Catalina 34

General Activities => Main Message Board => Topic started by: John Gardner on May 30, 2011, 06:59:24 PM

Title: Transmission?
Post by: John Gardner on May 30, 2011, 06:59:24 PM
Today I set out on a windless day, so engine on.  I'm sitting off to the side so don't see the knotmeter, but after a while the penny drops that with the engine rpm at my normal 2300, I'm only doing 4.3 kt.  Normally it's 5 point something, and it seems to me, now that think of it, that a few years ago it was more like 6.  I anchored and dived on the propeller - nice and clean and no dings. 
I checked the transmission oil level - right on the money.  The speed sensor is nice and clean and although it was reading lower than the GPS, it was only half a knot off.  The bottom was painted this winter and is nice and clean.  I haven't checked whether anything is wrapped round the keel - the Chesapeake is so murky, you can't see the keel from the propeller, and the possibility didn't occur to me till later, but in any case it's unlikely.  There's not many possibilities left.
Comments and wisdom would be much appreciated.ner
John Gard
Title: Re: Transmission?
Post by: John Langford on May 30, 2011, 10:45:25 PM
One possibility is that your tach is off and you are actually running the engine well below its normal cruising rpms. Can you get access to an electronic tach to check the boat tach?
Title: Re: Transmission?
Post by: David Sanner on May 30, 2011, 10:49:27 PM

I guess your transmission could be slipping...

I might start with a few tests:  

At wide open throttle, in neutral, what is your tack reading?
At WOT underway (no wind/seaway)  and what is your tack reading?
Should be close to the same... approx 3k.  Typical cruising rpm
is 80%+ of max rpm and if you're prop is sized well, your hull
is clean you should easily get above 6kts.

Do you notice any lost of thrust in high load situations...
such as accelerating with quick starts or reverse?

Assuming no major vibration, a cleanhull, prop looks good and you can get
close to the same RPM in neutral (around 3k) as you can under load but
still your SOG in quiet water isn't getting much above 5kts any where
near WOT you've certainly a problem.

... two things that come to mind are an under
pitched (damage) prop or a slipping transmission.

But I'd start with checking your tack reading and making
sure you're getting proper and accurate rpm under load.  

Title: Re: Transmission?
Post by: gwp on May 31, 2011, 06:49:21 AM
Start simple.....current or headwind? 
Title: Re: Transmission?
Post by: Jim Hardesty on May 31, 2011, 08:46:26 AM
I also slow down with a head wind.  Into a strong 25kn wind I don't get much more than 5kn of boat speed.  Not what I expected with 35hp.  My previous boat, a 30 footer with 15hp, I never noticed a loss of speed.  Haven't done any troubleshooting but a slipping transmission would explain it.
Title: Re: Transmission?
Post by: lazybone on May 31, 2011, 02:58:57 PM
Slipping trans would soon turn the fluid dark/black.
Title: Re: Transmission?
Post by: John Gardner on May 31, 2011, 06:29:20 PM
Thank you for your replies.
Tacho calibration:  Was done a few years ago when I upgraded the alternator.  At that time max rpm was just about 3000, so I'll check if that's still the same.  I'll check David's other speed/rpm thoughts at the same time.
The 2-bladed prop is clean and appears fair.  It was professionally repaired, faired, and balanced about 3 or 4 years ago after it hit something, so I think it's alright.
The only wind was the wind due to my motion, and current there was a little, possibly half a knot, which may explain the difference between GPS and knotmeter.
And the oil was clean.  Not sure if I'm pleased or not - if it was black that would probably give me the answer, expensively, but being clean leaves me still in doubt.

I will have a go at it this weekend.  I'll run across the wind in a current-free area and check knotmeter, gps, and tacho in both directions.  See what that turns up and let you know.
John Gardner
Title: Re: Transmission?
Post by: Ralph Masters on June 01, 2011, 03:44:23 PM
On Ciao Bella at 2000 RPM I normally show 5.7 - 6.1 on the GPS, and I max out at WOT at 2400 roughly  At WOT it normally pushes up to about 6.5 - 6.7 fast enough to make the old girl squat down and get that engine exhaust mark on the stern above the bilge discharge opening.  Messy to clean off, and hard to get to.

