3 blade aluminum to 4 blade SS?

[emilime75]

I am considering a 4 blade SS prop. The boat is an 06 Sea Ray 185 Sport with the 3.0L. Drive is the Alpha One Gen II w/2.00 gear ratio. The boat is used for cruising, spirited full throttle runs across the lake, and a tiny bit of tubing.

It came with an aluminum Mercury Black Max, 14-1/2" x 19P, 3 blade prop. This allowed for a WOT RPM of 4800 and a top speed of 38MPH via GPS. Conditions weren't ideal for a top speed test, pretty choppy, so maybe I could've squeezed another 1-2MPH out of it. 2 adults plus me on board. About a half tank of fuel. 2 small-medium sized coolers.

I then borrowed a friend's SS Quicksilver Laser II, 13-1/4" x 20P, to test. This felt to have a slower hole shot and seemed to take longer to get on plane. WOT RPM was also 4800 and top speed reached was also 38MPH. Conditions this time were smooth waters, so I believe this was all she had. Only me on board. About 4 gallons less fuel. 1 small cooler.

Considering the boat was significantly lighter during the SS prop test, I am somewhat baffeled by the results. I'd guestimate it was roughly a 375-400lb difference.

Aside from the usual desires of wanting to improve hole shot and top speed, the boat wanders drastically at low speed. This is what brings me to wanting to try a 4 blade prop, as I'm reading they help somewhat. I should add that I will also be adding Nauticus Smart Tabs somewhat soon.

With the above, what diameter and pitch 4 blade prop should I be looking at? Would it be beneficial/worth it to also go SS? Am I even on the right track?

 

[alldodge]

It came with an aluminum Mercury Black Max, 14-1/2" x 19P, 3 blade prop. This allowed for a WOT RPM of 4800 and a top speed of 38MPH via GPS. Conditions weren't ideal for a top speed test, pretty choppy, so maybe I could've squeezed another 1-2MPH out of it. 2 adults plus me on board. About a half tank of fuel. 2 small-medium sized coolers.

Prop slip 12%

I then borrowed a friend's SS Quicksilver Laser II, 13-1/4" x 20P, to test. This felt to have a slower hole shot and seemed to take longer to get on plane. WOT RPM was also 4800 and top speed reached was also 38MPH. Conditions this time were smooth waters, so I believe this was all she had. Only me on board. About 4 gallons less fuel. 1 small cooler.

Prop slip 16%

the boat wanders drastically at low speed. This is what brings me to wanting to try a 4 blade prop,

This is not true, all single prop Vee hull boats wonder at idle, just nature of the beast

You can either have great hole shot or great WOT speed. You can have good in both areas, but not great.

A 4 blade prop decreases slip which can be good, but also takes more HP to turn it. Going from a 3-19P to a 4 blade then need to drop two inches of pitch 4-17P. Its best if you could find a place to let you try some. No many but some prop shops will sell a prop and allow exchanges.

Now if you go to Hill Marine, they will exchange a prop about as many times as you want. You pay return ship each time
https://www.hillmarine.net/

 

[emilime75]

Prop slip 12%

Prop slip 16%

Sure, but how does that help when deciding on a prop with different characteristics, e.g. 3 blade vs 4 blade? Unless you're inferring to this being the difference in hole shot? I would've thought the weight difference would've aided in both hole shot and top speed.

This is not true, all single prop Vee hull boats wonder at idle, just nature of the beast

I'm aware of this, but have read many reports that a 4 blade has helped. I need another prop anyway, so I'm willing to try a 4 blade.

You can either have great hole shot or great WOT speed. You can have good in both areas, but not great.

I'm aware of this, as well.

A 4 blade prop decreases slip which can be good, but also takes more HP to turn it. Going from a 3-19P to a 4 blade then need to drop two inches of pitch 4-17P. Its best if you could find a place to let you try some. No many but some prop shops will sell a prop and allow exchanges.

Why does Mercury's Prop selector suggest staying the same or going the opposite direction? For a 4 blade, it suggests a 19 and a 21 SpitFire, depending on which of the above test results I plug into the selector.

