Thinking about going from aluminumto stainless???

[rhillman75]

I need some input. From my profile I have a 20 foot open bow, 4.3LX Mercruiser, and a Alpha One Gen 2. I currently run a Solas Rubex 19P, 14-3/4, 3 blade aluminum prop. At WOT I am hitting about 4400-4500 rpm and hitting about 35mph. If I drop the money and go stainless... what are the gains (if any?). I know the one big "con" is the inability to "give" when you hit something in the water.

 

[Scott Danforth]

Re: Thinking about going from aluminumto stainless???

you will gain a bit on the top end from the stainless. I have never hit anything hard enough with my stainless props to do any damage. my sister on the other hand took off the entire drive. doubt if aluminum prop would have helped. for what its worth, most of the time you will take out the prop hub. however when you really hit something, that is what insurance if for.

 

[Texasmark]

Re: Thinking about going from aluminumto stainless???

My first stainless prop (1973) was for a boat that if I hit anything I had to have the alum in the shop for repairs and that was just about on an outing basis....once a week. Put the SST on and ran the boat for over 7 years and nare a problem plus I had good performance out of it. Today, SS is all I run. Your money, your decision.

Mark

 

[Chris1956]

Re: Thinking about going from aluminumto stainless???

The gains in performance are small, IMHO. I went to a stainless prop since I would chew up an aluminum prop every year, hitting the bottom in my 18' BR 4.3LX Alpha. If you do go SS, go for a prop with some rake. Sounds like a 19" pitch is about right.

 

[tahoejag]

Re: Thinking about going from aluminumto stainless???

JMO....without knowing your drive gear ratio, your WOT range seems to be on the low side for a 19p prop. I'm running a 3 bld alum, 14 1/4x 21p 20 ft, 4.3l, alph I gen II, WOT at 4900 and 44 mph (gps), but that is with a 1:81 ratio. My engine WOT range is 4400 - 4800. That puts me at the top of the range (which i like it to be). If I were to go down on pitch, I would be over -revved for WOT. In your case if you went up to a 21p you wouldn't even be running at your MINIMUM rpm range for it would lower your rpms even more. I would try out a 17p and see where your WOT rpms land up. But again a 17p prop just to get to your high end of WOT range sounds odd.

For the alum to SS, wouldn't worry so much about hitting objects as most the hubs they make these days for SS props act as the same for the alum ones (the hub will go before anything else), unless they are a fixed hub. From experience of friends, they have claimed to get more top end speed with SS, as well as better bite/grab than their alum props. I believe in...you get what you pay for. Oh yes, it would be nice for me to afford a Merc Rev 4 SS (at aprx $500)...lol. But seriously, I have an alum and its been good to me, I am going to another alum (just b/c my budget), 4 bld though for better mid range and cruising speeds. Bottom line is it's up to you and what you can afford. I've yet to hear people that went to SS from alum regret it and what to go back to alum. Again, JM2C.

 

[jestor68]

Re: Thinking about going from aluminumto stainless???

If I were you, I'd be wondering why my 2500 lb boat powered with a 4.3L isn't running mid to high 40"s with a 19" pitch prop.

Your numbers don't compute. Turning 4500 rpm with a 19 pitch prop should be equal mid 40 mph; not 35.

 

[Chris1956]

Re: Thinking about going from aluminumto stainless???

Jestor, I had a similar boat as the OP, with the same powerplant. My 205HP 4.3LX could hit 40-42MPH, but that was about all. I would therefore be surprized to see him hit the mid-high 40s.

 

[tahoejag]

Re: Thinking about going from aluminumto stainless???

If I were you, I'd be wondering why my 2500 lb boat powered with a 4.3L isn't running mid to high 40"s with a 19" pitch prop.

Your numbers don't compute. Turning 4500 rpm with a 19 pitch prop should be equal mid 40 mph; not 35.

I agree with jestor68. The #'s just don't sound right. 1) 19p prop should have a bit more WOT rpm. 2) Maybe a bit more top end speed as well. Possible that your engine is not running at it's full rpm potential?? As I mentioned b for, I'm running at 48/49k WOT with a 21p 3 bld alum, top end 43/44 mph on gps. Just something to take into consideration for ya.

 

[jestor68]

Re: Thinking about going from aluminumto stainless???

To clarify my opinion; let me say that I ran the numbers through the calculator before posting.

