Tunnel Hull and Prop Pitch

VeroDDVeroDD Posts: 317 Deckhand
I've got a 17' McKee Craft Backwater center console with a 2002 90HP 2 stroke Yamaha. It's a semi-v with a tunnel hull. At wot it gets 5000 rpm and 34 mph. It currently has a 13.25" x 16 pitch stainless prop. Seems to me I should be able to get closer to 5500 rpm and close to 40mph with a smaller pitch. However, when searching props, I don't find any smaller than 15 pitch at 13.25". That would only give me a slight rpm improvement.
My question is, does the tunnel hull affect the max rpm and mph? If so, is there another way to improve performance?

Replies

  • FS DanFS Dan Posts: 2,353 Moderator
    tunnel hulls can aerate the water before it hits the prop which can lead to slippage.
    One thing to look at is engine height. A tunnel will allow you to raise the engine higher than normal.
    This will give you a shallower running depth and less lower unit drag.

    CMD
    Formerly Catmandew
  • pottydocpottydoc The thriving metropolis of Umatilla Posts: 3,168 Captain
    Vero, I got a 18 G3 tunnel hull with the same motor except it's a 2010. Mike will only turn 5k with a 13.25x15, and 36 mph, or 4700 with a 4 blade 12.5x17 and 30 mph. I think mine should turn at least 5500, but can't find a smaller pitch prop either.
  • gandrfabgandrfab Posts: 20,234 AG
    A prop shop can take some pitch out (or put some pitch in) your existing prop.
    :BUNNY gestapo

  • VeroDDVeroDD Posts: 317 Deckhand
    I've been thinking about raising the motor. The cavitation plate is just below the top of the tunnel.
  • pottydocpottydoc The thriving metropolis of Umatilla Posts: 3,168 Captain
    Got a jack plate on mine. It still won't turn the rpms even with the jack plate raised.
  • VeroDDVeroDD Posts: 317 Deckhand
    Got a jack plate on mine. It still won't turn the rpms even with the jack plate raised.
    That's interesting. I don't know what else to try. :huh It's not bad now, (within range 4500-5500) I just thought it would be better closer to 5500 rpms
  • Capt. PantsCapt. