Bayliner 175 overrev with 21P?

[severinbb]

Hey all,

I have a 2004 Bayliner 175BR with the 3.0L inline 4 stern drive. I have read *tons* on performance and props, and still haven't answered the perennial question: what is the best prop for my boat?

I've tested 6 props already. We usually ride light but for testing it was just me and 1/2 tank of gas. Conditions have been calm around 60F. All speeds are GPS.

1. Alpha 4, 20P 4-blade. WOT is 5200 at 43 mph.
2. Mirage Plus, 21P. WOT is 4700. Speed unknown.
3. Black Max, 21P. WOT is 5100 at 44 mph.
4. Revolution 4, 19P 4-blade. WOT is 5100 at 45 mph.
5. Laser II, 21P. WOT is 5000 at 47 mph.
6. HighFive, 21P. WOT is 5200 at 44 mph.

Some interesting findings:
- I'm over-revving. Actually I'm guessing my top speed is limited by the engine that doesn't want to rev more (not that I'd try...)
- My hull lifts very straight and level with the Alpha 4 and the Rev 4. I can power up slowly and just rise nicely and plane, surprisingly easily. With these props, there is little difference between planing and "not planing", which is great for slow watersports. With the other props, there is lots of bow lift and the boat has to get itself "over the hill".
- I didn't like the HighFive. I didn't think the holeshot was amazing, I didn't like the significant bow lift, and I didn't like how sensitive it was to trim (a touch too much up or down and it felt like I'd hooked some weeds). Oh, and I didn't lose any speed with it.

What I'm after (in order):
1. Minimal bow lift (it just seems to work against the hull design)
2. Hooked up feeling at speed (no slipping feeling)
3. Good holeshot (for deep water slalom starts)
4. Resistance to ventilation (the Alpha 4 and Mirage Plus ventilated much too easily)

Admittedly I've been riding light, but would adding 2 adults drop my rpm by 500 (or speed by 5 mph)?

Still, I don't want to go to a 23P and lose my low end (holeshot and slow watersports).

So, let's narrow this down to only 2 questions:
1. If you have a mid-2000s Bayliner 175, what prop works well for you? Please describe the performance.
2. Do you know of a prop that just pushes the boat forward with little bow lift? I'm assuming that's what I need (like the Rev 4).

 

[Texasmark]

Re: Bayliner 175 overrev with 21P?

2. Do you know of a prop that just pushes the boat forward with little bow lift? I'm assuming that's what I need (like the Rev 4).

The more conventional looking prop the better served you will be or try trim tabs. A lot of SS props, especially for bass boats are high performance and have a high "rake" which is the blades folded back from where they emanate from the barrel of the prop rather than coming straight out....that is what you want....blades that come straight out.

On the rest of it I can't help you.

 

[steelespike]

Re: Bayliner 175 overrev with 21P?

Numbers don't add up.Is this a Mercruiser?
using a 2.00 gear ratio a 20" at 5200 7% slip (a guess) should produce about 46 mph.Typical speeds with a similar setup usually produced speeds of 40-43 mph.using 4700 rpm the speed becomes 43
I think your tach is reading high and possibly erratic .Check the setting on the back and operate the switch a few times to clean the contacts. You have the 19" 4 blade faster than a 21 at 5100 highly unlikely.
you have the 19 at 45mph my calculations say 42.7 My 7% slip is approximate but your actual isn't likely to be 1 or 2% higher or lowerr.
and won't change the calculated result much anyway.

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

....that is what you want....blades that come straight out.

Hi!

Am I looking for a large diameter blade, then? (Like the Rev 4; not like the HighFive)?

Actually, the Rev 4, which worked well, has lots of rake. But I have a mental block preventing me from using a Rev 4 because it's huge and weighs a ton! I just feel like it's too much prop for my outdrive!

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

Numbers don't add up.Is this a Mercruiser?

Hi!

Yes, it's a Mercruiser with 2.0 gear reduction.

The tach is new, doesn't bounce around, and I've already tried all the other settings on it I'm pretty in-tune with engines and I think it's correct. (Use case: 5000 rpm sounds like the engine is overrevving, while 4800 sounds acceptable.)

The Merc prop slip calculator says that with the 20P (Alpha 4), I have 13% prop slip. I think the normal range is 10-20%? Anyway, with this prop, anything over 35 feels like I'm getting a lot of slippage, so a high prop slip % seems to jibe. Also this prop is aluminum and one blade has a (very) small dent; all the other props were SS and in very good shape.

^^^ This feel of high prop slippage is one thing I'm trying to cure.

