21p, where to go from here?

dwmmatt23

Cadet
Joined
May 28, 2008
Messages
18
hi all, i have a 1990 baja 17.5 ski boat with wake tower thats running a slightly modified (edelbrock man, carb ....) 4.3l yamaha. my question is that it has a stainless prop, the only markings on it shows its a 21p (diameter should be 14- 14 1/2). its hauls ***** out of the hole but im maxed out 6000 rpm befor im even on plane. going up to a 14x23 should only bring my rpm down @400 right? just need some more info on options and where to go from here, thanks
 

rndn

Commander
Joined
May 20, 2007
Messages
2,323
Re: 21p, where to go from here?

All things being equal, you gain or lose about 200 rpm's per inch of pitch.
 

09231960

Cadet
Joined
Jul 21, 2009
Messages
18
Re: 21p, where to go from here?

If by chance you decide to sell your 14 1/2 x 21 let me know.
Thanks
 

xxturbowesxx

Chief Petty Officer
Joined
Apr 20, 2008
Messages
491
Re: 21p, where to go from here?

what do you mean you are maxed out at 6k before you get on plane.. this sounds like a different issue
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: 21p, where to go from here?

Matt, welcome to Iboats prop forum and we will try to help you as much as we 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 I can, if you would prefer to not go to this much trouble there are other people who will 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 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 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 and turn the motor until the tape lines up with each other, 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
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. If you do not have a tach you can buy a Tiny Tach for $ 50
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
 

sho3boater

Petty Officer 2nd Class
Joined
Aug 4, 2009
Messages
168
Re: 21p, where to go from here?

I would look for a 23 or 25 to test or borrow and see where you are at. You might want a 4 blade (assuming this is an I/O) for pulling, but it may be slightly slower on top.
 
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