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How to get the right prop?


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So, I think I have determined I require a 12" diameter prop, 1" shaft, 1/12 taper, RH.

Not sure on pitch (gearbox ratio of 2.5:1, max engine revs of 3000, reckon boat is about 3.5-4 tonnes, 32 ft) but priority is to get boat moving more than anything so really just need something that'll do for now.

Having trouble trying to find anything suitable though; ebay has a few that seem like they would do except they're all LH for some reason. So if anyone knows of where I might be able to source a prop second hand or if anyone has one lying around that they might be willing to part with, let me know (in the Rochdale area but will travel).

 

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3 minutes ago, jennywren said:

Having trouble trying to find anything suitable though; ebay has a few that seem like they would do except they're all LH for some reason.

 

What's the gearbox? Is there any reason you can't use it in reverse for forward motion?

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1 hour ago, Mikexx said:

 

What's the gearbox? Is there any reason you can't use it in reverse for forward motion?

Googling seems to suggest its not a good idea?

My gearbox user manual (PRM120D) though specifically says it should only be used with a RH prop.

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1 hour ago, jennywren said:

Googling seems to suggest its not a good idea?

My gearbox user manual (PRM120D) though specifically says it should only be used with a RH prop.

I think the ubiquitous PRM150 can be used either way, but if your 120 manual says that, then certainly best to stick with an RH prop

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3 minutes ago, nicknorman said:

I think the ubiquitous PRM150 can be used either way, but if your 120 manual says that, then certainly best to stick with an RH prop

Nick, I think that only the later (and bigger ?) types of PRM can turn in both directions.

 

On my twin engined boat I have 2 exactly the same PRM boxes of which one is turning in reverse to go forward, which is perfectly alright for them.

 

Peter.

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1 hour ago, jennywren said:

Googling seems to suggest its not a good idea?

My gearbox user manual (PRM120D) though specifically says it should only be used with a RH prop.

The workshop manual is also very clear and in bold print says "IMPORTANT, RIGHT HAND PROPELLOR REQUIRED".

Just an idea.

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1 hour ago, nicknorman said:

I think the ubiquitous PRM150 can be used either way, but if your 120 manual says that, then certainly best to stick with an RH prop

Yes, the manual is for several models and says most of them can be used either way, but the 120 and one of the others had to be RH.

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On 22/06/2017 at 21:57, jennywren said:

12" diameter is what I meant. It's a GRP cruiser so not a very big prop.

I'm keeping an eye on ebay but will be doing all those measurements at least twice-and did already know I needed to check whether it was LH or RH so that also-before I spend any money.

What make is the boat most fibreglass cruisers are fitted with "standard" props so you may well be able to find the size from the makes owners club forum.

For example all  freeman 22 have the same prop except the 22 nb which is smaller as it has direct drive rather than a 2:1 box

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It would be useful to know the gearbox model number.  The PRM 150 and 160 can drive a LH or RH prop. I have just checked both manuals.  On these gearboxes it is the input shaft direction which is critical because the oil pump must run in the right direction.  If the pump runs backwards it would take generate any pressure.  On some models the pump can be moved to suit a clockwise engine.

 

Edited by mross
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3 hours ago, bargemast said:

Nick, I think that only the later (and bigger ?) types of PRM can turn in both directions.

 

On my twin engined boat I have 2 exactly the same PRM boxes of which one is turning in reverse to go forward, which is perfectly alright for them.

 

Peter.

See screenshot from PRM150 manual:

 

IMG_0621.PNG.0dc8fc69403a0453b5bc8f72badce6a0.PNG

 

But anyway, academic since OP has a PRM120.

Edited by nicknorman
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4 minutes ago, mross said:

It would be useful to know the gearbox model number.  The PRM 150 and 160 can drive a LH or RH prop. I have just checked both manuals.  On these gearboxes it is the input shaft dire tion which is critical because the oil pump must run in the right direction.  If the pump runs backwards it would take generate any pressure.  On some models the pump can be moved to suit a clockwise engine.

 

I have already said-it is a PRM120D, which can only drive a RH prop. I have the manual; that is what it says.

21 minutes ago, mad dog n' Englishman said:

Have a look at ebay item 1922244D3880. Not guite 12" but close. Could be worth asking for more information.

Garry.

Linky? Doesn't come up in an ebay search.

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2 minutes ago, nicknorman said:

See screenshot from PRM150 manual:

 

IMG_0621.PNG.0dc8fc69403a0453b5bc8f72badce6a0.PNG

Hello Nick, another slight misunderstanding, I didn't say that your PRM 150 wasn't supposed to turn in both directions, but only Jennies PRM 120, and that only the later and bigger boxes were good to do that, yours included, but my writing must have come over as confusing.

 

Sorry for the trouble I've caused you to have to find your gearbox documentation, I've got most of that information here too (somewhere) of Lancing.

 

Peter.

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