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07-24-2014, 08:00 PM
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#1
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Member
City: nl
Join Date: Oct 2013
Posts: 7
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Prop Shaft Size
Hi
I recently purchased 2x 4-236 perkins diesel engines with 23x 26 4 prop blades to repower my 34' tollycraft tri-cabin. Can I use the original 1.25 dia shafts with these engines and props? The trannys are 3:1 cr2 borg warners
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07-24-2014, 08:26 PM
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#2
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,149
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not sure of the horsepower or your planned cruising speeds but they sound like big props for a 1.25 shaft....especially with 3:1
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07-24-2014, 08:34 PM
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#3
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Senior Member
City: Merritt Island,Fl
Vessel Name: Sue Marie
Vessel Model: Prarie 29
Join Date: May 2010
Posts: 259
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The 4-236 is an 85 HP engine. That is a big prop on 1.25 those engine are rated at top rpm of 2800. Might work. Check with a prop shop.
John
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07-24-2014, 08:35 PM
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#4
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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What diameter are the props bored to? 23" dia is usually 1.75" minimum, maybe 1.5.
1.25 can handle 80hp at 3:1, but hanging that big wheel on it will really stress the tip of the shaft.
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07-24-2014, 11:13 PM
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#5
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Member
City: nl
Join Date: Oct 2013
Posts: 7
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The props have a 1.5 bore
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07-25-2014, 12:29 AM
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#6
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Guru
City: League City, TX
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 1,069
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Using the Boatdiesel.com Prop. Shaft Calculator I entered the following:
Perkins 4-236 85SHP - 2,800RPM
Reduction Gear - 3:1
Shaft Safety Factor - 5 (recommended)
Here are the results:
Stainless 304 - 1.94"
Stainless 316 - 1.94"
Monel 400 - 1.54"
Monel K500 - 1.30"
Aquamet 17 - 1.28"
Aquamet 18 - 1.35"
Aquamet 19 - 1.28"
Aquamet 22 - 1.19"
So, if your 1.25" shafts are made of Aquamet XX alloy or Monel K500, you should be safe. If stainless 304 or 316, they are considerably undersized.
There is a very old "Rule of One Fourteenth" where the prop diameter is divided by 14 to roughly evaluate the prop shaft size. In your case, 23" divided by 14 = 1.64" which is sort of in the middle of the calculated results above.
Finally, using Skene's shaft size calculations:
Shaft Horsepower - 85
Shaft RPM - 933
Bronze & Mild Steel - 2-1/8"
Monel - 1-3/8"
You can draw your own conclusions from the above. They all seem to indicate that 1.25" shafting will be too small for your application. The exception would be Aquamet 22 shafts. If there is any doubt, it would be better to err on the side of safety.
Just my $.02 . . . .
Larry
M/V Boomarang
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07-25-2014, 05:04 AM
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#7
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Guru
Join Date: Oct 2007
Posts: 22,553
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While I prefer paper , one of these FEEE downloads would answer your question.
- Elements of yacht design : Skene, Norman L. (Norman ...
archive.org › ... › Cornell University LibraryInternet Archive
Mar 8, 2010 - Internet Archive BookReader - Elements of yacht design ... metadata about the original images and the derived formats (OCR results, PDF etc.).
- Notes on Skene's Elements of Yacht Design - Boat Design Forums ...
Boat Design Net - the Boat Design and Boat Building Site › ... › Design › Hydrodynamics and Aerodynamics
Jun 5, 2013 - 15 posts - 4 authors
I recently downloaded the free PDF book, Elements of Yacht Design, by Norman L. Skene, and provided by Cornell University's Library in ...Recomend a Naval Architecture Textbook - Page 3 - Boat ...
3 posts
Jun 10, 2013
Principles of Yacht Design as design manual??? - Boat ...
15 posts
Oct 13, 2011
More results from www.boatdesign.net
- Elements of yacht design (Open Library)
https://openlibrary.org/books/.../Elements_of_yacht_designOpen Library
Apr 14, 2010 - Elements of yacht design by Norman L. Skene, 1904,Rudder publishing company edition, in English.
- Elements of Yacht Design - Norman Locke Skene - Google ...
books.google.com/.../Elements_of_Yacht_Design.html?id...Google Books
Title, Elements of Yacht Design. Author, Norman Locke Skene. Publisher, Rudder publishing Company, 1904. Original from, the New York Public Library.
- Skene's Elements of Yacht Design, Eighth Edition: Francis S ...
Amazon.com: Online Shopping for Electronics, Apparel, Computers, Books, DVDs & moreSkenes-Elements-Design.../0396079687Amazon.com
Skene's Elements of Yacht Design, Eighth Edition [Francis S. Kinney] on Amazon.com. *FREE* shipping on qualifying offers. Eighth Edition, m Fifth printing, .
