Outdrive and performance questions

[Reming870]

I am not sure where to direct this but I am looking for a bit of help improving performance.

Boat: 1979 Gradywhite 254 Kingfish, 25 or so ft. This is a deep heavy boat for its class. I am estimating 7500 lbs with gear.
Power Steering / hydraulic trim tabs
Engine: 2009 MPI 5.7 / 300 HP
Outdrive: Alpha one Gen II, or now the SEI equivalent SE116.
Prop: 16 diameter / 13 P / 3-blade
Primary use: Off shore fishing

Problem #1: Low end steering. I cannot stay straight on the low end. Boat is all over the place with constant correction needed.

Problem #2: Occasional prop spin. Sometimes the prop just washes out like there is no water hitting it at higher speeds. If I slow done and regain plane the problem goes away.

I have tried various props from 17P-11P. I have found that the 13P gives me the best performance with the 15P a close second. The only problem I have had with the 15P is slow to plane and not enough pop when riding 4-6 ft seas.

Should I consider any aftermarket add-ons that may help with these two issues? If so, which and why?

 

[Bondo]

Re: Outdrive and performance questions

I am not sure where to direct this but I am looking for a bit of help improving performance.

Boat: 1979 Gradywhite 254 Kingfish, 25 or so ft. This is a deep heavy boat for its class. I am estimating 7500 lbs with gear.
Power Steering / hydraulic trim tabs
Engine: 2009 MPI 5.7 / 300 HP
Outdrive: Alpha one Gen II, or now the SEI equivalent SE116.
Prop: 16 diameter / 13 P / 3-blade
Primary use: Off shore fishing

Problem #1: Low end steering. I cannot stay straight on the low end. Boat is all over the place with constant correction needed.

Problem #2: Occasional prop spin. Sometimes the prop just washes out like there is no water hitting it at higher speeds. If I slow done and regain plane the problem goes away.

I have tried various props from 17P-11P. I have found that the 13P gives me the best performance with the 15P a close second. The only problem I have had with the 15P is slow to plane and not enough pop when riding 4-6 ft seas.

Should I consider any aftermarket add-ons that may help with these two issues? If so, which and why?

Ayuh,.... It sounds like ya shoulda opted for the next lower gear ratio when ya bought the SE drive,...

At idle speeds, V-hull boats do that, then throw in wind, 'n currents,...
It Ain't blacktop yer drivin' on,...

At this point, ya got a Prop problem,...
I'll move this to the Prop forum,....

 

[steelespike]

Re: Outdrive and performance questions

The 254 is 5100 lbs dry weight, Do you have 2400 lbs additional? The gear ratio is sometimes on the out drive.
You can carefully count engine revolutions by hand to one revolution of the prop.
It just seems a 13" prop doesn't leave room for any fine tuning.
What is the wot rpm and gps speed with a light load?
I've read that smart tabs help control no wake wander.it would seem your hydraulics could do the same.
You can train yourself to anticipate steering changes and to avoid over correction.
I once drove a 24ft? Sea Ray in about 10 or 15 minutes in relatively open water I was getting the hang of it
I do wonder how well I would have done in more confined space.

 

[Reming870]

Re: Outdrive and performance questions

The drive ratio is 1.47. I do not think there is anything lower.

5100 is dry without a motor and drive. I figure 950# with drive + 5100 dry = 6050. Add 5 guys at 200# a piece and now = 7050#. Then gear, water, ice, fuel, etc... I am sure on the heavy side would be around another 400-500#. Fuel alone would be 125 gallons full.

I didn't record any speeds on the last trip. I will try to get some various speeds next trip if I can find some calm water.

I do know that motoring out heavy last trip with 3-guys and 2-kids (900#), gear, full tanks, I was holding 22-24 MPH at 4200 RPM. WOT would get to 5000 RPM but I never recorded the speed. I had a head-on wind at around 10 knots consistent and 2-3 ft seas.

 

[steelespike]

Re: Outdrive and performance questions

As far as I know the dry weight of a stern drive includes the power train.
If you compare similar models in outboard and stern drive the stern drive is about 1000 lbs heavier.
So the stern drive does include the drive system. There are subtle weight differences in various drive systems.