I have an Adams 12m launched in 1983. It has an Autostream 3B S series feathering prop on a shaft from a Yanmar 3HM motor driving through a KBW10E transmission.
The prop (from before I bought the boat) is overpitched meaning the motor wont do more than 1800rpm under load going forward. Motor specs are max continuous rpm of 3200.
The prop has pitch adjustment for forward and reverse. I understand the Yanmar crank rotates counter-clockwise viewed from the front and so clockwise viewed from the stern/flywheel.
Am I correct in thinking the transmission when forward is selected, reverses the motor's direction of rotation?
It is a pretty simple transmission constant mesh box with an input shaft and an output shaft. There is an intermediate shaft for reverse only. So in forward gear, the input cog drives the output cog directly hence reversing the direction of rotation. When reverse is selected, the input drives the intermediate cog which then drives the output, so the output shaft rotates in the same direction as the input shaft.
Is there anyone with knowledge of this engine/transmission combination who can confirm this or set me straight?
Reason I ask is that if the prop shaft rotation is counter-clockwise in forward gear (viewed from behind the prop looking forward), then as I understand it, the prop should be left handed. Receipt says it was supplied right handed. This can be corrected, but might go some way to explaining why pitch is so out of whack.
Thanks in anticipation
I think that gearbox should be running in a clockwise direction in forward gear ,,,viewed standing behind the prop looking forward. And I'm sure that gearbox has different ratios for forward and reverse .
Reverse rotation is slower than forward at any given engine rpm. The slower rotation will determine which gear is reverse, hence the correct direction of the prop rotation
Select to expand quotewoko said..
is it not possible to view the prop shaft / shaft coupling ?
I don't recall anything saying thats not possible.
It's the obvious place to look unless you want to stick your head in the water.
A couple of questions. Does the vessel reach hull speed at the 1800 rpm ? & does the engine rev to 3200 rpm, wide open throttle while in neutral?
Select to expand quoteQuixotic said..
Am I correct in thinking the transmission when forward is selected, reverses the motor's direction of rotation?
The engine only rotates one way. The gearbox changes the direction of the output shaft.
The KBW10E uses an idler gear for reverse, so reverse prop ration will be the same direction as that of the engine, while forward will be opposite direction. The 3HM engine is very similar to the GM series, which rotate anti-clockwise viewed from aft (ie looking forward).
Cheers, Graeme
Select to expand quotewoko said..
is it not possible to view the prop shaft / shaft coupling ?
Yes it is. I am away from the boat at the moment, I will study it in action it when I am next on the boat.
Select to expand quotewoko said..
A couple of questions. Does the vessel reach hull speed at the 1800 rpm ? & does the engine rev to 3200 rpm, wide open throttle while in neutral?
reaches an indicated 6.8 knots, but with a fair bit of black smoke. Engine revs to well over 2000 without load (and without smoke), Not sure it gets to 3200 - another observation to make when I have the chance. Opinion of the surveyor when I bought the boat was that prop was likely overpitched, Yanmar certified mechanic thought the same after doing a basic service on the engine.
Select to expand quotewongaga said..
The KBW10E uses an idler gear for reverse, so reverse prop ration will be the same direction as that of the engine, while forward will be opposite direction. The 3HM engine is very similar to the GM series, which rotate anti-clockwise viewed from aft (ie looking forward).
Cheers, Graeme
Thanks. Prop rotation being the same direction as the motor when reverse is selected, chimes with what I had thought. And the Clymer Manual covering these engines says (p99) the crank rotation is counterclockwise when viewed from the flywheel (this is the opposite of my original post). So when viewed from the stern, the prop will rotate counterclockwise when in reverse, and so clockwise in forward. Which means the prop should be right handed. That's good, because that's what's on the original paperwork for the prop as supplied twenty plus years ago. According to the installation and operating instructions for these propellers, there are two pitch adjusting screws on the prop (one for forward and one for reverse) and with pitch adjusting screws to starboard of the shaft on a right handed prop, the upper screw needs to be screwed out to decrease the forward pitch.