I, too, was surprised about the 19P, but it has huge blades and is larger diameter than the others. My Merc dealer, who is very experienced, expected that result. (Prop slip calc says 2%, which is suspicious, eh? It did feel very hooked up, much more so than any of the others. Also it's a 4 blade prop.) Hmm, maybe my boat just likes large diameter props, or lots of rake?

I agree that the numbers seem odd. On the one hand, I'm really overrevving, even with a 21P prop. On the other hand, I should be getting closer to 50 mpg, eh?

Maybe I should first concentrate on the "high prop slippage" feel above 35 mph. Is THIS typical of a mid-2000 Bayliner 175? The two props that felt hooked up at that speed were the Laser II and the Rev 4.

(The OTHER thing I'm trying to cure is the excessive holeshot bow lift.)

SB

 

[Texasmark]

Re: Bayliner 175 overrev with 21P?

Quote: "The two props that felt hooked up at that speed were the Laser II and the Rev 4.

(The OTHER thing I'm trying to cure is the excessive holeshot bow lift.)"

The Laser II is definitely a bow lifting bass boat type prop.....I know I had a Laser I. Don't know about the Rev 4. So, you need to get a plain ole prop as I mentioned.

Mark

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

The Laser II is definitely a bow lifting bass boat type prop.....I know I had a Laser I. Don't know about the Rev 4. So, you need to get a plain ole prop as I mentioned.

Hi Mark,

I hear you and am definitely leaning towards a 'plainer' prop than a 'fancier' prop

However, I'm trying to cure a problem with both basic props I tried (Alpha 4 20P 4-blade and Black Max 21P 3-blade): they felt like they were "slipping" at 35+ mph. (At WOT, both had 13% slip.) This problem also shows up as overrevving with no corresponding speed increase.

I think my hull must aerate the water at 35+ mph, so I should probably get a prop that tolerates this. Thoughts?

Specifically, is there a prop out there that tolerates aerated water and doesn't produce tons of bow lift?

SB

 

[Texasmark]

Re: Bayliner 175 overrev with 21P?

Well, that calls for cupping which helps to solve that problem and I agree with what you said about turbulence in front of the propeller. I think you can get "basic shaped" (non rake) cupped props for I/O's. They sell a lot of prop types on here. Check them out or go to the prop mfgr. customer service and see if they sell what you want.

Mark

 

[steelespike]

Re: Bayliner 175 overrev with 21P?

The speed of this setup surprises me In all the 3.0 I/O posts I've read I dont recall any 3.0 running over 43 mph. not to mention being in the shadopw of 50.While I've seen some flirt with 23" pitch as I recall they weren't pleased with the hole shot.That 175 must be a speedy boat.It doesn't strike ne as being particularly light at 2,000 lbs.dry weight.

 

[45Auto]

Re: Bayliner 175 overrev with 21P?

The Bayliner 175 tested at Boattest.com ran 44.1 MPH at 5300 RPM with a 21" 3 blade aluminum prop. Seems right in line with what the OP is seeing.

 

[steelespike]

Re: Bayliner 175 overrev with 21P?

Unless the calculator I use is screwy thats 16% slip.Same figures at a more normal 7% would be about 49.Never heard of a 3.0 making an honest 50 or so close to it in an 18ft boat. And they are running the boat at 500 rpm more than the 4800 rating.
Same figures using 4800 and 7% = 44.3 I'm using 2.00 gear ratio and my calculator doesn't take into consideration specific hull type.Planing hull is assumed.To this point my calculations have usually been reasonably accurate.Maybe I need to use a different calculator.
Tried two other calculators results are the same.

 

[steelespike]

Re: Bayliner 175 overrev with 21P?

A little more info 20" 4 blade 12% slip,21" mirage =42 mph at 10%,44 @6%,
Blk.max 21 13%,Rev 4 19 2%,lazer 11 21 5%,H5 21 14%.Don't understand the high slip numbers but::
Assuming everything is correct to me the Rev 4 in a 20"is the choice it should
deliver 4800-4900 rpm,a good hole shot with little bow rise,slightly higher top speed and best speed for a given throttle setting(based on the excellent slip numbers).

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

A little more info 20" 4 blade 12% slip,21" mirage =42 mph at 10%,44 @6%, Blk.max 21 13%,Rev 4 19 2%,lazer 11 21 5%,H5 21 14%.Don't understand the high slip numbers but::
Assuming everything is correct to me the Rev 4 in a 20"is the choice it should deliver 4800-4900 rpm,a good hole shot with little bow rise,slightly higher top speed and best speed for a given throttle setting(based on the excellent slip numbers).

