Re: Stus-List Propeller Sizing

[Steve Thomas via CnC-List]

You are getting about what you should expect from that engine and boat 
combination, so the propeller can't be too far away from optimum. Sailboats 
equipped with Atomic 4s were typically equipped with a 2 blade fixed prop, 12" 
in diameter by 6" pitch. The relatively shallow pitch as compared to a small 
diesel is due to the lack of gear reduction in the transmission. All else being 
equal, a larger diameter is more efficient, but the pitch might have to be 
reduced to match the torque available from the motor. I have a Gori folding 
prop on my 27 and I am quite happy with it. 

Steve Thomas
C MKIII
Port Stanley, ON


 David Morris via CnC-List  wrote: 
I determined at haulout this weekend our newly-acquired 1975 C 30 MKI,
Atomic 4, direct drive is equipped with a Gori two-blade folding prop,
measuring approx. 11.5". I have neither the experience or expertise to know
if this is a great prop for the boat, a lousy one, or, more likely,
somewhere in between. After a major tune-up on the engine, we seemed to be
able to run at around 6.2 knots in relatively calm water. Any advice,
suggestions, observations anyone would care to offer on prop selection would
be much appreciated.

 

 

 

David J. Morris, MBA
President, D.J. Morris & Associates Ltd.
427 Division Street, Kingston, ON Canada K7K 4A8
Tel. 613-531-4429
email: djmor...@djma-ltd.com
Member: Professional Writers Association of Canada 
Blogging at: http://davidmorrisjourneys.wordpress.com/

 



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Re: Stus-List Propeller Sizing

[Don Kern via CnC-List]

I replaced my old Martec model 778, Dia and pitch 12 X 5, 2 blade 
folding in 2008 with a Martec Mk III Eliptec 2-blade folding, 
non-geared.  However I do not believe Martec is in production any 
longer.  One of the big concern at the time was drag when racing and 
hull clearance. It was my understanding that two things happen with 
insufficient hull clearance - vibration when going forward and walking 
while backing.  There was a formula that I can not locate for hull 
clearance, my however 12" dia prop has a clearance of 8", which if I 
recall was right at the minimum.


Since my C Mk2 has an offset propeller (not on centerline), I found 
the J/105 Technical Committee evaluation of folding propellers 
interesting.  On Fireball the output flange to the propeller shaft is 
marked with a red lines at the 180 deg. apart, to show when the 
propeller blades are aligned horizontal to prevent a blade from drooping 
at low speeds.  I gave up jumping overboard in New England waters to put 
a rubber band on the prop before racing a long time ago.  I have copied 
the evaluation below:



"The J105 has always been delivered with a 15 inch Martec folding prop.  
The TC has analyzed whether the following replacement props are 
permissible (all 15 inch): Flex-O-Fold Standard and Racing versions 
(geared), Gori Standard and Racing versions (geared). Martec (geared), 
Max Prop (feathering).


Most of these props are "geared" props, which means that the blades are 
connected and open up in unison.   Arguably, this feature provides an 
advantage over the non-geared Martec since with the Martec, particularly 
in light air and choppy conditions, a single blade could potentially 
open up.   On the other hand, owners of standard Martec non-geared props 
are of course free to rubber band their props – although in cold or 
polluted waters this may not be an alternative in practice.


Flex-O-Fold claims on its website that its product has somewhat less 
drag than the standard Martec.  They reference a Cruising World test 
report from 1995 to back up their claim, although the test involved an 
earlier version of the Flex-O-Fold prop with smaller blades and, 
presumably, less drag.  Another independent test report they reference 
from 1997 indicates that the Flex-O-Fold and the Gori folding props have 
approximately the same drag, which coupled with the Cruising World 
report would indicate that the Gori, as well, may have less drag than 
the Martec.  Both these test reports indicate that the Maxprop has 
significantly more drag than the Martec, Flex-O-Fold or Gori.  
Notwithstanding these reports, Martec claims that its standard prop is 
“the lowest drag sailboat propeller anywhere”, but Martec does not 
provide any independent test results to back up that claim.  It is 
unclear which versions of the Martec were tested in these test reports. 
It is important to note that *the prop on the J105 is angled to the flow 
of water along the hull, thereby exposing the blades to the flow to a 
much greater extent than if the flow were parallel to the shaft* – the 
way the props were positioned in the tests.  These issues make the 
foregoing test reports of dubitable validity for our purposes.