Documents for the prop suggest half a turn of the adjustment screw to reduce pitch should increase engine rpm by 150. If the engine is to reach 3200 rpm under load that would require almost 5 full turns out of the adjustment screw. That's a hefty adjustment. Assuming it is better to be conservative, a somewhat reduce adjustment is probably a safer bet. Unfortunately I don't have the opportunity to lift my boat out of the water, adjust the pitch, return the boat to the water, conduct sea trials and then lift it out again for further adjustment, and so on till it is pitch perfect (sorry for the pun). I'm hoping to make it significantly better on one attempt, without overcorrecting, and if it needs further adjustment that will likely have to wait until it is next out for antifouling.
Select to expand quoteJolene said..
I think that gearbox should be running in a clockwise direction in forward gear ,,,viewed standing behind the prop looking forward. And I'm sure that gearbox has different ratios for forward and reverse .
Reverse rotation is slower than forward at any given engine rpm. The slower rotation will determine which gear is reverse, hence the correct direction of the prop rotation
Thanks, you first statement chimes with what Graeme has also said, and what I have now gleaned from a manual for the motor (about the direction of crank rotation). I am not sure how much different the ratios are between forward and reverse, and I'm also not confident I could reliably tell by eye the difference in shaft rotating speed in the two directions. Complicated by being unsure the load from the prop would be the same in both directions, given separate pitch adjustment for forward and reverse.
If the prop doesn't need dismantling to adjust it should be able to be done in the water. Another thing to consider is prop diameter. I recently cleaned a mates prop in the water and it made a huge difference
Select to expand quotewoko said..
If the prop doesn't need dismantling to adjust it should be able to be done in the water. Another thing to consider is prop diameter. I recently cleaned a mates prop in the water and it made a huge difference
Thanks. She's on a buoy in a bay which catches some swell. I am not confident I could do the adjustments working underwater with a spanner and an allen key with the boat moving with the chop/swell. Perhaps on a calm day. The prop is 16 inch and low revs/black smoke occur when the prop is clean.
Select to expand quoteQuixotic said..Jolene said..
I think that gearbox should be running in a clockwise direction in forward gear ,,,viewed standing behind the prop looking forward. And I'm sure that gearbox has different ratios for forward and reverse .
Reverse rotation is slower than forward at any given engine rpm. The slower rotation will determine which gear is reverse, hence the correct direction of the prop rotation
Thanks, you first statement chimes with what Graeme has also said, and what I have now gleaned from a manual for the motor (about the direction of crank rotation). I am not sure how much different the ratios are between forward and reverse, and I'm also not confident I could reliably tell by eye the difference in shaft rotating speed in the two directions. Complicated by being unsure the load from the prop would be the same in both directions, given separate pitch adjustment for forward and reverse.
On further digging a Yanmar engine operation manual says the KBW10 E as used with the 3HM comes with forward ratios of either 2.14 or 2.83, and a reverse ration of 2.50. So in reverse the shaft rotates faster or slower than forward for a given engine rpm depending which forward ratio the transmission has (slower than 2.14, faster than 2.83).
Just to follow up, in case anyone with similar issue comes across this thread. the problem is pitch. The feathering prop rotates clockwise for forward. The engine will do 3200 in neutral. The prop was clean and freshly propspeeded.Following the auto stream manual and adjusting the prop by 4.5 turns out, of the forward adjustment screw (manual states as rule of thumb decreasing pitch by half turn of the adjustment screw should increase engine rom by 150) if anything, made the problems worse. With the boat back out of the water after that attempt, prop was adjusted by eye for pitch, forward and backward to have much less pitch in both directions. This resulted in the adjustment screws being at the extreme of their range. After the de-pitching by eye, the engine happily revs to 2700 under load going forward (and would probably make it further), is not smoking and labouring when it does this and readily achieves 7.6 knots boat speed without being maxed out (was in an 8 knot limit channel.)
Somehow the self feathering prop has been seriously out of whack, such that it still isn't right when adjusted to the ends of the ranges of the adjustment screws. Next step is to remove and rebuild the prop.
