Prop Selection - Bayliner 175

[Scott06]

@Scott Danforth What prop brand/model did you run on your 15P 3 blade? All I can seem to find in a 14-1/2" diameter 15P 3 blade (and 4-3/4" gearcase) are some older Vengeance/Silverado SS props. I was hoping to find some aluminum props (due to lower cost, but also making the prop the sacrificial component on debris strikes) in this dimension, but can't seem to locate. Separately, I decided to order the reasonably priced 14-1/2" 19P 3 blade Black Diamond that I linked on post #27; which I'm guessing will be my "unloaded/high speed prop".

michigan vortex has them in 15"

Michigan Vortex 3-Blade Prop, Exchangeable Hub / Aluminum, 15.25 dia x 15, RH

Vortex is a high performance aluminum propeller that utilizes the XHS Xchangeable hub system.

www.overtons.com

here is a merc black max

Mercury Black Max 15.25x 15P Propeller 48-78116CP1

Shop Wholesale Marine for Mercury Black Max 15.25x 15P Propeller 48-78116CP1. Wholesale Marine offers one of the largest selection of boat propellers at low prices and same day shipping.

www.wholesalemarine.com

 

[gsbarry]

michigan vortex has them in 15"

Michigan Vortex 3-Blade Prop, Exchangeable Hub / Aluminum, 15.25 dia x 15, RH

Vortex is a high performance aluminum propeller that utilizes the XHS Xchangeable hub system.

www.overtons.com

here is a merc black max

Mercury Black Max 15.25x 15P Propeller 48-78116CP1

Shop Wholesale Marine for Mercury Black Max 15.25x 15P Propeller 48-78116CP1. Wholesale Marine offers one of the largest selection of boat propellers at low prices and same day shipping.

www.wholesalemarine.com

So these two props are 15-1/4" diameter. Does 15-1/4" fit an Alpha 1 (to clear the cavitation plate that is)? If it does fit, would that diameter perhaps be too large for the 3.0L to turn efficiently?

 

[Stinnett21]

Yes it will fit an alpha. Actually the Enertia ECO will even fit an alpha with a 16" diameter, hardly no room to spare but will fit. Not recommending it just making an analogy

 

[Stinnett21]

Have you checked out the Mercury Prop Selector online. Might get you close. Turning Point also has one.

 

[Scott06]

So these two props are 15-1/4" diameter. Does 15-1/4" fit an Alpha 1 (to clear the cavitation plate that is)? If it does fit, would that diameter perhaps be too large for the 3.0L to turn efficiently?

yes usually as you go down in pitch diameter tends to go up. None of these aluminum props are going to have so much bite that they will not turn, worry about that when you go with the higher end SS props.

check out mercs prop selector will make some general recommendations

 

[gsbarry]

@gsbarry if you look long enough no matter what anyone tells you there is somewhere else which will provide a different set of facts or opinion. Your posting above is true but also need to know where it was taken from. The question of where is need to determine how it was presented.

Saying a 4B provides better hole shot and better handling at slow speeds "IF" (note the if) your talking about a light boat with sufficient power. Your boat as 1 of the 2 items mentioned. It is a light boat but does not have sufficient power.

It is correct a 4B has more surface area and therefore has less slip. Slip is good and bad. Good so every turn of the prop bits in hard and moves the boat forward (with sufficient power) more efficiently. Bad because a motor needs to get the rpm's spun up fast to get into the torque band. So 4B does not allow the rpm's to come up fast.

The 3B has less area and has more slip. Good is with more slip the prop spins faster sooner and gets the motor into the torque band. Bad is more slip

So the rule of thumb due to differences in surface area, a 4B pitch equals a 3B with 2 inches of pitch added.

On a light boat a 4B will also provide more stern lift. Lift can be good and bad, and all depends on the boat

Last thing keep reading and find areas where folks here have provided input. Go elsewhere and read those things. When done decide which one you want to go with and try it. Only ask when done is make sure to come back and let us know what you did so the answers will be here for the next guy looking

Good luck

So when I get my 19P black diamond tested out, i should have a much better baseline to start from. That being said, as I do further prop testing, given the power limitations of the 3.0L, does it make sense that I should be targeting the higher end of the slip range? Like something closer to 20%? Or is that the wrong way to think about it? Should it just be more seat of the pants feel as to whether i like the performance or not? I played around with the Merc prop selector, but it seems like i need to have a better baseline for it to be of any value. It either won't give a result if the parameters are too suboptimal (like the prior owner prop I have on there), or if you put in more optimal parameters, it sort of just seems to mimic what you have already. I found the slip calculator pretty interesting.