Title: Re: Transmission?
Post by: Ron Hill on June 01, 2011, 06:45:44 PM
John : I'm sure that you changed Xmission oil this spring and it's at the correct level.  If you check the shifting linkage at the transmission and you get the full throw of the lever(at the transmission) everything should be OK.
Now if you changed to an Edson stainless shift lever at the helm then you need to adjust the throw below.  You might need to put the shift lever cable in the lower hole (more throw) from the top hole (more leverage).  A few thoughts
Title: Re: Transmission?
Post by: Ken Juul on June 02, 2011, 04:29:54 AM
Either your tach is way off or you are way overpitched.  The engine should get close to 3000 at full throttle in gear.  Suggest you calibrate the tach first.  Either borrow/buy a digital rpm counter or use the florescent light method.  Pretty sure the Florescent light method is described in the wiki, if not search for engine rpm or tach or similar.  Last time I saw anything about it was several years ago.

The tach has two adjustments, one on the back of the tach for the needle and the other a series of dip switches to match the tach to the alternator.  Both should be described in the wiki
Title: Re: Transmission?
Post by: dgill on June 02, 2011, 07:35:18 AM
Hey John,

There is a tach calibration tool in the Fleet 12 "Tool Box" that you can borrow. 

D. Gill
Title: Re: Transmission?
Post by: Ralph Masters on June 02, 2011, 08:29:39 AM
From the survey the prop is a 2 blade 15 X 14.  Not sure what the manufacture puts on as standard equipment.  I do know that I need to replace the tach because the hour meter does not work, has not moved since I bought the boat and the PO, who had it two years, said "oh yeah that's never worked".  So go figure.  I do know that if I go too fast then the admiral has me on the swim step scrubbing the black stuff off the transome back in port.


Title: Re: Transmission?
Post by: Ken Juul on June 02, 2011, 09:26:36 AM
I think that is the standard for the 2 blade. 

Another test you can fast will the engine run in neutral?  If it is close to 2400 then you know the prop pitch is ok and it is all tach.  If more that a couple hundred different then you have a couple problems.

If the loaded/not loaded rpms agree, then you can figure that your cruise rpm should be 18-1900 or 75-80% of max.  These engines don't like to be run for long periods at full throttle, the black on the transom is one sign you are working the engine too hard.

When you do replace the tach, it will be necessary to set it up for the alternator you have.  If instructions aren't provided, you know where to find them.
Title: Re: Transmission?
Post by: Ralph Masters on June 02, 2011, 09:45:36 AM
yep, the no load is about 2400 too.  Normal running is right about 1900 - 2000 when we motor.  If we go up to the 2300 - 2400 the temp starts going up, so I know the engine is loading there.  If we keep it at 1900 - 2000 it doesn't squat down and get the mark on the transome.  Great little engine really.  With the problem with the hour meter I just figured it was not reading correctly.  Some day that will be replaced, it's just down the list a bit.
Title: Re: Transmission?
Post by: Tom Soko on June 02, 2011, 01:55:34 PM
Ken and Ralph,
I'm pretty sure that a 15x14 is way too much prop.  The standard prop supplied with the C34 and C36 has been a 15x9 three blade or 15x10 two blade.  The tach might also be off, but probably the reason you are getting a dirty transom is the prop.
Title: Re: Transmission?
Post by: John Gardner on June 03, 2011, 07:13:22 PM
Today I did some investigating and thought you would be interested in the results.  A friend had the brilliant idea of using an optical tach on both the engine and the gearbox output, so I borrowed one from work.  The Hurth transmission manual on this website indicated that there is a label on the trannie to show what the ratios are forward and backward.  Great stuff.  I should have mentioned before, that I have a 25XP engine.

After a number of interesting contortions with mirror in one hand and flashlight in the other, I concluded there was no part number and no ratio label on my trannie.

