Need Help From You Guys That Have Prop Efficiency Calculators

[harringtondav]

I just test drove and picked up my new boat. No complaints, but I was surprised to see a 14.3X21 P prop on a VP 4.3 250 hp with 1.97:1 reduction. (250 hp was a bonus. The boat was ordered with a 240 hp).
This is dash tach and speedo data:
5800 rpm. 56 mph.
Boat weighed +-3000# at a CAT scale.
Two passengers <325#. Little gear on board.
Apparently the engine is speed limited at 5800 rpm. Throttle response on plane was impressive. Near instant speed increase with a touch of throttle.
I need a spare prop, and I think I could pitch up a bit. I'm used to Merc's 4700-4800 rpm limit, so I'm tempted to pull this boat's WOT down some. The speedo maxes at 60 mph, and I'm not looking for more speed, just less rpm if it doesn't degrade low end performance too much.
Suggestions, thoughts?

 

[gbeltran]

Mercury Racing has an app that calculates slip. According to it you have about 4.3% prop slip, not too bad actually. Yes you can probably go with 23, or if you have a 3 blade consider a 4. Whatever you choose, you do want to keep the engine in the recommended wide open throttle rpm range.......

 

[QBhoy]

I think you probably couldn’t or shouldn’t enter and count on any data taken from the dash gauges, when when entering data into a prop slip calculator, for the purposes of doing so, with the intent of getting a prop for the boat. 4 or 5% prop slip isn’t an impossible result, but it would need to come from a boat with a serious performance hull, stepped and with a pad, usually. Whilst almost totally aired out sitting up on the pad and an inch or two of hull and outdrive in the water only. If this is the case…you have it propped as good as things get on a boat like this. Brilliant. See if you can get GPS speed and if possible, at least. My dash speedo will show over 70 mph at anything over 60 mph gps real speed…but it’s never seen more than 67 gps in its life. And usually she’s less than that most days.

 

[harringtondav]

I'll download a GPS app for my phone and get more accurate data.
I was beating around the bush a bit. I'm thinking the boat/prop is geared a bit low for the power. My son and his tubing, wake boarding buds will love it as is. ...I think I could yank the Cypress Gardens pyramid team out of the water.
But for mid range cruising @ 35-40 mph the engine revs are much higher than with my old Merc 4.3 LX 180 hp 1.81 Alpha II. Power/weight is 15% higher with the new Regal and VP package.
I always carry a spare wheel, so I'll likely buy a 23P. If it's a dud, it will be a spare forever. If not, it will be wife's and my prop, and the kid gets the 21P.

 

[Scott Danforth]

Different motor technology than the lump you are used to. Its propped right. You need that motor spinning 5600-5800

 

[QBhoy]

I'll download a GPS app for my phone and get more accurate data.
I was beating around the bush a bit. I'm thinking the boat/prop is geared a bit low for the power. My son and his tubing, wake boarding buds will love it as is. ...I think I could yank the Cypress Gardens pyramid team out of the water.
But for mid range cruising @ 35-40 mph the engine revs are much higher than with my old Merc 4.3 LX 180 hp 1.81 Alpha II. Power/weight is 15% higher with the new Regal and VP package.
I always carry a spare wheel, so I'll likely buy a 23P. If it's a dud, it will be a spare forever. If not, it will be wife's and my prop, and the kid gets the 21P.

Good stuff. Yeah…you’ve got a lot more rpms with that newer type engine sure.

 

[tpenfield]

The 'new' engines have the variable valve timing, etc. which allows them to rev higher and still have mild/little valve overlap at idle speeds. So, you can get a lot more out of few cubic inches, as Scott indicated.

That boat is light (what brand/model? . . . I might have missed a prior discussion). If you want, you could try a 20 P 4-blade . . .

 

[harringtondav]

2022 Regal 1900ESX. VP 4.3 250 hp. SX-D drive.
I ordered the 240 hp VP, but it came with 250 hp. Apparently VP dropped the 240 hp. No price increase. Lucky me. The dealer whined a bit since Regal passed the increase to his invoice.
It is a GM 4.3. Its nice. Direct injection plus the features you mention. I went with VP since the offered Merc 4.5 wasn't available with closed/freshwater cooling and the VP is. And the VP had a 240 hp option, 40 hp more than the Merc. Also the VP is non-Cat. One less future maintenance headache.

 

[Scott Danforth]

its the same motor for 240 or 250 or if they sell it at 280hp, you just pay a bit more toward the warranty fund.

 

[Nashville]

Also the VP is non-Cat.

Non-Cat? If I recall correctly, Cats were a 49 state EPA mandate < 500 HP January 1, 2010 and after. California did the same around 2008.

 

[harringtondav]

Truly, really. I couldn't believe it was available, but it was/is. See attachment.
Go to Regal's site and design a 2000ES. ...Regal discontinued my 1900ES.
VP California only engines are designated as CAT, the rest are not. Note that both the Merc 4.5s are CAT. My best guess is the VP GM 4.3 with direct (into the combustion chamber) injection, variable valve timing on both intake and exhaust, closed pressurized cooling at near automotive coolant temps is a clean enough engine for most US states.
...I don't know much about the Merc 4.5, but I don't think it has the features above.

