiment. But the description of the symptoms on that page fit my boat exactly.

[hanleyclifford]

You have too much prop. Have the pitch reduced 1 number.

[sastanley]

ILikeRust...yes, your symptoms are such that the Indigo may help you. As Hanley mentioned, you should probably know what the pitch is on the current propeller & that may help shed some light on your situation..I'll bore everyone with my theory below.

In my case (Catalina 30), the prop I had was a two-blade 12" diameter x 7" pitch prop. I put an Indigo on (10" three blade x 7.4" pitch) & my performance numbers (max RPM, & cruising RPM) are honestly about the same. I do think the smaller diameter helps unload the engine enough to increase the available power (thus used by the 0.4" larger pitch) for a given boat speed and probably helps me punch thru waves a little bit better...the 10" prop is spinning the same speed as the 12" prop, but I have 0.4" more inches of bite per revolution, without any change in engine load. However, my boat was down for so long in between props (go see my thread titled "Indigo" for that saga ) that I can't tell for certain. It is certainly NOT any worse.

Folks that have high pitch propellers fit on their boats (sounds like your case given the inability to get over 1,600 RPM) see the most benefit from the Indigo. Tom Stevens has done extensive engineering on a lot of design inefficiencies related to the A-4 and that Indigo prop is probably the best compromise. I bet if we could get away with a 9" or 8" diameter prop to get the RPM's up even more he'd try it, but I bet by then you are losing too much blade surface area and running into blade design problems related to the big hub the blades have to spin around & attach to.

OK, there's my $0.02.

[ILikeRust]

Thanks for the feedback - I was assuming the prop was the issue.

I'm wondering, though, how it would have ended up with the wrong sized prop on there.

I mean, as I understand it, the Wanderer was fitted with an Atomic 4 at the factory, so surely the prop would have been properly sized for it?

It does seem that at some point in its life, the engine was replaced, as the boat is a 1968 and the engine is a 1983 (supposedly). But I would assume that they would have reused the propellor, or at least replaced it with the same one.

I suppose it is possible that along the way, somebody just messed up and didn't know what they were doing and stuck the wrong prop on there.

Just this past weekend, in digging into all the storage areas on the boat and cleaning out and organizing all the stuff the seller left aboard, I did find another 2-blade prop. I wonder if that was the original, and the one that's on there now is an incorrect replacement.

I guess when I have her hauled in a couple months I'll figure all that out. Maybe I'll just go ahead and pop that Indigo prop on there. What the hell, it's only money. At the rate I'm spending it on this boat, what's another couple hunnert?

[sastanley]

BOAT = Break Out Another Thousand!

I still try to refer to a Boat Buck as $100, but sometimes it is tough!

[ArtJ]

Originally Posted by ILikeRust

Thanks for the feedback - I was assuming the prop was the issue.

I'm wondering, though, how it would have ended up with the wrong sized prop on there.

I mean, as I understand it, the Wanderer was fitted with an Atomic 4 at the factory, so surely the prop would have been properly sized for it?

It does seem that at some point in its life, the engine was replaced, as the boat is a 1968 and the engine is a 1983 (supposedly). But I would assume that they would have reused the propellor, or at least replaced it with the same one.

I suppose it is possible that along the way, somebody just messed up and didn't know what they were doing and stuck the wrong prop on there.

Just this past weekend, in digging into all the storage areas on the boat and cleaning out and organizing all the stuff the seller left aboard, I did find another 2-blade prop. I wonder if that was the original, and the one that's on there now is an incorrect replacement.

I guess when I have her hauled in a couple months I'll figure all that out. Maybe I'll just go ahead and pop that Indigo prop on there. What the hell, it's only money. At the rate I'm spending it on this boat, what's another couple hunnert?

According to research done by Tom Stevens and others, boat manufacturers
routinely put props on boats that did not take advantage of the atomic 4
hp vs rpm curve. Typically they only allowed around 1700 rpm for 17 hp
which did not allow for any reserve power to be used in a nasty chop.
In addition it put heavy pressure loads on pistons and cranks .

Check out Indigo Electronics for a better discussion of the above

Regards

Art

[hanleyclifford]

When somebody asks how much you got in your boat, you just tell 'em...Everything...

[JOHN COOKSON]

A boat is a hole in the water into which one pours money!!!!

TRUE GRIT