Alu to SS - Ventilation issue ?? or Design feature ??

[Canufixit2]

Hi. I'll try to be short and specific ... I have a 18' pontoon with a 2018 60hp 4S Mercury with Command Thrust. I WAS running a Quick Silver Black Diamond Propeller Black Finish, 14 dia x 11 pitch, Right Hand Ran well with Max RPM at about 5800 and I was happy with this prop - although the Max WOT Rpm was a tad low.

I ran across an Ebay real bargain - a new SS VENGEANCE (14 X 10") MERCURY RH PROPELLER, 48-17310A46.

It Installed OK using a new Quicksilver 835257Q9 Flo-Torq III Hub Kit. Now New MAx RPM WOT at 6000.And, I like the New SS prop for smoothness, esp at idle, etc.

One issue, On full stop with WOT acceleration (hole shot?) I believe I'm getting some Ventilation for approx 5 seconds. Rpm seems to accelerate faster than my old Alu prop - and seems to spin up faster (rpm) and then "Bite" and take off. Engine is full down/in. Propeller does NOT have PVS (Propellor Vent system/holes).

Is this Normal? As this did not happen with the Alu Prop. Comment ? Suggestions ??? OK to use as is ???

 

[ahicks]

Have never had one do this to me, but if I was assured the venting would stop after 5 seconds every time, I'd be OK with that - as long as it didn't do it in a sharp turn as well. At that point it might be time to lower the motor.

That said, I think 4 strokes sound too busy when run at max rpm. Personal call maybe, but I've found that unless you really need max pulling power for towing duties, running the engine down about 500 rpm from max let's them produce about same speed/amount of power, without sounding nearly as busy. FWIW

 

[Canufixit2]

Hi, Thanks for the insight. As I never had this issue with the old alu prop - and no issue on tight turns, I believe the engine is deep enough in the water. I will try a tight turn with the SS Prop, but I'm not expecting an issue. I Think the Engine is powering up so fast, with the thinner SS Blades, that it's sucking in exhaust gasses at whole shot/Full power start..

SS Prop seemed to have better exhaust porting (larger) through the prop for through prop exhaust - adding to the ability for the PRop to suck in some exhaust in full power rev up. ??

As you probably know, Mercury has the "PVS" (prop venting system /holes) available in higher end props to add exhaust into the prop blade area to actually cause some ventilation and allow RPM to greatly increase - until the prop/boat speed increases to a point that the vent holes are no longer able to port gasses. At that point the prop "Bites" and engages the water at a higher RPM allowing higher torque and easier bow down. Ref Below.

So, I'm thinking some ventilation is OK as Mercury actually uses this in some designs (My SS prop doe NOT have the PVS holes. Just not sure why it's happening on my application/prop ??

https://e-ribbing.com/en/propellers/491-propeller-s-performance-vent-system-pvs-en.html

 

[Scott Danforth]

lower your motor a half an inch, or push the cooler aft about a foot.

 

[Canufixit2]

Thanks, I'm going to check for ventilation on tight turns at normal "trimmed out" motor position and full in /down position, also I will visually for position of cavitation plate wrt water levels at rest and on plane. However, as my aluminum Prop which is almost exactly the same as a my SS (Thinner blades and 1" pitch difference) I don't think it is related to motor height... I'll advise.

 

[Canufixit2]

I have also sent this question to Mercury Marine.... I'll advise response, but any input is much welcomed !!

 

[dingbat]

One issue, On full stop with WOT acceleration (hole shot?) I believe I'm getting some Ventilation for approx 5 seconds. Rpm seems to accelerate faster than my old Alu prop - and seems to spin up faster (rpm) and then "Bite" and take off. Engine is full down/in. Propeller does NOT have PVS (Propellor Vent system/holes).

Is this Normal? As this did not happen with the Alu Prop. Comment ? Suggestions ??? OK to use as is ???

Perfectly normal operation.

You dropped down an 1" in pitch which reduced the surface area (bite) of the prop. The low end torque is "over loading" the prop, for lack of a better word, causing it to slip until the HP required to move boat at a given speed falls below the slip threshold of the prop.

 

[Canufixit2]

Hi Ding Bat, Thanks.
So, If the prop is slipping, Is the Prop in cavitation or Venting by grabbing exhaust gases and encasing the blades causing the ventilation?
I ask as, I understand this, Cavitation effects from water to vapor and back again causes shock mechanical effects along with erosion of the Prop surfaces. Or in other words, Cavitation in bad and should be avoided, where ventilation slippages is OK and even designed into some high end props through the PVS holes.

I'm thinking if it's cavitation I should change the SS prop to next larger pitch. If it's ventilation, it's fine ... Opinion?? Thanks Much - and YOU AND EVERYONE Be SAFE OUT THERE !!!

 

[dingbat]

Hi Ding Bat, Thanks.
So, If the prop is slipping, Is the Prop in cavitation or Venting by grabbing exhaust gases and encasing the blades causing the ventilation?

I'm thinking if it's cavitation I should change the SS prop to next larger pitch. If it's ventilation, it's fine ... Opinion?? Thanks Much - and YOU AND EVERYONE Be SAFE OUT THERE !!!

It's not cavitation. Your simply overpowering the prop. More torque than the "bite" of prop can transfer. Spinning the tires in a car analogy.

