3 blade or 4 blade.

Discussion in 'Downeast Boat NEWBIES' started by Quik Fix 16, Nov 30, 2019.

  1. Quik Fix 16

    Quik Fix 16 Senior Member

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    Boat is hauled temporarily and there is some discussion in the yard about 3 or 4 blade props. Which is best? I have both and have been running the 4 blade, never had the 3 blade on. What y'all think.

    Admin please move to general discussions.
     
    Last edited: Nov 30, 2019
  2. WoundUpMarine

    WoundUpMarine Captain

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    I've always been under the assumption that 3 blades will be a little faster, but 4 blades should be smoother and have a better bite if you're loading up the boat. What are you trying to get out of changing props?
     
  3. Quik Fix 16

    Quik Fix 16 Senior Member

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    Happy with the boat now but wouldn't mind a little more speed. When I was putting this boat together I asked for recommendations on props from pros. Pitch Perfect and Acme as well as a couple of local prop shops. All said the same thing . 18 x 17, 4 blade. Thats what I'm running but I have 3 blade props in my pile.
     
  4. BillD

    BillD Captain

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    10 yrs back or so I owned a 31 Blackfin with twin Cummins 370s.
    Boat came with a pr. of 4 blade Dyna Quads.

    Michigan Wheel Dyna Quad inboard propellers

    I upgraded to the newer better bite DQX 4 blades.

    Michigan Wheel DQX inboard boat propellers

    Both prop designs were pitched for same "engine load".

    I ran the boat with the both sets of props and noted how "each design" performed.

    Rpms and speed remained more or less identical with both sets of props...BUT...

    the visual "prop wash" in the wake of the boat was quite different at 22-23 knot cruise speeds.

    One could easily see the "extra bite" of the DQX blade design in the prop wash. Wish I had a pic or video. The visual was dramatic.

    That's my recollection. I run a DQX design on my 25 T Jason with the Cummins 370.

    The "new to me" 27 H&H has a dyna quad now. I'll be upgrading to a DQX for next season.

    Just my 2cents

    Bill D
     
  5. Quik Fix 16

    Quik Fix 16 Senior Member

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    Bill, that is interesting. I know propeller engineering is way beyond my pay grade. Question, if both props performed the same, why change? Did the boat get on plane better with the extra bite?
     
  6. BillD

    BillD Captain

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    Yes, sorry, e
    Yes, the boat got up and out a bit quicker with the dqx blades.
     
  7. CEShawn

    CEShawn Captain

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    Somewhere I posted this on Hull Truth or here... On my GM26, I switched over to a DQX, was able to drop my RPM by 200-300 and get same speed...which over time is fuel...both props were done correctly... thanks to Doug in Fairhaven who now has passed away... wasnt a huge different but as an engineer I was happy...
     
  8. Quik Fix 16

    Quik Fix 16 Senior Member

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    I checked out the DQX props. Amazing how everywhere is the same price. You rich New England guys can go for something like that. I'm just a poor blue collar Eastern N.C. guy. $1200 x 2 is a bit much for something I don't really need. Guess I'll put the 4 blade back on and keep cruisin', fat, dumb and happy.
     
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  9. BillD

    BillD Captain

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    1st thing you need to do like most on this forum have done....is ditch the "extra engine" and use a multiplier of X1 instead of X2 :)

    Quick ?, what are you running for a hull? Looks like a Black Fin in the your profile pic ?
     
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  10. Quik Fix 16

    Quik Fix 16 Senior Member

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    I'm trying to ditch it. For sale now. I have some other single engine inboards but all, like this one, are Shamrocks. Very similar to a Black Fin. 31 Shamrock, 31 GS at Dudleys1.jpg Grand Slam.
    Maybe just hang a couple of egg beaters on a bracket!:eek:
     
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  11. eyecatcher

    eyecatcher Senior Member

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    I helped a friend repower his 31 grand slam and dial it in. His runs good with 4 blades 34 knots in the corner with a pair of 370 cummins. Coming from a previous Blackfin owner, it's a cool boat but I'd say it is nothing like a Blackfin. It is quite unique with its hull design, weight balance, layout, mini keel and cored hull. It was difficult to get it it ride right at the higher speeds above 23 knots. The 24 Grand Slam however is a Charles Jannace design like the north coast and blackfin.
     
    Last edited: Dec 3, 2019
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  12. Pedlyr

    Pedlyr Senior Member

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    Wait.....I live in New England........I aint rich...........What do I do?
     
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  13. Quik Fix 16

    Quik Fix 16 Senior Member

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    Agree, completely different boats. I was referring to looks. All my Shamrocks are Boynton built. I never had a problem with ride at speed over 23 knots. Maybe the difference in weight from the diesels. Weight distribution in general. I actually like the way it rides at WOT but can't afford it.
     
  14. Bern

    Bern Member

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    Apologize if this is hijacking the thread. A three blade propeller will push a boat faster than a five blade? Approximately how much, like a knot or two? The water is cleaner with less turbulence with fewer blades? I can see why more blades would be smoother. As one of the others chipped in; I'm a carpenter and just happy to have the propeller that came on the boat.
     
    Bern,
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  15. Blitzen

    Blitzen Captain

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    More blades adds more drag from the prop. 3 bladed props are almost always faster but lack the ability to handle higher blade loads due to the lack of surface area. So on a boat where the weight and loads change often, more blades tend to be more efficient at the cost of a little bit of top end speed.
     
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  16. Brooksie

    Brooksie Captain

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    I did the test on my boat a couple of years ago. 3 blade = more speed at WOT but less at cruise and when heavy. Also more vibration. 22x18 4blade vs: 22x20 3 blade
     
  17. eyecatcher

    eyecatcher Senior Member

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    I wanted to try the 3 blade acmes they have slightly more blade area than the popular 4 blade DQX. Would be interesting on the right application to see how they go compared to equivalant diam/pitch. I dont think they would work well on a downeast since they have a raked design, variable pitch and cup.
     

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