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Repower, prop sizing, TomCat 24

 
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Johnc_3



Joined: 09 Aug 2019
Posts: 5
City/Region: Whittier,
State or Province: AK
C-Dory Year: 1998
C-Dory Model: 24 Tomcat
Vessel Name: White Knight
PostPosted: Fri Aug 09, 2019 12:22 am    Post subject: Repower, prop sizing, TomCat 24 Reply with quote

Hello all, Iím looking for some advice specific to prop size. I have a 1998 C-Dory 24í TomCat repowered to two Mercury 115 command thrust out boards, approximate boat weight with passengers and gear is about 6200 lbs. The mercury engines design spec for top end is 5800-6000 rpm. Looking at Mercurys service manual it looks like a pair of Mercury SS Enertia 15Ē x 15P one LH and one RH should work. But I am hesitant to drop that kinda money with out being sure itíll work right. Anyone else do a repower with the Mercury 115 Command Thrusts. Wondering what you are running? My wife and I mostly use our boat to explore and shrimp out of Prince William Sound in Alaska.
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jennykatz



Joined: 15 Dec 2003
Posts: 1571
City/Region: naples
State or Province: FL
C-Dory Year: 2006
C-Dory Model: 23 Venture
Vessel Name: Little Treasurer
Photos: Jennykatz
PostPosted: Fri Aug 09, 2019 7:30 am    Post subject: props Reply with quote

We have a 23 cc (venture 23) with a 115 CT mercury We went to a 14 and 7/8 with a 17 in pitch WOT is 5800 rpm and 35 mph on a 4000lb boat and motor Previously we had a 115 Yamaha with a 13 and 7/8 with a 15 pitch prop .results at WOT 5800rpm and 35 mph
So you might go to a prop shop or dealer and ask to try the 15 pitch along with the 17 pitch and see where it goes although if you will be very heavy the 15 pitch will serve you better .These mercury engines have loads of torque with a 2.1 L engine same as the Suzuki 140 hp . Go on You tube and see how the new mercury walk away from 125 hp engines .Good Luck in your quest for the right prop .

BTW the guy at the prop shop said I wouldn't be able to run a 17 in pitch he said go with a 15 pitch He was very suprised at these new engines torque
Jim

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retired 8/08 from UAL, still working pt tm
Duck c-22 cruiser sold 6/23/08
06 Venture Cruiser with merc115CT
00 cd16 cruiser honda 40 sold 3/12
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Johnc_3



Joined: 09 Aug 2019
Posts: 5
City/Region: Whittier,
State or Province: AK
C-Dory Year: 1998
C-Dory Model: 24 Tomcat
Vessel Name: White Knight
PostPosted: Fri Aug 09, 2019 9:32 am    Post subject: Repower, prop sizing, TomCat 24 Reply with quote

Not much in the way of prop shops up here in Alaska. Local C-brat dealer unresponsive and Mercury outboard dealer not knowledgeable on Props. So kinda hangin out gathering more info before we change over. Currently running 14.5Ē x 19P peaking at 5200 rpm. Aluminum.
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Ferg



Joined: 18 Jun 2015
Posts: 152
City/Region: Oak Island
State or Province: NC
C-Dory Year: 2008
C-Dory Model: 25 Cruiser
Vessel Name: Here & Now
Photos: Here & Now
PostPosted: Fri Aug 09, 2019 9:47 am    Post subject: Reply with quote

I feel your pain, well actually I felt your pain about proper prop size

I never got the fuel economy I expected on my 25, and after a few years, I took the advice of several other C-Brats, and contacted Prop Gods. It was all done over the phone

Ken was incredibly helpful, and after giving him some basic information (boat type, engine size, weight, max rpm, top speed), he recommended a much different prop.

I went from cruising at ~2.2mpg to well over 3, and increased my WOT speed

https://propgods.com/
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Johnc_3



Joined: 09 Aug 2019
Posts: 5
City/Region: Whittier,
State or Province: AK
C-Dory Year: 1998
C-Dory Model: 24 Tomcat
Vessel Name: White Knight
PostPosted: Fri Aug 09, 2019 10:21 am    Post subject: Repowering, Prop size, TomCat 24 Reply with quote

Iíll follow up on that thank you.
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thataway



Joined: 02 Nov 2003
Posts: 16945
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Fri Aug 09, 2019 10:25 am    Post subject: Reply with quote

Definitely Ken at Prop Gods is the man to go to.

If you are getting 5200 with the aluminum 14.5 x 19", probably the 15 x 15 will be right--but I agree with contacting Ken..

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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL
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Johnc_3



Joined: 09 Aug 2019
Posts: 5
City/Region: Whittier,
State or Province: AK
C-Dory Year: 1998
C-Dory Model: 24 Tomcat
Vessel Name: White Knight
PostPosted: Fri Aug 09, 2019 11:13 am    Post subject: Repowering, Prop sizing, TomCat 24 Reply with quote

I called Ken at PropGods. He had great advice. He recommended Mercury Enertia 15x15 SS with hub to reduce vibration at lower RPM. He also recommended a OFS3 15x15 SS includes hub. About $1500 for Enertia with hub & shipping and $900 for OFS3 with hub & shipping.
Now Iím wondering if the Enertia will be worth the extra $600.
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Ferg



Joined: 18 Jun 2015
Posts: 152
City/Region: Oak Island
State or Province: NC
C-Dory Year: 2008
C-Dory Model: 25 Cruiser
Vessel Name: Here & Now
Photos: Here & Now
PostPosted: Fri Aug 09, 2019 11:45 am    Post subject: Reply with quote

When I talked with Ken, he offered 2 different prop manufacturers, like you, with a $600 difference.

I asked is there a significant difference, he said - not $600 worth.

Heís a good guy
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thataway



Joined: 02 Nov 2003
Posts: 16945
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Fri Aug 09, 2019 6:21 pm    Post subject: Reply with quote

Another person who has a lot of experience, and whom I have a great deal of respect for is Tom Clark. He and Ken most often come up with the same recommendations. Tom has on several occasions offered the OFS 3 15 x 15 as a substitute equivalent to the Enertia. I don't know about specifics of rake, cup, blade thickness, polish, etc as a comparison, but Tom mentions the OFS 3 as a "stern lifting" prop, which is what you want for the Tom Cat. I probably would go with the less expensive prop.

What many people neglect to factor in is all of the other parts of prop design, beside diameter and pitch. This is why there are different "models" of props, in the various designs-some are designed for fast bass boats, other for houseboats, or general runabouts...etc
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Johnc_3



Joined: 09 Aug 2019
Posts: 5
City/Region: Whittier,
State or Province: AK
C-Dory Year: 1998
C-Dory Model: 24 Tomcat
Vessel Name: White Knight
PostPosted: Thu Aug 15, 2019 12:53 pm    Post subject: Repower, prop sizing, TomCat 24 Reply with quote

A giant thank you to all for the information. Especially liked the referral to the PropGod. He was very helpful and open with information. I have a set of Powertech OFS3R15 and OFS3L15 on order and will report back after Iíve tried them out. Thank you all again. Great forum for information.
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akwagon



Joined: 12 Jun 2013
Posts: 3
City/Region: Anchorage
State or Province: AK
C-Dory Year: 2002
C-Dory Model: 24 Tomcat
PostPosted: Sat Aug 17, 2019 8:41 pm    Post subject: Reply with quote

Following
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