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Old 17-12-2019, 00:39   #1
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Hydraulic vs mechanical gearbox.

Looking at a repower and have the option of mechanical or hydraulic gearboxes.

I have a feathering prop.

Manufacturer aside, what are the advantages and disadvantages of each?

Matt
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Old 17-12-2019, 06:19   #2
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Re: Hydraulic vs mechanical gearbox.

Application is of most importance here. You need to give some information or any advice is just a shot in the dark.

What vessel? What HP? What propeller diameter? What type transmission is in the vessel now?
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Old 17-12-2019, 16:40   #3
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Re: Hydraulic vs mechanical gearbox.

Surprised you've had no more answers on this one, so I'll throw what I know at it.

Not sure how much of this is relevant to new gears, but one of the primary drawbacks to mechanical was the heavy engagement/disengagement forces needed for operation. I'm sure they've worked that one out by now.

Depending on the design, complexity can be an issue for either, but with the addition of a pressurized engagement loop, perhaps the tendency for 'complexity potential' related problems is greater with the hydraulic.

If multiple discs are used to transmit power, how they're held in tension (whether hydraulically of mechanically) seems to be the source of many problems.

It might make sense to narrow your choices and then ask about specific models so that their owners can provide relevant caveats based on personal experience.
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Old 17-12-2019, 21:33   #4
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Re: Hydraulic vs mechanical gearbox.

Sorry, assuming everyone knew what sort of boat I sailed.

50 hp diesel going into a 42 footer, around 15 tons. Feathering prop is a Kiwiprop.

Favouring one of the kubota derivatives like Beta or Nanni.

Both come with options for hydraulic or mechanical.
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Old 17-12-2019, 21:56   #5
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Re: Hydraulic vs mechanical gearbox.

Mechanical. Hydraulic is an ask for leaks. Beta over Nanni, too, because of parts $$. Don't add complexity. The reasons for keeping it all simple are sound.

Ann
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Old 17-12-2019, 22:17   #6
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Re: Hydraulic vs mechanical gearbox.

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Originally Posted by JPA Cate View Post
Mechanical. Hydraulic is an ask for leaks. Beta over Nanni, too, because of parts $$. Don't add complexity. The reasons for keeping it all simple are sound.

Ann


This was the direction I was favouring. But it was also cheaper, and when it is cheaper I get nervous.
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Old 17-12-2019, 22:25   #7
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Re: Hydraulic vs mechanical gearbox.

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Originally Posted by JPA Cate View Post
Mechanical. Hydraulic is an ask for leaks. Beta over Nanni, too, because of parts $$. Don't add complexity. The reasons for keeping it all simple are sound.

Ann
Hi I have to agree with Ann, however I would take a look at WM Diesel, Kubota based and very well put together by John Wichard in Sydney.
Regarding the gearbox, the only offering I can add is avoid multi plate systems like the hurth!
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Old 17-12-2019, 23:43   #8
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Re: Hydraulic vs mechanical gearbox.

For 50 hp it's hard to beat the simplicity of the cone clutch mechanical gearbox.
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Old 18-12-2019, 00:11   #9
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Re: Hydraulic vs mechanical gearbox.

Our 43 hp Nanni/Kubota has a Hurth/ZF 10 mechanical box. The original one failed just after we bought the boat, and I replaced it with like... nervously. Those trannies don't have a good reputation, but ours now has >5000 hours and is still working as new. Go figger! But I've changed the ATF religiously with every oil change (<200 hours) and that is apparently quite important with these gears. They only hold 350 mL, and it gets damn hot at times, so short life time.

I believe that Beta offers a better mechanical box on the 50 (which is a slightly larger displacement version of ours) and I'd have no worries about that one. If they offer a bigger one as optional, I'd go for that, just in case~

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Old 18-12-2019, 01:15   #10
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Re: Hydraulic vs mechanical gearbox.

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Hi I have to agree with Ann, however I would take a look at WM Diesel, Kubota based and very well put together by John Wichard in Sydney.

Regarding the gearbox, the only offering I can add is avoid multi plate systems like the hurth!


Yes, John was my preferred option, but I simply could not afford the reasonably small premium he charges. I suspect the premium is good value, but not something I have a choice with.

Funnily, it was talking to him that got me worried about gearbox choices.
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Old 18-12-2019, 01:17   #11
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Re: Hydraulic vs mechanical gearbox.

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Our 43 hp Nanni/Kubota has a Hurth/ZF 10 mechanical box. The original one failed just after we bought the boat, and I replaced it with like... nervously. Those trannies don't have a good reputation, but ours now has >5000 hours and is still working as new. Go figger! But I've changed the ATF religiously with every oil change (<200 hours) and that is apparently quite important with these gears. They only hold 350 mL, and it gets damn hot at times, so short life time.

I believe that Beta offers a better mechanical box on the 50 (which is a slightly larger displacement version of ours) and I'd have no worries about that one. If they offer a bigger one as optional, I'd go for that, just in case~

Jim


Noted, I will see what the upgrade will cost.

P.S. planning to do the work in Tassie, so I’ll be hitting up the tassie connections for advice on where I can park the boat while I fit the engIne.
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Old 18-12-2019, 01:18   #12
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Re: Hydraulic vs mechanical gearbox.

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For 50 hp it's hard to beat the simplicity of the cone clutch mechanical gearbox.


Good to hear. I certainly like the simplicity of not needing an oil cooler.
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Old 18-12-2019, 02:48   #13
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Re: Hydraulic vs mechanical gearbox.

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Yes, John was my preferred option, but I simply could not afford the reasonably small premium he charges. I suspect the premium is good value, but not something I have a choice with.

Funnily, it was talking to him that got me worried about gearbox choices.
I've had some dealings with John, and he is a good bloke for sure. One thing to consider: he mentioned to me last time we spoke that he was hoping to retire "soon". I was not happy to hear this, but he's a lot older than I was when I retired, so kept my mouth shut (for once).

I reckon his engines would be first rate, and as long as he's in biz I have no doubt that he would support them fully... but his future plans would surely intersect yours, and possibly to your detriment.

It would be a shame (for me) not to have his friendly little shop there in Mona Vale!

Jim
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Old 18-12-2019, 03:33   #14
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Re: Hydraulic vs mechanical gearbox.

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Good to hear. I certainly like the simplicity of not needing an oil cooler.
When I acquired my boat it had a hurth box attached to one of John's 50 hp engines and it started to slip at around 860 hrs, his advice was that he no longer supplied those boxes and recommended a PRM mechanical replacement, almost a direct drop in for not much more than the cost of having the Hurth rebuilt. So far so good.
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Old 18-12-2019, 05:15   #15
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Re: Hydraulic vs mechanical gearbox.

My preference would be for straight mechanical, with a multi plate wet clutch, one driven by helical gears so that the higher the torque placed on them, the tighter they are compressed. This solves the hard engagement issue, and will keep the clutch pack from ever slipping under load.
A multi plate wet clutch pack is what is used to harness motorcycle engines that make in the hundreds of HP, and of course you’re left hand disengages the clutch every shift so there is no tough engagement either.
However motorcycles don’t usually have helical cut gears that force the plates together, they usually rely purely on Springs.
Cone clutches have been and are a source of problems. I assume they must Ben cheaper to manufacture, cause I can’t come up with any reason to use them myself.
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