Logo
FULL SITE MENU

20 foot 1997 Maxum 2050 bowrider propeller question

G

gica69

Regular Contributor
[FONT=&quot]I am using this boat offshore in SOCal to occasionally go to the Channel islands, yes I know it's a bowrider but it works great. I recently rebuilt the Alpha 1 gen 2 drive myself successfully.[/FONT]
[FONT=&quot]So the propeller on the boat is a 14.5x18 aluminum, not the original size which broke, one that I bought awhile back. I am not too happy with it especially in semi choppy waters. The gas mileage sucks but these are gas guzzlers compared to let's say my friend's Trophy II 115 outboard that can do 247 miles per tank. So I will never be able to reach such a performance since I have a 5.7l sterndrive. Carb is rebuilt to specs and adjusted properly. Going to the Channel Islands from Oxnard is roughly a 12 miles trip with another 6 there and coming back I spend roughly 14 gallons of gas. And in semi rough water with winds of over 12 knots even more. You guys probably know about it.[/FONT]
[FONT=&quot]My question is can I get a different propeller that can get the boat on plane below 20mph that it does right now. At WOT I get 4100rpm and 40 miles per hour speed. 30 rpm is 30 miles an hour. This motor specs say 4200-4600 RPM. I don't care about speed since yesterday was the first time I could take it and actually reach 40mph the ocean was the calmest I have experienced in a long time. It's August after all.[/FONT]
[FONT=&quot]So what size propeller and pitch and why? Thanks in advance.[/FONT]
 
I have a 21 open bow, much heavier then your boat. 3600lbs dry weight, with one battery and 20 gal gas.
Add extra batterys gear another 30 gallons, beer and a few friends. Now easily over 4000 lbs.
5.7 and drive is 1.5:1 ratio
I run a 21 pitch aluminum 3 blade, plastic hub standard prop for mercruiser.
I run 4900 at 52 mph all day.
I can plane off at 3000 ish rpm and once on plane back it off to 22-2500 rpm and run around 20-25 mph.

If your boat only hits 4100 rpm, is drive trimmed up?

If drive is trimmed and all you get is 4100 rpm you may have other issues.

Have you confirmed tach is accurate?

Most standard boats at or near sea level with 5.7 should have a drive ratio of 1.5 or possibly 1.47 to 1. Have you confirmed your drive ratio?

Based on normal 3 bladed aluminum props, using my information above,

If I go to a 19 pitch I will plane off quicker but over rev at wide open throttle. Like 5200/5300 rpm.

If i go to a 23 pitch prop I will plane off slower and my wide open throttle may be 4600 but i may stay at or slightly increase my MPH by maybe 1-2 mph.

So if you only concerned with quicker acceleration which may help to plane off quicker, you go down a pitch.

Not sure where u got a 18 pitch unless its a 4 blade.

But if its a 3 blade I would start at a 17 pitch and if thats not enough try a 15 pitch.

Of course I am NOT a prop guy. I have suggested what typically works for a boat that actually functions as it was designed.

Note: When solid rubber hub aluminum props were available, my boat ran a 19 pitch. 4800 ish and 52 mph.
When they went to plastic hub I had to go up to 21 pitch to achive same basic rpm and mph. The 19 pitch plastic hub prop put me over 5200 rpm.
 
You should be shopping for stainless cupped prop. If you want to spend a little extra, then have a prop shop get you a prop that is optimum for your needs. They can help with selection and even do some measured-mile testing to get the best one. It's worth the money if you use the boat a lot.
 
Jack...

Re: "Note: When solid rubber hub aluminum props were available, my boat ran a 19 pitch. 4800 ish and 52 mph.
When they went to plastic hub I had to go up to 21 pitch to achive same basic rpm and mph. The 19 pitch plastic hub prop put me over 5200 rpm. "

Any idea as to why??? Prop mechanics for replaceable hubs ????
 
sandkicker said:
Jack...

Re: "Note: When solid rubber hub aluminum props were available, my boat ran a 19 pitch. 4800 ish and 52 mph.
When they went to plastic hub I had to go up to 21 pitch to achive same basic rpm and mph. The 19 pitch plastic hub prop put me over 5200 rpm. "

Any idea as to why??? Prop mechanics for replaceable hubs ????
Click to expand...
No idea
Never asked just changed up a pitch to solve issue.

May have to do with less weight/mass to rotate.

All I can figure....

There was no other changes to anything other than prop.

Also both solid hub and plastic hub were Mercruiser brand props new.
 
