6K WOT top speed 30 mph

[westexasrepublic]

as the title reads took the boat out, finally got tac working and read 6K WOT and topped out at 30 mph, I could feel it run out of gear, not to mention let off since I was above my 5500 recommended max RPMs.

<<<<<<<<<currently running 4 bladex10.5x11pitch>>>>>>>>>>>>

what should I be running to get 5500 and higher top end?

 

[solar7647]

Re: 6K WOT top speed 30 mph

If WOT is 6k and you are looking for 5500k you need to increase your pitch 2 inches. Every inch you increase your pitch you will decrese RPM about 200-300rpm. The increase in pitch will give a little better top end but will also effect your hole shot possible meking it a little slow getting out of the hole. Also a 3 blade prop is usally a little faster as well but suffers when it comes to bite, and will be very noticable in turns.

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

ok so a 13 pitch, but thats assuming I keep that same setup right? for instance I read that I should also step it up a couple more inches if I go to a 3 blade from a 4 blade? so Should I be looking at <<<<< 3 blade X15 pitch>>>>> and to help "bite" should I be stepping up the radius? my 10.5 seems TOO SMALL for a 70hp

everyone keeps telling me the size dosnt matter only pitch, and to those people I say ok, give me your 12r" prop and ill give you a 6r" prop

 

[hwsiii]

Re: 6K WOT top speed 30 mph

On a 70 Hp you should be running close to a 13" Diameter prop. I have a form if you will fill it out I will try to help you. If you would rather not fill the form out there are other people who 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 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
7A If you have a mercruiser and don?t know the ratio get your serial off the outdrive and go here http://www.sterndrives.com/mercruisersterndrives.html
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 forgoing 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

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

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

1. Year, make and model of boat
>79' Fiberglass Star
2. Length, width and base weight of boat, look for boat decal on back of boat
>14'x5'6

2a.What is the recommended HP for your boat
>30-70hp max

3. Number of people and gallons of gas normally on boat
>2 people w/12 gallons

4. What do you use the boat for
>fishing

5. Is it a Deep Vee and if so how many degrees of deadrise
>n/a

6. Year, make and model of motor
>79' Mariner 70hp

7. HP and gear ratio of motor IMPORTANT
>70hp 1.5

7A If you have a mercruiser and don?t know the ratio get your serial off the outdrive and go here http://www.sterndrives.com/mercruisersterndrives.html

8. Manufacturer?s recommended Wide Open Throttle (WOT) range
>5500 rpms

9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
>1"1/2

10. Is it a bass boat or does it have a pad bottom
>shallow tri hull

11. Does it have a hydrafoil, dolefin or trim tabs
>no, but should I?

12. Make, model, diameter, pitch and whether SS or aluminum prop
>4 blade composite 10.5x11

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
>6200rpms @ 30mph w/2 people and 10 gallons

14. Are you at sea level or a higher elevation, give us the elevation in feet
>1900 ft above sea level (San Angelo, Tx)

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 forgoing could be the reason your prop is not attaining full RPM
>replaced all electrical and is working as new

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
>it has been on for the 3 years I owned it, just never knew my Rpms untill I recently got tac working

17. Does the prop show any damage that you can see
>no

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
>maintain max WOT 5500rpms and improve top end without buying $tainless $teel. Aluminum options if possible.

 

[hwsiii]

Re: 6K WOT top speed 30 mph

In my analysis of your boat performance with that prop i found it to have a prop slip factor of 30%, which is ridiculously high. My assumption is that your composite prop is flexing and creating the extra prop slip. I am curious to know what brand of prop you are using. There is no way you should need a hydrafoil for that boat to hold the stern up. Here are my numbers.

Prop Slip

I am recommending a Turning Point Hustler prop in a 12" pitch, it should let the motor get very close to maximum RPM and since it has very good blade geometry it should help increase your speed without all of that prop slip.


Price: $92.98
You Save: $26.52
Compare: $119.50
Discount: 22.3% Off
Add Hustler Aluminum Propeller Prop: H1-1012 Hub: 11 To Your Cart

Propeller Specifications:
SKUrop #H1-1012Hub #11
Manufacturer: Turning Point
Brand: Hustler
Material: Aluminum
Diameter: 10 - 3/4?
Pitch: 12?
Blades: 3
Rotation: Standard (Clockwise)
Usually Ships Within: 1 Business Day

If you have any more questions I will be happy to answer them.



H

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

http://boatpropellers.iboats.com/Ma...9982/?**********=560567251&*******=538261764] <this is what you reccomended

http://boatpropellers.iboats.com/Ma...16941/?**********=560567251&*******=538261764 <this is what I was looking at.

Ill explain myself first, I read that I should go 2" more on pitch for rpms to reach 5500, and 2" more (total 15" pitch) to accomadate going with a 3 blade. So why would a 12" pitch be better than the 15" I was looking at? not to get ahead of your response, but it seems that Hustler props are top of the line? and you mention in previous post that diameter should be close to 13" the Hustler option is 10"3/4

 

[lowkee]

Re: 6K WOT top speed 30 mph

I'm a bit confused as to the 12" recommendation as well. If the current blade is 11" pitch and running @ 6200RPM, wouldn't you need to go 15" pitch to get it down to 5400RPM (4" x 200RPM per inch)?

 

[hwsiii]

Re: 6K WOT top speed 30 mph

Unless your prop has lost diameter from sand and mud or you have a blade messed up these are the calculations. Your 4 blade prop is not acting like a 4 blade prop or your prop slip would be about 9% instead of 30%, that is the reason I didn't deduct anything for going from a 4 blade to a 3 blade. The hustler has very aggressive blade geometry and that is another reason I didn't deduct anything for the change as well. If you were to change to a 15" pitch these are about the RPMS you can expect, in my opinion.


Prop Change

H

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

ok somethings obviously not right, and I think I figured it out by going back to the calculator that I used to find gear ratio, the slippage was defaulted @ 30%

so I screwed up your calculations by possibly giving you an incorrect gear ratio, but now that im looking I cant find it anywhere. how do I calculate gear ratio?

 

[hwsiii]

Re: 6K WOT top speed 30 mph

That would certainly change my numbers, because I used the prop slip to decide I didn't need to take into account a change from 4 blades to 3.
Put a piece of tape on the prop and also on the lower unit and then put a mark on it. Then pull the plugs and turn the motor until the the marks lineup and seem how many revolutions that was. You cannot calculate gear ratio, you can only guess close, that is why you do it with the motor.


H

 

[hwsiii]

Re: 6K WOT top speed 30 mph

If you would tell me the year I may can help you find it.


H

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

6. Year, make and model of motor
>79' Mariner 70hp

 

[hwsiii]

Re: 6K WOT top speed 30 mph

I forgot I already tried and it is not in my database.


H

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

I counted 2, so roughly 2?

 

[hwsiii]

Re: 6K WOT top speed 30 mph

Then I recommend the 13" in that same prop, it will bring you down to right at 5,500 RPM.


H

 

[westexasrepublic]

Re: 6K WOT top speed 30 mph

Ordered> Husterler Turning Point 10.5X13 w/ hub assembly... results coming next thursday. http://boatpropellers.iboats.com/Ma.../9981/?**********=819656083&*******=772517434

Never had one with an unattached hub, is there anything I should know before using this type of prop?

 

[hwsiii]

Re: 6K WOT top speed 30 mph

No, it will come with the instructions of how to put it together.


H