Original aluminum still available for 4..3L, 1.81 geared, Alpha 1

[stephenson]

Hi All,

Boat is Sea Ra 195 BR with original prop Mercury 3 blade, 13.75X21 aluminum - tore it up on bottom so replaced it with 3 blade Turbo stainless in 14.25X20. While this was pretty good top end it was 2-3 mph slower than the original aluminum), during hole shot the bow got higher than it did with the original aluminum. So, I next tried out a Quicksilver 5 blade (QST5) and it worked incredbly well for keeping bow down, accelerating very well and pulling skiiers - but cost about 6-8 mph - and it allows a bit of over-rev to occur so I have to watch it. I have since changed the boat's location to a deep, very clean lake (Smith Mountain Lake, in VA), dont use the boat for skiing as much, and would like to get more top end. I looked to see if could find a 3 blade stock prop in aluminum and 13.75 X 21, but for some reason can't in the prop application charts I've seen ...any ideas on what might have happened to the original 13.75 x 21 size - or, am I reading the charts wrong?

I'm only owner and it's been a great boat - very few hours, sadly, though

Thanks!!

 

[steelespike]

What year is the boat?
Without your wot rpm and gps speed with each prop.we can't really evaluate your tests.
Usually a 5 blade does better on powerful boats.
For instance what rpm and speed was original prop?What rpm and speed was the14.25 X 20 . What is the diameter and pitch of the 5 blade?
The 2 extra blades add drag which may change pitch and diameter.On your 4.3 a 5 blade isn't likely to be fast but should have amazing grip and control.
If you want a prop that may have the speed of your original try a 21" Turning point Hustler.
at this point it would be considered a starting point.

 

[stephenson]

1995 ...in fact it was the only year Sea Ray 195 bow riders were built ...not sure why, but that's another story, I suppose. Original prop WOT about 51 mph indicated ...the Turbo stainless was 3-4 mph or so slower than the stock aluminum indicated ...I did gps test with the Turbo vs the QST5 about two years ago and came up with the following: QST5 - 2.5-3 sec hole shot (just moving for steerage then full throttle, full trim down) until bow dropped to plane. Boat didn't labor to get up and then bow down, it just sort of popped up and then flattened. Bow still rose, but not as much and for not as long. Put the passenger in the back and wasn't much difference. Yanking it around at very low speed, it just sort of hung on the prop without fuss at very high turn rates, don't think I ever got it to cavitate - planes down to around 14-15 MPH and then slowly dissolves off plane. Very little porpoising at higher speed trimmed. 3000 RPM trim down (21.3MPH), trimmed a bit but maintaining 3000 RPM (21.1MPH) ... slip 28.6%, 4000 RPM trim down (32.2MPH), trimmed up a bit more and pulled back to maintain 4000 RPM (32.8MPH) ... slip 19%, 4500 RPM trim down (36.7MPH), trimmed up a bit more and pulled back to maintain 4500 RPM (37.7MPH) ... slip 17.3%, WOT was 4800 RPM trimmed down (39MPH), trimmed up a bit more and let run to WOT at 5000 (I know is over RPM) was 42MPH ... slip 15.5%. 3 Blade Turbo - 5-6 sec hole shot, bow comes way up and hangs there for about two seconds and then moves rapidly down. Yanking around at low speeds and high throttle can induce cavitation without too much effort ... doesn't hang on the prop the way the QST 5. 3000 RPM trim down (24.5MPH), trimmed a bit but maintaining 3000 RPM (24.8MPH) ... slip 17.8%. 4000 RPM trim down (35.5MPH), trimmed up a bit more and pulled back to maintain 4000 RPM (36.5MPH) ... slip 9.5%. 4500 RPM trim down (40.4MPH), trimmed up a bit more and pulled back to maintain 4500 RPM (41.4MPH) ... slip 8.3%. WOT was only 4600 RPM trimmed down (40.6MPH), trimmed up and let run to WOT at 4790 RPM was 44.9MPH ... slip 5.5%. Gauge speed was 10-15% off ...always read higher than gps computed. At issue is that I recall the stock prop was solid 4800 rpm at 51-52 mph indicated ...would simply like to try another stock 13.75 x 21, but doesn't show up on prop charts ...does appear to be available if I simply do a search for 13.75x21 ...can't remember who made the stock prop ...

