which prop for a seafarer 228 with a F225?

[DoctorOctopus]

i have a 22' 1987 seafarer with a 2016 F225 on a bracket.
When it was running the old 2-stroke i ran at 50-53 top speed. I can rarely get up to full RPM near 6000rpm. Really around 5000 rpm
The newer F225 four stroke rarely gets above 40. I cruise at 24 mph 3.2 MPG 3300RPM.
I am very dissapointed with my top speed on the new motor that I otherwise love.

I had heard that Yamaha had issues early on with the four stroke where they were putting them out with the wrong props.

I presently have a saltwater II 15/15 prop.
It was suggested that I move to a 15/19 pitch prop.

Has anyone done this and gotten improved top speed and RPM?

 

[glacierbaze]

First, can I have your old prop?
I'm still running 225 two stroke, but I would guess 17 or 19 pitch would be the starting point.
Do you still have the old prop, and did you try it on the new motor?

 

[seasick]

What was the 2s hp rating? your new motor weighs about 100 pounds more
What is your WOT for the 4 stroke?
You probably just cant assume that the old prop may work better on the new motor since I believe the gear ratio is different.

Since you have a bracket and a heavier motor, the stern may be sitting lower in the water. That may cause the motor to sit lower in the water. Can you see where the anti ventilation plate is sitting with respect to the water line?

 

[DennisG01]

As noted, the big "data point" is your top end speed and WOT RPM... along with what the old engine HP was. From your description, it sounds like you're not maxing things out. The way you said "rarely" leads one to believe it's more about conditions than a true top speed.

There's more information that is missing and something seems to be off with your numbers, as well. You've got a good cruise and we can probably assume your hole shot is good otherwise you would have mentioned that. But if you were TRULY only getting 40MPH then your engine would absolutely be screaming and over revving and you probably would have mentioned that, as well.

Is your speed GPS-based or using the speedo on the dash?

 

[DoctorOctopus]

What was the 2s hp rating? your new motor weighs about 100 pounds more
What is your WOT for the 4 stroke?
You probably just cant assume that the old prop may work better on the new motor since I believe the gear ratio is different.

Since you have a bracket and a heavier motor, the stern may be sitting lower in the water. That may cause the motor to sit lower in the water. Can you see where the anti ventilation plate is sitting with respect to the water line?

The 2-stroke was the same horsepower. Yamaha evidently, admits to propping the 4HP engines incorrectly as the same prop does NOT work the same on the larger 4-stroke engines. This error continued for several years. this is the same rated prop as the 2-stroke which is why I'm questioning changing it.

The 4-stroke does indeed sit lower in the water and is 200 or so pounds heavier. my skeg touches the water (i paint it) by about 3 inches whereas it did not before.

 

[DoctorOctopus]

As noted, the big "data point" is your top end speed and WOT RPM... along with what the old engine HP was. From your description, it sounds like you're not maxing things out. The way you said "rarely" leads one to believe it's more about conditions than a true top speed.

There's more information that is missing and something seems to be off with your numbers, as well. You've got a good cruise and we can probably assume your hole shot is good otherwise you would have mentioned that. But if you were TRULY only getting 40MPH then your engine would absolutely be screaming and over revving and you probably would have mentioned that, as well.

Is your speed GPS-based or using the speedo on the dash?

I will run her all-out this week and let you know the WOT RPM. I got higher RPM when trimmed nearly out of the water but it did not seem right under way. also no increase in speed. my hole shot is amazing and the boat comes right out of the water. I may be sacrificing top speed for hole-shot. I am using the GPS speed. The engine is not screaming under way. I am only getting 5000 RPM, which makes me think that I actually need a lower pitched prop to get max RPM 15/13.. although everyones advice has been to try a larger 15/19.

 

[DennisG01]

You're definitely not going to be going lower -- regardless of whatever that info is about Yamaha propping them wrong - although, ultimately, this falls on the dealer or the customer as the same engine can be used on different boats and may require a different prop.

But there's no way you should need to go down in pitch. Something else has got to be off as your numbers just aren't jiving with what they should be when running a 15". Your engine should be at, or above, the MAX RPM rating when trimming up and running hard.

I'm not there running the boat with you and I don't know your experience, but thoughts that are going through my head... improper trim use, fouled/damaged running gear, excessively heavy load, low compression on the engine, etc.

True MAX RPM & speed is attained by going full throttle and continuing to trim up until speed no longer increases and/or the prop starts to ventilate.

 

[seasick]

I wasn't asking about the skep being in the water when the motor is tilted up. I was asking where the ant ventilation plate sits when the motor is tilted down ( vertical). The plate for a transom mounted motor should be about level to an inch lower than the bottom of the keel. For bracket mounted motors, the plate needs to be set up higher. A starting point is 1 inch higher for every foot of bracket depth. This is not an exact science and the type of bracket can affect that setting. If your bracket provides some floatation ( and rests in the water), the amount of the raising of the motor will be less.
As a start, see where the ventilation plate when on plane. If it is several inches, the motor is probably too low.
That said, your current prop if probably incorrect.

 

[DennisG01]

Seasick... good point about the height of the engine. Being too low wouldn't affect hole shot and low/medium speed much at all. But because of the extra drag it will certainly affect top end. I guess an assumption was made (at least on my part), that the new engine was put on in the same spot as the old one and is the same length shaft.

 

[DoctorOctopus]

i will check the ventilation plate with when I get back to the boat
I’m sure the engine is mounted in the exact same spot as the 2-stroke on the Grady drive bracket

The WOT is 5400 and 40 mph
I can tilt up the engine very high (doesn’t feel right though ) and get nearly 6000 rpm but the top end is still 41mph so a pointless waste of gas

I wasn't asking about the skep being in the water when the motor is tilted up. I was asking where the ant ventilation plate sits when the motor is tilted down ( vertical). The plate for a transom mounted motor should be about level to an inch lower than the bottom of the keel. For bracket mounted motors, the plate needs to be set up higher. A starting point is 1 inch higher for every foot of bracket depth. This is not an exact science and the type of bracket can affect that setting. If your bracket provides some floatation ( and rests in the water), the amount of the raising of the motor will be less.

As a start, see where the ventilation plate when on plane. If it is several inches, the motor is probably too low.
That said, your current prop if probably incorrect.