Folding Prop / Engine Vibration

[dce]

We have just purchased a 1989 C34 and during the test sail and survey we found excessive vibration from the engine.  We were told that the engine mounts are in good condition, but the prop is flopping around and at low rpm's there is excessive vibration that gets less at higher rpm's.  The prop is a folding 2-bladed Martec prop, but we do not know the age. 

We want to minimize the vibration.

1. Can anyone tell us what the stock prop was for a 1989 C34.

2. Is it most likely that the vibration is from the prop and not something else like the engine mounts?

3. If we switch to a 3-bladed prop, what size and manufacturer are recommended?

Thanks  - Diane and Brad
Hull #904

[Stu Jackson]

Diane and Brad,

Welcome, and we know we'll be able to help.

One place to start looking is this Guide to C34 Website Technical Resources:  http://c34.org/bbs/index.php?topic=2629.0

If your engine mounts are OK, slop could come from a number of places:

loose flange coupling

loose zincs on the shaft

need for new cutlass bearing

If you access the Knowledgebase, you can use its Excel spreadsheet format to read about the issues.  If you join the C34 IA you can read the Tech Notes Online.

You can also SEARCH on this message board for all those items.

[Ken Juul]

What rpm were you trying to idle at?  Most of us have found that 1000 is about as low as you want to go.  Engine vibration is normal in the 700-850 range. 

If the cutlass was bad, a good surveyer should have found it, as well as a loose zinc, during the survey.  Could very well be the prop.  The Martec has a good reputation, might want to give it a good cleaning, make sure it smoothly folds and unfolds through the full range of motion.  Ensure both blades can reach the full open postion.  If one blade isn't opening fully it will certainly vibrate.  2 blade props do vibrate a bit more than 3 blade, but it should not be excessive. 

Use the index Stu mentioned, or search the site using the search function in the top menu bar.  Lots of discussions on different props, no need to re write it here.

Welcome to the community, I think you will love your new boat.  Please see the note to new message board members near the bottom of the list.  Gives several hints on things to do to help us help you with your questions.

[Jeff Kaplan]

diane and brad, another place to look for the vibration is the prop shaft itself. on #219, i have a terrible vibration when tacking around 2,000 and above. when back down to 1800rpms or lower, vibration smooths out but still there. got mechanic out for sea trials a few weeks ago, and he thinks it's coming from the shaft log, where shaft goes thru boat, and that the shaft might be slightly bent. the shaft is only 3 years old with new cutlass brg also installed at that time, but last season, i snagged a lobster pot and it got all wrapped around shaft but good and this might have bent the shaft very slightly so when under power and shaft is whipping, this might be causing the vibrations. really won't know till boat comes out for winter and shaft removed and sent out for inspection. just another place to look. good luck...jeff

[Bob K]

Diane and Brad,
If you discover the problem is caused by your Martec, you can send it back to Martec for reconditioning.  It costs somewhere around $150 - $200.  We had a similar problem with the Martec 2 blade on our C27, and it worked fine for years afterward.  Have it done during winter haul, and you'll never miss it.
Bob

[John Gardner]

Some experience for you that may or may not be relevant.

Always, but especially during the last two or three seasons I've had vibration from the propellor shaft, to the extent this season that it limited the max rpm I was prepared to go to (about 2000 rpm - quite speed limiting).  The nature of the vibration is like a pair of engines that are not quite synchronized - the intensity/volume of the vibration comes in waves on a cycle of every 2 seconds or so.

The prop was repaired and balanced after meeting a log a couple of seasons ago, so I was confident in the prop.  The cutless bearing is in good shape.  Last winter on the recommendation of the boat yard I removed the Vetus engine mounts I had put in and put back the original style mounts (wouldn't you know - it was just a couple of months after I had thrown the old ones out).  I didn't do as they recommended and replace the Vetus Bullflex coupling.  However, I re-checked the alignment of the engine.  This season, no improvement.  I wondered whether harmonics were being set up between the prop and the prop shaft strut - I know there is a minimum distance one is supposed to have because of this problem - so I slid as much of the prop shaft out of the coupling as much as I dared (about half an inch) and tried it out.  Vibration is much reduced. I don't know what distance I have there now; unless I go swimming, it will have to wait till winter.  Since I now have only about 1 inch of engagment of prop shaft in coupling, I am trying to dream up a way to push the prop shaft back a little bit further in the hope of totally eliminating the vibration.

