Prop sizes for 1976 70HP Evinrude?

[Elfred]

What prop would be recommended for 1976 70 hp 3cyl Evinrude on 16 ft cobia?

 

[Fun Times]

Re: Prop sizes for 1976 70HP Evinrude?

Hi there Elfred, Welcome to iboats. To be able to receive the most helpful information out of you question, it's always best to start your own personal thread versus adding on to the end of another thread like you had done. So I went ahead and took the privilege of creating your own thread for you.

Now for our iboats experts to be able to help you out further, We would need a bit more information from you so they could try to assist you better. Hope this helps, Good luck.

If possible, here's an essential data list that would be required,
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

 

[Elfred]

Re: Prop sizes for 1976 70HP Evinrude?

Thank you for your reply and the new thread. This problem arose when I was coming in to the dock from a trip. I shifted to neutral to coast and when I tried to shft to forward or reverse there was no response. I figuredit was a problem in the linkage. Yesterday when I went to examine the linkage, I noticed there was no propeller on the motor. So I don't have the propeller.

The boat is a 1965 Cobia, 16 feet. The motor is a 1976 70 hp Evinrude with manual tilt . I just got the boat and should have checked the propeller but didn't. So I am trying to get advice with what I have. The propeller that was on the motor workedfine. My use of the boat is for pleasure. No more than four people on board.

Thanks for any advice.

 

[jestor68]

Re: Prop sizes for 1976 70HP Evinrude?

A 17 pitch prop would seem to be a reasonable starting point. Depending on the weight of the boat, a 15 pitch might be required.

Since you don't know what size was on there, you're starting at square one. It might help to use a prop selector to get a general recommendation of a place to start.

Any idea how much the boat weighs?

Is it something like this boat?

 

[Artwerke]

Re: Prop sizes for 1976 70HP Evinrude?

Probably a 15" , but definitely pin the propnut.

 

[Elfred]

Re: Prop sizes for 1976 70HP Evinrude?

Thanks for the reply--very helpful. The boat looks like the photo you sent and according to a used boat dealer who has the same boat, the boat would weigh 1000lbs and the motor 200lbs. Thanks for any advice.

 

[Elfred]

Re: Prop sizes for 1976 70HP Evinrude?

Thanks for all the help. I can now summarize the information. The boat is a 1969 , 16ft. Cobia runabout. It apparently weighs about 1000lbs. The engine is1 1976 70hp Evinrude and weighs about 200 lbs. I will use the boat for pleasure carrying no more than 4 people. High speed is not an important issue. I would like to plane with 4 people at good speed.

 

[jestor68]

Re: Prop sizes for 1976 70HP Evinrude?

Does the boat have a tachometer? You need a tach to determine if the motor is turning up within it's recommended rpm range; which I believe is 5000-6000 rpm for your motor. It needs to turn up at least 5500 rpm to develop full power( 70 hp @ 5500 rpm).

I'd test a 17 to see if it'll get 5500 rpm; if not, drop to a 15 pitch.

It really depends on the health of the motor( it's a 1976).