Now if you go to Hill Marine, they will exchange a prop about as many times as you want. You pay return ship each time
https://www.hillmarine.net/

I'll consider that once I decide what to actually buy.

 

[jimmbo]

What is the WOT rpm range for your engine? 4200 -4600. or 4400 - 4800? Being a Mercrusier, there should be a Label on Flame Arrestor with the info.
You might be propped perfectly, regarding the Black Max lineage of Props.
An extra Blade will kill the top end. If you want better holeshot, you could vent the prop, but the placement and size of the vents can make or break that option.
It is almost Impossible to chose a Prop by looking at the Specs. At some point you have to spend money, and SS props can get expensive.
As for what others say... unless they have the same boat, engine, load, and boat at the same Elevation above Sea Level, at the same Ambient Temp... what worked for them, YMMV

 

[alldodge]

Sure, but how does that help when deciding on a prop with different characteristics, e.g. 3 blade vs 4 blade? Unless you're inferring to this being the difference in hole shot? I would've thought the weight difference would've aided in both hole shot and top speed.

Slip is how well the prop holds (bites) and transfers forward motion. A 19P prop with zero slip will move 19 inches forward per revolution.

The 19P had less slip so it was more efficient at transfer. If the 20P had same diameter then most likely the speed may be the same but the WOT rpm would be 200 rpm lower

My opinion is always stick with 3-blade unless your unable to get what you want, and its not speed your wanting to achieve. The 4-blade will hold better but takes more power. The larger diameter will hold better then smaller but then again takes more power.

A 4-blade will also increase lift, and the lift can cause the need to redistribute the load and trim because it may porpoise

Why does Mercury's Prop selector suggest staying the same or going the opposite direction? For a 4 blade, it suggests a 19 and a 21 SpitFire, depending on which of the above test results I plug into the selector.

Have no idea, never used it but others have and has not been a great tool

 

[Scott Danforth]

the laser was only a 13" prop vs your current prop. those two almost wash each other out.

I wouldnt put a 4-blade SS prop on a 3 liter.

in my 3.0 powered boat, i kept 3 props. a 15p, a 17p and a 19p. the 19p was for long-distance cruising (40-80 miles), and the 17p was for general all-around boating and the 15p was for water-sports. No way to get a better hole shot (requiring a lower pitch) and a better top end (requiring a higher pitch and more power) with a single prop.

 

[Scott06]

Your numbers seem pretty good for a 3.0. 38-40 mph max

i had a 170 sea ray with a 3.0 for 20 years ,like Scott D I had multiple props for different uses. I settled on two pitches of Michigan vortex 4 blades depending on use . 18” 4 blade for general cruising use and tubing , 16” 4 blade for skiing. I hate to say don’t waste the money on SS for a 3.0 but reality is doesn’t have enough power to take advantage of it. The aluminum 4 blades were relatively cheap and worked well for my primary use loaded towing would recommend the vortex highly.

you mention merc recommending a 19-21 “ Spitfire I have one but that prop doesn’t have much bite like a revolution 4 or enertia. I get about the same WOT rpm on my current boat (sea Ray 200 sport 5.0) with a 23” spitfire that I do with a 21” revolution 4 and 21” Vensura/offshore.

As mentioned the higher performance and cost stainless props bite better and with a lower HP engine like you have holeshot will suffer as engine can’t spin up as fast into fat part of power curve. I get my best holeshot with the Vensura but get 20% slip at wot. The revolution 4 that bites better gives best top speed ( event better than 3 blade enertia) because it has lowest slip and allows more trim at WOT. It holeshot isn’t quite as good as the vensura.

I think you were seeing that with laser II engine can’t spin up as fast due to grip and more pitch. Fact that this trade off of holeshot didn’t gain more top speed means that is at the limit of the engines power.

 

[achris]

Why does Mercury's Prop selector suggest staying the same or going the opposite direction? For a 4 blade, it suggests a 19 and a 21 SpitFire, depending on which of the above test results I plug into the selector.

Because that calculator works to get the engine WOT right in the middle of the rev range.. And you are currently right at the top...

Already said, but I'll say it too.

3 blades middle of the rev range, for top speed.
5 blades just over the top of the rev range, for best acceleration. If you're going to be pulling tubes/skiers, then about 200rpm over the top of the normal recommended WOT range is 'recommended'.

