prop size for best performance

[roscottjr]

I just bought a 1988 20ft Maxum Bowrider with a 125hp Force outboard. Right now it has a stainless steel prop but I am unsure of brand and size. What is the best brand, size, and pitch prop for this boat to get best performance from skiing, kneeboarding, general boating, and speed?

Also, considering the reputation these engines have, what type prop should I use in case the prop were to hit something in the water? Ive heard stainless steel props normally break other things as well if they hit something hard enough.

Robert

 

[steelespike]

Re: prop size for best performance

Prop selection is more complicated than just a boat and motor combination
unless someone has the exact same setup.
hwsiii should be along.He has a prop picker program but he'll need some details.In the mean time please read the stickies at the top of the page.
And the helps on the iboats prop store page.
You prop may have numbers on the barrel or under the prop nut.
If you can get us the prop size and your present max rpm and speed(gps is best)we can get started.If you have any questions we'll be glad to help.

 

[roscottjr]

Re: prop size for best performance

Im afraid I wont be of much help here. I just got the boat and have not taken it out yet. Well, I havent taken it out to where I can go above idle yet. My tach does not work so I wont be able to give rpms. I guess I was more or less curious to what the original prop size may have been but information will be great as I know nothing in the prop department.

Robert

 

[CharlieB]

Re: prop size for best performance

If you recently acquired the boat there are a number of maintenance items that your should check out before attempting any WOT runs to ensure that the motor is capable of performing and NOT self-destructing.

Spark test
Compression test
Carb clean
fuel pump rebuild
clean fuel tank pick-up tube
Replace primer bulb and hoses
Replace water pump impeller
Check out charging system, a bad rectifier can cause the tach to fail to function
Change gear case oil

A lack of fuel or lack of cooling water WILL toast that motor,and I'm sure that you don't want anything to go wrong with your new toy.

ALWAYS use a quality Marine TCW-3 2-stoke oil at 50:1 with a name-brand mid-grade fuel. Preferably without alcohol, if available in your region.

Learn to do all the above yourself and save a lot of $$$$$$, plus you'll have the satisfaction of knowing that your motor should last a couple of lifetimes

 

[roscottjr]

Re: prop size for best performance

CharlieB:

Thanks to this forum, I have already gone thru all those maintenance items you have listed along with others such as wiring and such. The gauges themselves are bad, the charging circuit IS charging the battery. Due to the information I found on here, I checked the charging circuit first when I found the tach did not work. The tank has been drained and the fuel looked and smelled fine but I would rather use the fuel in something a little cheaper such as my weedeater rather than go ahead and use it on this motor. With the reputation this motor has I dont want to take any chances. However, myself and the guy I bought it from took it on a WOT test run before I bought it so everything was working fine then, I didnt pay attention to the gauges at that time though.

And yes, I do all my own maintenance and mechanic work on my boats as well as my vehicles. Ive just never had a Force engine before.

 

[hwsiii]

Re: prop size for best performance

Scott, welcome to Iboats prop forum and we will try to help you as much as we can, but there is certain information that is needed in order to help you. Working over the internet and not being able to see the boat or prop the question is about makes it much harder to propose a solution to the correct prop that you need, and most people don?t know the make and model of the prop . When we get information in bits and pieces we continually have to look back and forth to try and piece the information together. The following form has all of the information that is needed to help you with your problems in finding the right prop. If you do not know all of the information that is asked for on the form please give us the most information you have available as I have a program I designed to find the right prop for any planing hull boat that needs this information. It requires time to find all this information when we have to look for it and in my defense I expect you to be willing to expend as much effort in finding the right prop as I do. We hope to be able to help you get the best prop we can for your particular uses, and this information is required to do that. It is not as simple to pick the right prop as most people coming to this forum think it is, that is why we ask so many questions, it is for your benefit we ask all these questions.
There are other people who can help you that don?t need this much information, if you would rather wait for them just don?t fill out the information I am requesting. And if you have a stainless steel prop or are changing to one the blade geometry of the prop can make a lot of difference in speed, RPM and the handling characteristics of the boat. Most of my calculations are done assuming an aluminum 3 bladed prop will be used, when changing to a SS or 4 blade prop, or changing within SS props we need to discuss what you are trying to accomplish.

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

 

[roscottjr]

Re: prop size for best performance

1. 1988 MAXUM Bowrider
2.
2a. 125hp
3. 6 people 20 gallons
4. General boating, future kneeboarding, posibly skiing
5. Deep Vee, where do I find the dead rise?
6. 1988 Force 125
7. 125hp ,unaware of the gear ratio but would like to know what it is.
8.
9.
10. Not a bass boat, no pad bottom ( I assumeing this means a flat spot at the rear of the hull)
11. None of these
12. make model diameter pitch unknown, SS prop
13. Have not been to a lake yet to go WOT.
14. Not sure but close to sea level
15. Performed these checks when going over entire boat to be sure everything is the way it should be.
16. Previous owner installed this prop. Says the boat is fast and has no issues pulling tubes or skis
17. No damage
18. Again, have not been to a lake where we can go faster than idle speed

I didnt realize all the information it takes to find a good prop. The one that is on it may be fine but we havent taken the boat out for a WOT run yet so I cant answer some of the questions at this time. A few of the questions I simply do not know where to find the info. My tach is bad and we dont have a GPS. I may be just jumping the gun here and may not have a problem at all. I guess Im just trying to get ahead of the boat so to speak.

Robert

 

[hwsiii]

Re: prop size for best performance

Robert that is a good idea, but you need to fix the tach and borrow a GPS handheld or even some phones have them. After you get a Wide open throttle RPM and speed come back and we will be glad to help you.


H