Prop Experience For An 18' With 150 4S

[Kyhl]

Hi,

I've tried out a couple props on a repowered 18' Tourney Sport and am looking for suggestions on where to go next, before going the Jay modified route.

What are other's experiences?

First try was a 19" Vengeance.

Pro's

Ran great.

Had 300rpm's to spare before maxing.

Good hole shot.

Enough bow lift.

Con's

Blew out easy on acceleration and cornering.

Long looping corners with it trimmed down and backed off to 3,500 rpm and it would make the boat shudder as it slipped then grabbed. Higher than that (speed or trim) and it would just blow out.

Blew out easy when accelerating from cruise to WOT.

Second try, Enertia 18".

Pro's

Better grip on acceleration and turning.

Still 300rpm from redline.

Con's

Lost 2mph.

More bow lift than I need.

I already talked to Jay and his suggestion to modify a Vengeance 17" but once that happens I'm stuck with it. Any suggestions on where to go next before I modify one?

[hydro]

Blow out is usually a function of the prop design combined with motor height and trim angle, so I bet a 17" Vengeance prop will still show blow out issues. To really diagnose prop setup you need to post the recorded motor RPM's and a GPS speed, then the observations of performance and handling. The comment on "300 RPM to redline" for both a 19" and 18" prop sounds like a measurement issue as you should see a couple hundred RPM difference with that pitch change.

What brand of motor? what is the recommended WOT RPM range? What RPM is it turning at WOT? What was the top recorded speed for each prop? Give this info and it should help you to get some better answers.

[Kyhl]

It's a Merc 150 4S.

Max rpm is 5,800.

The 19" Vengeance ran 5,500rpm @ 48mph (gps). Using an online calculator that equals 6.8% slip. That would be perfect if it had better grip.

The 18" Enertia ran 5,550rpm @ 46mph. Calculated to a 6.6% slip. From what I gathered out of the Merc site and some research, the Enertia was supposed to give better grip and bow lift. It did.

I expected more rpm out of the 18" Enertia with similar top speed as the Vengeance but it didn't happen. Also don't need the extra bow lift of this model but if it fixed the grip issue I could live with it.

Using the slip efficiency of 6.6% at 5,750 on a 17" Enertia should drop down to 45mph.

Jay suggested modding a 17" Vengeance for better grip while keeping the rpms down. I want this to be the last resort option because I won't be able to try another option after a mod. It probably will work but....

Based on the Enertia results, I don't see trying different options in that line.

Thought I'd post here for input before taking a shot in the dark on another model and size combo.

Does anyone know of at discription of the design goals of each of the Quicksilver props? Looking at the Merc page they don't really give much of a discription of the differences between each model. Or maybe I'm not understanding what they are trying to say.

Basically, is there an alternative that is similar to the Vengeance line with better grip without adding bow lift?

[hydro]

It sounds like the Enertia prop did fairly well for you in your testing. How did you like the hole shot, overall handling, and the way the boat rode? Top speed is not everything. Running at 5500 RPM is right in the middle of the the I-4 Four Stroke 150 recommended operating range according top Mercury's HSOforum.

Check their Propeller Calculator for more info on the design of the props you have tested.

[BobT]

I wonder if you really can use the W.O.T. rpm as a gauge for determining the correct prop. I have a 2011 90hp Etec and my engine tops out at exactly 5,500rpm, which coincidentally is the maximum rated rpm of the engine. It does this no matter if I have one or more passengers. I'm beginning to think that the computer is programmed to limit W.O.T. to 5,500rpm maximum regardless.

Anyone know if I'm correct about that?

[fishnowworknever]

I wonder if you really can use the W.O.T. rpm as a gauge for determining the correct prop. I have a 2011 90hp Etec and my engine tops out at exactly 5,500rpm, which coincidentally is the maximum rated rpm of the engine. It does this no matter if I have one or more passengers. I'm beginning to think that the computer is programmed to limit W.O.T. to 5,500rpm maximum regardless.

Anyone know if I'm correct about that?

I can't tell you that for sure...But what happens if you trim up too high and begin to cavitate? Does it over-rev?

[Kyhl]

The Enertia hole shot was fine, so was the Vengeance.

The Enertia had too much bow lift. My bow already rides high on this boat. Raising it more makes it difficult to see, especially when running at cruising speed 36-40mph. Opening it up levels it out some but the option would be to trim down to counter act the prop rise when cruising. That seems counter productive to the fuel economy of cruising.

Does someone know where to find the bow lift comparisons between the different models. If the Vengeance had the right amount of lift while sacraficing grip, and the Enertia had too much lift with the right amount of grip are there other models that fall between these two? Are they outside these two?

It would be nice to see a comparison of the amount of lift at least, grip would be nice too, between the different models. What I know is that the Enertia has more lift and grip than the Vengeance.

Here is Merc's descriptions by model. Can someone translate? Based on this, maybe the Rev4 or Mirage Plus might be the next option to try. I don't know.

Is "Strong bow lift" less than "Higher rake"? Is "High rake" less than "Higher rake"? If so, maybe the Tempest is the next one to try.

Vengeance General purpose line

Enertia Higher rake

VenSura Strong bow lift

Trophy Plus Increadible bow lift, holds better than a three blade in turns

Mirage Plus Large diameter high output blade geometry

Laser II High rake

Tempest plus High rake and bigger cup

Revolution 4 Cousin to the Tempest but with better holeshot and mid-range over the Mirage

[BobT]

Never been able to over-rev it no matter how high I trim it up. I've never seen it above 5,500. This is why I suspect the computer is programmed to protect the motor from excessive rpm.

[delcecchi]

I have never been able to figure out the "bow lift" thing. does that have to do with trim?

[Kyhl]

My understanding is adding rake, aka, leaning the blades back without changing pitch, assists in raising the bow.

So given rake relates to bow height, does "higher" in their marketing speak mean more than "high"?

And where does "incredible" and "strong" fit between "high" and "higher"?

I don't know.

Sounds like cupping should add grip. The more I think about it, the more I'm leaning toward Jay's suggestion, after trying the Tempest? It's a crapshoot.

[delcecchi]

OK, rake "raises the bow". I am just trying to visualize the forces. Seems to me that no matter how the prop is raked or cupped the thrust is straight back along the line of the prop shaft. To the extent that the motor is trimmed so the prop shaft is not parallel to the surface of the water when running the bow will go up or down.

I guess I see how the blade design would let you run different amounts of trim before blowing out, or maintain thrust with the prop shaft not parallel to the direction of travel, but that is about all.

Maybe "bow lift" just confuses me. The prop is on the back, can't do anything to the bow. It can push down on the stern.

I bet that is it. With rake on the prop you can maintain the thrust as the direction the prop is pointing is no longer parallel to the direction of travel, so thrust doesn't drop off as the trim angle varies. And to gain that advantage, you give up efficiency at small or zero trim angles.

[Kyhl]

Maybe there is something to that combined with some complaints that the hull on these boats tend to porpoise.

Maybe they don't need a prop with lots of rake and also should not be trimming as high. I don't feel like I need to trim very much.

I really liked the way the Vengeance worked except for grip in corners or accelerating off cruise. Hole shot was great, ride was great with little trim needed, and no porpoising.

To get the most out of the Enertia I had to trim the carp out of it and would end up porpising.

[BoxMN]

Try a tempest, they are great for walleye style boats. We have 19" on our 150efi on alum boat, and my stepson has 19" tempest on his Merc 150 4s and a triton glass boat (Fishhunter). Has lots of bow lift and very very good balance between handling and bow lift and speed. Feels much like a hi-5 in handling, but faster (and has reverse power). Good luck.