Personally, I would go back up in the pitch.

 

[Canufixit2]

Thanks All .... Mercury response as follows .....

Good Afternoon xxx,

Thank you for your e-mail regarding your Mercury engine, serial # 99999999. We appreciate the opportunity to respond to your concerns.

What you are describing sounds normal when comparing a 3 blade to a 4 blade propeller. Once the propeller bites, your performance is improved but it takes a bit more to get the bite because it is less surface area to water contact. Perfectly fine to use it as it is.

We hope this information is helpful to you. Should you have any further questions or concerns, please contact our Customer Service department

Sincerely,

Mercury Outboard Customer Assistance

 

[QBhoy]

Hi. In my opinion...this is a simple one. The vengeance is just pure and simple....a crappy prop. It’s just a heavier and shiny version of the same cut, as a black max...except...the black max is better any time I’ve known them compared. Never known a vengeance to put perform the same pitch standard ally prop. Total gimmick of a prop. I think mercury should actually recall them all and melt them down into something useful ! Just my thought. If anyone out there has some real data to say otherwise...I’d be amazed.

 

[QBhoy]

Ps...another reason to get rid of the vengeance, would be that as far as I know...you will be on the limiter at around 6000 rpm. I’d think you want to be a little under for all round best results. All the best.

 

[Canufixit2]

Thanks, Could just be the Prop as you say .... Also, The RPM I listed is per my Tach. Checks with Vessel view shownit to be about 1 to 2 grand higher than actual ....

 

[Stinnett21]

Here's my Vengeance input. 2002 Bryant 214 open bow, 5.0 MPI, Alpha 2, Quicksilver Silverado (Vengeance equivalent) 14x19:
3000 rpm 16% slip
4000 rpm 12% sllp
5100 rpm (WOT) 52 mph (GPS) 8% slip.
I'm very happy with it although I've never compared to anything else. Just hard to convince the family to spend $700 on a good Mercury prop on an already good running boat. Mercs prop selector suggests an Enertia ECO 16" pitch. That would be leaving only 1/4 inch from touching the bottom of the vent plate on the Alpha 2. Ugh not sure about that.

 

[dingbat]

Here's my Vengeance input. 2002 Bryant 214 open bow, 5.0 MPI, Alpha 2, Quicksilver Silverado (Vengeance equivalent) 14x19:
3000 rpm 16% slip
4000 rpm 12% sllp
5100 rpm (WOT) 52 mph (GPS) 8% slip.
I'm very happy with it although I've never compared to anything else. Just hard to convince the family to spend $700 on a good Mercury prop on an already good running boat. Mercs prop selector suggests an Enertia ECO 16" pitch.

Those slip figures are pretty high. Throwing 13 to 16% of your fuel burn out the window.

I’m in the 5-8% range with the Enertia pushing a heavier boat.

After 30+ years of marriage, it is far easier to ask For forgiveness than permission.

 

[Stinnett21]

Please note the 12 to 16 slips weren't at WOT. I'm in your range at WOT with the Vengeance. And yes I like your marriage advice lol.

 

[dingbat]

Please note the 12 to 16 slips weren't at WOT.

Don't know about you, but I don't care how much slip I have at WOT. I can count the number of minutes I run WOT in a season on a couple of fingers.

I'm concerned about slip at cruise (4200 - 4500 rpm) where I spend the majority of my time. At those rpm I'm running at 5-6% slip.

What is your cruise RPM?

 

[Stinnett21]

Seems like whenever slip is discussed it's measured at WOT. I cruise just on plane which is generally, depending on load of course, around 2800-3000. Not after speed. Just love to cruise.

 

[dingbat]

Seems like whenever slip is discussed it's measured at WOT. I cruise just on plane which is generally, depending on load of course, around 2800-3000. Not after speed. Just love to cruise.

You see WOT slip quoted because its the easiest data to collect and interpret.

Slip is the inefficiency of a prop to convert engine torque into thrust at a given horsepower or rpm that manifests itself as the difference between theoretical prop speed and actual speed.

Done right, you should take figures from the entire RPM range and plot them as a slip curve. From there, you can compare different props to see which prop is most efficient at the speeds you normally run your boat.

https://www.mercuryracing.com/prop-school-part-6-slip/

 

[QBhoy]

Here's my Vengeance input. 2002 Bryant 214 open bow, 5.0 MPI, Alpha 2, Quicksilver Silverado (Vengeance equivalent) 14x19:
3000 rpm 16% slip
4000 rpm 12% sllp
5100 rpm (WOT) 52 mph (GPS) 8% slip.
I'm very happy with it although I've never compared to anything else. Just hard to convince the family to spend $700 on a good Mercury prop on an already good running boat. Mercs prop selector suggests an Enertia ECO 16" pitch. That would be leaving only 1/4 inch from touching the bottom of the vent plate on the Alpha 2. Ugh not sure about that.

That’s great going to be fair. Especially for a vengeance. Not convinced that an enertia eco would be much good on your boat...but certainly convinced that if you are seeing those figures with a vengeance...just think how good it would be with a tempest plus or the normal fast version of the enertia. I have my fast boat down to about 3% slip with the enertia. Yet to try the tempest.