Conference vicki::boats

    
    
     If this is one of the electric shift OMC I/O's- the clutche springs
    in the lower unit could be bad.
    
     I doubt a mechanical problem- sounds like:
    cavitation
    hub slipping
    clutch slipping
    
    
     Based on the symptoms, and IF you have an electric shif I/O , I would
    look there- unless there is way too much pitch on your prop for the
    baot/motor combination
    
    Cavitation is caused by either too much "up tilt" on the I/O or lots of
     critters on the lower unit/bottom. On wooden boats, a distorted hull  
    could cause this also
    
                my 2�
     Dick
    

    This is older (1977) Mercruiser model 888 (188 Hp) I/O on a Sea
    Ray 22' 220 Cuddy Cabin. The symptoms occured with the outdrive
    in the down most position. There are no critters on the outdrive
    or bottom (it's only been in the water a few weeks, and only a "slime"
    as accumulated - which I've wiped off with a sponge). Again I trusted
    Marine USA to select the right prop/pitch given the model Mercruiser
    and size of boat and use (family cruising on salt water).
    
    john

    
    
     JOhn:
    
    Sorry- if I read your note a little more carefully, I would have seen
    that it was a Mercruiser. 
    
     Something sure isn't right- do you have a tach in your boat?- thast
    should tell you what Rpm you are at when the problem occurs. If it does
    it at a lower rpm as the load increases, would indicate a probable hub
    problem, since with a higher load, the torque to move a given speed
    increases and therefore the speed ( same torque) at which the breakaway
    torque in the hub is reached is lower.
    
    A quick way to tell if the hub is slipping is to paint the prop /hub
    white. IF the hub starts to slip, the paint will be chipped away around
    the black rubber hub and be readily visible.
    
     It's got to be either the hub or cavitation, THe mercruiser is all
    mechanical drive with a dog clutch. If something was slipping, like a
    bad spline on the driveshaft or the clutch dog jumping in and out,
    there would be either thumping and banging or some noises that would
    make you know something was wrong.
    
     I'm not all that knowledgable about mercruiser outdrives- I know that
    OMC made a High profile " and "low profile" outdrive- the difference
    was that the low profile sat lower in the hull- the distance between
    the engine driveshaft centerline and the caviataion plate was
    different. If you hooked up a low profile leg to a high profile
    motor/rear housing-the cavitation plate would be above the bottom of 
    the keel= cavitation!.
    
       Could be somebody ( read unreputable dealer?) have pulled a swap on
    the outdrive assembly? I'd check model no's to make sure you have the
    right set up. A quick check would be  to see if the cavitation plate on
    the outdrive is level with or just slightly below the keel. A lot of
    these outdrive legs are interchangeble mechanically but not operably-
    for example my OMC comes with 4 different gear ratios in the upper gear
    case, but the rest of the assembly is the same- from 100HP to 245 HP,
    and  later models were a different leg length.
    
     If the leg was changed out and a higher ratio of output/input speeds
    was installed, too much torque will be applied to the prop( it will try
    to turn too fast) and will torque overload. If it didn't slip, the
    symptom would be inability to get the engine to reach max rated rpm.
    I accidently put a 14diax21 pitch prop on my boat ( supposed to be
    14x14), I vcouldn't get the rpm past 3200(rated at 4200). Lousy
    performance, too.
    
       If there was no clanging or banging, then the problem is slipping
    hub or cavitation.- Check the hub as mentioned previously, and if the
    boat is out of the water, or if you can dive down and look at the
    cavitation plate, you should be able to find the problem.
    
    BTW- if there are gouges, big nicks, rough edges on the plate, that can
    cause cavitation also.
    
     Does it do it with the outdrive further out?? You mentioned it acts
    up with the outdrive in the full down position. Could be that you are
    too bow heavy under certain conditions and simply pushing the stern
    right up out of the water. 
    
    
    
     Dick
    
    
    
    
    
    
     
    
    
    

    Thanks again Dick. I had hoped to put a stop to this problem with a new
    propeller, I don't expect a new propeller to have its hub breakaway
    under normal use. I just don't want to accept that my new prop could be
    suffering the "spun hub" syndrome. I guess it is possible that the
    propeller was defective from the factory, or that the dealer sold a
    prop that can't take the torque of my engine (which can't be a lot as
    compared to engines sold on modern boats). It is a MerCruiser
    Quicksliver prop. 
    