Thanks, Quixotic, that is really helpful. I recently fitted an Autostream propeller to Kinora and had to lift out again to adjust the pitch using the "1 turn equivalent to 300 rpm" rule. It seems to be fine now but I now know to keep an eye on the extent of the available adjustment. We may be near the limits now and not know it. I'd be interested to hear if rebuilding the propeller fixes your adjustment problem.
Cheers,
Kinora
Yes I will follow up after the prop has been dismantled. Not at all sure how it ended up so wrongly pitched. I certainly don't think it came that way when it was first installed several owners back in 2002. When the prop was first bought the pitch was 10 inches on a 16 inch prop. Somewhere along the way it has got seriously out of whack. I am not sure how, as it was that way when I bought the boat. But I do know the previous owner caught a rope in the prop to the point where it pulled the shaft skeg almost out of the hull. But the prop shows no external, visible signs of damage, and speaking to the shipwright who did the repairs he said the prop wasn't altered as part of the repair work, though of course it was removed and reinstalled. In any case, will report whatever can be gleaned from the disassembly and inspection in a few weeks.
Select to expand quoteQuixotic said..
Yes I will follow up after the prop has been dismantled. Not at all sure how it ended up so wrongly pitched. I certainly don't think it came that way when it was first installed several owners back in 2002. When the prop was first bought the pitch was 10 inches on a 16 inch prop. Somewhere along the way it has got seriously out of whack. I am not sure how, as it was that way when I bought the boat. But I do know the previous owner caught a rope in the prop to the point where it pulled the shaft skeg almost out of the hull. But the prop shows no external, visible signs of damage, and speaking to the shipwright who did the repairs he said the prop wasn't altered as part of the repair work, though of course it was removed and reinstalled. In any case, will report whatever can be gleaned from the disassembly and inspection in a few weeks.
Your prop may have been reinstalled for left hand rotation instead of right hand (clockwise) when it was last removed from the shaft.
Select to expand quoteJolene said..Quixotic said..
Yes I will follow up after the prop has been dismantled. Not at all sure how it ended up so wrongly pitched. I certainly don't think it came that way when it was first installed several owners back in 2002. When the prop was first bought the pitch was 10 inches on a 16 inch prop. Somewhere along the way it has got seriously out of whack. I am not sure how, as it was that way when I bought the boat. But I do know the previous owner caught a rope in the prop to the point where it pulled the shaft skeg almost out of the hull. But the prop shows no external, visible signs of damage, and speaking to the shipwright who did the repairs he said the prop wasn't altered as part of the repair work, though of course it was removed and reinstalled. In any case, will report whatever can be gleaned from the disassembly and inspection in a few weeks.
Your prop may have been reinstalled for left hand rotation instead of right hand (clockwise) when it was last removed from the shaft.
Yes, I've been harbouring that suspicion for a while, hence my earlier questions in the thread (when away from my boat) about the crank rotation on my Yanmar 3HM, and the effect of the gearbox in reversing that, when in forward gear and so on. I don't yet know enough about the way Autostreams are put together to know whether/how it might be possible to reassemble a right handed prop to operate as a left handed prop, but I'm working on it...
If I recall correctly the pitch range is different for reverse . That range is swapped from left to right rotation by advancing or retarding a number of gear teeth on the hub when the propeller blades are in a known position,, hence the left and right timing marks on the hub. Basically by the sound of it the relationship between your stops and your blade angle is out , whether it's rotation confusion or just something that was overlooked when the prop was last assembled.
Select to expand quoteJolene said..
If I recall correctly the pitch range is different for reverse . That range is swapped from left to right rotation by advancing or retarding a number of gear teeth on the hub when the propeller blades are in a known position,, hence the left and right timing marks on the hub. Basically by the sound of it the relationship between your stops and your blade angle is out , whether it's rotation confusion or just something that was overlooked when the prop was last assembled.
Thanks. I am certain the relationship of the blades to the stops is fundamentally wrong, as the stops have had to be set at their absolute limit to get close to a decent pitch. You can see what I mean from this piccy. Ignore the position of blades as they are not on either stop in this piccy. It's clearly a crazy amount of adjustment. Hence the need to pull the prop off, dismantle and try to figure out whats wrong with the way it's assembled.
