Fishin, the first thing I can see that is wrong is that you are using a 19" pitch when you definitely should not be using over a 17" pitch prop, and possibly you need even less pitch depending on the hull form. I show you have a 1.93:1 gear ratio and your motor should turn right at 5,500 RPM at WOT, please verify this.
Then you have to take into consideration are you using the right blade geometry prop on the boat as that can certainly create bad performance problems such as slow speeds and porpoising.
I show a boat of that weight and HP, depending on the particular hull form you have, should do in the mid to high 30 MPH. So if you theoretically are only doing 25 MPH you are missing a lot of speed. You need a GPS WOT speed and I can tell you how much prop slip you are experiencing and that always help to determine if it is a motor problem or something else.
The porpoising issue an be caused by weight distribution in the wrong places and/or water in the hull and and/or the wrong blade geometry prop.
If you will fill this form out I will help you as much as I can.
Iboats Boat and Motor Info
1. Year, make and model of boat 1992 Maxum 2100LDC
2. Length, width and base weight of boat, look for boat decal on back of boat21 ft long , 8ft beam , weight is aprox. 1600 lbs.
2a.What is the maximum recommended HP for your boat 150
3. Number of people and gallons of gas normally on boat 2 people, 12 gallons
4. What do you use the boat for Mostly cruising, some tubeing.
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor 1992 Force L-drive
7. HP and gear ratio of motor IMPORTANT120 hp Gear Ratio = 1.93:1
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 then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, 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 5200-5500
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 Cuddy Cabin
11. Does it have a hydrafoil, dolefin or trim tabs NO
12. Make, model, diameter, pitch and whether SS or aluminum prop Unknown mfgr. 13X16 3-blade aluminum (almost new)
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
RPM ___4400________ Speed ____26mph_______ No. of people ___3_________ Gas __8 gal.______
14. Are you at sea level or a higher elevation, give us the elevation in feet 725
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 All seem OK
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop Just bought this boat, not very old prop , WOT and speed seem low.
17. Does the prop show any damage that you can see NO
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 More top end speed and faster planeing.
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