    This is why I turned to the weeds or cavitation theories. Weeds because
    they are there, and when I cleared them (or seemed to clear them)
    things seemed OK for a little while - then it would come back.
    Cavitation because of this problem has given me doubts that I got
    the right propeller, I don't know how qualified the parts person who
    sold it to me was, and felt that such a short pitch might cause
    cavitation as speeds increase. Reaching for straws bceause I don't know. 
                                                                      
    If someone could say, sure weeds will cause that, I wouldn't worry.
    Much. But if someone could say, a weed fouled outdrive/prop exhibits
    different symptoms than I'd worry a lot more. As I said, all the guests
    on board made it impossible for me to throughly test this out. 
    
    The boat has a tach, but it is one of those 45� arc types that make
    it difficult to judge accurately where things are happening. Also
    when this happened I didn't take time to look at the tach, I backed
    off on the throttle immediately - for fear of causing damage to
    engine/outdrive. Finally, when I got everyone off the boat, I took
    it for a spin, full throttle, no problems. But still, I wonder.
    
    john

    CALL SOMEONE WHO REBUILDS/RESTORES PROPS, MOST OF THEM CAN
    CALCULATE WITHING REASON WHAT PROP YOU SHOULD HAVE. WEEDS
    WILL CAUSE THIS PROBLEM. SORTA. I HAVE A SMALL OUTBOARD
    WHEN THE PROP PICKS UP WEEDS IT LOOSES IT.
    
    TRY IT AGAIN, BUT DO CHECK FOR WEEDS.
    
    JIM.

    You wanted to hear... Weeds will cause the prop to break loose.
    With everything trimmed out, any amount of weeds will cause my
    Bravo i/o to cavitate.
    

...for a 220CC with a 188 is 14 (dia) x 17 (pitch) cupped. When I needed them
(not for a few years now), I was able get them from Merc (Quicksilver),
naturally, and Michigan.

I have little else to add to the problem discussion, but for what its worth:
I never had this symptom except when I did spin the hub, which I did twice,
once on rock and the other in a tangle with a piece of fishing net. My rebuit
and somewhat modified "188" was putting out around 210 hp and I pulled skiers
(sometimes more than 1), towed other boats, cruised about wtih a full load
of people and equipment, and even pulled a 'footer once. I doubt that you are
overloading your prop.

Dave

    I have a problem that I thought this is the right topic to sneak
    it in.By the way I own a sailboat but my problem is related to 
    power (transmission)
    Last week while maneuvering with my engine on(Inboard Yanmar 3HM
    30 hp) I heard a hollow sound under the stearn and the boat stopped
    responding.Uncertain if I had lost the prop or not I jumped in the
    dingy and pocking with the boat hook I felt_could not see because
    of murky water-that the prop was still there.Next thing was to check
    the transmission and there,where the prop shaft coupling..meets
    the transmission casing now I can see about one inch of spline of
    the transmission output shaft exposed.The transmission oil had gone
    to the bildge thru the hole of the casing that the coupling should
    have been tight against it.
    Well it seems that the prop shaft and coupling has move 1" away 
    from the transmission casing towards the stearn of the boat.
    To evaluate a little further I powered up for a few minutes and
    noticed that the shifting gear works and also the transmission,
    looking at the output shaft,it turns one way when I shift forward
    and the other way when I shift reverse.The prop shaft doesn't follow
    though.It looks like it doesn't connect.On the other hand the prop
    shaft will turn from the power of the water turning the propeller
    while under sail alone.That means to me(unqualified opinion) that
    the problem lies in the connection of the trans.output shaft with
    the prop shaft at the coupling,but then how we cover the exposed
    spline?
    A co-worker suggested that I may have caught rope,weeds or netting
    on the propeller which got stuffed so tight between the prop and
    the hull that the prop shaft and coupling sprang 1" outwards.
    Well, does anybody has any ideas,suggestions,assumptions of what
    could have happen,how bad it can be,any similar experiences etc.
    I have to get some education fast in case I deal with the yard
    mechanics.Right now I can hardly challenge them with what I know.
    This week end I am going to try and clean any debri on the propeller,
    if there is any,with the hope that when clean the shaft will spring
    back to its place and the only thing I have to do is add some
    transmission oil.I can dream can't I ?