Prop Help: F27 Mercruiser 305

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zedtwentyate
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Prop Help: F27 Mercruiser 305

Post by zedtwentyate »

Hello firends,

Now that i've replaced the carb, it's time to move on to a new project. I think it's time for a new prop. I'm concerned that I don't have the correct prop on the boat and its in rough shape (i think). Can anyone offer advice? From what the old search function has told me, I need a 14 x10 on this boat and as you can see in the pictures, this prop is a little ambiguous. Looks like someone stamped over the original size. Maybe it was reworked?

WOT - 3900 RPM @ 20-21 MPH

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Kegan

1986 Trojan F-27 (SOLD!!!)
1989 Trojan 10 Meter Mid Cabin
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prowlersfish
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Re: Prop Help: F27 Mercruiser 305

Post by prowlersfish »

Looks like it was a 13x10 reworked to 13x12 . Your just slightly low on rpm 14x10 would be a good choice but you could always redo the prop to 13x11 and that would give close to the same results .
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The Dog House
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Re: Prop Help: F27 Mercruiser 305

Post by The Dog House »

I believe the WOT range for that engine is 3800 - 4200, so it seems you are propped correctly. What is the horsepower rating for the engine? If the engine is only making 200 hp like many 305s of that era, I think the problem may be that the engine is undersized for the boat. My Chrysler 318 making 225 hp is a bit underpowered in my opinion. I'm cruising at 18 mph at 3000 rpm.
1993 Sea Ray 200 Overnighter OB with 1993 Mercury 150 hp Outboard
1979 Starcraft 14' Rowboat with 2011 Mercury 9.9 hp Outboard
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zedtwentyate
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Re: Prop Help: F27 Mercruiser 305

Post by zedtwentyate »

The 305 is a 230 hp motor...
The Dog House wrote:I believe the WOT range for that engine is 3800 - 4200, so it seems you are propped correctly. What is the horsepower rating for the engine? If the engine is only making 200 hp like many 305s of that era, I think the problem may be that the engine is undersized for the boat. My Chrysler 318 making 225 hp is a bit underpowered in my opinion. I'm cruising at 18 mph at 3000 rpm.
Kegan

1986 Trojan F-27 (SOLD!!!)
1989 Trojan 10 Meter Mid Cabin
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zedtwentyate
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Re: Prop Help: F27 Mercruiser 305

Post by zedtwentyate »

To achieve a nice cruise of 18mph, I would be in the 3500-3600 RPM range...
Kegan

1986 Trojan F-27 (SOLD!!!)
1989 Trojan 10 Meter Mid Cabin
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Paul
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Re: Prop Help: F27 Mercruiser 305

Post by Paul »

I run a 14 x 9 NiBrAl Cupped on mine with a 350 and a 1 : 1 Velvet drive. Boat's a little heavier that most F-26s however WOT is 4600, cruise at 3600 and 19-20 mph.
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Re: Prop Help: F27 Mercruiser 305

Post by The Dog House »

zedtwentyate wrote:To achieve a nice cruise of 18mph, I would be in the 3500-3600 RPM range...
I believe the common prop for a newer F26/F27 is a 14 x 10 cupped prop. The cupping basically makes the prop equivalent to a 14 x 11 uncupped prop. I would think that a 14 x 10 cupped prop should give you ~18 mph at ~3000 rpm, but I'm just guessing. Hopefully someone with a newer (straight inboard) F26/F27 and a 14 x 10 cupped prop can post their performance numbers.
1993 Sea Ray 200 Overnighter OB with 1993 Mercury 150 hp Outboard
1979 Starcraft 14' Rowboat with 2011 Mercury 9.9 hp Outboard
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Re: Prop Help: F27 Mercruiser 305

Post by prowlersfish »

The Dog House wrote:
zedtwentyate wrote:To achieve a nice cruise of 18mph, I would be in the 3500-3600 RPM range...
I believe the common prop for a newer F26/F27 is a 14 x 10 cupped prop. The cupping basically makes the prop equivalent to a 14 x 11 uncupped prop. I would think that a 14 x 10 cupped prop should give you ~18 mph at ~3000 rpm, but I'm just guessing. Hopefully someone with a newer (straight inboard) F26/F27 and a 14 x 10 cupped prop can post their performance numbers.

