What to begin with

dozerII

Admiral
Joined
Oct 25, 2009
Messages
6,527
Hi Everyone. I am replacing the O/B on my boat with a completly rebuilt one and the dealer is including a new prop. I need some recomendations as to where to start.
The boat is a 1984 Starcraft SS160 16' open bow I am guessing it weights around 1200lbs. When I brought it home the boat, motor and trailer weighed 1700lbs but the boat had saturated foam and plywood floor.
The replacement O/B is a 1993 Johnson 90 hp with tilt/trim. I am not sure what the recomended wot rpm is, my Evenrude 115 was 5600 to 5800 if I remember right.
The boat will be used mostly for fishing, but I occationaly pull a tube.
Thanks

Glen
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: What to begin with

You also might try reading this for a better understanding of changing props for better performance, and for what the major differences are between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057

Dozer, welcome to the forum, 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 or just use the numbers for reference in your reply and type in your information.

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 outdrive IMPORTANT
If you don?t know the gear ratio, you need to pull the plugs out of the motor 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.

AntiventilationPlateStraightEdge-2.jpg


10. Is it a bass boat or does it have a pad bottom and is it on a bracket, if so how far does the bracket extend from the stern.

11. Does it have a hydrafoil, dolefin, whale tail or trim tabs and is the motor on a bracket, and if so how far back from the stern is the bracket

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 prop I recommend 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
 

dozerII

Admiral
Joined
Oct 25, 2009
Messages
6,527
Re: What to begin with

HWSiii Thanks for the reply, That is some great information and I will be glad to do the home work you suggested. At the present time I have never had this boat in the water and I don't have the motor yet. The shop selling me the motor is including a new prop and I would like to know what is a good size to get, to obtain a start point. I am sure they will include what ever pitch and diamater I wish.
Glen
 

mpsyamaha

Petty Officer 1st Class
Joined
Jun 8, 2007
Messages
395
Re: What to begin with

its hard to guess, but i would think something like a 13.25" x 17p would be in the ballpark.
 

180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
Re: What to begin with

Talk to the shop, they should let you water test a few and keep the one that fits your needs.
 

dozerII

Admiral
Joined
Oct 25, 2009
Messages
6,527
Re: What to begin with

Thanks for the replys and info. I would love to try a few different ones but the place I purchaced the O/B from is 700 miles away and will be shipping me the unit. The closest marine dealer to where I live is a two hour drive, so it won't be easy to make changes.

Glen
 
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