Kubota Engine Chapter 2

[lindai]

Thank you to everyone who made helpful suggestions about finding someone to
fix the Kubota engine on our Finesse 21. We eventually got Marine Services
from Tollesbury to come and sort out the mucky fuel system and the engine
runs fine now.

Our first sea trial didn't go too well - we managed to go about 100 yards at
a speed of 1 knot, before smoke started pouring out of the lockers and we
lost all power/ steerage and were drifting helplessly towards the mud. My
husband leapt into our old Avon dingy and managed to tow us to the nearest
pontoon (along with another kind soul in his dingy).

Next day we phoned Marine Services to explain that the boat still didn't go,
and they agreed to come out again (after taking my credit card number as a
precaution). It turns out that the drive belt on the hydraulic gearbox had
snapped (it didn't occur to us to check this as we thought the boat was on
fire) and produced smoke as it slipped and got hot. We couldn't get a
replacement so the engineer, Dave, borrowed the belt from the alternator.
So far so good - we now have a boat with a rotating prop and flat batteries!

That evening we decided to go out on sea trial number 2. Well the 'G' force
was incredible. My face was pushed back so far that my ears met round the
back of my head. We managed a stunning 2 knots. We went out of the marina,
turned round and came back into our berth, several sea snails overtook us on
the way in.

I know that boat used to live on the broads, but I can't believe the
previous owners installed an engine (12hp) and hydraulic drive which could
only manage 2 knots! I'm at a complete loss as to what to do next. Surely
a 12hp engine should be capable of pushing along a 21ft wooden boat! I am
rapidly running out of money and the will to live. Yesterday I thought
seriously about throwing the inboard away and sticking an outboard on the
back.

Any suggestions gratefully received!

Linda



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[vyv_cox]

Not a lot of information to go on, and I have never owned anything with a hydraulic drive, but here are some thoughts.

1. 12 HP is ample for the boat. I had a 29ft yacht with a shaft drive Kubota 12 and it was OK to about 6 knots.
2. Is the engine delivering its full power? Did Marine Services consider it to be working well or does it smoke, spit and generally run rough?
3. Assuming engine is OK, turn to the hydraulics. You have a pump on the engine, a motor on the prop and oil pipes in between. Is the failed belt a symptom of the problem or a coincidence?
4. First thing, is the system full of clean oil and is the filter clean? If not, maybe excessive pressure has burnt out the belt. Could there be any airlocks?
5. Do the pump and motor turn easily by hand? Do the motor and prop turn easily by hand, or perhaps has someone over-enthusiastically tightened the stern gland?
6. Is the prop roughly the right size? Check by downloading a program <A target="_blank" HREF=http://www.castlemarine.co.uk/ShopFront.htm>here</A>
7. If the answer to all of these is positive then you will have to look at the sizing of the pump and motor. Enquiries to the manufacturer should then advise if they are compatible and match the engine power.
8. My final thought is the switching. Somehow you need to establish that the valves are working correctly and not restricting the flow. A systematic bleeding programme may need to be devised.

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[Birdseye]

agree with the other poster - 12 hp should be ample.

check that the engine is running at the right speed ie about 3500 / 4000 revs when flat out. if it is running much slower, then the max it can develop will be much less than 12 hp. but the bit that puzzles me is the belt drive. i would not have thought that one drive belt would transmit 12 hp from engine to pump. suggest you phone someone like fenner power transmissions to find out.





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[Strathglass]

Hydraulic drives are not very efficient. Saying that you should get more speed than that.
Assuming all the hydraulic valves are functioning correctly then perhaps the previous owner was happy with just some drive and the system has never been correct.

Mention has been made of prop size, this is very difficult to calculate unless you know the ratios of the hydraulic pump and motor.
As questioned earlier does youe engine run at normal speed at full revs? or does it labour or over rev?.

If this is wrong then in your case the simplest way to change the gearing (if it is requires) would be to alter the pulleys from the engine to the pump.

Just another avenue to look at.

Iain

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[dickh]

Your Kubota engine should be good for 3600 revs flat out under no load. Under load you will probably get slightly less than this. The problem appears to be between the engine and pump. Normally on Hydraulic systems with an engine driving the pump. the pump would be mounted permanently to the back of the engine via a backplate. Your appear to have a belt drive from the engine to the pump. If this is the case it is not a good setup unless the whole setup is rigid AND the pump is suitable for belt drive, (AND the engine has a Power Take Off suitable for side loads) as usually a hydraulic pump is end driven without any side loads to speak of. If the pump is belt driven you have to have a pump with additional bearings to take the side load.

More information is needed to give a better answer.
What is the Hydraulic Pump and what is the reference No.
What is the Hydraulic Motor and Reference No.
What belt drive is fitted - ie belt size and pulley diameters.

If you can find a local hydraulic engineer to have a look at it he may be able to give better idea of what the problem is. I agree that Hydraulic drive is not very efficient but should be more than sufficient for your purpose.
Also as suggested try Fenner drives or Bearing Services Ltd(from Yellow pages) who will be able to help on the transmission side but probably not for the final propellor size.

I would persevere with the existing setup and try the suggestions above.
Good luck and keep us informed of progress.



<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[kds]

An 8 h.p. outboard would give you 5 + knots, no hassles and a load of storage under the cockpit.
It is worth taking care with the mounting.
Good luck.

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