Over propped?

[rickinnj]

In forward, my engine maxes out at 970 rpm.
In neutral, she revs to the moon and back.

1. pulled the plugs - very sooty and dry.
2. compression test - 120,120,100,120.
3. pulled flame arrester - no change.
3a. choke is open
4. loosened packing gland - no change.
5. pulled exhaust off the manifold - no change.
5a. no loose flakes or obstructions inside the manifold.
6. dumped my old fat butt over the side to inspect the prop - clean with no fouling.

This year I changed out the Indigo 10x7 for a Darglo Featherstream 12x7. I knew I'd lose some rpm with the 2 inch extra diameter, but not this much!

Suggestions?

Rick Bushie

[rickinnj]

oh, and I don't have a vacuum gage...nor a back pressure gage. I know those are the next questions.

another oh, the rpm quoted above is shaft rpm (direct drive)taken at the output coupling with a laser optical tach. I don't have an engine tachometer.

[ndutton]

To eliminate them as possibilities I'd check the timing and centrifugal advance operation. No way a 12x7 is seriously overpropped. You should get 2000 RPM in forward all day long with a 12x7.

[rickinnj]

advance weights are free and lightly lubed.

timing set to best rpm under what little load I can put it under.

[JOHN COOKSON]

Are you running on three cylinders not four? Easy to check. Pull the spark plug wires one at a time while the engine is running under load and note any change in performance.

ex TRUE GRIT

[ArtJ]

My Tartan 34c had a 12x 7 or x 8 with a direct drive A4 when I bought it 20 years ago. The boat
maxed out at 1700 rpm producing 6 knots in calm water.
In a heavy chop it would lug and only produce 2 or 3 knots.

The Indigo prop was specifically designed for this boat. With it
the boat can do 6.6 in calm waters and over 5 in heavy chop with a clean bottom. The trade off is a much weaker reverse thrust

I have seen other people try to use the Indigo on a A4 reduction drive on a Bristol 32
which did not produce more than 4 1/2 knots. I gave him my old prop and it worked much better for him.

Best Art

[joe_db]

Originally Posted by rickinnj

In forward, my engine maxes out at 970 rpm.
In neutral, she revs to the moon and back.

1. pulled the plugs - very sooty and dry.
2. compression test - 120,120,100,120.
3. pulled flame arrester - no change.
3a. choke is open
4. loosened packing gland - no change.
5. pulled exhaust off the manifold - no change.
5a. no loose flakes or obstructions inside the manifold.
6. dumped my old fat butt over the side to inspect the prop - clean with no fouling.

This year I changed out the Indigo 10x7 for a Darglo Featherstream 12x7. I knew I'd lose some rpm with the 2 inch extra diameter, but not this much!

Suggestions?

Rick Bushie

Something is way wrong. That prop is a normal A4 size assuming it is a 2-blade.
Are you sure the laser tach is working right?
Is the prop shaft free? You should be able to turn it by hand easily in neutral.
Are you SURE you have the right firing order? There is way to swap the plug wires and get a fairly smooth 2 cylinder engine.
You need a vacuum gauge. You really need one. Moyer sells them, there are tons on FleaBay and Amazon, the local car parts place sells them, and so on.
Are you sure the prop is clean? My boat has been fouling at an incredible rate this year.

See photo - the gauges let you know what is going on. High vacuum and low RPM means the engine is at least trying.

[Dave Neptune]

You don't have enough torque for that much blade area if it is a 3 or 4 blade. The reason the indigo rev's up is the blade area is matched to the torque of the A-4.

The 12 x 7's you here of on the A-4's are almost all 2 blade props. I ran the Indigo on my E35MKII and it worked great in all conditions.

And if you're racing you'd do better with the 3 blade rating than the feathering with that big ball dragging through the water.

Dave Neptune

[joe_db]

Does your prop look like this?


If so, you are WAY over propped. You need a 12x6 or 12x7 TWO blade prop!

[rickinnj]

Joe, Dave, John,
that is my prop...three blade feathering. I'm fairly certain the strobe-tach is working, but regardless, the engine just barely rises off of high idle speed and maxes out there. I've been reading the forum long enough to realize that I need an installed tach, a vacuum gage for the fuel line, a vacuum gage for the intake manifold, a back pressure gage available as needed, etc, etc, etc... I just never seem to close that loop. she's definitely firing on all four...I used a test light to short out each plug one at a time and watched for rpm drop. Prop is clean and feathering properly, I dove on it Sunday morning. Shaft rotates freely.

I assume that I'm the only person alive who hates the Indigo prop. I've found it absolutely worthless in reverse, and barely acceptable in forward to drive my relatively small boat at 4.5 knots max.

The Featherstream, even barely off idle, gives instant response in reverse. I like that. That being said, I can't abide taking six months to steam 200 yards to the pump out station.

[JOHN COOKSON]

Originally Posted by rickinnj

The Featherstream, even barely off idle, gives instant response in reverse. I like that. That being said, I can't abide taking six months to steam 200 yards to the pump out station.

Not trying to be argumentative here...........

I found after that awhile I got the feel of how my boat handled in reverse and I didn't mind the fact that reverse control wasn't quite should be.
The prop pushed the boat forward well. I used the engine to push the boat forward most of the time. Reverse control was very minor and incidental so I let it be.

ex TRUE GRIT

[indigo]

Rick,

I see from my records that you had Indigo Prop S/N 1474 on a C&C 30. Indigo props are installed on nearly 60 C&C 30s with no reports of the issues you have outlined.

With your 25 ft waterline length, you should be able to make 6 knots at 2000 RPM all day long. If you were only obtaining 4.5 knots then there is something terribly amiss with your A4.

As for reverse performance, the Indigo prop requires significantly more RPM in reverse to obtain suitable reverse thrust. Having said that, I am sure you are aware that you have to hold back on the shift lever to keep the tranny in reverse and at the high RPMs, the reversing gear elements sound quite awful. That is just the way they are. As a reference point, I was able to stop my 12,000 lb. Tartan 34 in about 2 boat lengths from a 6 knot ahead speed. It was a very rowdy experience but the Indigo prop provided plenty of reverse thrust to get the job done.

I would pick the Forums many brains for possible A4 issues. There is definitely something that has not yet been addressed.

The new feathering prop you have is definitely too much prop for even an A4 that is operating properly.

Tom Stevens
Indigo