Wrong Prop?

[BigBoatinOkie]

I recently bought a 1984 Wellcraft 180 Elite XL I/O. It has a Mercruiser 228 hp Chevy 305 Engine and Mercruiser Alpha 1:1.47 Outdrive with 14 1/2 X 22 Stainless 3 blade prop. The boat has a top speed around 50 mph, but I noticed that at WOT It was only turning about 3300 rpm. I don't have a manual for my boat, but common sense tells me that this engine should run well over 3300 rpm. Maybe 4200-4500? Not sure. Do I have too much Prop? I have a 14 1/2 X 20 aluminum prop I could use, should I try it? This boat doesn't plane very fast either, but it's pretty stern heavy. I have Bennett trim tabs, but they don't work.

 

[hwsiii]

Re: Wrong Prop?

Okie, I ran an analysis on your numbersand with those I found that you are showing a negative slip of -9% and that is impossibleif I have the right Gear ratio. I show you should be turning between 4,200 and 4,600 RPM by fatory spes with a gear ratio of 1.65:1, please verify this. I would suspet the tahometer as the suspet in this ase. You might try and turn the swith on the bak bak and forth a few times to help lean the eletrial ontats and see if that will make it work right. But hange to the 20" pith and take oit out with a mehanis tah and see what RPM and speed you get and ome bak and tell us what it is. Long timeto plane is a lassi sysmptom of being over propped.


H

 

[BigBoatinOkie]

Re: Wrong Prop?

I took the boat back out and ran it with the 20" pitch. The holeshot was much improved and it planed out faster. The top speed came down to 45 all trimmed out while the rpms at WOT went up to 3500. Is the 1.47 gear ratio a high geared drive? I know in truck rear ends the lower the number, the higher geared it is, is it the same with outdrives? I liked the way the boat ran today, if I could get just a little better holeshot without sacrificing much more top speed that would be fantastic. Of course, when I get the trim tabs working, that will help I'd bet.

 

[hwsiii]

Re: Wrong Prop?

Okie, every time the motor turns 1.47 revolutions the prop turns 1 omplete revolution. I an tell you that you are putting a major strain on your motor running it in that over propped ondition. Please fill this out and i will do an analysis.

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 maximum 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. manufacturer 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, use a board under the keel and stiking out to the anti ventilation plate for a referene
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. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. 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

 

[BigBoatinOkie]

Re: Wrong Prop?

Iboats Boat and Motor Info
1. Year, make and model of boat 1984 WellCraft 180 Elite XL
2. Length, width and base weight of boat, look for boat decal on back of boat
Length - 17'7"
Beam - 7'2"
Weight - 2125
2a.What is the maximum recommended HP for your boat 228 HP
3. Number of people and gallons of gas normally on boat 3-4 adults and 20 gal.
4. What do you use the boat for Skiing, Tubing, Kneeboarding
5. Is it a Deep Vee and if so how many degrees of deadrise 20 Deg.
6. Year, make. manufacturer and model of motor Mercruiser 5.0
7. HP and gear ratio of motor IMPORTANT 228 hp 1:1.47
8. Manufacturer?s recommended Wide Open Throttle (WOT) range I cannot find this info. Do you know?
11. Does it have a hydrafoil, dolefin or trim tabs Non functioning trim tabs in full up position.
12. Make, model, diameter, pitch and whether SS or aluminum prop Precision 14 1/4 X 20 aluminum 3 blade
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.
3500 rpm, 45 mph, 10 gal. gas, 3 total ppl. 635 lb.
14. Are you at sea level or a higher elevation, give us the elevation in feet
1000 ft.
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 No tune up yet, just purchased boat. Busts right off everytime, sounds awesome.
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop only used once
17. Does the prop show any damage that you can see. very light damage, i filed edges smooth
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. WOT is only 3500 rpm, slow to plane
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.

 

[hwsiii]

Re: Wrong Prop?

I should have this ready shortly.


H

 

[BigBoatinOkie]

Re: Wrong Prop?

Wow, you reply quickly. Especially for 1:30 AM

 

[hwsiii]

Re: Wrong Prop?

I am a late night person. LOL


H

 

[BigBoatinOkie]

Re: Wrong Prop?

That speed is not by GPS by the way. But I had just installed a new speed sensor thing, and it read just like the old one did. And i was running beside my dad's boat the other day and we were within 1 mph of each other at 20. I think it's pretty accurate.

 

[hwsiii]

Re: Wrong Prop?

My alulations show you should be running a 17" pith prop, and I would reommend a Solas Amita 3 blade prop for about $ 95 right here at Iboats. You should get about 4,400 RPM out of it and be able to get about 43 MPH with this prop. But your hole shot will be outstanding and when you pull up skiers it will jerk them out of the water versus what you are doing now. I show your maximum reommended RPM to be 4,600.


H

 

[BigBoatinOkie]

Re: Wrong Prop?

I haven't been in the boating game long, but I figured that I could run more than a 17" prop with a V8 in an 18' boat. Guess I figured wrong. Thank you so much for your help and expertise sir.

 

[hwsiii]

Re: Wrong Prop?

My reommendation is to hek your tahometer before you do anything, bring a shop tahometer with you on your next test run before you buy a prop. I believe your tah is lying to you. But when I use the numbers you gave me that is what it shows.



H

 

[BigBoatinOkie]

Re: Wrong Prop?

I will definately try a different tach and GPS on my next run. Unfortunately, it will be another week before I can go out again, and i'm runnin out of summer. I will report back with my findings. Thanks again.

Andrew

 

[hwsiii]

Re: Wrong Prop?

You are very welome Andrew.


H

 

[BigBoatinOkie]

Re: Wrong Prop?

Hey hwsiii, I got some new numbers that seem a little more reasonable.

Speed - 50 mph
RPM - 4000
Total passengers - Me 275 lbs. and maybe 50lbs. of gear
Prop - 14 1/4 X 20 Precision Stainless 3-blade
Fully trimmed

 

[hwsiii]

Re: Wrong Prop?

Stainless or aluminum.

11. Does it have a hydrafoil, dolefin or trim tabs Non functioning trim tabs in full up position.
12. Make, model, diameter, pitch and whether SS or aluminum prop Precision 14 1/4 X 20 aluminum 3 blade

H

 

[BigBoatinOkie]

Re: Wrong Prop?

I apologize, for I told you wrong the first time. The prop is stainless steel. My bad.

 

[BigBoatinOkie]

Re: Wrong Prop?

Does the new data change anything?

 

[hwsiii]

Re: Wrong Prop?

Yes, I would go with an 18" pitch prop in the same exact prop you are running right now.


H

 

[BigBoatinOkie]

Re: Wrong Prop?

Great, that's what i was thinking. Thanks.