Hello all, I’m looking for some advice specific to prop size. I have a 1998 C-Dory 24’ 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 15” x 15P one LH and one RH should work. But I am hesitant to drop that kinda money with out being sure it’ll 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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Repower, prop sizing, TomCat 24
- Thread starter Johnc_3
- Start date
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
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
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/
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/
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 I’m wondering if the Enertia will be worth the extra $600.
Now I’m wondering if the Enertia will be worth the extra $600.
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
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
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 I’ve tried them out. Thank you all again. Great forum for information.
Well finally got the replacement 15.25 x 15 PowerTech SS props on and did some testing. For my application the 15 pitch is not enough, Rpm was over 6000 and only 28 knots. Will trade them out for next size 15.25 x 16. That should pick up my speed and load my engines about right. So season is about done here in Alaska for me. Will continue this process next spring. Thank you to all for your suggestions.
I also have a 1998 Tomcat 24. Mine is powered by twin Tohatsu 115 TLDI 2-strokes - not counter rotating. I run Solas aluminum 4 blade 12.75 dia x 17 pitch. I can run almost 40 kts if the boat is light, but never do. I prefer to cruise at around 18 kts. The gear ratio on these engines is 2:1.
It sounds from your post that you are looking for a higher top speed. I would suggest that to gain more speed you need to keep the 19 pitch but reduce the prop dia a little so the engines hit the intended max rpm. I think your latest props will give you great efficiency and quick acceleration, but not a high speed. I am not a prop expert but I have found that generally for increasing top speed, the pitch needs to be increased.
I would be interested to know what props you stick with.
Good luck.
It sounds from your post that you are looking for a higher top speed. I would suggest that to gain more speed you need to keep the 19 pitch but reduce the prop dia a little so the engines hit the intended max rpm. I think your latest props will give you great efficiency and quick acceleration, but not a high speed. I am not a prop expert but I have found that generally for increasing top speed, the pitch needs to be increased.
I would be interested to know what props you stick with.
Good luck.