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Old 04 March 2020, 17:24   #1
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What prop size

Hi all,

I’m after a new prop for my 7.2m rib. I’m currently running a yammy Hpdi 150 and want a new prop.

I have taken the old one off and I can’t see any writing or numbers on it anywhere which is weird in itself, so I have no idea I’m afraid what size or pitch it is.

The motor is fairly old and i fanccy a change in prop so I can get the same speed and performance but maybe drop the revs a bit to achieve that, if possible. I’m thinking to achieve this I will need a higher pitch than normal, would that be right?

Could anyone on here either recommend a size and pitch please and whether or not to go 3 or 4 blade?

Thanks in advance

Craig
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Old 04 March 2020, 17:38   #2
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What prop size

Quote:
Originally Posted by Chanchan168 View Post
Hi all,



Iím after a new prop for my 7.2m rib. Iím currently running a yammy Hpdi 150 and want a new prop.



I have taken the old one off and I canít see any writing or numbers on it anywhere which is weird in itself, so I have no idea Iím afraid what size or pitch it is.



The motor is fairly old and i fanccy a change in prop so I can get the same speed and performance but maybe drop the revs a bit to achieve that, if possible.



Could anyone on here either recommend a size and pitch please and whether or not to go 3 or 4 blade?



Thanks in advance



Craig


Whatís your current WOT with your existing prop. What is the WOT rpm for your engine?
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Old 04 March 2020, 17:44   #3
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Gonna need to figure out what you have.
https://youtu.be/Uzv_m_Gm1es

Then... Work out if changing pitch makes sense.. it's always comprising something to gain something else...
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Old 04 March 2020, 18:16   #4
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Wot is 4500-5500 range. Current is circa 5200. Can’t see any markings on prop or hub, so have no idea on diameter or pitch.
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Old 04 March 2020, 18:41   #5
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Quote:
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Wot is 4500-5500 range. Current is circa 5200. Canít see any markings on prop or hub, so have no idea on diameter or pitch.
Not realy much room for improvement there your pretty much bang on. You certainly dont want to pull rpm off by overpropping it to reduce rpm. Thats more harmful than being underpropped
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Old 05 March 2020, 02:57   #6
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Would increasing the diameter and reducing the pitch slightly make it more efficient by decreasing the slip?

This would reduce the tip clearance which may well throw up its own probems.
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Old 05 March 2020, 06:12   #7
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Is it ally or stainless?
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Old 05 March 2020, 07:52   #8
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Thanks. What I am trying to achieve is to get the same speed output but at lower revs to put less stress on engine. I was hoping that a slightly smaller diameter with a larger pitch, may achieve this.

Mine is ally at the moment
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Old 05 March 2020, 08:13   #9
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Quote:
Originally Posted by Chanchan168 View Post
Thanks. What I am trying to achieve is to get the same speed output but at lower revs to put less stress on engine. I was hoping that a slightly smaller diameter with a larger pitch, may achieve this.

Mine is ally at the moment


Quite the reverse happens. You will be putting additional stress on the engine by increasing pitch.
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Old 05 March 2020, 08:25   #10
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Quite the reverse happens. You will be putting additional stress on the engine by increasing pitch.
Even by dropping slightly the diameter? Oh really, I was hoping that increasing pitch would mean the boat moves through the water further with each rotation, therefore I could drop the revs slightly to get the same output.

I understand that an under revving engine is just as bad or worse than an overrevving engine due to coking, ecu and fuel issues, so I guess the engine needs to able to operate in the wot range even if you don’t push it that far.

Thanks anyway. Appreciated
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Old 05 March 2020, 10:56   #11
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you could get 5% more out of a stainless prop talk to steel developments they were great with me offering advice there's more to it than pitch and diameter for fine tuning
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Old 05 March 2020, 13:29   #12
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Canít see any markings on prop or hub, so have no idea on diameter or pitch.
I linked to a YouTube video that shows how to measure.

But I'm not convinced changing will achieve much. Try not driving so fast!
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Old 05 March 2020, 15:30   #13
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Quote:
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you could get 5% more out of a stainless prop talk to steel developments they were great with me offering advice there's more to it than pitch and diameter for fine tuning
Will do thanks
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Old 05 March 2020, 17:02   #14
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Quite the reverse happens. You will be putting additional stress on the engine by increasing pitch.
Hit the nail on the head
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Old 05 March 2020, 17:06   #15
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I linked to a YouTube video that shows how to measure.

But I'm not convinced changing will achieve much. Try not driving so fast!
Seen that, thanks
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Old 05 March 2020, 21:07   #16
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you could get 5% more out of a stainless prop talk to steel developments they were great with me offering advice there's more to it than pitch and diameter for fine tuning
I spoke to Steel Developments recently about reworking one of my stainless props and had the most unhelpful woman on the end of the phone.

The prop has gone elsewhere now.

I have previously used Poole Propulsion and Propeller Revolutions but neither seems to be around any longer.
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Old 06 March 2020, 04:20   #17
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>>> spoke to Steel Developments recently

It's odd... I've had them be as helpful as anyone can be... and then quite the reverse... with similar enquiries a few months apart.
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Old 06 March 2020, 05:14   #18
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Hit the nail on the head


Aye, but what do we know
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Old 06 March 2020, 07:23   #19
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Unhelpful woman new one on me
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Old 06 March 2020, 07:58   #20
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Unhelpful woman new one on me


I thought you were married
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