Flexofold Prop problems

[peaman]

Any additional tests I can do to get to the bottom of this, or additional thoughts would be most welcome!

Along with @Nick J 's thinking, you are sorting out an issue that could be in your transmission, or at your prop. It would be productive to eliminate one or the other. An observer who can watch the prop shaft inside the boat, along with an observer (maybe you) watching for prop wash, ought to have some chance of determining where the "lag" occurs, between shifting into forward, and when or if forward thrust is observed. The shaft watcher will know, from cable movement when the shift occurs into forward and they should see the shaft immediately start turning at a steady speed. That moment communicated to the cockpit/ prop-wash watcher should be informative. If shaft speed is hesitant, the issue may be in the transmission.

This may have been addressed already: When you shift into gear, the crank at the transmission should be "loose" but engaged. There should be no pressure from the cable placed on the crank. Pressure from the cable should only exist while shifting from fwd to neutral to reverse, and once in gear, or neutral, there should be no pressure.

 

[peaman]

how I can measure the transmission gear ratio?

The model number or other data from your transmission should inform you of the forward and reverse ratios. A handheld tachometer would confirm what actually happens.

 

[Nick J]

I've only used on to check my tachometer, but I'm thinking the process is the same. These usually come with a sticker you place on something that's rotating, then point the gun at it and it counts how many times the sticker passes the beam.

For engine RPM, measure it at the fly wheel
For shaft RPM, measure it at the coupler

For the gear box ratio, a quick google search brings up:
A Hurth HBW-50 gearbox has multiple gear ratios depending on the specific model and configuration. The two main forward ratios are 2.05:1 and 2.72:1, while the reverse ratio is consistently 1.86:1 for both.

You should find your gear ratio stamped somewhere on the transmission. Maybe a fellow O34 owner could help out here?

Hopefully, you measure close to what your transmission is supposed to be producing across your RPM range. If its off, it's a good indication that your transmission is slipping.

Either way, at $24 it's a fun tool to have in your kit.

 

[bertboyer]

An observer who can watch the prop shaft inside the boat, along with an observer (maybe you) watching for prop wash, ought to have some chance of determining where the "lag" occurs, between shifting into forward, and when or if forward thrust is observed. The shaft watcher will know, from cable movement when the shift occurs into forward and they should see the shaft immediately start turning at a steady speed. That moment communicated to the cockpit/ prop-wash watcher should be informative. If shaft speed is hesitant, the issue may be in the transmission.

Thank you. We did something like this and both of us took positions watching prop wash while the other person viewed shaft rotation. When we shift into forward (or reverse) we see immediate rotation. However, shifting in forward only results in prop wash half the time. When no prop wash occurs, we throttle down about half way and hear the clunk. If prop wash occurs, we seem to observe the shaft spinning faster right after we hear the clunk. We will try to get some numbers when we try again with the tachometer later this weekend.

Once on the boat (with our manuals), I will also try to find the specific model of the transmission and precise gear ratios (thank you @Nick J). I see the same gear ratios on the web, but hopefully have documentation to confirm.

@peaman: You said This may have been addressed already: When you shift into gear, the crank at the transmission should be "loose" but engaged. There should be no pressure from the cable placed on the crank. Pressure from the cable should only exist while shifting from fwd to neutral to reverse, and once in gear, or neutral, there should be no pressure. When we shift into gear, we definitely see the cable move the shift lever on the side of the transmission. Is this what you mean when you refer to the "crank at the transmission"?

 

[bertboyer]

Maybe a fellow O34 owner could help out here?

Indeed! there are three other O34s at our yacht club (as well as Loren Beach just down the road) and I have been racing with the previous owner of our O34. He has been helping with diagnosis, but we are stumped. I'm trying to get a couple of the other O34 owners to help diagnose.

 

[peaman]

When we shift into gear, we definitely see the cable move the shift lever on the side of the transmission. Is this what you mean when you refer to the "crank at the transmission"?

By "crank", I mean the fitting that the cable connects to at the transmission, the fitting which converts the linear motion of the cable to the rotational motion of the transmission shifting shaft. That shaft should settle into exactly three positions: forward, neutral, reverse. The purpose of the cable is to cause the shaft to turn, by use of the crank, from one of those positions to another. Once shifted, the cable should be "free", in that you should be able to wiggle the shifter at the helm as well as the crank on the transmission shaft without shifting the gear. Likewise, you should be able to wiggle the crank at the transmission shaft without shifting gear. That should be the case at each of the three (FWD-NEU-REV) natural transmission shift positions.

If you were to push the helm shift lever into forward gear and there was no wiggle room between the crank at the transmission back to the helm, I would suspect that the transmission is not fully in forward gear.

 

[Nick J]

By "crank", I mean the fitting that the cable connects to at the transmission, the fitting which converts the linear motion of the cable to the rotational motion of the transmission shifting shaft. That shaft should settle into exactly three positions: forward, neutral, reverse. The purpose of the cable is to cause the shaft to turn, by use of the crank, from one of those positions to another. Once shifted, the cable should be "free", in that you should be able to wiggle the shifter at the helm as well as the crank on the transmission shaft without shifting the gear. Likewise, you should be able to wiggle the crank at the transmission shaft without shifting gear. That should be the case at each of the three (FWD-NEU-REV) natural transmission shift positions.