It shows that the typical 19 ft bow rider(if there is such a thing) with a 4.3L turning a 19 pitch prop at 4800 rpm should be able to do between 47 mph(theoretical) and 43 mph(8% slip). That sounds like a reasonable expectation, based upon my experience preparing like boats for customers for 20+ years.

Even his numbers of 4500 rpm yielded 44 mph(theoretical) and 40 mph(8% slip). His 35 mph equaled 20% slip.

Therefore my suggestion that he perhaps has other issues to sort out before running out to buy a stainless prop.

Let's face it; your boat might have done those numbers when new, but it's sixteen years old now. Maybe 41 or 42 mph is all that it will even do again, without a new/reman motor.

 

[Chris1956]

Re: Thinking about going from aluminumto stainless???

Jestor, What gear ratio are you using? Different years had different ratios for V6 motors.

BTW - no offense, but I think you expect too much speed out of that powerplant...

 

[jestor68]

Re: Thinking about going from aluminumto stainless???

jestor, what gear ratio are you using? Different years had different ratios for v6 motors.

Btw - no offense, but i think you expect too much speed out of that powerplant...

btw- 1.81

 

[jestor68]

Re: Thinking about going from aluminumto stainless???

I don't feel that it's unreasonable to expect this boat to do 40 mph with 190 hp, if the motor is reasonably healthy. The most cost effective solution would be a Solas Amita 15.5 X 17 pitch. It will get those slip numbers down and greatly improve your performance at a fraction of the cost of SS.

 

[jkust]

Re: Thinking about going from aluminumto stainless???

I don't feel that it's unreasonable to expect this boat to do 40 mph with 190 hp, if the motor is reasonably healthy. View attachment 172464 The most cost effective solution would be a Solas Amita 15.5 X 17 pitch. It will get those slip numbers down and greatly improve your performance at a fraction of the cost of SS.

Just to understand this a bit more. The 4.3 is an LX...is it a 4bbl or EFI LX? It's a 96 so presumably it is a Vortec and the LX should have more than 190 PHP. Having had a standard 190hp but with a far heavier boat and a cheap 21" alum prop and of course just being a member here and also knowing about a hundred other 4.3 owners, you are starting in a deficit. Your low speed and low rpms don't compute to a prop issue imo.

 

[jestor68]

Re: Thinking about going from aluminumto stainless???

The 1996 4.3L LX Gen+ is rated at 190 HP( 2 barrel carb). The 1996 4.3L LXH Gen + is 205 HP(4 barrel version).

BTW- That is right out of the specifications page of my 1996 4.3LX Gen + owners manual.

 

[Tail_Gunner]

Re: Thinking about going from aluminumto stainless???

I need some input. From my profile I have a 20 foot open bow, 4.3LX Mercruiser, and a Alpha One Gen 2. I currently run a Solas Rubex 19P, 14-3/4, 3 blade aluminum prop. At WOT I am hitting about 4400-4500 rpm and hitting about 35mph. If I drop the money and go stainless... what are the gains (if any?). I know the one big "con" is the inability to "give" when you hit something in the water.

I currently run a Solas Rubex 19P, 14-3/4, 3 blade aluminum prop. At WOT I am hitting about 4400-4500 rpm and hitting about 35mph.

You have serious issues..check your tach...use gps...weigh your boat how clean is the bottom now that could drag down that hard but i cannot see your engine still turning 4500 under a heavy load. A 3.0 would do better than that with people

 

[jestor68]

Re: Thinking about going from aluminumto stainless???

The see two issues here; the first is engine power being down after 16 years; the second the prop being less than ideal for the application(20% slip). This assumes that the motor is tuned as well as it can be.

Nothing much can cure the lose of power due to age. A compression test can verify the relative health of the motor. As a point of reference, new compression for that motor is like 180 psi.

 

[scott8058]

Re: Thinking about going from aluminumto stainless???

I agree with most that switching to a stainless will give a few more mph on top end but idt it will get you much past 40 i'd check for other problems bc that does sound slow. On the other hand my cousin found a mint 96 chaparral 19ft 4.3l with only 150 hours on it and it will touch 50 with just 2 people in it so who knows! Good luck

 

[jkust]

Re: Thinking about going from aluminumto stainless???

At best you are dealing with the symptom of a larger issue with a different prop. The 4.3 with its low hp has a ton of power when you get down to it. It powers my boat up to 51.8mph on GPS with 1000 more lbs of weight and my boat is a slowpoke by 18 foot standards not intended for speed. Don't waste a dollar on a prop without diagnosing the problem.