Hydraulic Gearboxes

[Boater Sam]

Many were fitted with PRM 160 boxes too. And of course there was the Delta.

 

[fisherman]

He put the bolt into the wrong clutch then?

On that box, and mine, (500n I think from memory) you only got 'ahead' so if ahead was astern due to a wrong handed prop.....

Edit: in the handbook online rotation is selectable, but not the 150

PRM150
1) Remove the 9 hexagonal bolts securing the rear manifold to the gearcase and taking care not to lose the small socket wrench located inside it, take off the manifold complete with oil pump.2) Rotate the input shaft until two socket screws in the clutch align with the two holes in the rear of the gearcase.
3) Insert the socket wrench through the two holes and tighten each screw in turn; this locks up the clutch plates, providing drive for a right-hand rotating propeller. (Note: left-hand rotation cannot be provided).4) Refit the rear manifold and tighten the bolts to a torque of 30Nm.5) Ensure that sufficient oil remains in the gearbox to avoid further damage.

 

[Boater Sam]

On that box, and mine, (500n I think from memory) you only got 'ahead' so if ahead was astern due to a wrong handed prop.....

Edit: in the handbook online rotation is selectable, but not the 150

PRM150
1) Remove the 9 hexagonal bolts securing the rear manifold to the gearcase and taking care not to lose the small socket wrench located inside it, take off the manifold complete with oil pump.2) Rotate the input shaft until two socket screws in the clutch align with the two holes in the rear of the gearcase.
3) Insert the socket wrench through the two holes and tighten each screw in turn; this locks up the clutch plates, providing drive for a right-hand rotating propeller. (Note: left-hand rotation cannot be provided).4) Refit the rear manifold and tighten the bolts to a torque of 30Nm.5) Ensure that sufficient oil remains in the gearbox to avoid further damage.

I didn't know that of the PRM 150. The larger boxes, 160, 240, 280 etc you can lock either clutch

 

[TNLI]

Going round the boatshow last week - discussing an engine replacement - one of the items that kept coming up was a hydraulic gearbox.

These seem to be larger and more expensive than mechanical boxes, but have the advantage of being able to deliver full power in both directions.

Do hydraulic gearboxes have any other benefits or disadvantages? Are they quieter, smoother or help with shaft alignment?

A good hydraulic box made by Borg Warner or the PRM will outlast most manual boxes, but the requirement for a small heat exchanger does complicate the plumbing slightly. Obviously you need to make sure that you can get parts for the model you have, (Easy for the common ones like the PRM 150). The srvice manuals are fairly easy to download for free, and in the case of the common models there are a few very good clips on Youtub showing how to overhaul them, and how the emergency gear shift works.
Main disadvantage is that they are larger and heavier than maunal boxes, and one last minor advantage that some boat designers like, is that a hydualic box can be installed in a different location to the engine. If done correctly in design terms, that can make the power train a real quiet one, as a hydraulic box makes less noise than a manual one, so if the engine is in a heavily sound proofed enclosure, and the exhaust is lagged with a good silencer, it might even be classed as a silent drive system.

If I was to chose between the 2 types of box, I would not be biased one was or the other, but would just go with the flow and select the most popular one. Finally stay clear of TMP gearboxes, as they are direct salt or fresh water cooled and once they corrode, its a bin job.

 

[Refueler]

With a PRM if the oil gets low it takes a second or two to engage. If it gets really low, of course, there will be metal to metal problems, as the input shaft from the engine is still rotating

My PRM .. when the oil level gets low ... first it gets noisy .. as level drops lower - it starts to lose drive intermittently - finally not driving at all until oil is topped up.

 

[Plum]

, and one last minor advantage that some boat designers like, is that a hydualic box can be installed in a different location to the engine.

I think you are confusing a hydraulic drive (which allows remote engine location) with a hydraulic gearbox (where the gear trains in the box are selected hydraulicly, such as a PRM150 and some VP gearboxes)

www.solocoastalsailing.co.uk

 

[Boater Sam]

Ignore TNLI, he is a crazy who offers balloon flights, builds a scrap rescue module he thinks is a boat in a pub car park.