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1973 Johnson 65 HP Powershift Propeller

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  • 1973 Johnson 65 HP Powershift Propeller

    Hey all,

    I need alittle insight as I am new to the boating world. Over the weekend I was invited to go out on my brother in laws boat ( 15ft Gemini ) and do some fishing. While going out on the boat I had notice when we cleared the no wake zone and we throttled up the boat just would not gain rpms and my brother in law went to the front of the boat and then the boat started to gain rpm and plane out. Being a mechanic myself I told him thats not right. He has recently put a new prop on it and I noticed it was a S/S prop and the other one was an aluminum. It seemed to me like he may have gotten the wrong pitch prop but he says that there's something in the prop that when if it hits something hard enough that internally something will give before it does any damage to the lower unit. Does this sound right ? I would think that if that were to happen you wouldnt be able to run in the water atall, but nonetheless it ran extremely well ontop with no vibrations once rpms were gained except for the fact it wouldnt come out of the hole for nothing untill the bow was loaded. Is there any way I could find what the proper pitch would be like an oem spec ?
    Sorry for such a long 1st post but wanted to give all the info 1st shot.


  • #2
    Re: 1973 Johnson 65 HP Powershift Propeller

    First, there is no "standard" or one size fits all for any engine except for some of the very small outboards. The reason props with various pitches are available is that the manufacturer has no idea what boat or load the engine will need to push so they aren't even shipped with props. A motor on a pontoon takes a very different prop than one on a fast hull. The dealer generally installs a prop based on what boat the engine is hung on, unless the engine and boat come from the factory as a package. The only way to tell what prop you have is to look at the barrel of the prop for numbers such as 12-3/4 x 15 (12-3/4 diameter x 15 inches of pitch). Sometimes there will be a part number on the prop -- again its either on the barrel or on the face of the hub behind the nut. The only other way to tell what you have is to visit a prop repair shop and have them put it on their pitch gauge. Since we have no idea what engine is involved here, what the wide open throttle rpm is with the current prop and what the current prop is, we can offer very little assistance.

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    • #3
      Re: 1973 Johnson 65 HP Powershift Propeller

      I understand prop/boat/motor combos would be next to impossible to match up without all the other input info. What about parts internal to the prop and or prop shaft that would give on an abrupt impact like I mentioned prior ? Is there such a thing ? I did mention in my post title that the motor is a 1973 Johnson 65 HP Powershift is there something else you need to know to figure out what type of engine I am dealing with ?

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      • #4
        Re: 1973 Johnson 65 HP Powershift Propeller

        Most boats that size would use a 17 inch prop, lightly loaded, a 19 might be fine. Back in 1973 Johnson did ship the engine with a 13 X 19 prop.

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        • #5
          Re: 1973 Johnson 65 HP Powershift Propeller

          Most props have a rubber bushing between the hub (the part with splines through which the prop shaft protrudes) and the outer blade area of the prop. Should you strike something solid, that rubber cushion breaks its bond and the hub slips inside the blade area thus reducing the chance of damage to lower unit gears. The idea is to sacrifice the prop rather than the much more expensive lower unit gears and its housing. There are other replaceable hub systems but they function in much the same manner. A prop with a rubber bushing must be repaired by a prop shop if the bond is broken and the prop slips.

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          • #6
            Re: 1973 Johnson 65 HP Powershift Propeller

            Sounds good to me. Seems like a good effective way for prevenative failure. With that theory in mind if the hub has separated from the prop hitting something would the boat still be operable like it was ? He will be bringing the boat by on Wed so ill have a better look to see when I pull the prop off. Also will be able to see what markings are stamped on the prop as far as size/pitch and maybe a manufacture of it. Thanks for the info so far and ill post up what I find after Wed.

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            • #7
              Re: 1973 Johnson 65 HP Powershift Propeller

              Originally posted by bubbyman View Post
              .....and we throttled up the boat just would not gain rpms and my brother in law went to the front of the boat and then the boat started to gain rpm and plane out. Being a mechanic myself I told him thats not right.
              ....that's normal for a small underpowered boat or one being to heavily loaded at the back. So, normal operating procedure would be just that; move weight forward until you're on plane, and then move the weight aft again. The cure: buy a stronger engine and/or a bigger boat. A lower pitch prop may also help, but may then lose you some top-end speed as well.

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              • #8
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                Re: 1973 Johnson 65 HP Powershift Propeller

                If the boat has power trim; trimming in (down) would help it get up. If manual then you might have to live with it.It would be good to find out the max wot(wide open throttle)rpm.And max speed with a gps.It's not good for the motor to operate outside it's max wot rpm rating,either too hi or too low.
                Of course if the prop is right performance and mpg will be at its best.
                Not a bad idea what with prices being what they are.

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