cmayer85 chaparral 187 Prop Size

prop size?
can you please help me with finding a good prop size for my boat.


Iboats Boat and Motor Info

1. 1983 chaparral 187xl

2. 17.67 feet long and weighs 2200 (pounds dry). The beam of this craft is 86 inches

2a. 150hp i think

3. usually 3-6 people and i fill it up everytime before going out

4. general, cruising, skiing/wakeboarding

5. not deep v

6. 1983 fresh rebuild this year less than 1 hour on it, omc 5.7 260 hp

7. 260 hp dont know gear ratio, it had a 3.6L in it before and outdrive is stringer 800 with v6 on it

8. i believe it is 4600 or 4800
9. dont know
10. not bass boat
11. no
12. aluminum prop 14.5x19
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 ___stopped it from over revving at 4600rpm________ Speed ___30mph________ No. of people ____2________ Gas ____25 gallons____
14. 4500 feet roughly
15. yes everything in working order
16. was a spare we just tried out
17. no damage
18. i want the boat to reach its full potential, i would think it would do 50 mph+ with the 260hp motor and a small boat. i do ski a bit but the holeshot is not my top priority, top speed is more of a priority.

Re: cmayer85 chaparral 187 Prop Size

Mayer, if I use the original gear ratio that came with the 3.8L engine it shows a gear ratio of 1.77, please check this by

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 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.


Right now using the 1.77 gear ratio I find you have a prop slip of over 35%, and that is ridiculous for a boat like yours, so we need to find out what is causing this. It could possibly be the wrong RPM, wrong gear ratio, or wrong prop pitch, or wrong speed (use GPS) but whatever it is we have to find out before we can find the right prop. Try turning the switch on the back of the tachometer 6 or 8 times to clean the electrical contacts and make it work right.


H