alpha 1 gear ratio ?

[Ccoe1]

I have a 305 5.0l v8 220hp pushing a '99 searay 210 sundeck. Fully loaded for a day on the water is about 4200lbs. My outdrive is an alpha1 gen2 with 1.62 gears in it.
I talked to mecruiser direct today about my setup because I am having prop selection issues and they told me I should be running 1.47 gears in my outdrive for my setup. I have talked to 2 marine mechanics and they told me to stay with the 1.62 gears.
Looking for your professional opinions.
Thanks in advance .

 

[achris]

Re: alpha 1 gear ratio ?

What issues with prop selections are you having?

For the record as long as the props are in the 15" to 23" range, I'd stay with the 1.62...

I had an interesting 'event' with my boat. It had a 4.3LX in, with a 1.84:1 drive, and was running a 21" prop... Worked really nicely. Updated the engine to a 4.3MPI, but that engine came with a 1.62:1 drive. Prop is now a 19"... It runs a bit quicker, 43 knots as opposed to about 39.5 knots, but I can feel the difference, unfortunately, not in a good way .

It works like this. More ratio reduction requires a higher pitch prop spinning slower. A slower spinning prop is more efficient, and less likely to cavitate. That's why I can feel the difference between the 1.84:1 and the 1.62:1... What I should have done, and will be when I next update the engine, is specify the higher reduction....

So, to add to my already way too long post.... If you want to change the ratio, and the prop selection is still in the right range, move to 1.81:1, not 1.47:1....

There you have it... In a (rather large) nutshell.....

Chris.......

 

[Ccoe1]

Re: alpha 1 gear ratio ?

From the research that I have done, the 1.62 gears are recommended for v6 engines with 185 hp to 205hp. And the 1.47 gears are recommended for v8 engines with 205hp to 280hp.

 

[achris]

Re: alpha 1 gear ratio ?

From the research that I have done, the 1.62 gears are recommended for v6 engines with 185 hp to 205hp. And the 1.47 gears are recommended for v8 engines with 205hp to 280hp.

Partly correct....

The V6s started out with 1.84, then as the engine output (horsepower) increased the ratio was dropped to the 1.62...

The 350 V8 is 1.50/1.47:1

The 305 with a 2bbl has always been 1.65/1.62:1

Chris......

 

[Ccoe1]

Re: alpha 1 gear ratio ?

Also mercruiser told me if I stick with the 1.62 gears I should be running a 14.5" x 20p prop for standard use. If I were to change the gears to 1.47 I would need to drop down to a 14.5" x 18p prop. He claimed it would be less stress on my motor and in turn be more efficient.

 

[achris]

Re: alpha 1 gear ratio ?

Also mercruiser told me if I stick with the 1.62 gears I should be running a 14.5" x 20p prop for standard use. If I were to change the gears to 1.47 I would need to drop down to a 14.5" x 18p prop. He claimed it would be less stress on my motor and in turn be more efficient.

Can't see how that would be... Thinking about the maths... Less reduction, lower pitch prop... Same boat speed, same engine speed, same 'stress'....

If you want less 'stress', do what I have done, find the 'right' prop pitch, then go one size (2") SMALLER.... The whole boat feels so much better. It's more responsive, less noisy, same on fuel, but you can hear the engine working less.... As long as you don't want to run WOT all day, it works really well. I boat in the Indian Ocean, the number of days per year I can run WOT, can be counted on the fingers of one hand...

Chris......

 

[Ccoe1]

Re: alpha 1 gear ratio ?

Im am only asking this because I am going to have my outdrive serviced and while its apart I want to have everything done one time. Im all about preventative maintanence and making things right.

 

[Ccoe1]

Re: alpha 1 gear ratio ?

I dont plan on running wot much but I just want everything to be correct. I just bought the boat this summer and I am very anal, just want things to be correct.

 

[achris]

Re: alpha 1 gear ratio ?

Changing gear ratios is not really a maintenance item...

What size (pitch) prop are you currently running, and what boat speed and engine speed are you getting at Full noise?

 

[achris]

Re: alpha 1 gear ratio ?

I dont plan on running wot much but I just want everything to be correct. I just bought the boat this summer and I am very anal, just want things to be correct.

Anal's good... Me too....

 

[ktbarrentine]

Re: alpha 1 gear ratio ?

VERY happy with my 14.25"x19p prop on my 1.65r 5.0L 205hp engine pushing a 20' chap.... Terrific hole-shot, on plane in no-time, 50(gps)MPH top at WOT. Just my 2cents.

KB

 

[Ccoe1]

Re: alpha 1 gear ratio ?

Changing gear ratios is not really a maintenance item...

What size (pitch) prop are you currently running, and what boat speed and engine speed are you getting at Full noise?

I am running a 14.25" x 21p 3 blade aluminum black max, wot is 4500 and top speed 43mph. I bought a brand new prop cause the previous owner told me that was stock. The prop on it when I bought it was badly beat up.

 

[Ccoe1]

Re: alpha 1 gear ratio ?

VERY happy with my 14.25"x19p prop on my 1.65r 5.0L 205hp engine pushing a 20' chap.... Terrific hole-shot, on plane in no-time, 50(gps)MPH top at WOT. Just my 2cents.

KB

Im thinking I'm going to end up with that prop. This is good to hear. What prop manufacturer are you running.

 

[achris]

Re: alpha 1 gear ratio ?

Personally, I feel 4500rpm is a little too slow.

For your application, a 14"x19" stainless steel 'Vengance' or 'Laser II' (I know they are a little bit more $pendy), but well worth it... I also know that some (uninformed) people say having a SS prop will damage the gears if you hit something in the water... Yes, the gears might get damaged, but no more than with an ali prop... The problem with ali, with higher horsepower, they flex too much, and become more inefficient...

Dropping down to 19" should bring the revs up to about 4900rpm at WOT... Perfect! Right at the top end of the range.... and a bit of headroom if you have a few friends on board one day.... (My engine will run to 5100+ if I push it all the way..)

Chris.....

 

[Fun Times]

Re: alpha 1 gear ratio ?

Personally, I feel 4500rpm is a little too slow.

For your application, a 14"x19" stainless steel 'Vengance' or 'Laser II' (I know they are a little bit more $pendy), but well worth it.

+ 1, The vengeance prop works really well with the alpha drive. There is a really good chance that your overall speed & performance will improve to your liking going with an 14 X 19 SS-vengeance Merc part #(48-16316A46) It's worth the extra $ if you have it to spare.

 

[achris]

Re: alpha 1 gear ratio ?

Just to continue on the 'Vengance' theme. It's basically the same pattern as an aluminium 'Black Max' prop, but in Stainless Steel.

I have 2 of them, a 17" and a 19". My 17" is my 'everyday' prop. If I know the weather is going to be really nice and flat, and I'm light-loaded, on goes the 19" and down goes the hammer...

On the previous engine (also a V6 with a Gen II drive) I mainly used 4 blade 'Offshore' series props. They come in even inches of pitch 18, 20, 22.... They were great, especially because the smaller blades and high rake allowed seaweed to just slip passed them, no fouling. That's the one thing I do notice with the 3 blade props....

The only reason I have an ali prop, is as a 'get me home in an emergency' spare....

 

[Ccoe1]

Re: alpha 1 gear ratio ?

I am going to stay with 1.62 gears and reprop, I do like the thought of a ss prop but I am generally in shallow waters and couldnt stand the thought of grinding a ss prop through the gravel.