 

[alldodge]

Slip is determined by design of prop, type of boat and hull. It's part of the calculation not something to shoot for

This is Bblades calculator which can determine all numbers just by entering the ones missing and it will calculate the one missing. Don't work trying to change slip, it's an outcome of a given prop
https://bblades.com/propeller-slip-calculator/

 

[Scott Danforth]

The 19p was a Solas stainless. The 17p was an unknown stainless that was reworked at Green Bay propeller

The 15p was a Michigan

 

[Scott06]

Slip is determined by design of prop, type of boat and hull. It's part of the calculation not something to shoot for

This is Bblades calculator which can determine all numbers just by entering the ones missing and it will calculate the one missing. Don't work trying to change slip, it's an outcome of a given prop
https://bblades.com/propeller-slip-calculator/

100% he will have enough slip with any of these aluminum props that if pitch is right he will get the holeshot he is looking for.

my 23” spitfire AL 4 blade has almost identical wot rpm as my 21” Revolution 4 …

 

[cyclops222]

High percentages of slip WASTE engine H P !!!!
You want 5 to under 10 % SLIP.
100 % slip means at WOT in forward gear. The boat would not move.

 

[Pmt133]

Honestly slip is the last thing I look at. If it's performing the way it should be, the numbers fall where they fall. Anything under 25% is fine and anything under 10% is exceptional. If all other performance parameters are where they need to be but slip is 17% that's fine. Same if it's 8%. Now if I lose 5mph somewhere that's a different story.

I'll also say a prop with really low slip (bites hard) is going to be a dog on a 3.0l. This was covered earlier. And I've dealt with it on my 3.0l boat.

 

[jlh3rd]

I would strongly don't start going down yet another rabbit hole, the thread has gone from not enough advance to all kinds of other areas

There is to much compression but that so far has not shown it's the problem, just noting of a possible issue.

Suggest; go back to the prop first and change it and see how it preforms. Then advance timing by 2 to no more then 4* to see what changes

Document the results and then if needed lets start chasing other areas

lol...and this isn't a rabbit hole?
Who started the compression topic "rabbit hole "
Don't highlight my post and gaslight it as a rabbit hole.
My comments are to the OP , not you. He can take it or leave it. His time, his money, his boat.
Just because you're a moderator doesn't give you insult rights.

 

[jlh3rd]

this is excellent advice !

same to you

 

[Lpgc]

Is prop slip similar to torque convertor slip and stall speed?

Hypothetical boat tied to a dock so it can't move, the faster the prop spins the more slip but also tries to push the boat with more force.

There is obviously some slip relative to boat speed or the boat would need a clutch or torque convertor or it would stall when put into gear... But that doesn't mean that if it's 17" pitch and spins twice per second at idle rpm when we drop it into gear it isn't pushing 34" of water per second?

How would a graph of boat speed versus prop speed look?

How would a graph of prop speed versus speed it pushes water look?

 

[Pmt133]

I guess slip kind of can be approximated as a torque converter but also not... on take off it lets the prop spin up until it bites and picks up speed so kind of. But once you're moving it's just a measure of lost forward movement compared to how much it should move for a given revolution. Problem is you'll get a different slip number for every 19 pitch prop with a different geometry.

Calculations based on pitch alone are okay at best but without knowing the actual blade profile and what it truly would move in 1 revolution... its just one tool we have to compare performance. I ran a 17p and a 19p prop on my boat when it was still a 3.0l. The 17p spun about 50 rpm higher at wide open. If I recall correctly at every speed the slip numbers were more or less identical. Boat was slower everywhere though. Seeing wot slips of around 10% would indicate either prop is correct. But the 19 was the better choice as it ran faster for the same WOT rpm (and other RPM) everywhere. That's why I use it more as the last check than anything.

Ultimately, performance is performance and everything will fall into place depending on application. There is not a once size fits all situation.

 

[gsbarry]

Honestly slip is the last thing I look at. If it's performing the way it should be, the numbers fall where they fall. Anything under 25% is fine and anything under 10% is exceptional. If all other performance parameters are where they need to be but slip is 17% that's fine. Same if it's 8%. Now if I lose 5mph somewhere that's a different story.

I'll also say a prop with really low slip (bites hard) is going to be a dog on a 3.0l. This was covered earlier. And I've dealt with it on my 3.0l boat.

That last part about the 3.0 is where my mind was going. I guess by sticking with 3 blades I should just expect slip numbers on the higher end and be satisfied with that given the motor. Not necessarily a target, but to be mindful that I won’t find a “magic” prop that performs well acceleration/torque wise AND has low slip, given the low power.

 

[cyclops222]

Just remember how important SLIP is.
A 400 hp motor with a 25% slip efficiency prop.
Will lose a race to a 350 hp motor.
And burn a lot more fuel every trip.

 

[alldodge]

Just remember how important SLIP is.
A 400 hp motor with a 25% slip efficiency prop.
Will lose a race to a 350 hp motor.
And burn a lot more fuel every trip.

Not true

 

[alldodge]

Just because you're a moderator doesn't give you insult rights.

Insult , hummm

 

[jimmbo]

I reread the Thread, I didn't see anything Insulting...