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Old 27-11-2006, 20:57   #46
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Arrrr, hang about Adam. I don't think going down in pitch will cause you to suffer. It will in fact, greatly improve the boats performance. The engine MUST be able to rev to max or damn near max RPM when in gear. If you do not get that or close to, then the engine is overloaded and in this case, so is your trany. The HP increases as the RPM rate rises. So by getting the gearing correct, you end up with more "zip" in your manouvering. You will find acceleration and deceleration will improve greatly and most importantly, every single example I know of, the boat has always had an increase in top speed when the correct pitch has been fitted.
Correctly pitching that prop is your number one priority. Right alongisde the gearboax being sorted of course. Prop diameter is not quite as a negative to performance. Although, the bigger the diameter, the more torgue required to turn it due to friction in the water. So usually a bigger diameter would require a lower RPM of shaft speed, which would mean a greater gear ratio. Small diameter props require a faster shaft speed. Unfortunatly, I don't have a programme that predicts prop diameter. But that is becuase there are an awful lot of variables that have to be figured into the equation to give you that info and this is normaly done at the design stage or a prop designer can give you a good stat point. Needless to say, there are some exacting limitations set by you hull that will determin the upper point of prop diameter and you can not go above that point.
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Old 27-11-2006, 21:52   #47
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Quote:
Originally Posted by AdamY
o
It used to be driven by a Volvo 37hp engine and is now driven by a Yanmar 20hp engine. It is a large 18"X12 fixed two blade prop and this trip is really the first time it has been run for 1100 miles in a row. I am told that the correct prop will see me able to run the engine at it's max rated RPM of 3400 and that the fact that I could only get 2800 out of it before would indicate that I am over propped.
Just a quick note. As you've probably seen, the KiwiProps site has a page with four benchmark installations of the kiwiprop on the 2QM20, with suggested pitch, diameters and max rpms for four different gear ratios:

http://kiwiprops.com/range.htm

The 2.14 gear ratio shows a 22 pitch, but the others are 20. Three of the four examples show a max rpm of 2800, and one is 2700. It appears that this prop wouldn't run at 3400 rpms either, if installed.

Anyway, could this give some indication of pitch and rpm for other three blade props as well? Good luck!

Jim H

p.s. thanks to all for this thread.
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Old 27-11-2006, 22:39   #48
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Adam;
Are you sure you have the 2QM20? Any reference I can find for the 2QM20 has a max. rpm of 2800. Am I missing something here?
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Old 28-11-2006, 03:47   #49
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Adam,
Another question. Are you sure of the current size/pitch/rotation of the prop? The Volvo would have been a left handed prop and the Yanmar should require a right.
Which leads me to think, if the PO didn't get a new prop at the repower. He just changed the shift cable to pull the other way. This would mean you've been running on the reverse clutch pack this whole time.
There should be arrows on the trans case the point to foreward, do they when going foreward?
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Old 28-11-2006, 08:12   #50
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Here's what Boatdiesel.com says
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Old 28-11-2006, 08:27   #51
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Adam, it's amazing how small of an engine you can use with the right prop. I tweaked a 42'x24k lb cutter with 16hp diesel and was able to harness all the hp. It took 3 times to the prop shop for tweaking. Prop calcs get only get you in the ball park. I took the engine torque curve and propped to that spec for running full throttle while running static at the dock. That put the engine at max continuous when running in calms or when punching though nasty chop. It just happened that way but the point is to tweak the prop when running a small engine. Most sailboats are not propped to max efficiency and waste motor hp, etc. I've done this on several sailboats and could never get a 2 blade to match a 3 blade's performance.
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Old 28-11-2006, 11:38   #52
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Wow Rick, what a lovely calculation. Is this a software programme or has someone done the calcs and filled in the spaces for you or or or???
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Old 28-11-2006, 15:39   #53
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www.boatdiesel.com

Wheels the calculation is completed after you fill in all the blanks. This is an excellent diesel forum, however I'm not certain how accurate this worksheet is.

Rick in Flolida
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Old 28-11-2006, 21:23   #54
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Mate. Great site. I could look like an expert with having info from a site like that. :-)
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Old 28-11-2006, 21:43   #55
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Wheels,

You hardly need this site my friend

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Old 07-12-2006, 10:17   #56
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Back to life...

Not the tranny, me.

We got the plague from a visiting friend and have been in bed for the past week.

I am now back to tackling the tranny.

I cant find a reasonably priced replacement so I have chosen the rebuild option. I spoke with Seattle Propeller and they told me if the engine can get to it's rated RPM it mustnt be over propped and I was mistakenly assuming the max under load should be closer to the max unloaded. I checked my service manual and the max loaded RPM is rated at 2800 so the prop must be okay.