The Technical Committee obtained samples of each of the Flex-O-Fold, 
Gori, Martec geared and Martec non-geared props in order to resolve the 
conflicting test results and manufacturer claims.  In side-by-side 
comparison it was clear that the standard non-geared Martec presented a 
significantly smaller "bulk" to the flow of water than the geared Martec 
or any of the Flex-O-Fold or Gori options, largely because the geared 
props have much larger hub diameters (to accommodate their gears) than 
the standard non-geared Martec.  Hence, the resistance of the geared 
Martec, Flex-O-Fold and Gori props will be somewhat greater than that of 
the standard Martec.  In conversations with the top US representatives 
of Martec, Flex-O-Fold, and Gori, each of them confirmed that for a 
J/105 application, the most significant drag factor among the folding 
props being evaluated was the size of the hub, and that their respective 
geared hub props would have more drag than a comparable size non-geared 
Martec prop.


The TC has therefore concluded that all these geared blade props are 
legal substitutes for the standard Martec prop provided they have a 
diameter of at least 15 inches.  In addition, based upon the above test 
reports, the TC is of the view that the Maxprop feathering prop also has 
somewhat more drag than a standard Martec of the same diameter and, 
therefore, is a class legal prop for the J105 as long as its diameter is 
at least 15 inches.  The TC expresses no view on props other than those 
listed above."


Don Kern
Fireball 12708
C Mk2
Bristol, RI

On 10/31/2018 4:34 PM, Charlie Nelson via CnC-List wrote:
If your Gori is sized properly based on the engine, transmission and 
clearance (all likely given your performance), you probably have the 

Re: Stus-List Propeller Sizing

[Charlie Nelson via CnC-List]

If your Gori is sized properly based on the engine, transmission and clearance 
(all likely given your performance), you probably have the lowest drag 
propeller available.
 
Tests years ago on propeller drag in a water tank(published in Yachting 
magazine) showed that the Gori had the least drag of any ~ 20 brands that were 
tested. You can probably get better performance
with others in terms efficiency under power (reverse or forward), but you would 
be hard pressed to get a prop with less drag when sailing. 

Charlie Nelson
1995 C 36 XL/kcb
 
 
 
 
 
cenel...@aol.com

 
 
-Original Message-
From: james via CnC-List 
To: David Morris via CnC-List 
Cc: james 
Sent: Wed, Oct 31, 2018 3:44 pm
Subject: Re: Stus-List Propeller Sizing



David,

I'm a fellow Afourian and I would say that the performance you  are getting 
is impressive for a folding prop. My question with  your setup is what 
happens in chop and waves? If you are satisfied  with the rough weather 
performance and you want to stay with a  folding prop, I don't think you 
would be able to do much (or any)  better than what you have. The Indigo 
prop is very popular for  direct drive A-4's and would give a substantial 
boost in rough  weather performance. It would also increase the longevity 
of your  engine by reducing the loads. Just for your information, My a-4
  has a reduction gear and a 16x10 two blade fixed prop. Wide open  
throttle is 3200rpms and 6.5 knots. Cruise is 2500-2700 rpms  (depending on 
the skippers mood) and 6-6.2 knots. Rough water  really kills performance 
and I usually motorsail with the main.  Joe is right on the money...

