What props fit a ’79 Evinrude 35?

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Viewing 7 posts - 11 through 17 (of 17 total)

  • vintin


    Replies: 580
    Topics: 19
    #47588

    My understanding is larger diameter is better when pushing (more thrust) big loads and small diameter is better for light go fast boats. I’d suggest going for smaller diameter and then select the pitch to get the motor reving at the top of it’s rpm range with it loaded at it’s lightest load. That way the motor won’t over rev. In the small go fast boat that you are talking about it may be that adding even one passenger might change the optimum propeller. A working tachometer tells all.


    wetwillie


    Replies: 91
    Topics: 15
    #47590

    Interesting. I think the 10" diameter that came with it is the smallest available. If all goes as I’d like it to, I’ll be getting it wet tomorrow.
    I’ll report back with some numbers if I do. You know, Dan, that I’ll be gunning for you with my Runabout come Spring. 😉


    wetwillie


    Replies: 91
    Topics: 15
    #47606

    I took advantage of the unseasonably mild temps today and got my FC Rocket wet. The Chinese LED tach I bought off eBay worked for about 15 minutes. Long enough to get a reading at WOT. Looks like 10 x 13 is the right size prop for my application because it was taching 5270 RPM at WOT. Now to begin looking for one in better shape. Mine has some serious wear and a small piece missing on one blade. FWIW, WOT = 29 mph.


    outbdnut2

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 1705
    Topics: 91
    #47669

    Racing props are usually very small diameter/large pitch, but you lose low=end torque for planeing it off if you ever do carry a big load or pull skiers/tubers
    Dave


    wetwillie


    Replies: 91
    Topics: 15
    #47683

    So Dave, based upon your response, do you think I should be looking for a smaller diameter with a greater pitch? If so, I’m open to suggestions both with regard to #s and a source other than eBay.
    Thanks!


    outbdnut2

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 1705
    Topics: 91
    #47685
    quote WetWillie:

    So Dave, based upon your response, do you think I should be looking for a smaller diameter with a greater pitch? If so, I’m open to suggestions both with regard to #s and a source other than eBay.
    Thanks!

    If you are just out for max speed with no load other than yourself in that small boat, max pitch/min diameter without loading down the max RPMs is the thing, but you can end up with too much pitch and it will start loading the motor down. Best to get a tach and check RPM with the prop you have first. Best to run near or slightly above manufacturer’s max rated RPM for max speed. I have a 1976 35 HP Johnson (essentially the same motor up have) on a lightweight, 1957 12′ Crestliner Commodore12, decked aluminum runabout that I drive sitting at a steering wheel in front. I tried a 15 inch pitch and had to back off to a lower one because it performed bad when I had a passenger or two along; and even when alone in it, with the lower pitch prop, I liked the way it did acceleration recovery after it slowed some (or I slowed it some) when taking a quick, tight corner – it was slightly slower on top end, but a lot more fun to drive.

    For max speed, (you probably already know this), Shim the motor up higher on the transom using paint stir sticks under the transom clamps until you get so high that the prop starts to lose it’s grip in medium waves, then take out one stirstick – you can usually gain 1 to 3 MPH that way – I check speed on my boats with a portable GPS unit. The lower the motor sits in the water, the more the lower unit behaves like a big club being dragged through the water. AS you do this, adjust the trim pin angle as high as possible without it bouncing at wide open throttle – this will lift the boat up for least drag of boat surface in the water, but too high, it can bounce and it will cavitate on tight corners – I like to live with a bit of cavitation on corners as long as it’s not bouncing on the straightaway. Remember that the less boat in the water makes it harder to handle,so be sure you learn the boats limits in various waves at various speeds. I grew up doing everything you shouldn’t in a boat back inthe late 1950s/early 1960s, and I don’t recommend these setups unless a person is willing to take things easy until you learn the limits of your configuration – these things can flip.

    On your model motor, you will not find a super selection of available props, as it is not a popular racing motor. A 2-blade prop will also be faster than a 3 blade, but good luck finding one! Maybe Michigan makes one.
    Have fun!
    Dave
    Below is my son and daughter in that boat with my dog who loves boats:


    wetwillie


    Replies: 91
    Topics: 15
    #47689

    Thanks for the feedback, Dave. I’ve already checked the MPH (using a GPS app on my phone) and RPM (with a digital tach) at WOT, as noted earlier. I tried trimming the motor up one notch but it porpoised at speed and I lost 2 mph. Shimming the motor up is on my To Do list. I hadn’t considered a 2 blade prop but would want one IF I could find one.

Viewing 7 posts - 11 through 17 (of 17 total)
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