going to 4-blade, which one?

[93maxum4.3lx]

boat: 93 maxum 18' open bow
motor: 4.3 LX ~ 190 HP
drive: mercruiser alpha 1.81 ratio
current prop: mercruiser "Vengeance" 14x19 SS
holds 30 gallons fuel

with 400lb of people, full gas, and a stingray hydrofoil, 42mph at 5100rpm before i pulled it back, it might have made it to 5200 or 5300.

with 800lb of people, full gas, and the hydrofoil REMOVED, it did 43mph at 5000rpm WOT.

The motor is supposed to be 4600rpm or 4800rpm max, depending on what source you trust.

All speeds GPS.

I would like to keep the hydrofoil off, but I miss the stern lift. The 'foil kept the boat very level while getting on plane; without the foil the bow spends 3-4 seconds in the air before getting on plane. With the foil on, the transition was very smooth and effortless.

I know that smart tabs are the answer; but I fear they will be unsuitable for a recreational boat (people getting in and out of the rear of the boat, hitting them with their knees, trying to climb on them, whatever). I know the 'foil is the wrong solution to the problem but it does seem to work well...

I normally cruise the boat around 3600-4000rpm.

So, to get to the point, I'm looking at a prop that meet the following goals:

1 give me stern lift to help the boat get on plane more quickly and replace the stern lift that the foil gave
2 give some more bite to help get the boat on plane more quickly
3 help keep the boat more level at lower speeds for towed tubes/toys
4 not give up too much top speed (I'd like to stay at/above 40mph)
5 not raise WOT RPM
6 not drop WOT RPM below 4500-4600

I keep coming back to a baypro II, but I am worried that the 18pitch will fail me on goals 4 and 5, and i'm worried that the 20pitch would fail me on goal 6 and possibly harm the holeshot if it's too much pitch for my setup.

any comments are appreciated!

 

[IVAZ]

Re: going to 4-blade, which one?

I'm not a prop expert but I can tell you that you will still over rev with a 4 blade 18 pitch prop.
I have 175hp Merc 4.3 with 1.84 gear ratio. I went from a 14.25"x 19 pitch 3 blades to a 14.25"x 19 pitch 4 blade. I can still over rev my engine easily. The hole shot increased dramatically and the bow rise decreased. I pull a big tube and I?m very happy with this prop. I babysit the rpm's so I don?t over rev it but most of the time I cruise it at about 3700 rpm.
You will lose a lot of top speed with the 18p imo.

 

[WTR4FUN]

Re: going to 4-blade, which one?

I would recommend a 4 blade 21 pitch prop. You want to get those rpm's down, and you should pick up some stern lift with the 4 blade. You will also gain some top end.

 

[junior1113]

Re: going to 4-blade, which one?

id run that close 4600 if you want it to last the longest. 20" pitch 4blade with stern lifting characteristics should do the trick put you about 4700. i think 19x4 rpms would still be too high about 4900. and 18x4 is way to high at 5100. 20x4 you will gain hole shot, top speed, fuel efficency, and over all performance.

 

[ramster]

Re: going to 4-blade, which one?

I've tried a bunch of props and the best for me so far is the Mich. Wheel Appollo 14.25X20 four blade, If you are over reving a 19 that much, I would go with the 20 four blade. Bay Pro II sounds like a great prop, but because it is so efficient it may load your motor a little too much, Props like the Turbo and Stilletto act like they are 1 or 2 inches higher because of their design, the Apollo seems to be just right for my boat, great holeshot and I get 55mph at 4800 with the wife and kids on board and 3/4 tank of fuel. My Stilletto 21 3 blade was great for flat out speed with just me, but my motor could only spin it to 4400 rpm, that's after I switched to a four barrel, which gained me around 200 RPM on a 5.0 220 HP Glastron SX 195. I would still like to try a BP II, but for the money you can't beat the Apollo IMO.

 

[ramster]

Re: going to 4-blade, which one?

I've tried a Vortex Al 14X20 4 blade and easily over reved that, I also tried a Solas Amita Al 14X21 4 blade and could only spin it to 4200 RPM. My speed was always pretty close but big changes in RPM's. The Apollo put me right in the sweet spot for my boat.

 

[sleeper]

Re: going to 4-blade, which one?

I bought a 14x20 stiletto bay pro II 4-blade and it lowered my rpm by more than I liked with a full load. I switched to the 18 pitch and with our normal load its perfect.

The 20 pitch version that I tried 1 time is on ebay right now if you are interested, it will sell cheap.

 

[93maxum4.3lx]

Re: going to 4-blade, which one?

sleeper - what prop did you have before the baypro 14x20? can you provide more data (mph, WOT rpm, etc.) with your previous props vs. the baypro 14x20?