James Taylor

Delaney

1976 C 38

Oriental, NC



On 10/30/2018 10:04 AM, David Morris  via CnC-List wrote:




I determined at haulout this weekend our  newly-acquired 1975 C 30 
MKI, Atomic 4, direct drive is  equipped with a Gori two-blade folding 
prop, measuring approx.  11.5”. I have neither the experience or 
expertise to know if  this is a great prop for the boat, a lousy one, 
or, more  likely, somewhere in between. After a major tune-up on the
  engine, we seemed to be able to run at around 6.2 knots in  
relatively calm water. Any advice, suggestions, observations  anyone 
would care to offer on prop selection would be much  appreciated.

 

  

 

David J. Morris, MBA
  President, D.J. Morris& Associates Ltd.
427 Division Street, Kingston, ON Canada K7K 4A8
Tel. 613-531-4429
email: djmor...@djma-ltd.com
Member: Professional Writers Association of Canada 
Blogging at: http://davidmorrisjourneys.wordpress.com/

 
  
  


  

  
  
Virus-free. www.avast.com 

  

 
  
  
  
  
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Re: Stus-List Propeller Sizing

[james via CnC-List]

David,

I'm a fellow Afourian and I would say that the performance you are 
getting is impressive for a folding prop. My question with your setup is 
what happens in chop and waves? If you are satisfied with the rough 
weather performance and you want to stay with a folding prop, I don't 
think you would be able to do much (or any) better than what you have. 
The Indigo prop is very popular for direct drive A-4's and would give a 
substantial boost in rough weather performance. It would also increase 
the longevity of your engine by reducing the loads. Just for your 
information, My a-4 has a reduction gear and a 16x10 two blade fixed 
prop. Wide open throttle is 3200rpms and 6.5 knots. Cruise is 2500-2700 
rpms (depending on the skippers mood) and 6-6.2 knots. Rough water 
really kills performance and I usually motorsail with the main. Joe is 
right on the money...


James Taylor

Delaney

1976 C 38

Oriental, NC


On 10/30/2018 10:04 AM, David Morris via CnC-List wrote:


I determined at haulout this weekend our newly-acquired 1975 C 30 
MKI, Atomic 4, direct drive is equipped with a Gori two-blade folding 
prop, measuring approx. 11.5”. I have neither the experience or 
expertise to know if this is a great prop for the boat, a lousy one, 
or, more likely, somewhere in between. After a major tune-up on the 
engine, we seemed to be able to run at around 6.2 knots in relatively 
calm water. Any advice, suggestions, observations anyone would care to 
offer on prop selection would be much appreciated.


David J. Morris, MBA
President, D.J. Morris & Associates Ltd.
427 Division Street, Kingston, ON Canada K7K 4A8
Tel. 613-531-4429
email: djmor...@djma-ltd.com
Member: Professional Writers Association of Canada
Blogging at: http://davidmorrisjourneys.wordpress.com/


 
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Re: Stus-List Propeller Sizing

[Della Barba, Joe via CnC-List]

That is not true with A4 direct drive boats. The redline RPM of an A4 is 3600 
RPMs. Outside of a few planing powerboats or perhaps the reduction gear A4s, 
none of them get near that. Many direct drive A4 boats are massively over 
propped and hit maybe 2000 RPM. The 10x7 Indigo 3 blade will get you 2400-2500 
RPMs. For a 2 blade A4, 12x6 is a good starting point.
Gasoline engines do not carbon themselves to death the way RPM restricted 
diesels do.
Joe
Coquina

From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of ALAN BERGEN 
via CnC-List
Sent: Tuesday, October 30, 2018 11:04 AM
To: C 
Cc: ALAN BERGEN 
Subject: [EXTERNAL] Re: Stus-List Propeller Sizing

The  prop diameter should be as large as possible while still clearing the hull 
by a couple of inches. When you run the engine at full throttle, you should be 
able to reach rated rpm. If the engine runs more than 5% over rated rpm, the 
pitch is too low. If the engine cannot reach rated rpm, the  pitch is too high.