By the way, per the discussion of the gearbox earlier in the thread, the forward ratio on mine is 2.14 and reverse is 2.50.
Based on my amateur calculations, for a pitch of 10 inches, the blade angle needs to be 11.5 degrees, which at engine revs of 3200 and shaft speed of 1495 rpm, with a16 inch prop will generate 6.9 knots of boat speed at 44% slip. 3200 is the max continuous rpm for the 3HM. The slip's a guess, and given with the adjustment shown below, the boat has got close to 8 knots, I'm guessing the slip in practice is less, even tho' a chap at Austral Props suggested it'd be closer to 50% or more. My boat is an Adams, which are generally easily driven, so I suspect the slip is less than for some others.
Below is a cutaway from the Autostream Manual. The stops limit the rotation of the prop body on the shaft, which in turn limits the extent to which the blade sprockets (and so the blades) get turned by the body sprocket. This makes me all but certain the blades are one or more teeth (probably more than 1) out of alignment relative to the body sprocket. If so, this can be remedied by disassembling the prop and rotating each blade by a tooth at a time, until I get them as near as possible to the right pitch (11.5 degrees) while having the pitch adjustment screws in the middle of their range. That will be the coarse adjustment as it has to be done in whole teeth, then the screws can be used to achieve the fine adjustment.
I'm inclined to have the pitch the same forward and backwards, to the extent that's possible, as the the lower ratio of the gearbox in reverse will soften this a bit. It is nice to be able to pull up quick by hitting reverse, if necessary. A side benefit of all this is de-pitching should also reduce the amount of prop walk (it's been operating more like a paddle wheel at the pitch it's had!).
I have my auto stream pitched quite fine in reverse,,, maybe a bit too fine. It's a bit long in the tooth when pulling the boat up. It keeps prop walk to a minimum but that's also a bit of a disadvantage as i mostly dock to port in reverse. My gear box is also a reduction in reverse so a bit more bite from the prop wouldn't hurt. Every time I go under to give the prop a clean I think about adjusting it.
Select to expand quoteJolene said..
I have my auto stream pitched quite fine in reverse,,, maybe a bit too fine. It's a bit long in the tooth when pulling the boat up. It keeps prop walk to a minimum but that's also a bit of a disadvantage as i mostly dock to port in reverse. My gear box is also a reduction in reverse so a bit more bite from the prop wouldn't hurt. Every time I go under to give the prop a clean I think about adjusting it.
Best not to rush into these things...
In case others refer to the thread, the final outcome is that the Autostream had been mis-assembled when last removed and put back on (before my time).
The feathering works due to a pinion gear at the base of each of the three blades engaging with a crown wheel attached to the prop body as visible in the cutaway image in my earlier post. The prop body turns on the shaft until a stop is engaged (in one direction for forward and the other for reverse). As the body (and the blades and pinion gears) rotates around the shaft, the blades' angle changes.
When assembling the prop on the shaft, it is crucial the blades are exactly in the feathered position (ie exactly fore and aft). This has to be done while a line etched on the forward face of the inner prop body is aligned to another mark/notch on the outer forward face of the prop body. There are two of the latter marks, once labelled as R and one as L, depending whether the prop is being assembled for right handed or left handed use (when going forward). Mine needs to be right handed. If one or more blades is slightly out of alignment when assembled, then the pitch of those blades will be wrong. Being out be a tooth (ie the blade pinion(s) engaging the crown wheel one tooth to the left or right, doesn't cause a large change in the visible alignment of the blade but does significantly alter the pitch for forward and reverse. So care is required to ensure all 3 blades are exactly fore and aft when the parts of the prop body are brought together, while the marks on the forward face remain in the correct position.
Mine was at least a tooth out on all three blades. The pitch adjustment was reset by Austral Propellers to 9 inches for forward and 11 inches for reverse (due to different gear box ratios in forward and reverse), and the prop was then correctly reassembled on the shaft.
Top boat speed on a short run was 8.3 knots, without the engine labouring or the black smoke that previously occurred at anything more than half throttle and anything above about 4 knots of boat speed (previously top speed eventually reached 6 and a bit knots but the motor was not happy and there was plenty of soot).