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07-25-2014, 09:46 AM
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#8
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Guru
City: LI or Fla
Join Date: Jul 2013
Posts: 1,148
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For displacement speed those engines and gear ratios sound like a nice match up, the shaft size is "acceptable" if propped correctly (not the ones listed) full RPM plus an extra 100 verified by photo tach. You may have room in the strut to use a thinner walled cutless bearing to fit 1 1/2 shafts (aquamet 22) which would make a real nice setup.
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07-27-2014, 10:07 AM
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#9
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Guru
City: Fort Myers - FL
Vessel Name: ORIGINAL
Vessel Model: Hi Star 55
Join Date: Jul 2011
Posts: 669
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With a 85HP and 23x26 prop you cant turn at 2800 rpm. If you use low rpm, you need low Power and can use a 1.25" shaft. The best is 1.75"
Sergio "Alemao" Sztancsa
Sent from my iPhone, using Trawler Forum
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07-27-2014, 10:40 AM
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#10
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Guru
City: Fort Pierce
Vessel Name: Florita Ann
Vessel Model: 1982 Present
Join Date: May 2014
Posts: 1,935
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As everyone else, I agree the shafts are really small however from my limited knowledge, you should be ok if your props are balanced. Wobble will do the shafts in post haste. Keep em clean, balanced and you should be OK. Hit something, run aground better check em out. I run 250 hp Cummins, 2:1 tranny with a 1 3/8 shaft. I watch the barnacles, cause the imbalance will snap the shaft.
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07-28-2014, 04:44 AM
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#11
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Guru
Join Date: Oct 2007
Posts: 22,553
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The shafts biggest danger is docking IF the tranny is shifted quickly at high >PANIC!< rpm.
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07-28-2014, 05:17 AM
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#12
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Member
City: nl
Join Date: Oct 2013
Posts: 7
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Hi I checked the props that came with the 4-236 perkins and the dia is 1 3/8 so they must have been on Aquamet or Monel shafts. I am going to see what my 1 1/4 shafts are made from and go from there. I have been talking to a prop guy here and he seems to think my shafts will work so I am leaning towards using them.Thanks everyone for the info and I will let you know what happens.
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07-28-2014, 06:30 AM
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#13
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Guru
City: Fort Pierce
Vessel Name: Florita Ann
Vessel Model: 1982 Present
Join Date: May 2014
Posts: 1,935
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Quote:
Originally Posted by FF
The shafts biggest danger is docking IF the tranny is shifted quickly at high >PANIC!< rpm.
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Uggggg, yeah, dat too..
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07-28-2014, 09:52 AM
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#14
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Guru
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
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Since this is a large 4cyl engine hooked to a big prop w a deep reduction torsional vibration should be much higher than usual.
Lots of trolling or/and very low idle speeds could very well be problematic. Also damper plates may not last long.
__________________
Eric
North Western Washington State USA
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07-28-2014, 11:51 AM
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#15
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Guru
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48 (sold)
Join Date: Apr 2008
Posts: 10,186
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Quote:
Originally Posted by rayman62
Hi I checked the props that came with the 4-236 perkins and the dia is 1 3/8 so they must have been on Aquamet or Monel shafts. I am going to see what my 1 1/4 shafts are made from and go from there. I have been talking to a prop guy here and he seems to think my shafts will work so I am leaning towards using them.Thanks everyone for the info and I will let you know what happens.
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As you said, determining the material of shaft construction is essential. Until you know this, all is a guessing game.
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07-30-2014, 04:49 PM
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#16
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Guru
City: Pender Harbour, BC
Vessel Name: Gwaii Haanas
Vessel Model: Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,791
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I have a 250 Cummins with Twin Disc and a single 2.5" shaft, 36" wheel. Mine's bigger than yours! 8^)
__________________
Don't believe everything that you think.
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07-30-2014, 04:52 PM
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#17
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Guru
City: Pender Harbour, BC
Vessel Name: Gwaii Haanas
Vessel Model: Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,791
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As an aside, I recently discovered that if you move the shift lever into gear slowly, the clutches seem to take up the slack more smoothly and there is no clunk in the shifting. Sounds much less like mechanical thrashing. It seemed with a Velvet Drive, after pausing, a fast shift at idle worked best. Quite a difference. Pausing is important with both, it seems.
__________________
Don't believe everything that you think.
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07-30-2014, 05:58 PM
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#18
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Guru
City: Here
Join Date: Sep 2012
Posts: 2,940
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PM me with an email address and I'll send you the ABYC shafting spec.
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02-09-2015, 05:26 PM
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#19
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Member
City: nl
Join Date: Oct 2013
Posts: 7
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I found two letters stamped on the shaft they say AQ and are not magnetic so I'm hoping thry are aq 22
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02-09-2015, 06:13 PM
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#20
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Guru
Join Date: Dec 2007
Posts: 4,021
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We once had a 30' Tolly that had Aquamet shafts as OEM.
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