This is a link to the propeller measurement in diameter and the timing check. The idle is running from 650 up varies, so the timing does too. It clearly shows in the video.
 
gica69 said:
Technical difficulty there, sorry about that.
https://www.dropbox.com/sh/4mo78yzfpz68avi/AAB2L9y8rmk2dLptrMT3p4Osa?dl=0
Click to expand...
And the drive is completely down at 4100 on a really flat SoCal surface that doesn't happen every day at the marina.

Just thought of something, the accelerator cable that goes on the carb, I have long suspected that it needs some adjustment since when using the remote control to accelerate it doesn't respond right away. I wonder if that limits the amount of throttle that can be achieved?
 
Last edited:
First off you have a 1997 which has a Thunderbolt V

You may also have a knock sensor, just forward of starter with a single blue wire.

The Timing control varies the timing
MBT mean best timing.

In order to set base timing you have to connect a jumper in order to do so.

It may be me but I couldnt hear a 500 rpm change.

Also based on the video it sounds a lot higher than 640 rpm.

Get the timing instructions and start there.


Maybe your base is so far off you cannot achieve full timing advance meaning instead of ~ 32* btdc full advance you may only be achieving ~ 24 * btdc. This is only a suggested idea.

Not being there only allows for a guess.

Wr have no idea what you have done right or wrong.
 
kghost said:
First off you have a 1997 which has a Thunderbolt V

You may also have a knock sensor, just forward of starter with a single blue wire.

The Timing control varies the timing
MBT mean best timing.

In order to set base timing you have to connect a jumper in order to do so.

It may be me but I couldnt hear a 500 rpm change.

Also based on the video it sounds a lot higher than 640 rpm.

Get the timing instructions and start there.


Maybe your base is so far off you cannot achieve full timing advance meaning instead of ~ 32* btdc full advance you may only be achieving ~ 24 * btdc. This is only a suggested idea.

Not being there only allows for a guess.

Wr have no idea what you have done right or wrong.
Click to expand...

Got the info but it's a purple and white wire to ground
 

Attachments

  • 20210815_103641.jpg
    20210815_103641.jpg
    207.5 KB · Views: 47
Last edited:
Your idle variation issue was due to your timing light which was triggered off the spark plug wire and being altered by the timing control module.

Spec is more likely 8*btdc at 650 rpm in water in gear.

If you have a sticker on engine that says 10* btdc then that is correct.

This is a system that is,
Set base with jumper, and thats it.
Timing module controls full advance.
You cannot change Max advance unless you increase base timing. Base + timing module = total andvance.

Another thing,
You will never reach maximum WOT unless you trim outdrive up.
Doing that lifts boat out of the water a small amount.
Driving with the trim all the way down causes fhe bow to stay down witch slows boat down, both max rpm and mph
 
Last edited:
In some cases you can flip the boat running WOT with the trim all the way down even in flat seas. This is specifically addressed in the owners manual, and the installation manual. It can also induce chine walk and other unpleasantries.
 
o2batsea said:
In some cases you can flip the boat running WOT with the trim all the way down even in flat seas. This is specifically addressed in the owners manual, and the installation manual. It can also induce chine walk and other unpleasantries.
Click to expand...

A 20-21 ft open bow with a 5.7 running 40-50 mph.
IT AINT GONNA HAPPEN. Take my word on this.

Fish tailing occurs mostly when a over powered boat for its size is "put together"...
He is running a factory design, I would doubt even get close to that condition....

If this was a 20 ft with a high performance big block and a very custom stainless steel prop that pushed this boat over 60+ mph then you advice would be relevent.

That boat should handle 55 mph with drive trimmed to max hieght without skipping a beat!

I commonly work on friends 18 checkmates with 5.7 and a qualty SS prop that rountinely run 60-70 mph with no issues
 
Last edited:
kghost said:
Your idle variation issue was due to your timing light which was triggered off the spark plug wire and being altered by the timing control module.

Spec is more likely 8*btdc at 650 rpm in water in gear.

If you have a sticker on engine that says 10* btdc then that is correct.

This is a system that is,
Set base with jumper, and thats it.
Timing module controls full advance.
You cannot change Max advance unless you increase base timing. Base + timing module = total andvance.

Another thing,
You will never reach maximum WOT unless you trim outdrive up.
Doing that lifts boat out of the water a small amount.
Driving with the trim all the way down causes fhe bow to stay down witch slows boat down, both max rpm and mph
Click to expand...

Yes I do have a sticker that says 10⁰. There is a picture of it above. So what should I do, I don't care about WOT and speed I go 10 to 20 miles out to the islands. I want to change the propeller. Do I care about 4100 max RPM when I have to get 4200 to 4600? Or is that WOT only. Do I change the pitch to 17 to add more RPM? Won't that waste more gas.
What can I do to save some gas besides going slow?
 