I suspect that due to some erroneous information I got from the mechanic who rebuilt my tranny combined with his failure to properly install the oil seal and some long runs (over 48 hours in a row) the transmission must have run dry and burned up. As a consequence of this MER has suggested that I send them my transmission to have it inspected for problems relating to dry running. Their admonition being that if it ran dry I might not be able to detect all of the possible failures and rebulding it might lead to a short life after the fact.

Sadly I cant find a way to get it out without removing the whole bell housing and that means finding a jack and supporting the rear of the engine. This is most unfortunate as I was hoping I could just unbolt the clutch case from the bell housing and leave the engine on it's mounts but upon further inspection it looks like the bolts that hold the bell housing and clutch case together unbolt from the inside of the bell housing and can only be removed after taking them off the engine. It also occurs to me that there is no way to slide the tranny aft without actually taking the rear mounts completely out since they mount on the rear of the bell housing. Still I suspect that as long as I leave the bottom nuts alone that the alignment wont suffer and all will be fairly straight forward.

Oh well, I am off to find a bus to the Napa Auto Parts here in Ensenada in hopes we'll be able to find a small bottleneck jack there.

Thanks again for all your help,
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Old 07-12-2006, 21:32   #57
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Make a list of all the tools...

I hope that I'm too late and your tranny is fixed.
My suggestion is to make a list of all the tools that you think that you might need and buy them.
Having the right tools on hand means that you can be sitting there scratching your head and suddenly the solution occurs and the problem is fixed.
Same for spare parts but one can end up with a lot of unused spare parts.
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Old 07-12-2006, 23:07   #58
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All the best Adam. I'll look forward to hearing the end of the saga sometime soon.
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Old 29-01-2007, 11:53   #59
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Has anyone heard from Adam?

Adam, you okay?
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Old 29-01-2007, 12:43   #60
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Thumbs up

Havent posted to the website in some time now, I would like to say this is because I have spent the last 3 months turning Estrella into a new boat but the truth is we have been taking it easy while getting the neccesary projects mostly done.

Family visits for the holidays etc have helped to delay us.

It seems that I overcomplicated my analysis of this problem (one of my least favorite idiosyncrasies) I met a british fellow who was averse to paying to have work done and insisted i do my tranny myself. When I told him I was gonna pull it myself and send it to Seattle he challenged me with the phrase "Want me to do it for you?"

I didnt want him to do my work for me so I set about pulling the tranny myself trying not to pull the engine in the process. When I was ready to try and pry that stupid bell housing (why I need a bell housing instead of a nice small gearbox I'll never understand) out of the tiny space behind the motor. I asked him to come help me lift it out and when he arrived he chastised me for my attempt to not pull the motor. I dont want to make this fellow sound mean or rude, he was niether, but he kept making me do things right and I hate that ;-)

Anyway he told me I was going to make more work for myself by trying to avoid work and that I should pull the motor. "If it were me my motor would be on the cabin floor and I would have alll the room I need to work." He convinced me to pull the motor and told his wife he would be busy for a few hours and set about helping me lift the motor out of the engine room and slide it forward on the stringers.

Before this point this guy would come up to me and tell me he spent the previous night thinking about what could be wrong with my transmission. I cant say how grateful I am to have met him.

When we pulled that transmission out he said we should pull it apart and see what looks wrong. I noticed when I took the coupling off that there were loads of metal shavings in the space between the flange and the coupler. When we examined the tranny we found that the keeper nut holding the flange onto the tranny was not sufficiently secured. It seemed to have been hand tightened and then deformed. If you live in Portland OR I would advise against calling Cascade Boat Builders even though they are the local Yanmar dealer they will send the work to Terry Foren and he did not do a good job on my tranny.

It was Steve's (the british fellow) opinion that this was the cause of the slippage. We pulled it off and took the tranny apart and found that the guts looked fine, the friction plates were not smooth and he figured if we just tightened that keeper the tranny would work fine.

Since it was apart I put the old discs in (with Steve's help of course) and after running all over Ensenada I found replacecment seals for the tranny. The old discs were warped and discolored (though they would have been serviceable).

I am putting in a new bulkhead today and then heading back out to the anchorage tomorrow and leaving Ensenada after I watch the Bears win the Superbowl (Go Bears) for the first time since I was 8 years old. The tranny is back in and the engine seems in good alignment. I tested the tranny by putting her in forward gear tied to the dock and running the engine up to full load. She now wont exceed 2800 RPM in forward gear, also the new seals dont leak a drop and the tranny showed no indication of heat whatsoever so I am optomistic that all is well down there.

For the record the rebuild wasn't bad at all. I have to thank Steve on S.V. La Reve for his help and Yanmar for having such an excellent service manual. It actually had 2 sections on how to rebuild the KBW10. 1 was "How to rebuild using a bearing puller" and 2 was "How to rebuild using a hammer."

Thanks to everyone here for their valuable help and if anyone needs to rebuild a KBW10 just let me know ;-)
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