74 evinrude 50hp prop help

[Andy in NY]

okay, my new-to-me 1974 evinrude 50hp currently has a 13x19 prop on it, but its pretty dinged up. i have a 13 3/4 x 15 prop that came off a 73 evinrude 50hp that has a new hub and is in alot better shape. can i use this prop? how will it effect performance?

 

[hwsiii]

Re: 74 evinrude 50hp prop help

Andy,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. 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, and most other people who are trying to help you will need the same 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 exact prop you need 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. 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 and RPM.

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
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
8. Manufacturer?s recommended WOT range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Does it have a hydrafoil or trim tabs
11. Make, model, diameter, pitch and whether SS or aluminum prop
11. WOT RPM and speed from prop, how much gas and how many people in boat for test data

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

 

[Andy in NY]

Re: 74 evinrude 50hp prop help

1. Year, make and model of boat - 1970 starcraft jupiter
2. Length, width and base weight of boat - 15'10", 6'9", 750 without motor
3. Number of people and gallons of gas normally on boat - 2 adults 3 small children 6 gallons
4. What do you use the boat for cruising and tubing
5. Is it a Deep Vee and if so how many degrees of deadrise - no
6. Year, make and model of motor - 1974 evinrude
7. HP and gear ratio of motor - 50, unknown
8. Manufacturer?s recommended WOT range - 5500
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches - unknown, not currently on boat
10. Does it have a hydrafoil or trim tabs - i have a hydrafoil that i was thinking about putting on, but doesnt currently have one.
11. Make, model, diameter, pitch and whether SS or aluminum propmake unknown, currently has 13x9, want to know if 13 3/4x15 will work
11. WOT RPM and speed from prop, how much gas and how many people in boat for test data- n/a, boat not currently operational

 

[hwsiii]

Re: 74 evinrude 50hp prop help

Andy, if it is a 2.42:1 gear ratio you should be running a 17" prop, the 15" will probably work until you get a 17" pitch but be careful not to turn too many RPM. You ought to do about 30 MPH.

H

 

[Andy in NY]

Re: 74 evinrude 50hp prop help

Andy, if it is a 2.42:1 gear ratio you should be running a 17" prop, the 15" will probably work until you get a 17" pitch but be careful not to turn too many RPM. You ought to do about 30 MPH.

H

okay, i just wanted to know if that prop would be okay to use... like i said it has a new hub in it... and the prop on the motor is pretty dinged up. btw, in the questions i accidently put that what was on there was 13x9, should be 13x19 just fyi.


so ultimatly i should be using a 13x17 prop?

how will each different size affect performance?

 

[hwsiii]

Re: 74 evinrude 50hp prop help

The 15" pitch will make the boat jump out of the hole when you give it gas but top speed not as fast and can potentially overrev and hurt the motor.
The 17" wil have a good hole shot but not as good as 15" and will not let the motor turn too many RPM and a little faster than the 15" and will help the motor last a long time.
The 19" will have a bad hole shot and it will lug the motor because it will not let the motor attain the correct RPM and thus reduce motor life.

H

 

[Andy in NY]

Re: 74 evinrude 50hp prop help

The 15" pitch will make the boat jump out of the hole when you give it gas but top speed not as fast and can potentially overrev and hurt the motor.
The 17" wil have a good hole shot but not as good as 15" and will not let the motor turn too many RPM and a little faster than the 15" and will help the motor last a long time.
The 19" will have a bad hole shot and it will lug the motor because it will not let the motor attain the correct RPM and thus reduce motor life.

H

Great, thank you so much for your help! I'll get back to you with my results as soon as i splash the boat.

 

[hwsiii]

Re: 74 evinrude 50hp prop help

That sounds good.

H

 

[Andy in NY]

Re: 74 evinrude 50hp prop help

Well, she splashed on saturday!

first run with the 19p prop was with 6 gal gas, 2 adults (230 and 210) and 1 kid (about 50). moderate chop.

motor trimmed to second hole, top speed 23 consistant, managed to hit 24 and 25 a few times for a second

second run, about 3 gal gas, 2 adults 3 kids (230 140 80 50 25) moderate chop.
motor trimmed to 3rd hole, top speed 25, seeing 26 and 27 for a millisecond!


I was going to put on the 15p prop, but it wouldnt slide on! it came off a 73 50 hp, same motor. but it was like it wouldnt seat right, and the washer wouldnt catch the splines and the castle nut wouldnt go on far enough to get the cotter pin through.

 

[hwsiii]

Re: 74 evinrude 50hp prop help

Andy you didn't give us any RPM readings, where are they. LOL



H

 

[Andy in NY]

Re: 74 evinrude 50hp prop help

Andy you didn't give us any RPM readings, where are they. LOL



H

I dont have a tach... sorry... i plan to add one as soon as i can though. dunno if it will help, but heres a video.

 

[hwsiii]

Re: 74 evinrude 50hp prop help

Andy, without a tach you are trying to see in the dark, and it is NOT possible. From the video it sounds like the motor is not turning up to its stated RPM of 5,500. Spend the money for a tach and then we an see what is really happening with your boat and motor. Don't buy a prop without first buying a tach. My recommendations.



H