I have a 16 ft ski/speed boat that I damaged the prop on a few days ago. I ran into a sunken tree trunk at almost idle speed. I immediately lost power and had to idle my way back to the dock. When I removed the prop it has a bend in the rear outter section and the thrust washer looked like it was grinding into the prop. I checked everything on the gear housing out and all looks ok. Im hoping a simple prop change will be it??? Can someone tell me the proper size propeller I would need for my boat??? Im not sure if the old prop is a good size. Im looking into getting a stainless one..
If you know what your WOT rpm was with the old prop, that will tell you if the prop was sized properly, I believe that engine is 5k rpm at WOT. Going to an SS prop may require a slightly different pitch to maintain the same rpm but you'll be in the ball park.
I personally prefer an aluminum prop, I'd rather replace a prop then chance drive train damage.
Thanks for the responce brynifer I didnt even think of it that way. I just checked out some prices and Im defenitely going with an aluminum one..
I went to my local marine parts store and they found a number on the prop that was PJ-81 it also said Michigan but they were not able to match up with anything on there books. Anyone know what size prop this would be????
Why don't you ask Michigan (www) what the number means.
On your choice to stay with Alum because of the price.......gotta do what ya gotta do ! Butttttttttt if you want some performance from your hot dog boat, then you need a hot dog prop and the additional fun you have with it will surely offset anything you deprived yourself of so as to be able to afford a HP prop.
But, as mentioned. If you decide to upgrade, follow the recommendations herein and the best bet is to work out a deal with your supplier whereas you can try several props to get the optimum design.
Believe that's a 91 insted of 81...19P would be the pitch.
The recommended RPM of that engine when it was built was 4500-5500.
We've found by many, many hrs of run-time on the cross-flows 5800 WOT works best over-all...due to the junk fuel we have now compared to the fuel we had when this engine was built.
Ziggy, welcome to Iboats prop forum and I will try to help you as much as I 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 humanly possible, if you would prefer to not go to this much trouble there are other people who will gladly help you. My expectations are that you are willing to expend as much time and energy as I will to find a better prop for your boat.
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 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.
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.
You also might try reading this for a better understanding of changing props for better performance.