I'm watching your ebay auction.

thanks!!!

 

[Tail_Gunner]

Re: going to 4-blade, which one?

I bought a 14x20 stiletto bay pro II 4-blade and it lowered my rpm by more than I liked with a full load. I switched to the 18 pitch and with our normal load its perfect.

The 20 pitch version that I tried 1 time is on ebay right now if you are interested, it will sell cheap.

That should be a very good choice. My first choice as matter of fact if all of the above posted stat's are correct

 

[sleeper]

Re: going to 4-blade, which one?

sleeper - what prop did you have before the baypro 14x20? can you provide more data (mph, WOT rpm, etc.) with your previous props vs. the baypro 14x20?

I'm watching your ebay auction.

thanks!!!

I have a 14x21 turning point hustler aluminum that I still love and use regularly. It turns 4800rpm and around 46-47mph in my boat with a 2 person load. I bought the 14x20 stiletto 4-blade, and my WOT rpm was around 4600 rpm with the same load at around 45mph. The problem is, I wanted a watersports prop for tubing and skiing when we take friends along. When we have 5-6 people on the boat the rpms were too low with the 20 pitch and it didn't pull skiers up like I wanted. I bought the same stiletto 4-blade prop in the 18 pitch variety, and it is awesome, even with a heavy load. I just have to watch my rpm when lightly loaded, it will go to 4900-5000rpm. Usually if it will just be me and wife and dog I put on the 14x21 turning point anyway. I highly recommend the bay-pro II though. Hole shot and midrange acceleration are unreal. It planes at a lower speed, holds good in tight turns without venting, and really lifts the boat out of the water at cruising speed.

Smart tabs are the other answer btw, they totally transform the boat. I could not go back to not having them. Looking at your current info, the 20 pitch might be the ticket for you. You see 5100rpm now, minus 150 rpm for 4th blade, minus 200 rpm for +1 pitch, leaves you around 4700-4800rpm depending on load.

 

[93maxum4.3lx]

Re: going to 4-blade, which one?

i am still torn between the 14x20 and 14x18 baypro II.

would the 14x20 still give better holeshot/acceleration than my current 3-blade even though it's of a higher pitch?

I am wondering if the 14x18 would be better, considering that the extra blade will drop the rpm a bit, and the extra cupping design will also drop rpm a bit, that the 14x18 may have the same WOT RPM as what I have now, probably a touch less MPH, but a tremendous boost to wholeshot and midrange efficiency/planing speed.

a 14x19 baypro II would be perfect....

 

[sleeper]

Re: going to 4-blade, which one?

With the 14x18 stiletto, the 4th blade and one lower pitch will offset each other, you will still be over-revving the engine by quite a bit most likely.

Going from a 3-blade to 4-blade for me the hole shot was much better, even with an rpm loss. The extra blade area really helps.

You don't have to get a Stiletto, there is a Solas HR titan 4-blade SS in a 14x19 that I also hear great things about if that is what pitch you think you need.

I just tried several until I got the one I wanted. It would be a great time to try the 20 pitch by buying mine off ebay for considerably less than new

Go ahead and get smart tabs too, they are well worth it. Just make an example out of the first person that tries to use them as a ladder.

 

[wca_tim]

Re: going to 4-blade, which one?

I really like the solas Titan 4 blade I bought in 21" a lot for an all around prop on my v-6 powered bow rider, but it may still put your rpms a bit high.

You could probably turn a vented (newer) 23" laser two for an good increase in top speed.

the mercury vensura got great marks for i/o boats that were'nt pushing a lot of horsepower. They never really got as popular as projected, and are around for decent prices "used" a 21 would be a very good all around for your set up possibly but I don't have personal experience with one of these.

Ideally you could find a local shop of friend that'll let you try some out. Where (about) are you located?

 

[gss036]

Re: going to 4-blade, which one?

I thought the mercury vensura 4 blade was "BOW" lifting design prop?? Could be wrong though, I have one and the Merc site says it is a bow liting type.

 

[93maxum4.3lx]

Re: going to 4-blade, which one?

I bought sleepers' baypro II on ebay; I'll post results when I get it installed on the boat. hopefully it will be the ticket!!!

 

[JoLin]

Re: going to 4-blade, which one?

Another vote for the Solas Titan HR-4. I put one on my old stern-heavy Pro-Line and it made a big difference. It's designed for stern lift. Great prop.

Believe the Stiletto Bay Pro is designed to have good stern lift capabilities, too. That was second on my list, because at the time it was about $100. bucks more expensive than the Titan.