The two targets are mutually exclusive... Pick one or the other, or have multiple props (like most of us)...

With a 3 litre engine, material becomes almost irrelevant. (Try to stick to SS with higher HP engines, due to the aluminium tendency to distort under high torque.)

Chris........

 

[Texasmark]

the laser was only a 13" prop vs your current prop. those two almost wash each other out.
...............
No way to get a better hole shot (requiring a lower pitch) and a better top end (requiring a higher pitch and more power) with a single prop.

Well sir, then why are props ported? That's the whole point. Bass boats are heavy at the transom (batteries, fuel, livewell) and have to get up on the "Pad" to get their 65 mph top end. Since you said, can't do it with one prop, and happened to quote a Laser, having had one, er ah 2, currently running a Laser II........enter the ported prop, like the original Laser I had back in 1989. Punch out of the hole and the prop acts like a shallow pitch....get up to speed, the holes close off, the boat shoots forward, tweak the trim, on the pad, bow rises, and away you go.

Since the boat is an I/O I have seen recommendations that ported props are not recommended. I have no idea as to which piece of information is correct, the folks that make props for inboards with ports, or the folks that use them and are dissatisfied.

 

[Scott Danforth]

ported props work great with 2-stroke outboard to get the RPM's up by unloading the prop at low speed by increasing slip until there is sufficient forward movement

The 3.0 I/O is a turd of a motor on the performance side, and the 115hp version even more so and the ported prop wont help at all. I should have clarified, that on a 3.0, you cant get one prop to work for better hole shot and better top end. you need multiple props.

 

[QBhoy]

Hi
Are you sure about that laser 2 being a 20” pitch ? That would be a very strange pitch for a laser 2 suited to an alpha drive. Perhaps it’s been worked on. Either way I wouldn’t base any results or future prop selection on the idea.
Could be crucial for you to consider.

Id also add that it sounds like you are doing really well with the black max. They can be great props on boats like this and hard to improve on when they are just right for the boat. Although i have a small suspicion that if you tried a laser 2 19” and a little extra trim they usually allow...you might see 40 gps and equal or better hole shot to the black max.

 

[achris]

...The 3.0 I/O is a turd of a motor on the performance side, ....

I wouldn't go as far as calling them turds. Granted, they are not performance engines, and they were never designed to be and they don't cost as much as a V6 or V8 either. What they are is great for smaller boats, in the 5m to 6m range, with great fuel economy... Not everybody wants to be doing 45 knots, and in a lot of places, the weather's not going to allow that even if you could. They also take up quite a bit less floor space than a bent engine too.

As we say in -26,134, horses for courses.

Chris........

 

[Starcraft5834]

I had a heavy cuddy (sold last year) it had a 3.0. It had a 3 blade prop on it when bought it. had to much pitch wouldnt get out of the hole, I put a 4 blade on it with less pitch. (15), it jumped out of the hole nicely. I am a 4 blade advocate for sure... 3.0 engine lacks power, that said.. there are a lot of them out there running well... I needed more room and bought a new 20ft toon with 115 Merc 4 stroke last year.... yea,, it's pretty sweet.... going 30 in a Toon is a hoot too LOL

 

[Texasmark]

Hi
Are you sure about that laser 2 being a 20” pitch ? That would be a very strange pitch for a laser 2 suited to an alpha drive. Perhaps it’s been worked on. Either way I wouldn’t base any results or future prop selection on the idea.
Could be crucial for you to consider.

Id also add that it sounds like you are doing really well with the black max. They can be great props on boats like this and hard to improve on when they are just right for the boat. Although i have a small suspicion that if you tried a laser 2 19” and a little extra trim they usually allow...you might see 40 gps and equal or better hole shot to the black max.

I am running an old style Laser II, square vent ports, 20P, name and pitch clearly stamped on side of the tube.

 

[QBhoy]

I am running an old style Laser II, square vent ports, 20P, name and pitch clearly stamped on side of the tube.

Ah. What you have that running on. I was almost certain that especially the older ones, were always odd pitch numbers for big gearcases and outdrives. The even were smaller gearcase and never outdrives.