 

[stephenson]

Not sure why server ran all the text together ...was broken Into paragraphs.

 

[steelespike]

They are working through a site update so strange things are still happening.
All those figures are nice to help analyze individual overall performance.
Keep in mind the numbers are only as accurate as the input.
Typical slip is usually double digits single digit slip while possible
should be considered suspect especially a rig runnig below 5000 rpm
where prop speed is roughly 1/2 that of the motor.
Your goal prop numbers don't add up. 52 at 4800 21" prop 1.81 ratio calculates to
​ a little over 1% slip just not possible.
A more reasonable slip 13% adds up to about 5300 rpm.
10% about 5200.
I think a 23" prop is more typical for 52 mph.
While your prop may have performed very well I don't think 51 or 52 were likely.

 

[stephenson]

52 was the indicated with gauge - about 5-6 mph less as read out on GPS. Question is, how can I get another stock prop ...

 

[steelespike]

Is this obsession just to prove a point?
Are you afraid a different prop won't measure up.
Is there enough prop left to have it repaired?Though no guarantee it will be the same?
If its a Merc prop the number under the nut may indicate some details about it.
Have you measured it? is it actually 14 3/4 inches? Measure from center of the bore to the tip of a blade and double it.
There are probably 1/2 a dozen aluminum prop that would match or beat your 19 year old prop.
As far as finding your prop get the numbers off of it call a well established Merc. dealer have him decipher your numbers.
You do realize 1/4" differece in diameter is unliklely to make any difference it might even be easier to turn.
There is no doubt that there are any number of basic aluminum props with higher technology
than your old prop.

 

[stephenson]

Hmmm ... not really an obsession, but the stock prop was a bit faster than the Turbo, didn't nose up as much during hole shot, pulled a skiier better - no all that said, the 5 bladed 19 pitch QST is certainly better at getting a skiier up and stays flatter during the process - also is cool to hang on the prop at lower speeds. So, after having lived with the QST5 for a few years, I thought I would compare.

Back to your earlier post, the 195 BR is 2350 pounds dry and the GPS was pretty darn consistent during my analysis runs ...the tach could be off, but it had been consistent, as well, since new.

The stock one was 13.75 x 21 vice 14.75 x 21. It's pretty messed up and I recall rebuilds don't always end up as perfect as the from the factory props (my dad was in the prop repair biz when I was a kid and I recall him talking about how aluminum props with short blades were more difficult to work on than the larger bronze props).

 

[steelespike]

The Turbo was an inch less than than your stock prop isn't likely to be as fast. It very likely had good bow lift which tends to cause some bow rise on hole shot
slowing hole shot for skiing as well.
I know that the Solas Amita and Turning point Hustler props are more technically advanced than your old prop.

 

[jestor68]

Michigan Match 13.75 X 21. Right there in the iboats prop section.

It appears that Mercury does not offer that diameter in the 21 pitch aluminum any more. Their current offering will perform the same or better.

The Quicksilver Siverado/Mercury Vengeance is also available in the same size if you prefer SS.

If you really want to get serious, an Enertia 21 pitch would be the hot ticket. It's about a 13.5 diameter.

 

[steelespike]

There's a guy that knows prop detail.

 

[stephenson]

Just got to lake and examined original prop (on the shelf) .. part number is 48-78122-21 and marked with 13 3/4 x 21 .. there is an "L" inside square indentation, and the number "43" inside on the bronze hub.

 

[stephenson]

Swapped out the QST 5 blade back to the Turbo stainless (confirmed is 14 1/4 x 20) way faster ...much more "satisfying" cruise at 3000 rpm about 27 mph gauge (very comfortable and smooth) ..3200 rpm about 31 mph and 3400 about 34 mph ...wot with full tank and me was about 47 mph. Other than the excessive bow lift on hole shot there isn't much to not like .... So, back to the question of how to get back to the original 52 mph gauge speed and slightly better hole shot ...with the original 3 blade stock aluminum or some other aluminum substitute (since in don't need stainless ). What is the cheap option for the original 13.75 x 21?

 

[YoungMind]

Michigan Match 13.75 X 21. Right there in the iboats prop section.

Umm... ^^ Michigan Match are very good props. Most likely as close as you will get to exact original.