 

[Scott Danforth]

Higher temps mean lower NOx

 

[Nashville]

Truly, really. I couldn't believe it was available, but it was/is. See attachment.
Go to Regal's site and design a 2000ES. ...Regal discontinued my 1900ES.
VP California only engines are designated as CAT, the rest are not. Note that both the Merc 4.5s are CAT. My best guess is the VP GM 4.3 with direct (into the combustion chamber) injection, variable valve timing on both intake and exhaust, closed pressurized cooling at near automotive coolant temps is a clean enough engine for most US states.
...I don't know much about the Merc 4.5, but I don't think it has the features above.
View attachment 349045

Thank you. I’ll be darn. For kicks and giggles I read through VP’s TDS for this motor and noticed a footnote on Page No. 1 re. EPA… “Approved for limited use”. I then attempted a read through the EPA rule that brought us these catalyzed wonders of over complexity now plying the waters. While there’s not enough beer to get through the fine print, and I didn’t drink nearly enough going from page to page, it looks like an OEM can sell up to 0.5% of its average annual production non-catalyzed. You are a fortunate man Sir… 10 more HP, and no Cats. Priceless. You do have a pair of O2 sensors riding with you though.

 

[harringtondav]

Update.
I loaded a GPS speedo app and bought a 23P Solas 3 blade alum prop.
Results have me a bit perplexed. The 23P prop predictably pulled WOT rpm down to 5300 rpm from 5800 with the OEM 21P. WOT GPS speed essentially a wash at 50-51 mph. Slip also about the same around 17+%. Hole shots to plane were essentially the same and awesome.
So...looks like I have a 50 mph boat, which is OK with me. I'm more interested in mid range efficiency, and 17% slip WOT doesn't seem all that efficient.
I'm looking for recommendations. I can afford another prop. @QBhoy mentioned in a similar thread a 4 blade prop was the only way to reduce slip. 14.2X21 4 blade is my only option here. ...any others?

 

[Texasmark]

2022 Regal 1900ESX. VP 4.3 250 hp. SX-D drive.
I ordered the 240 hp VP, but it came with 250 hp. Apparently VP dropped the 240 hp. No price increase. Lucky me. The dealer whined a bit since Regal passed the increase to his invoice.
It is a GM 4.3. Its nice. Direct injection plus the features you mention. I went with VP since the offered Merc 4.5 wasn't available with closed/freshwater cooling and the VP is. And the VP had a 240 hp option, 40 hp more than the Merc. Also the VP is non-Cat. One less future maintenance headache.

Go-Fast.com > Knowledge base > Find your prop slip > Prop slip calculator

This is a shot of a 2:1 gear ratio running a 14P prop at 5500 RPMs. The first result is the speed obtained if the prop were like a screw turning in a piece of wood. The last result is due to water not being a solid and is the GPS derived boat speed. The number between these is the prop slip. On fast boats this number will be in the single digit range. As the boat requires more draft when on plane the number will rise....an I/O with a heavy load and high dead rise of the hull at the transom will run 18% or more for a number.

Plug in your numbers starting with gear ratio, omitting the :1 part and move across the chart to max speed. Then jump to the last block and plug in your actual measured speed click on the slip box for your answer.

You can work around the equation by removing data in a box and punching that heading...like when you are trying to solve for another prop. You have to guess at your slip but this will give you some idea as to where you want to go.......beats WAGs!

 

[QBhoy]

Update.
I loaded a GPS speedo app and bought a 23P Solas 3 blade alum prop.
Results have me a bit perplexed. The 23P prop predictably pulled WOT rpm down to 5300 rpm from 5800 with the OEM 21P. WOT GPS speed essentially a wash at 50-51 mph. Slip also about the same around 17+%. Hole shots to plane were essentially the same and awesome.
So...looks like I have a 50 mph boat, which is OK with me. I'm more interested in mid range efficiency, and 17% slip WOT doesn't seem all that efficient.
I'm looking for recommendations. I can afford another prop. @QBhoy mentioned in a similar thread a 4 blade prop was the only way to reduce slip. 14.2X21 4 blade is my only option here. ...any others?

I probably said it’s the only way to increase slip

 

[harringtondav]

Go-Fast.com > Knowledge base > Find your prop slip > Prop slip calculator

This is a shot of a 2:1 gear ratio running a 14P prop at 5500 RPMs. The first result is the speed obtained if the prop were like a screw turning in a piece of wood. The last result is due to water not being a solid and is the GPS derived boat speed. The number between these is the prop slip. On fast boats this number will be in the single digit range. As the boat requires more draft when on plane the number will rise....an I/O with a heavy load and high dead rise of the hull at the transom will run 18% or more for a number.

Plug in your numbers starting with gear ratio, omitting the :1 part and move across the chart to max speed. Then jump to the last block and plug in your actual measured speed click on the slip box for your answer.

You can work around the equation by removing data in a box and punching that heading...like when you are trying to solve for another prop. You have to guess at your slip but this will give you some idea as to where you want to go.......beats WAGs!

Thanks. ...same 17% slip the Merc racing calculator gave me.
My question is how do I reduce the slip % which is essentially the same with 21 and 23P three blade alum props.

 

[dingbat]

Thanks. ...same 17% slip the Merc racing calculator gave me.
My question is how do I reduce the slip % which is essentially the same with 21 and 23P three blade alum props.

Increase diameter, cup or introduce a new prop design.
Going from a SS 14.25 x 17 - 4 blade to a SS 15 x 15 - 3 blade (Inertia) did the trick for me.

 

[harringtondav]

Increase diameter, cup or introduce a new prop design.
Going from a SS 14.25 x 17 - 4 blade to a SS 15 x 15 - 3 blade (Inertia) did the trick for me.

Thanks. Your success story and other's show the counterintuitive can work.

 

[QBhoy]

Thanks. ...same 17% slip the Merc racing calculator gave me.
My question is how do I reduce the slip % which is essentially the same with 21 and 23P three blade alum props.

You go stainless and quality. Like a tempest plus 3 blade or an enertia 3 blade.