Hey, SS, you've done all my homework for me

Yes, it's a planing hull. In fact, there isn't much in/on the water at 45 mph!

Yes, I think the HIGH slip numbers are what I'm feeling (feel of prop slippage; not hooked up).

I don't know about the LOW slip numbers. Are those even possible?

I confirm that the Rev 4 worked really well... I'm just intimidated by its size and weight

Later this week I'm trying a Bravo I and a Tempest Plus (which is the 3-blade cousin to the Rev 4). I'll report back!

 

[steelespike]

Re: Bayliner 175 overrev with 21P?

Slip is the actual movement through the water compared to the theoretical distance it would travel if carved through a solid.ie: A 12" pitch would move 12" forward in one revolution
through a solid but through water it will lose a certain percentage. Depending on the prop and boat.I'm not an expert on slip But I think that 2% would be unusual and possibly suspect but I think 5% is certainly possible and cosidered excellent.A big heavy boat would produce higher slip numbers.
I wouldn't worry about prop weight. It doesn't affect performance and if the motor idles at the correct speed and is shifted crisply without dragging or jaming it in gear wear will be about the same.
Idle too fast and poor shifting procedure can cause excessive wear with any prop.

 

[Texasmark]

Re: Bayliner 175 overrev with 21P?

Slip is the actual movement through the water compared to the theoretical distance it would travel if carved through a solid.ie: A 12" pitch would move 12" forward in one revolution
through a solid but through water it will lose a certain percentage. Depending on the prop and boat.I'm not an expert on slip But I think that 2% would be unusual and possibly suspect but I think 5% is certainly possible and cosidered excellent.A big heavy boat would produce higher slip numbers.
I wouldn't worry about prop weight. It doesn't affect performance and if the motor idles at the correct speed and is shifted crisply without dragging or jaming it in gear wear will be about the same.
Idle too fast and poor shifting procedure can cause excessive wear with any prop.

I run right at 12% on a very light boat with a high performance prop.

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

I run right at 12% on a very light boat with a high performance prop.

Hi!

Out of curiosity, what is your slip at "high cruise" versus WOT?


SB

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

Foreward

I've done more testing and finally selected a prop for my 2004 Bayliner 175. Here are my notes and findings.

Test conditions were generally calm, 50-60F, sea level, with 1-3 adults on board.

What I'm Looking For

• I don't like an over-revving / just-churning-water (slipping) feeling above 35mph. I think this is a combination of prop slip and engine noise vs load.

• I don't like the prop to ventilate easily. My hull seems to aerate the water above 35mph, especially in hard turns.

• I don't like the impression of going over a hill before planing. On my BL175, bow lift seems to be undesirable since it works against the "Advanced Planing System" or "oversized reverse chines as well as planing strakes" with 19 degrees of deadrise (shallow V). This hull comes up on plane very quickly, neutrally and level with the right prop.

• I want decent holeshot (for deep water slalom starts).

• I want to be able to maintain 15mph and 30mph easily.

The Props

• Alpha 4 20P (equivalent to a 21P, they say). Minimal bow lift. Good holeshot. Stern drops when it falls off plane at 14mph. Handles OK at speed except that it ventilates severely on hard turns and incorrect trim. It also feels like it's slipping above 35 mph. WOT is 43mph at 5200rpm.

• Mirage Plus 21P. Minor bow lift. Slow holeshot. Handles well at high speed (35+ mph). Felt like too much prop for the boat and overall felt sluggish. WOT is ~44mph at 4700rpm.

• Black Max 21P. Major bow lift. Good holeshot. Falls off plane at 17mph. Handles well at speed. Resists ventilation. Feels like it's slipping above 35mph. WOT is 44mph at 5100rpm.

• Revolution 4 19P. Good holeshot. No bow lift. Can't tell difference between fast-displacement and slow-plane (10-20mph OK)! Very good feel at speed but due to holding power, rpms drop in hard turns. WOT is 45mph at 5100rpm.

• Laser II 21P. Major bow lift. Slow holeshot. Falls off plane at 17mph. Feels best at high speed (35+). WOT is 47mph at 5000rpm.

• HighFive 21P. Some bow lift. Decent holeshot. Falls off plane at 15mph. Handles OK at speed, but not great. Feels slow if trim isn't perfect. WOT is 44mph at 5200rpm.

• Bravo I 22P. No bow lift. Slow holeshot. Falls off plane at 15mph. Handles OK at speed. Felt like too much prop for the boat and overall felt sluggish. WOT is 44mph at 4650rpm.

• Tempest Plus 21P. Minimal bow lift. OK holeshot. OK at slow plane but best above 14mph. Handles excellent at speed. WOT is 45mph at 4900rpm.

