power or prop problem

[CowboyPhD]

I've read that in forwoard I shouldn't be able to throttle up to more than 3000 RPMs or the prop is not the ideal size. I can not only hit 3000, I get creeped out when I get to 4000 and have to throttle back down. It feels like I could go even further, but the screaming of a red-lining A-4 makes me uncomfortable. Usually this means my prop is the wrong size, but could it be a transmission slippage issue? Any help would be greatly appreciated.

[Chip Hindes]

I had the same problem with my completley overhauled A4 on its maiden run this spring. The boat would accelerate smoothly up to about three-four knots, then the engine would suddenly race and boat speed would actually drop. Don't have a tach so can't say what it was turning, but you can bet I didn't let my brandy new motor run there for more than a second or so.

What boat, what prop, and at what boat speed is this occurring?

I suppose there is a remote possibility the prop is so undersized it is cavitating, but I believe it's most likely your transmission is slipping.

When I mentioned this to the marina guys who had been servicing my boat for the previous owner the past five years, they laughed and said they had never seen a sailboat with a prop and motor combination bad enough to cavitate. Further, that the motor before the overhaul never had enough power to move the boat, let alone slip the transmission or cavitate the prop.

Adjusting the tranny is incredibly simple; just one click on the adjusment collar per the manual cured my problem.

[Don Moyer]

Your RPM indications are totally unreasonable for any prop even close to the correct size for an Atomic 4; therefore (assuming your tachometer is correct), your forward clutch assembly is probably out of adjustment, allowing for slippage.

Don

[CowboyPhD]

Thanks, Don.

I'll give the adjusting collar one notch (the old fat notch collar), fire her up again, and check where she max's out on RPMs. I'll get back to you on this Sat.

[CowboyPhD]

I adjusted the revering gear one more notch but was till able to rev up to 4,000 rpms. I figure either the prop is in such bad shape (nicks and dings) that it's cavitting or my tach (less than a year old) isn't working. Am I on the right track? Is there a way to check my tach?

[sunnnnseeeker]

You can check the tach with another tach meter. Buy or barrow a tach meter - they have 2 leads, one for ground and the other clips on the negative post (-) on the coil. Then compare the tach on the boat to what the tach meter says. Take note that tach meters are rated for number of cylinders so if you have the more common 8 cylinder tach meter you double the reading for the 4 cylinder engine. At 4000 rmp your A-4 would be screaming for you to back off the throttle.

If anything a dinged up prop would put more drag on the engine, unless someone changed the pitch on the blades. Test it in the slip tied to the dock. In forward gear rev the engine and if it jumps to 4000 rmp and little or no water is being stirred out the back the transmission is slipping. Take a look at the drive shaft and you should be able to tell if it is really spinning solid or slipping. If it is throwing lots of water and really pulling on the pilings, the prop and transmission are probably good. With it doing all that work I doubt it would make it to 4000 rmp. Don't pull the dock apart!

[Chip Hindes]

Find somebody with a tach/dwell meter. Anyone into older cars or who did their own maintenance before the days of computer controlled ignition (say 1980 or earlier) should have one.

I do.

[tenders]

Forget verifying the tach. Your common sense is telling you what you need to know.

> the screaming of a red-lining A-4 makes me uncomfortable

I doubt anybody would characterize an A4 running at 2000 RPM but showing 4000 RPM as "uncomfortable." But 4000 RPMs is an uncomfortable speed for an A4, and it sounds like you're hitting it.

Adjust the transmission another notch. Are you sure you adjusted it the right direction the first time? Did somebody put something dumb like Slick 50 in the crankcase? Or something smart (but misguided) like synthetic oil? Maybe a quick swim is in order to make sure the blades are still attached to the prop? It's not impossible for them to break off through electrolysis or collision. sunnnnseeeker's idea is a good one. In calm conditions the engine will churn plenty of water when you're tied up at the dock.

[sunnnnseeeker]

I want to retract my suggestion to do a power test in the slip. I am afraid that if this is not done in a controlled manner and all systems are not strong something is going to break; especially if the engine, transmission and prop are working as they should. Possibilities; pull the dock apart, pull the cleats off the boat, snap the lines and someone gets hurt. We don't want that - don't do it.

[CowboyPhD]

Fear not Sunnnnseeeker, I pull on docklines (two each side on 12" cleats with 1/4" stainless backing plates) just about every weekend. My A-4 was frozen when I got her. That was the only way to test my mistakes, frustration, and lack of knowledge without having to be towed back in.

[msmith10]

I agree with Tenders. Your transmission is slipping or your prop fell off. If the engine is screaming it's running too fast. My A4 couldn't hit 4000 RPM in gear if it were being towed.