But the point of this ramble is...don't forget to ensure there is good separation between prop and strut.  (Maybe someone else can recommend a distance, but I'm presently aiming for a couple of inches.)

[George Pyrpiris]

John,
What kind of Prop do you have?
George

[John Gardner]

George,

It's a fixed two blade prop.  The original to the best of my knowledge.

Yesterday I managed to put a 1" spacer between the engine gearbox and the bullflex coupling.  I went for a swim and I have about a two inch space between the prop hub and the strut.  However, it didn't give much, if any further improvement.

John

[Ron Hill]

dce : The stock 2 bladed prop is a 15" (dia) X 11" (pitch).  The standard 3 bladed prop is a 15" X 9". 
Most of us with a 3 bladed props have increased the pitch to 10" or 10.5".  DO NOT exceed the 15 inch diameter (for ANY prop) or you'll get buffeting on the under side of the hull.   

[Kyle Ewing]

Regarding prop/strut clearance, everything I've read and been told says the prop should be no farther from the strut than the diameter of the prop shaft--1" in our case.  If the prop is too far away from the strut it can cause flexing of the shaft.

The shaft itself can be slightly bent.  If you have a local propellor shop (i.e. Airmarine in Chicago, http://www.therightprop.com/) take the shaft when you take in your propellor for conditioning.  They can check the shaft trueness.

[arthur]

I bought a 1997 Catalina 34 MKII two years ago with a folding prop.  I had little vibration the first year, but this year it began vibrating.  I was told the prop was worn and needed to be rebuilt.  After cruising for three plus weeks on Lake Michigan I've decided a fixed prop would best suit my needs; more power in head-on seas and quicker power for docking.

In the August issue of Mainsheet in the Technical Articles I read Mike Vaccaro's report on "Propeller Data Request".   I sent a e-mail to Mike and he replied with what I believe to be helpful information in my case.  Upon his suggestion, I contacted "Campbell Sailer" propellers in Canada.   We have exchanged a number of e-mails and they have convinced me that their 14x8 prop is the best prop for my boat.  It will have less drag than the standard Michigan Prop (about 20%) and should push my size boat faster than the standard 15x9 prop.

They did a test on three C34 MKII's  two brand new and one three years old.  The 1st new boat had a standard 15x9 Michigan prop and was slowest; the 2nd new boat with the standard 15x9 Michigan prop was 0.4 kt faster; and the 3rd boat ( three years old) with the Campbell Sailer 14x8 was 0.3 Kt faster than the 2nd boat.  I will be buying a Campbell Sailer prop this come spring.

[David Sanner]

Arthur,

So cambell is saying a lower pitch and smaller diameter prop will provide better performance.  Being that 15x9 is under pitched if anything (certainly w/ an M35) I'm curious to hear why their 14x8 would drive our boats faster.

I guess there's a lot that can be done with the shape of the blade and the M35/Hurth combo that they put in the MII does have fairly high prop RPM but I'm still surprised and curious.

Also in the example you mentioned why was there a 0.4 difference between the first two boats, did they give a reason as they seem to be the same boat & prop.

[Ken Juul]

The Campbell prop has a unique shape.  It uses dynamic shaping to push the water rather than a flat paddle.  I think mine is a 14x8, rpm at full throttle is about 2800 (M25xp) so it has quite a bite and pushes the boat right along.  If I remember I'll take some pictures next time I pull the boat.

[sail4dale]

Have you checked out Flexofold???

I have a 15 x 10 and it works well on my M35 engine.  Backing is great and I cna cruise at 7+ knots.  It's price is right.