Motor position on your 20-24 foot grady

[SmokyMtnGrady]

Hey Guys,
KY Grady stopped by my house the other day and we chatted and had a lunch together. It was dreamy, two 228 owners breaking bread. Anyway, John noticed that Mid Carolina Marine mounted my 4.2 liter F250 on the first hole (top hole) on the motor mount motor side. When he got home his is mounted on the 3rd hole motor side. He gets 6,100 RPM top speed 42.

As mine is mounted I only get 5,500 RPM top speed of 46. I am thinking it's too low. I am taking it in for it's 100 hour service and I am thinking of asking them to move it up at least 1hole on the motor side.

So, where are the bolt positions on your Grady? I am thinking the smaller boats might run the same bolt positions. Thanks.

 

[Doc Stressor]

My F250 is at the second hole on my 226 and it's a little too low. But it's a little too high on the third hole and I got some blowout on sharp turns. That's actually OK for most people, but I find that I get a bit of a squirrely ride in big seas if the motor is just a bit too high. It's a personal thing with me and that's why I don't like boats with single bracketed motors. The right position for optimal speed and economy gives most of them funny handling in rough seas.

It's pretty easy to tell if your motor hight is close to right. Let somebody drive the boat with the engine trimmed for best operation and take a look at the anti-ventilation plate. There should be NO WATER running over the top of the plate.

 

[Halfhitch]

I repowered my 205 tournament with a 4.2 liter F225 and the dealer mounted it in the second hole. (one empty hole showing in the bracket above the top bolt). The tech said that was standard from Grady.

 

[seasick]

Assuming both hulls are the same, motor models are the same, props are the same, bottoms are similar and weights are similar ( as well as many other factors) , why would you think your motor is too low? When I look at the numbers you stated, I would say that your rigging is performing better. You get 4 mph more at top end and you are turning 600 fewer revs. Maybe I am missing something but don't those numbers that tell you that the first setup is running with a lot more prop slip.. His motor may be rev limiting due to slip. You can calculate prop slip manually or using one of the many calculators available online. Run your stats and see how you are doing.

 

[SmokyMtnGrady]

Seasick, you could be right. My factory rigged 3.3 liter maxed out at 6,000 RPM and I got 42 mph with a 4 blade prop. With the new motor it never exceeds 5,600 RPM and a top speed of 46. John rigs boats in Kentucky and said it was in the safe mode as it were.

I don't really max it out much. But, then again having it a half inch higher might help cruise performance . I think the antiventilation plate might be out of the water. I am not certain.

The boat does not ventilate or cavitate in tight turns . I don't lose power when towing a tube in tight turns for water sports.

I just don't want to be leaving performance on the table . Maybe it's ideal where it is.

 

[Doc Stressor]

KY Grady is running a 3.3 L F225 vs Smokey's 4.2 L F250.

 

[SmokyMtnGrady]

KY Grady is running a 3.3 L F225 vs Smokey's 4.2 L F250.

So, Doc, you're a smart boaterman , if you were in my shoes, leave it or move up one? I think two might be too much. I don't recall the position of the OEM installed motor.

 

[SmokyMtnGrady]

Grady says it should be the 2nd hole for the F250 4.2 liter . So, there you go.

 

[Parthery]

I think the max recommended RPM range for that motor is 5000-6000. If you can only turn it up to 5500 rpm you either need a lower pitch prop or to raise it up.

I'd raise it up one hole and see how it does....if you don't like it you can always lower it.

For the record, my 225 OX is in the second hole. Turning the 17" Mirage Plus to WOT gives me 5400. (2 stroke range is 4500-5500)

 

[seasick]

I think the max recommended RPM range for that motor is 5000-6000. If you can only turn it up to 5500 rpm you either need a lower pitch prop or to raise it up.

I'd raise it up one hole and see how it does....if you don't like it you can always lower it.

For the record, my 225 OX is in the second hole. Turning the 17" Mirage Plus to WOT gives me 5400. (2 stroke range is 4500-5500)

The Yami specs for a F225 and F250 on a 225 Seafarer both call for mounting on hole #2 so it would appear that the motor is in the non standard hole. Nevertheless the performance still looks better to me.I am not sure now if the propping is the same.
The spec for wot is 5000 to 6000. I don't really see a concern if wot is 5500 and the boat apparently handles well.
I was not able to confirm if the gear ration for the 3.3l is the same as the 4.2l . Are they both 2.0?