Alan Bergen
35 Mk III Thirsty
Rose City YC
Portland, OR


On Tue, Oct 30, 2018 at 7:04 AM, David Morris via CnC-List 
mailto:cnc-list@cnc-list.com>> wrote:
I determined at haulout this weekend our newly-acquired 1975 C 30 MKI, Atomic 
4, direct drive is equipped with a Gori two-blade folding prop, measuring 
approx. 11.5”. I have neither the experience or expertise to know if this is a 
great prop for the boat, a lousy one, or, more likely, somewhere in between. 
After a major tune-up on the engine, we seemed to be able to run at around 6.2 
knots in relatively calm water. Any advice, suggestions, observations anyone 
would care to offer on prop selection would be much appreciated.



David J. Morris, MBA
President, D.J. Morris & Associates Ltd.
427 Division Street, Kingston, ON Canada K7K 4A8
Tel. 613-531-4429
email: djmor...@djma-ltd.com<mailto:djmor...@djma-ltd.com>
Member: Professional Writers Association of Canada
Blogging at: http://davidmorrisjourneys.wordpress.com/


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Re: Stus-List Propeller Sizing

[ALAN BERGEN via CnC-List]

The  prop diameter should be as large as possible while still clearing the
hull by a couple of inches. When you run the engine at full throttle, you
should be able to reach rated rpm. If the engine runs more than 5% over
rated rpm, the pitch is too low. If the engine cannot reach rated rpm, the
pitch is too high.

Alan Bergen
35 Mk III Thirsty
Rose City YC
Portland, OR


On Tue, Oct 30, 2018 at 7:04 AM, David Morris via CnC-List <
cnc-list@cnc-list.com> wrote:

> I determined at haulout this weekend our newly-acquired 1975 C 30 MKI,
> Atomic 4, direct drive is equipped with a Gori two-blade folding prop,
> measuring approx. 11.5”. I have neither the experience or expertise to know
> if this is a great prop for the boat, a lousy one, or, more likely,
> somewhere in between. After a major tune-up on the engine, we seemed to be
> able to run at around 6.2 knots in relatively calm water. Any advice,
> suggestions, observations anyone would care to offer on prop selection
> would be much appreciated.
>
>
>
>
>
>
>
> David J. Morris, MBA
> President, D.J. Morris & Associates Ltd.
> 427 Division Street, Kingston, ON Canada K7K 4A8
> Tel. 613-531-4429
> email: djmor...@djma-ltd.com
> Member: Professional Writers Association of Canada
> Blogging at: http://davidmorrisjourneys.wordpress.com/
>
>
>
>
> 
>  Virus-free.
> www.avast.com
> 
> <#m_-8873611121891266791_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>
> ___
>
> Thanks everyone for supporting this list with your contributions.  Each
> and every one is greatly appreciated.  If you want to support the list -
> use PayPal to send contribution --   https://urldefense.proofpoint.
> com/v2/url?u=https-3A__www.paypal.me_stumurray=DwICAg=
> clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI=
> 9w3G7Cf8YfQnrjmtuNxwDJYr3JMv9f1pAfgAJ9xXYQQ=eY7MGZm-
> ox1o3m9zLLDvZme6VW26veqjMcA4EWFuCRM=ulGCOUuuNxaQ5FW1FGoY8_
> AnSxRGTq2wQangEahYpRs=
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Stus-List Propeller Sizing

[David Morris via CnC-List]

I determined at haulout this weekend our newly-acquired 1975 C 30 MKI,
Atomic 4, direct drive is equipped with a Gori two-blade folding prop,
measuring approx. 11.5". I have neither the experience or expertise to know
if this is a great prop for the boat, a lousy one, or, more likely,
somewhere in between. After a major tune-up on the engine, we seemed to be
able to run at around 6.2 knots in relatively calm water. Any advice,
suggestions, observations anyone would care to offer on prop selection would
be much appreciated.

 

 

 

David J. Morris, MBA
President, D.J. Morris & Associates Ltd.
427 Division Street, Kingston, ON Canada K7K 4A8
Tel. 613-531-4429
email: djmor...@djma-ltd.com
Member: Professional Writers Association of Canada 
Blogging at: http://davidmorrisjourneys.wordpress.com/

 



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