It lists a small cup so that maybe equal to 1/2"" of pitch
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zedtwentyate
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Re: Prop Help: F27 Mercruiser 305

Post by zedtwentyate »

Thank you for all the info. Looks like i need to read a little about props...i have no clue what I'm talking about.

From the sounds of it, I have two options:

1. re work the prop I have
2. Buy a new prop...or a used one.

I saw "Prop Shop" in a few other threads. Is there a reliable one that I should contact? I'm not looking to pay an arm and a leg for a prop for an old boat, but I do understand they aren't cheap!
Kegan

1986 Trojan F-27 (SOLD!!!)
1989 Trojan 10 Meter Mid Cabin
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Re: Prop Help: F27 Mercruiser 305

Post by prowlersfish »

What area are you in ? I can recc some shops but best to deal local ask your marina or on the dock
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Re: Prop Help: F27 Mercruiser 305

Post by gitchisum »

My F26 with a FB ran about 16-18 mph depending on load @ 3100 rpm's This was a 233 mercruiser ( 351 block) 1977 model year. I know I had one cyl that was about 5% behind the the other 7, and I had 4500 hrs on the boat when I sold it. This hull is REALLY sensitive to loading and I ended up with Tab extensions ( basically whale tails!!!) to compensate for having 5-6 people in the cockpit area. ( didnt help that I had 3 downriggers with 15lb weights hanging off the backend)

I was running a cupped 14X10.
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zedtwentyate
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Re: Prop Help: F27 Mercruiser 305

Post by zedtwentyate »

gitchisum wrote:My F26 with a FB ran about 16-18 mph depending on load @ 3100 rpm's This was a 233 mercruiser ( 351 block) 1977 model year. I know I had one cyl that was about 5% behind the the other 7, and I had 4500 hrs on the boat when I sold it. This hull is REALLY sensitive to loading and I ended up with Tab extensions ( basically whale tails!!!) to compensate for having 5-6 people in the cockpit area. ( didnt help that I had 3 downriggers with 15lb weights hanging off the backend)

I was running a cupped 14X10.

I'm in Syracuse, NY. Maybe there's a forum member who wants to part with a 14x10 pro?
Kegan

1986 Trojan F-27 (SOLD!!!)
1989 Trojan 10 Meter Mid Cabin
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Re: Prop Help: F27 Mercruiser 305

Post by MattSC »

What rotation is your current prop? I switched rotation when I re-powered years ago. I still might have my old RH 14x10 nibral cupped dyna-jet prop laying around Prior to the repower my old 318 cruised around 17-18 knots at 3100 rpm and around 25 at 4000 rpm. That is the Diameter and pitch prop that my boat was shipped from the factory with.
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zedtwentyate
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Re: Prop Help: F27 Mercruiser 305

Post by zedtwentyate »

Well thanks to MattSC, the boat is now running a 14x10 cupped prop. She runs waaaaaaay better. At 3100 she is doing just about 20MPH. Max seems to be between 24-26 but I can still only get to 3900 RPM. I'm beginning to think there may be an issue with my tach.

Thanks again for all the help. I couldn't have accomplished anything on this boat without you guys!
Kegan

1986 Trojan F-27 (SOLD!!!)
1989 Trojan 10 Meter Mid Cabin
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Re: Prop Help: F27 Mercruiser 305

Post by The Dog House »

zedtwentyate wrote:Well thanks to MattSC, the boat is now running a 14x10 cupped prop. She runs waaaaaaay better. At 3100 she is doing just about 20MPH. Max seems to be between 24-26 but I can still only get to 3900 RPM. I'm beginning to think there may be an issue with my tach.

Thanks again for all the help. I couldn't have accomplished anything on this boat without you guys!
Congratulations! It sounds like your performance is right where it should be. These boats are definitely NOT speed boats. :mrgreen:
1993 Sea Ray 200 Overnighter OB with 1993 Mercury 150 hp Outboard
1979 Starcraft 14' Rowboat with 2011 Mercury 9.9 hp Outboard
Former boat: 1971 Trojan F26
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