Another Prop Question

buda

Seaman
Joined
May 6, 2008
Messages
51
I have a 1989 Bayliner Trophy 1903 with a 125 HP Force , with a SS prop. 13.5 x 17. The question i have is this. I was checking the boat out today and i was running about 5000 RPM but the MPH gauge was only showing 30 MPH.
Should that boat run faster than that. Could it be the pitch of the prop.

Thanks Buda
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Another Prop Question

Buda, if you will fill this out I will try 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 motor 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 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 Tiny Tach for $ 50
RPM ___________ Speed ___________ No. of people ____________ 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
 

buda

Seaman
Joined
May 6, 2008
Messages
51
Re: Another Prop Question

Thanks for the reply Commander.
I'M not sure what the MPH of this boat is suppose to be. A friend of mind and me was checking out the boat and motor. The prop. is not the origenal i bought the prop. on ebay and and had the prop. pitched from 15 degrees to 17. The boat got up on plane kinda fast and ran at about 5000 RPM and the MPH gauge was showing around 30 MPH , BUT the gauge might be off. I have an aluminum prop. with a 15 degree pitch that i'm going to try and see what happens. And see what the difference is. I don't know if the hydrofoil makes any difference. I might take it off and see what happens.

Thanks again Commander
buda
 

wingtime

Cadet
Joined
Aug 12, 2009
Messages
22
Re: Another Prop Question

The outcome of this thread interests me since I have a 1989 Force 125 and I'm trying to get the right prop for it. I just put the motor on a 20' aquasport walkaround. I'm getting 4100-4200 @ WOT and 27-28 MPH on the GPS. To the best of my knowledge my prop is a 13.25 x 15. I say that since I'm going by the part number on the prop. I have no idea if has been repitched or not. BTW the motor and prop combo came off a 20' Renken cuddy that I had and it pushed that around just fine.

PS the engine has great compression and is firing on all cylinders so I doubt I have a power problem.

Thanks Bruce
 

buda

Seaman
Joined
May 6, 2008
Messages
51
Re: Another Prop Question

I appoligize for not getting back sooner. I took the boat back out with the aluminum prop. with the 15 degree pitch. It ran about 33 MPH at around 5200
RPM. I'm going to have the aluminum prop. changed to a 19 degree pitch just to see what happens.

To Bruce
If the prop has been repitched they stamp it on the prop. The SS prop. I had was a 13.5x 15 and i had it repitched to 17. The aluminum i just tried out is a 13.5 X 15 but i'm going to have it changed to a 19 pitch. The 125 Force i have has great compression . It runs about 5200 RPM at WOT. I hope everything go great for you.

Buda
 
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