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Prop selection for Q25 w/300 Verado

Discussion in 'Members Zone: Props and Power' started by Mscott, Jun 24, 2019.

  1. Vikingstaff

    Vikingstaff Well-Known Member

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    That’s because us Mercury owners are well, pretty cool people. :cool: :D
     
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  2. Dahbull

    Dahbull Active Member

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    Update,

    Tested my setup with the below results.

    1) Q25 with cladded arch
    2) Yamaha F300A
    3) Half tank of gas
    4) two adults for load
    5) 10 MPH Wind at back
    6) Prop 16” pitch 15.5” diameter 3-blade Saltwater Series II
    7) 6000 RPMs when trimmed to max up motor position with 37 MPH speed
    8) 5850 RPMs when trimmed for best speed with 38 MPH speed
    9) throws a rooster tail about 50’
    10) Able trim motor to full up trim position without ventilating prop or exceed motor RPMs.

    With motor trimmed full up I can even turn the boat without ventilating the prop.

    I’m looking for overall best performance of speed and RPM while still pushing a load (this is a pontoon)

    1) Is the motor mounted to low? If so, should I move the mount 1 or 2 holes up (down from the motor perspective)

    2) what prop diameter and pitch should I be using?

    Thanks to anyone that has similar setup. From my research I have found the Mercury motors (300 - 400 HP) mounted using the top hole (same as my setup) put the ventilation plate about 0.5 - 1.5 inches above the bottom of pontoon. With Yamaha I have found that mounting their motors places the ventilation plate at the bottom of the pontoon.

    Any insight on the exact location of the ventilation plate height compared to the bottom of the pontoon with the motor trimmed to level the ventilation plate as compared to the bottom of the pontoon is appreciated. Second, when the motor is trimmed as described, what is the distance between the pontoon and the start of the propeller?

    Thank You
     
  3. Folsom Dan

    Folsom Dan Member

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    It definitely sounds like your motor is way too low. I can’t even picture a full trim up position running in the water - sounds almost unbelievable.

    Is the boat on a trailer? If yes, can you get a picture of the location of the ventilation plate compare to the bottom of the pontoon?

    It’s really hard to offer an opinion on the prop until you get the motor height figured out. The drag created by the lower unit that far in the water will make it difficult, if not impossible, to get a proper prop on the boat.

    Is it still under warranty? This should be something the dealer takes care of.

    ***Edit to say if it’s the same boat as in your signature pic - the motor on that boat is trimmed out of the water. Are you certain you can trim it all the way up and not have the prop ventilate? Something seems odd there. ***
     
  4. JDB

    JDB Member

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    The Anti Ventilation Plate .5" to 1.5" Above Tube Bottom is a very good range in my opinion.

    My 2275 FSI ESP runs 48 to 49 with a moderate load and 300 ish HP from a Yamaha like yours.

    If the arch adds 1000 lbs maybe you are in the OK Range on speed but it really sounds like you might have dirty tubes or water in a tube ?? but I suspect you have checked the obvious stuff.

    Your prop is ideal but your load seems High IMO.
     
  5. Alicedream

    Alicedream Well-Known Member

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    My motor is a Yamaha 300 on a slightly smaller boat. As I stated above, with that arch I think you’re about at the right speed. I get 47 mph occasionally but I am a solid 45 to 46 mph boat. Max RPM is about 5800 trimmed. Do I think there is another MPH or 2 possibly with the raising the motor 1 hole, yes. Not worth it to change to me as I am have been really happy with the performance. A thousand pounds is a lot of weight.
     
    Last edited: Jul 9, 2019
  6. DaveyJ

    DaveyJ Well-Known Member

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    I think you’re thinking tilt when he’s talking about the trim as indicated on the gauge.
     
  7. Folsom Dan

    Folsom Dan Member

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    Could be. Power tilt/trim are the same thing . . . same button, same motor. The tilt/trim gauge doesn't necessarily read the limits of available trim. If I get to the "top" of the gauge in my boat - the prop is on its way out of the water.

    When you trim an outboard - you should trim it up enough so that it is just short of ventilating - it shouldn't matter what the gauge reads. Trim up (slowly) until speed drops and rpms increase (ventilation begins), then trim down slowly until the prop grabs good again.

    https://www.boatus.com/magazine/2014/june/staying-in-trim.asp
     
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  8. DaveyJ

    DaveyJ Well-Known Member

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    I guess I was basing my answer on my boat where the trim gauge is right on. When my gauge hits the fully up mark on the gauge is when it transitions to tilt. I’ve had 2 props on the boat that wouldn’t blow out while on the gauge. They may have just started to ventilate but hadn’t lost more than maybe 1 mph from peak.
     
  9. Jb75

    Jb75 Well-Known Member

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    If the boat runs 37 at 6000rpms and 38 at 5850 then when in the up position the prop is trimmed to far and losing grip (increase rpm and decrease speed) so I don’t think you’re able to trim fully and not ventilate. I have a Yamaha 250 (same length lower unit) and moved it up a hole. May be just a touch faster but I get more ventilation with the same prop you are running. I wouldn’t recommend it unless you are only looking for top speed. Mine is going back down next time it’s at the shop. But every boat is different and that arch may put more weight to the stern thereby sinking your cav plate lower. Good luck and try to enjoy the tweaking. I’m always messing with mine and I’ve found that most of what I change brings me right back to a 46/47 mph boat where I started....just with less cash.
     
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  10. Paint Man

    Paint Man Active Member

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    I have a 19 R23CW with a cladded arch and Yamaha 300CA I’m running a 15 1/2 x 17 SW11 prop. I max out at 5800 RPM and 47 MPH. The boat does seem to sit low to the stern compared to my last boat a GCW with sport arch. My motor is also mounted in the last hole. I would like to get to 6000RPM but the boat performs so well with this setup. I’m leaving mine as is. Andy
     
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