Re: Selecting the right Prop for my boat
Mister, I show a 1988 4.3L 6 cylinder to have 205 HP and a gear ratio of 1.65:1 and a WOT RPM of 4,800,
please verify this. At an elevation of 5,000 feet you have to remember that you lose at least 30 HP and can lose a good bit more if the humidity is real high. You don't say what kind or size of prop you are running so I can't do a prop slip analysis or anything else with the information you give. You definitely have a problem somewhere though, because I show at sea level you should be doing over 40 MPH.
Please fill this form out and I will be glad to 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 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
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, number of blades 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 digital tavhometer and hour meter here:
http://cgi.ebay.com/ebaymotors/Tachometer-Hour-Meter-Outboard-Jet-Ski-Quad-Go-Kart_W0QQcmdZViewItemQQ_trksidZp4634Q2ec0Q2em14Q2e l1262QQhashZitem27ab0dee04QQitemZ170373541380QQptZ MotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
RPM ___________ Speed ___________ No. of people ____________ Gal. Gas ________
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