Findings

• All props handled OK at idle in fwd. The HighFive and Bravo I weren't so good in reverse.

• The 4- and 5-blade props were smoother than the 3-blade ones, but there were other, more significant differences to decide between them.

• Some of the 4- and 5-blade props feel more "draggy" above 35mph than the 3-blade ones. I think this is because they actually have more drag (due to more blades cutting through the water).

• The difference between one adult (driver) and 3 adults is 100rpm and a couple of mph.

• The props that were best at high speed were also the worst at holeshot.

• The props that were best at holeshot must be monitored to prevent over-revving the engine!

• The best props for this boat are the ones that have minimal bow lift.

• Some 19P props behave like 21P, while some 21P props behave like 19P. I think this has to do with "holding power" (operation in aerated water).

• A prop that holds well will drag down rpms in hard turns (but they pick up after). I think this is no worse than no rpm drop but still have a speed drop, and it's certainly better then getting major ventilation.

• Performance Venting System (PVS) didn't seem to do much. (The Tempest Plus had plugs with large holes, but it still didn't rev quickly through 1000-3000.)

• There is no perfect prop for this boat -- they are all compromises.

The Short List

Since I'm looking for minimal prop slip, resistance to ventilation, level acceleration to planing, decent holeshot and easy-to-maintain watersports speeds, it came down to the Alpha 4, the Tempest Plus and the Rev 4, so I ran them again, back-to-back this time.

The differences between them were: (1 - best, 3 - worst)

	Alpha 4	Tempest Plus	Revolution 4
holeshot acceleration	1	2	1
ability to maintain low plane speed	3	2	1
prop slip above 35mph	2	1	1
resistance to ventilation	3	1	2
no steering torque	2	2	1

Decision and Final Thoughts

The Alpha 4 20P, which is 1/3 the price of the others, is a good value for this boat. (It's 3rd out of 8 tested.)

The Rev 4 19P is not perfect, but it is the best of the bunch tested here.

I noticed that the Rev 4 revved out very well between 3000-4000 on holeshot. I have yet to experiment with the PVS on this prop (solid plugs were installed during testing) but I may be able to improve the (already decent) 1000-3000 acceleration.

 

[steelespike]

Re: Bayliner 175 overrev with 21P?

Wow thats a lot of testing with some interesting results. Your slip estimates on the final 3 were pretty much right on with the Rev 4 at an amazing 2% and the Tempest at a respectable
7% and the Alpha at a fairly normal 12%
Just a thought the Rev 4 in a 20" assuming 2%slip might add 1/2 a mph and put the motor a shade closer to its rated rpm @ 4900. Opening the plugs might maintain hole shot,though if I remember right opening the plugs on a I/O prop doesn't have as much effect as that on an outboard. A 21" at 4700 could be close to 46 mph. Of course going to 21 would depend on the 20 results.
By the way, if I remember right the motor will lose more speed in a left hand turn than a right.

 

[Texasmark]

Re: Bayliner 175 overrev with 21P?

Hi!

Out of curiosity, what is your slip at "high cruise" versus WOT?


SB

I took the data once. If I can find it I will share it with you. Obviously it's not 12% but the shape and weight of the boat dictates that it won't be too bad. I can get on plane in 2-3 seconds so that speaks somewhat for the performance of the hull at the lower speeds.

Mark

 

[severinbb]

Re: Bayliner 175 overrev with 21P?

Wow thats a lot of testing with some interesting results. Your slip estimates on the final 3 were pretty much right on with the Rev 4 at an amazing 2% and the Tempest at a respectable
7% and the Alpha at a fairly normal 12%
Just a thought the Rev 4 in a 20" assuming 2%slip might add 1/2 a mph and put the motor a shade closer to its rated rpm @ 4900. Opening the plugs might maintain hole shot,though if I remember right opening the plugs on a I/O prop doesn't have as much effect as that on an outboard. A 21" at 4700 could be close to 46 mph. Of course going to 21 would depend on the 20 results.
By the way, if I remember right the motor will lose more speed in a left hand turn than a right.

Thanks for the feedback! I remember that you suggested the Rev4 20P previously and you may be right, but I won't be back on the water until spring!

For the record, with my 2:1 i/o gear reduction, I calculate that the Rev 4 had 7% prop slip at 5000 / 42mph. (Dunno how I calculated the prev result!?) An interesting finding here is that prop slip % goes down as speed goes up, i.e., for Alpha 4 20P:

rpm	mph	slip
3750	30	16%
4200	34	15%
4900	40	14%
5100	42	13%

Interesting last comment. I'm going to check that out!