Re: Which pitch?
B, Silvertip is 100% right, Lowering the RPM below Minimum recommended WOT will 95% of the time INCREASE your fuel usage and lower your fuel economy.
You might try looking at this post to get an idea of how to change your prop for better performance, in my opinion.
http://forums.iboats.com/showthread.php?t=365653
A 4 blade prop will normally help a boat like yours because of the high weight to power ratio, as it will lower your prop slip to gain back speed that is being wasted with high prop slip. Your expert is probably right about the 4 blade Power Tech, but I try to approach it from a mathematical approach as well to vindicate my theories. If you would like my help fill out this form with everything that you know about your boat, and I will be glad to help you as much as humanly possible.
Just copy this form to your computer and paste it into a word processing program and fill it out, then paste it into your post.
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, 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 the bottom of the transom of boat if it is an outboard in inches, use a straight edge or a board under the keel and sticking out to the anti ventilation plate for a reference, and take about 4 pictures for us to see.
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Manufacturer, model, diameter, pitch, number of blades and whether SS or aluminum props.
IMPORTANT
1.
2.
3.
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 less than $ 50
RPM ___________ Speed (GPS)___________ 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
by only using the control on the console, checked compression, looked at the plugs and checked spark, is the bottom of the boat clean and barnacle free, and have you checked the Tachometer against a mechanics tach, 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.
1. 3000 RPM
2. 3500 RPM
3. 4000 RPM
4. 4500 RPM
5. 5000 RPM
6. 5500 RPM
7. 6000 RPM
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
