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  1. #1

    Unhappy Complete loss of power

    Hi, I am new to sailing and I am looking for some advice. I have a 50% share in a 25ft yacht (1978).

    The original (inboard) yanmar 8hp diesel engine is only able to propel the boat at about 0.5 knots. We got the boat in February and at first we could do 4 - 5 knots under power no problem.

    Today we struggled for 20 minutes to beat a 14mph wind to get back on to our mooring. We were getting blown backwards (slowly) at one point!

    There is also a fair bit of white smoke after about 10 minutes of running the engine. We have discovered about 10% water in the fuel filter. Would water in fuel cause the boat to run at 0.5 knots?

    Other checks we have done so far:
    * oil seems ok, it's black - no milky residue.
    * raw water inlet not blocked
    * water coming from raw water exit (although not lots)

    I am hoping to rule out a problem with the cylinder head gasket Is it possible that our problem could be caused by water in the fuel?

    Your thoughts please?

  2. #2

    Default fuel

    It is not likely to be water in the diesel as that is what your water trap is for but if you allowed the water to get up to the filter you may have blocked it.
    So try getting a new fuel filter as that would give you this kind of problem.

  3. #3
    Join Date
    Feb 2008


    Assuming that the engine is achieving the same revs as you used to get.......maybe a scrub-off is needed......especially the prop?
    Water in the diesel will not be helping........I would drain the tank and save as much of the diesel as you can.
    It might also be a good idea to fit a diesel water separator......

  4. #4
    LittleShip's Avatar
    LittleShip is offline Registered User
    Location : In the water .... most of the year!!
    Join Date
    Jul 2003


    Do you have a feathering prop, it maybe stuck ??


  5. #5
    oldsaltoz is offline Registered User
    Location : Australia, East coast.
    Join Date
    Jul 2001


    White smoke can be an indication of unburned fuel, check the air intake filter (if fitted) is clean, some have a fine wire mesh that need degreasing and flushing from time to time.

    How long since the prop was inspected, it may be fouled, or have a rope or other hung up in it.

    A dirty hull can half your speed.
    Growing old is unavoidable. However, growing up is still optional.

  6. #6
    Refueler's Avatar
    Refueler is offline Registered User
    Location : Far away from hooray henrys
    Join Date
    Sep 2008


    4 -5 kts is slow anyway - so that was suspect at start of ownership.

    You do not say what rpm engine is running at for original 4 - 5kts and this later 0.5kts ... is it different - is engine failing to rev ?

    If failing to rev - white smoke can be steam and yes water in fuel. If so - it will lead to failure of the engine very quickly.

    If its revving as before but just speed is seriously down - it's prop ...

    If you had a rope of other stopping prop performing - you'd know all about it as the boat would shake that a whores knickers coming off ! Not often this problem would be without large vibration.
    It could be lack of prop folding out or setting pitch ...
    It could be prop loose on shaft or lost its keyway so just turning by limited friction with shaft ....

    IMHO - you need to a) check RPM of engine, check to see what that white smoke really is, (unburnt fuel is usually black exhaust - that's what I was told anyway ...), have boat lifted to see why drive is not happening ... checking all drive train.

    TBH - lack of info and access to see actual boat makes any reply real guesswork - needs a proper guy to check it out on-board.

  7. #7
    Join Date
    Oct 2008


    where is the boat located, Med. UK ? once with a 34ft yacht in Alcudia Marina I thought my gearbox etc was cream puffed, but a quick look underwater showed a growth on the prop as big as an eagles nest,(barnacles) we could only manage half a knot to the hoist, sounds pretty similar to your problem, and the smoke from the exhaust might indicate overworking the motor.
    Time is of the moment.

  8. #8

    Default Thanks

    Thanks for all this. Very helpful advice.

  9. #9
    john_morris_uk is offline Registered User
    Location : Home near Exeter, work in Hampshire, boat in Plymouth
    Join Date
    Jul 2002


    If my boat was only making 5 knots with the engine revs more or less ok, I would be having a look to see if the prop shaft was still going round!

    As others have said, what sort of prop? I lost the keyway to a prop once and eventually the prop fell off (which was a bit embarressing at Cowes week!)

    I agree that boats with lots of growth can seem incredibly sluggish. Correction - they ARE incredibly sluggish. Still 0.5 knots seems a bit excessive, and I suspect the prop or the gearbox or the drive train somewhere.
    [B][I]Wishing things away is not effective.[/I][/B]

  10. #10
    john_morris_uk is offline Registered User
    Location : Home near Exeter, work in Hampshire, boat in Plymouth
    Join Date
    Jul 2002


    My previous post should have read "If my boat was only making 0.5 knots with the engine reves more or less ok"

    Apologies for the typo but I seem to have lost the ability to edit my own posts - probably due to the extremely slow connection speed I am on from sea.
    [B][I]Wishing things away is not effective.[/I][/B]

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