If you are not seeking max Rpm and max Mph.
There is not much you can do with your set up..

Boat gas usage is measured in gallons per hour NOT miles per gallon.

Example, my boat heavy 21 ft open bow same basic engine as yours. 63 gallon gas tank
On a small fresh water lake where i use it, I can blow thru 30 gallons in a weekend without even trying.

It is what it is.

If you are currently using the Webber carb, they have their weeknesses.
A common good replacement (direct bolt on) is the Edlebrock marine carb. These seem to work very well but other than slightly better adjustability and possible better perfromance you gas usage will be what it will be.

If your boat runs well, just use it as is.

Next boat make sure its slightly over powered and fuel injected that way you can sqeeze as much gas milage out of it as possible..
Carbed engines burn lots of fuel and that is pretty much the way it is!!
 
I have a merc carb 2bbl. I just rebuilt it. So you saying I should not try to go down in pitch to 17 and leave the diameter be just to get the rpm to specs? So the rpm is not important? If I do lower the pitch will that affect the consumption negatively?
 
No thats not what i am saying.

But a pitch change would get u close to 4400.

A new propperly cupped prop will make a positive difference, its the pitch that is needed to be figured out.

Feel free to try any prop you want to achieve closer to what you want.

Not sure you will save any fuel but you may get a bit better perfromance.

So you have a 230hp 5.7?

I have a 5.7 4bbl 260 hp

So mine should use more fuel than a 2 bbl.

As suggested in an earlier post. Go and talk with some of the coastal marinas and see what they reccomend. Some may allow you to water test before you purchase.
 
Last edited:
The cupped ones are cut by a place to a certain measurement right? Top or sides. My 5.7l is 250 horses maybe 260.
What numbers do you get at WOT RPM speed, and what size prop do you have, even though the boat is bigger by a foot.
Mine is an open bow too.3000 plus weight for sure.
 
No
A brand new prop, at least from mercury the edges at the radius is cupped.

I get the best overall performance with a new prop.

But I always hit anything submerged so I run rebuilt props at half the cost. The rebuilts are NOT cupped and the difference in performance is noticable.

My performance is all in a earlier post.#2

My boat is 4500 loaded up and possibly more based on how many fat bastards i am floating and drinking beer
 
Last edited:
Ok so you have 21 pitch and diameter is what 14? My drive is 1:47:1 yours is 1:5:1, you get 4900 rmp I get 4100 and not loaded
Got to get me some fat buddies hahaha. Your boat is heavier so rpm will vary of course. ****.
 
Talked to a place here on Reseda and the guy there was telling me that there is something odd that I don't show different
numbers. My compression was ok on all 8. Timing is great didn't test it at higher rpm the guy said I should. The carb has just been rebuilt by me and by the book.
He said not to change the 14.5 and go down 1 inch in pitch to get the rpm above 4200. I need to 4200 to 4600.
He said I can go to 16. But to try 17 first.
He thought I should have been fine at 18 didn't know why I was having the issues?
Another guy with a 22 Chaparral is using a 14.5x17 and says he gets 4800 rpm and 46mph easily. His volvo penta270 v8 with 1:6 gear ratio.
So that's where I am. I am looking at a 14.5x17 from Turning Point or Solas. To see what happens, not knowing the original the came with the boat has me with a lack of knowledge about this for now.
 
Your issue at this point seems to me nothing more than the prop.

The fact you get to 4100 rpm you are ok timing wise.

If you were not getting past 2400-3000 then that is a different issue.

Not knowing the 18 pitch history, the best thing to do is try a 17 pitch.

Oh it is not critical you dont get max rpm. What would be crtical if you were over reving like 5000 + rpm.
And that would only shorten the engine and drive life span.
 
Ok so above 4200 at wot is not necessarily a must. Nonetheless when I dock I always have to reverse to break, it seems to be going a tick too fast, I of course got used to it like this and adrift to the dock in neutral, and that because there is nobody there.
When I was in Laughlin to go to the annual gathering of friends from to Mohave lake different story. Hundreds of boats everywhere in the marina. So drifting there is a nono.
 
I just turned the engine and the pulley spins clockwise so the flywheel should go left. Good thing I checked.[
ATTACH=CONFIG]27623[/ATTACH]
 

Attachments

  • Screenshot_20210816-210951_Chrome.jpg
    Screenshot_20210816-210951_Chrome.jpg
    156.8 KB · Views: 43
99.9% of all single engine pleasure boats (Sterndrive) are Left hand (Looking at flywheel) or Standard rotation.

For dual engine, dual Sterndrive boats today, Both engines are typically Standard rotation and the Counter rotation is done in one of the lower units.
 
Back
Top