 

[93maxum4.3lx]

Re: going to 4-blade, which one?

So, I ran the new 20 pitch bay-pro II and have some interesting results.

all speeds GPS:

4 people, vengeance 19p, sea level: 43mph at 5000rpm.

same 4 people, bay pro II 20p 4-blade, 3000ft alt: 38mph at 4300rpm.

Impressions of the BP II on the boat:

Positive: ride is awesome, really smoothed out. whole power package felt much smoother. passengers loved the difference, the running attitude of the boat on plane is much nicer and it took ALL the harshness out of cutting through waves - MAJOR improvement in smoothness of ride even in choppy water. Everyone much happier at speed! Also noticed better headway at idle (~ 600rpm) and high idle (~ 1000rpm).

Negative: I didn't seem to gain any holeshot. There is less bow rise, but I was expecting some kind of overall improvement in planing time but there didn't seem to be any. I also wasn't expecting to lose 5mph, even taking into account the altitude difference.

Overall, I'm not sure what to think. I'm wondering if the prop just isn't a good fit for the boat. The 19p vengeance has a calculated prop slip of 13.4%, and the baypro is coming out at 15.5% - not what i expected at all! I thought the BP would have less slip...not more. I know the altitude will take some motor power away, but that shouldn't affect the prop slip numbers.

So, now I'm soliciting advice again. My first reaction is that I need the 18p baypro II; but I'm not sure it would work out either. based on sleepers numbers the 18p will turn about 350rpm more; if the 18p prop slip is the same as the 20 (15.5%) then that comes out to only 37mph at altitude and it MIGHT make 40mph at sea level at 5000rpm...

sleeper - can you post some mph info for your 18p? how is the 18p holeshot over the 20? did your prop slippage go up or down over the 20p? Anything you could add would help tremendously, especially since you've had experience with both these props now.

everyone else - any thoughts on why the prop slip is higher with the BP II? suggestions on what to try next, especially in something that will give ride quality improvement comparable to the BPII, but perhaps give me a touch more RPM and less slip? does slip % improve the faster you spin the prop, maybe making the baypro in 18 pitch more efficient since I could turn it faster?

I'm also re-considering the solas HR titan 4 - blade now, in 19 pitch. Should give me a bit of RPM back, keep the awesome 4-blade ride, and with a touch of luck it will slip less on my hull and not lose much speed over the old 3 blade.

any thoughts/comments appreciated!!! Bay pro II 18 pitch, or solas HR titan 4 in 19 pitch??

 

[hwsiii]

Re: going to 4-blade, which one?

Maxum, welcome to Iboats prop forum and we will try to help you as much as we can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as I can, if you would prefer to not go to this much trouble there are other people who will help you.

Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H

 

[sleeper]

Re: going to 4-blade, which one?

4 people, vengeance 19p, sea level: 43mph at 5000rpm.

same 4 people, bay pro II 20p 4-blade, 3000ft alt: 38mph at 4300rpm.

sleeper - can you post some mph info for your 18p? how is the 18p holeshot over the 20? did your prop slippage go up or down over the 20p? Anything you could add would help tremendously, especially since you've had experience with both these props now.

the 20p prop on my boat was 4600rpm and around 45mph on the gps, which works out to about 6% slip which is nearly impossible except that the 20p BPII acts like a 21p prop which is 12% slip.

The 18p prop on my boat is around 4950+-rpm and I have seen 44mph on the gps which works out to 6% slip also but if you figure it acts like a 19p prop then you get 10% slip.

The hole shot with the 18p is awesome, but I have only compared it on my boat with the 20p BPII also and with my 21p TP hustler.

The BPII is a very grippy prop based on my experience as well as what I have read. It lowered my rpm more that I expected. I think you need to run the boat with the new prop at sea level for a direct comparison though before you make any changes.

 

[93maxum4.3lx]

Re: going to 4-blade, which one?

I'm surprised that the 18p was only 1mph slower for you. That makes me more comfortable with the thought of trying the 18p on my boat. I hope you don't mind one more question - how would you rank the difference in holeshot of the 18p vs. the 20p? You've mentioned more than once that the 18p was awesome, but didn't mention if the 20p was just ok, or pretty bad, or what.

I will often be running the boat at this 3000ft lake on day trips; and it's more likely i'd be pulling at this lake too. So, even though it's not a good comparison to my previous sea-level runs, I still need to factor in the overall performance at this lake and I think the 20p just isn't getting it. Shooting myself in the foot for not swapping to the 19p vengeance on that same day for back to back comparison..... still dissapointed in the speed too but if that's all she's got then so be it; i want the smooth ride and a good holeshot!