I have recently become the owner of a twenty year old narrowboat. The boat is powered by 1.5 BMC engine and has hydraulic drive. The engine runs well but I have recently experienced the loss of hydraulic power. This has effected the speed and manoeuvrability of the boat. What can I do to solve this problem.
First I need to be sure that you do mean a hydraulic drive and not a hydraulic gearbox. I will answer for a hydraulic drive where the only connection between engine assembly and propshaft is a pair of flexible hydraulic hoses. If it turns out that you mean a hydraulic gearbox please email again.
Whenever these symptoms appear the first thing to do is to check that nothing has wrapped around the prop. On a hydraulic system this can cause such a pressure rise that the pressure relief valve opens and dumps oil back into the reservoir. Even if you have a gearbox check this first.
I assume that you have been keeping the reservoir toped up to level with the correct fluid? I suspect some “do everything” oil sold to farmers will be OK. If you have any data in a manual or affixed to the reservoir then use that type of oil – much depends upon the type of pump and motor.
Next make sure that the control cable is moving the spool valve (looks like a block with a number of pipes on it and a lever at one end) lever to its correct position for ahead & reverse. It might just be a loose cable anchor point at either the control or the valve end.
If all the above are OK make sure nothing has gone wrong with the way the propshaft is coupled to the hydraulic motor. The coupling may have come loose.
I think it would be worth having a look at the pump driveplate (fitted to the engine flywheel – especially if you can hear rattles or bangs coming from inside the flywheel housing.
Now it starts to get expensive.
If you can beg or borrow a high pressure hydraulic test gauge and find a way of fitting it you could measure the pressure being produced, but I have no idea what it should be because prop size has a great influence on it.
If you can see the outlet (inside the reservoir) for the PRV, see what it does whilst at normal ahead or astern speed. If it is leaking all the time either something is loading the system (fouled prop, overtight stern gland, partially seized motor etc) or a faulty valve. It might be adjustable, but I would have concerns over the 20 year old spring inside.
Finally you have to consider wear in the pump, motor, or valve assembly. If this happened suddenly I would suspect a failed seal in the valve. Once you get to this stage I think you will do better with an agricultural or plant (JCB etc) type fitter than a boatyard engineer.