If you were to push the helm shift lever into forward gear and there was no wiggle room between the crank at the transmission back to the helm, I would suspect that the transmission is not fully in forward gear.

That's a good check. Going further down that path, to isolate cable issues form transmission issues, you could disconnect the shift cable and manually flip the lever. Hopefully your access is good enough to get you hand in there safely.

 

[bertboyer]

Going further down that path, to isolate cable issues form transmission issues, you could disconnect the shift cable and manually flip the lever. Hopefully your access is good enough to get you hand in there safely.

Access to the lever is easy. I will give it a try in a couple days when I can get back to the boat!

 

[Captain Pete]

Thank you. We did something like this and both of us took positions watching prop wash while the other person viewed shaft rotation. When we shift into forward (or reverse) we see immediate rotation. However, shifting in forward only results in prop wash half the time. When no prop wash occurs, we throttle down about half way and hear the clunk. If prop wash occurs, we seem to observe the shaft spinning faster right after we hear the clunk. We will try to get some numbers when we try again with the tachometer later this weekend.

Once on the boat (with our manuals), I will also try to find the specific model of the transmission and precise gear ratios (thank you @Nick J). I see the same gear ratios on the web, but hopefully have documentation to confirm.

@peaman: You said This may have been addressed already: When you shift into gear, the crank at the transmission should be "loose" but engaged. There should be no pressure from the cable placed on the crank. Pressure from the cable should only exist while shifting from fwd to neutral to reverse, and once in gear, or neutral, there should be no pressure. When we shift into gear, we definitely see the cable move the shift lever on the side of the transmission. Is this what you mean when you refer to the "crank at the transmission"?

If I am understanding you correctly, you are seeing shaft turning when shifting into gear at all times, but the prop is only seen to be turning half the time? If that is the case it makes me wonder if the prop may have become a "spun prop". I experienced that once with a 22' inboard outboard. The shaft was turning with what I can only describe as the innards or core of the prop that are touching the shaft (which may have been a hard rubber-like seal or inner core, I can't recall correctly as it was many years ago) while the metal blades cast with the outer core were not spinning. A trip to a local prop shop and $160 later the spun prop was repaired with a new core, probably press fit. I don't know if sailboat props are of similar build.

 

[bertboyer]

you are seeing shaft turning when shifting into gear at all times, but the prop is only seen to be turning half the time?

Exactly. The shaft spins all the time when shifting into gear, and the prop spins all the time in reverse, but only 50% of the time in forward. Easing off the throttle results in a "clunk" noise that often results in prop wash, but not always. We want to fix the situation so the prop opens in forward all the time as the rear dock is close and we don't want to get pinned against it.

If you go to the initial post I made in this thread (#1) you can see two videos of the prop. The first one with the diver moving it open and closed, and the second video of the prop opening and spinning while the diver sat on the dock with his GoPro on a stick filming.

 

[Loren Beach]

Easing off the throttle results in a "clunk" noise that often results in prop wash, but not always

My guess from anecdotal evidence (stories...) over the decades is that the clutch plate material in the transmission can start to slip as it ages. I have seen similar complaints from other owners of the Hurth 50 model. I recall that some owners here have replaced with a new transmission, albeit that may have required moving the engine mounts forward slightly. (Easier on the Olson than the Ericson's of the era, IMHO.)
All that said, some owners with slipage have changed brand of trans, fluid and "cured" this, at least for a while.
We never had slippage on our prior Hurth 50, after approx 2300 hours; and the last five years I was running Amzoil synthetic ATF in it - I have no idea if that actually helped, but it made me feel like I was doing something helpful for it. Even if only spending a bit more money.

 

[bertboyer]

some owners with slipage have changed brand of trans, fluid and "cured" this, at least for a while.
We never had slippage on our prior Hurth 50, after approx 2300 hours; and the last five years I was running Amzoil synthetic ATF in it - I have no idea if that actually helped, but it made me feel like I was doing something helpful for it. Even if only spending a bit more money

Thank you. From what I have read, it seems like more viscosity is beneficial in preventing slippage, and I was considering adding 30W oil as others on this site have done. Before doing so, I wanted to make sure it won't harm the transmission. If you or others know of "other brands" of ATF that may have helped with slippage, please let me know. Also, if anyone has had a negative experience adding 30W oil (or just strongly recommends against doing so), please share that information as well.

In the meantime, I am waiting to receive the tachometer that @Nick J recommended.

 

[peaman]

Also, if anyone has had a negative experience adding 30W oil (or just strongly recommends against doing so), please share that information as well.

If you go this route, I think you will want to make sure to get non-detergent oil. The detergent properties are for internal combustion engines, but might cause issues in your gear box.

 

[Kenneth K]

I switched over to 30W thIs past season. Wasn’t having problems with the transmission yet, but just did it preemptively because of all the issues I’ve heard about the old Hurth 50s. One thing I did, out of an abundance of caution, was to do three cycles of drain-fill-run-flush with the new oil. I know, when draining, it’s hard to get all the old fluid removed completely, and I don’t know if oil and ATF are mix-compatible fluids. Maybe that was overkill.

The transmission ran great all season!