I went ahead anyway with runs in neutral, and in gear, loading the engine by trying to pull my helical mooring out of the ground, first in reverse, and then forwards.  I didn't have the courage to pull against the mooring at max rpm.  I concluded that the boat tach was reading a bit low, and assuming no slip, calculated the gear ratios.  It just so happens that the calculations closely match the example shown in the manual (1.86 reverse, 2.05 forward), so I'm concluding no slip.  Max true engine rpm in neutral was 3217.

Then I went out and did some motoring.  There was just me, and I wasn't prepared to go below for long enough to make measurements, so I had to content myself with using the measurements on the mooring to estimate true rpm from the ship's tacho.  Two main conclusions were my knotmeter is under-reading by about a knot, and the max rpm under load is 3125 indicated, 2952 estimated actual (i.e. a loss of 265 rpm due to load).  Running at 80% of this value gives a true speed of about 5.1 kt.  I'll try to attach an excel spread sheet with all the details - I may be successful or not, but thank you for your interest and help.

Moored neutral   Tach   Eng rpm   Tran rpm    GPS   knotmeter              tach o'read      
                   1130   1076                                    idle           5%      
                   1500   1445                                               4%      
                   2000   1881                                               6%   Tach over-reading about 5%   
                   2500   2380                                               5%      
                   3350   3217                                    max rpm   4%
Moored reverse   1100   1016            546                         idle           8%   Gear ratio    1.86
                   2000   1896            1013                                    5%   Gear ratio    1.87
Moored forward   1100   1034            508                                    6%   Gear ratio    2.04
                   2000   1900            932                                    5%   Gear ratio    2.04

Motoring forward      estimated                                     % max rpm      
                   2400   2286                   5.0   4.0                      77%      
                   2700   2571                   5.5   4.5                      87%   Ktmeter under-reading by ~1 kt   
                   3100   2952                   6.3   5.0           max rpm   100%      
Title: Re: Transmission?
Post by: Ron Hill on June 03, 2011, 07:26:27 PM
John : Thanks for the data.

You should have a HWB 50 Hurth transmission which has a ratio of a 2:1
I don't recall where the data plate is on the housing case, but it's probably painted over!  A thought
Title: Re: Transmission?
Post by: Indian Falls on June 04, 2011, 07:08:05 AM
I thought you'd like this...
Now you can see the potential for damage from running low on oil and overheating causing all those clutch discs and springs to call it quits.  Looks like there is a clutch pack for forward and one for reverse. 
Title: Re: Transmission?
Post by: Ralph Masters on June 04, 2011, 09:06:38 PM
Moored neutral WOT 2800. WOT forward underway 2300.

Ciao Bella
Title: Re: Transmission?
Post by: John Gardner on June 05, 2011, 05:27:00 AM
Wow, all that stuff in such a little casing.  So much opportunity for "Whoops, seem to have a bit left over"
Title: Re: Transmission?
Post by: David Sanner on June 06, 2011, 12:42:22 AM

John my first thought is that your transmission is fine.
(Your RPM at WOT while moored seems to suggest it's not slipping)

2nd (assuming your test was on flat water, little wind or current)
you've either got a really dirty bottom or it might be time to look
into another prop if you want travel 20%+ faster.

I have a 25XP with about 2k hours.  With a freshly
cleaned bottom I do about 6.3kts at cruise rpm which
is just over 80% of my max rpm underway at WOT.
(I believe I also loose one to two hundred rpm when
in gear vs. neutral at WOT.)

If you're bottoms is a little bit dirty that could explain
a 1/2 kt loss but you're still coming up short.

Good news is that if you don't mind going a bit slow
you hopefully have to spend a dime.  If you want
to get an extra knot a nice folding prop is cheaper
than replacing your transmission and you surely
notice a nice bump while sailing as well.

btw, my old three blade 15x9 came in a few tenths of
a knot slower than my current geared folder and didn't
really do any better in a seaway.

Title: Re: Transmission?
Post by: Ralph Masters on June 06, 2011, 08:12:41 AM
You weren't going up hill were you??