Max tachometer RPM of Universal M-35BC / prop upgrade

[Bill W]

I am new to this forum and would like to know if anyone else has experienced reduced boat speed under power with the M35BC engine on my 2002 MKii.

With a clean bottom at 3,200 RPM I am barely able to get over 5.1 knots.  I have increased the RPM above 4,300 for short periods and the boat speed can get up around 6 knots.  No smoke or vibration at 4,300 RPM either.  I suspect I may have a problem with my tachometer as I did not think the RPM's would be able to go as high as they do.

I am considering replacing the original 2 blade fixed prop with a folding 3 blade with hopes it will drive the boat faster, however I want to figure out the RPM issue first.

Any insight or advice from others that may have had the same experience would be appreciated.  Also any comments on what brand and spec of folding prop others have gotten for the MKii...

Thanks!

Bill

[Dave Spencer]

Welcome to the forum Bill!

Prop appears to be undersized.  And if you can get to 4300 rpm, it's undersized by a lot.  However, I doubt the M35 can get to 4300 rpm.  (well, maybe once )  I would be suspicious of your tach if you recorded 4300 rpm.  It would be worthwhile for you to check actual rpm on the crankshaft with an optical tachometer ... relatively inexpensive on amazon or elsewhere. Something like this:  https://www.amazon.ca/Digital-Photo-Laser-Tachometer-Contact/dp/B001N4QY66/ref=sr_1_1?ie=UTF8&qid=1519916537&sr=8-1&keywords=Digital+Photo+Laser+Tachometer+Non+Contact+Tach+RPM+Meter
FWIW, with my M35AC, I get about 5 kts at approx 1900 RPM and at WOT (3200 rpm) I get 6.6 to 6.8 kts. 

[Jim Hardesty]

My experience is similar to Dave.  I recommend the optical tack and search here for how to calibrate the tack if necessary.  I have a 3 blade maxiprop.  Motors great and I tell everyone that's it's the best sail change I've made.  Only downside is$$
Welcome Bill
Jim

[Noah]

I have a smaller engine, a 25XP and use a 3-blade (15x10) flexofold. Also $$$. But, it works well.

[Dave Spencer]

I have a feathering Vari-Prop.  Excellent but very big $$$.  Thanks to the PO for making this investment because I'm likely too cheap.

[Ron Hill]

Bill : Jim is correct. Purchase/borrow a laser tac and check the actual engine RPM against your engine tac instrument.
I believe that you are going to find that your instrument tac is in error!!

A thought

[Noah]

Here is some good info on various props:
http://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

[Stu Jackson]

As an old ragbagger from waaay back, we're still luggin' around a 15x10 buckets behind us.  Oh, gosh gee willikers!!!   

Now that we've moved, we motor a LOT more. 

No moving parts, but light air the folders are miraculous.

Next season I'm going to have to learn how to sail in less than 20 knot winds.  It's a different type of sailing here in BC, with "destinations" either a short 1 hour away, or more than 3 1/2.  Nice to have the choice.

Now in Roche Harbor, Friday Harbor tomorrow.  I'm still in AWE of sailing n these great new venues.  And views.

Like everywhere, though, it's the people. 

[Ken Juul]

The laser tachs are great, but really all you need is a florescence light tube.  Works better if you do it at night or cover the companionway
http://www.catalina36.org/articles/reference/dieselAndPropellerTutorial.htm

on the back of the tach or on the circuit board it is mounted to are a series of little toggle switches (dip switches).  The correct settings can be found in the tech wiki.  There is also an adjustment screw on the back of the tach to adjust the needle position.  Another possibility is a previous owner (PO) may have changed the pulley on the alternator, the tach gets its signal from the alt, smaller pulley will make it spin faster.

[Ron Hill]

Guys : Ken is correct about the florescent light, but you MUST have 60 cycle AC current !! 

Laser tachs are about $25 and easy to use !!

A few thoughts

[andre]

What's the best rpm at idle for a M35bc. Thank you.

[Jim Hardesty]

My manual says 800-1000 rpm.  I set my engine to the lowest rpm that it runs smooth then throttle up to warm-up.
Jim

[andre]

Thank you I think mine is too low

[Mick Laver]

Bill
I suspect your tach is way off. As others have noted, an el cheapo strobe (~$25US) will do wonders. Per the M35B manual (p10) max rpm is 2900-3000, and cruising range is 2000-2500. With our Flex-o-fold 15x9 in flat water (and a clean bottom) we’ll reach hull speed at the upper end of the cruising range. There seem to be diminishing returns going over 2500, so that’s where we’ll usually “set it and forget it” on longer passages.

I second all comments on folders/furlers. One of the best investments you’ll ever make.

[Dark n Stormy]

I got a free strobe app for my smartphone.  Cant get the name as the phone is being used by Davey Jones right now.  just go to app store and search.  It flashes at a certain frequency and you can adjust that frequency in the app until the mark (tape, crayon, paint pen) on the crank pulley becomes stationary.  Try it for different RPMs and compare to tachometer.  the use of the app was for record players or something.  FREE!

Good luck,

Brent