 

[Greyduk]

I think the max recommended RPM range for that motor is 5000-6000. If you can only turn it up to 5500 rpm you either need a lower pitch prop or to raise it up.

I'd raise it up one hole and see how it does....if you don't like it you can always lower it.

For the record, my 225 OX is in the second hole. Turning the 17" Mirage Plus to WOT gives me 5400. (2 stroke range is 4500-5500)

Parthery, What MPH do you get at 5400 RPM? I have a 17" Mirage plus that I am thinking of trying on my 223.

 

[SmokyMtnGrady]

The Yami specs for a F225 and F250 on a 225 Seafarer both call for mounting on hole #2 so it would appear that the motor is in the non standard hole. Nevertheless the performance still looks better to me.I am not sure now if the propping is the same.
The spec for wot is 5000 to 6000. I don't really see a concern if wot is 5500 and the boat apparently handles well.
I was not able to confirm if the gear ration for the 3.3l is the same as the 4.2l . Are they both 2.0?

Gear Ratio of the 4.2 is 1.75:1

I am curious more about cruising RPM and speed. Raising the motor would seem to improve top end. Will the reduction of drag improve mid range speed and fuel economy.

 

[Ky Grady]

Gear Ratio of the 4.2 is 1.75:1

I am curious more about cruising RPM and speed. Raising the motor would seem to improve top end. Will the reduction of drag improve mid range speed and fuel economy.

Why wouldn't it??

Less drag, better performance, more efficient.

 

[Ky Grady]

My performance for my 3.3 F225 was based on 2 people, 56 gallons of fuel, no curtains, calm water, no bottom paint. Motor in top hole on bracket, 3rd hole on motor, so one higher than Grady reccomends as initial rigging setup. Mid-Carolina rigged Bob's to low to even start with, so at minimum, need to atleast raise it one hole to bring it into Grady specs.

6000 rpm with top speed of 42, swinging a 4 blade 16P prop. No blowout in hard turns. I don't run those rpm's regularly, just checking performance and to see what I could run.

 

[Doc Stressor]

You should see a nice improvement in both top speed and economy when you raise your engine. Mine ran OK at the third hole, but as I said, I don't like the ride. With your bracket, you should be able to go higher than me since the water displaced by the hull will run higher that far behind the boat.

I've been in Ky Grady's boat with its previous owner and it did not blow out the prop despite the engine at the third hole.

I think the manufacturers tend to mount outboards lower in order to avoid handling issues that can arise under certain loads and running conditions. Just playing it conservatively I guess.

 

[Ky Grady]

Being in the marine industry, manufacturers will mount and prop a motor conservative. The average owner is interested in turning the key and go, not getting the full, fine line performance out of their motor. Those of us that understand, know, for the most part, you can tweak and adjust props and height to get the most performance out of the motor within it's operating range. That's the safety margin I was speaking about with Bob on Sunday for the average consumer.

 

[Parthery]

Parthery, What MPH do you get at 5400 RPM? I have a 17" Mirage plus that I am thinking of trying on my 223.

42 at 5400 RPM. But you have to trim it way up. The Mirages like to run near the surface.

I had a 223 with a 225 OX...that one ran 42 at 5400 as well.

 

[seasick]

Gear Ratio of the 4.2 is 1.75:1

I am curious more about cruising RPM and speed. Raising the motor would seem to improve top end. Will the reduction of drag improve mid range speed and fuel economy.

That's my confusion. I see the ratio on the Yami site as 2.0. Did it change with newer models?

 

[SmokyMtnGrady]

That's my confusion. I see the ratio on the Yami site as 2.0. Did it change with newer models?

That I can not confirm. The 3.3 is no longer on their website. They say 1.75 : 1.

I am looking forward to moving it up 1 hole. I am hoping my fuel economy will improve at cruise.

 

[Ky Grady]

As Doc mentioned, I think you could get away with 2 holes since we are on brackets. I have no issues with blowout.