Possible Issues Reaching Top End?

ShaneCarroll

Chief Petty Officer
Joined
Feb 10, 2009
Messages
639
I have a feeling my boat is not going to its full potential speed, and am starting with thinking it may be due to my prop. I have a 92 Sea Ray 18' bowrider, with the Mercruiser 3.0L 115HP. The WOT RPM's are in the 4300 to 4400 range. I currently have a 14 x 19 pitch SS prop. I have no problems planing, heck, the bow doesn't even come out of the water hardly. My issue is with top end, I don't even think I'm hitting 33MPH. Any suggestions? Should I try a lower pitch prop? Thanks in advance.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Possible Issues Reaching Top End?

Shane, 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 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
 

ShaneCarroll

Chief Petty Officer
Joined
Feb 10, 2009
Messages
639
Re: Possible Issues Reaching Top End?

I appreciate the help, however I will not be able to answer most of those questions for two and a half weeks, as I am in Ohio, and my boat's in Florida. I will get back to you then, thanks.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Possible Issues Reaching Top End?

Does the boat have trim tabs or a foil on it?Does the hull seem to respond when you trim up?
 

ShaneCarroll

Chief Petty Officer
Joined
Feb 10, 2009
Messages
639
Re: Possible Issues Reaching Top End?

The boat has no trim tabs, but it does have the doel-fins (the fins on the outdrive). Planing has never been an issue, it planes very quickly. My issue is that I just think my top end is too low. My speedometer's broken, but from what another boater with gps said, I might have hit 33. My tachometer hits 4300-4400 at WOT.
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: Possible Issues Reaching Top End?

Could be the fin causing top speed issues . . . But the lower rated early 3.0s at 115 hp are not going to push an 18 footer a whole lot faster. WOT RPM is 4200 - 4600 so you are right down the middle. I would say not very far off engine performance wise although some tweaking and removal of the fin could get you 3 - 4 MPH . . .
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Possible Issues Reaching Top End?

I agree with Q 100%.


H
 

ShaneCarroll

Chief Petty Officer
Joined
Feb 10, 2009
Messages
639
Re: Possible Issues Reaching Top End?

One last question, probably a dumb one, but do I have to worry about the holes for the bolts when I remove the fins? I wouldn't think so, but just want to make sure.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Possible Issues Reaching Top End?

They will reate no problems.


H
 
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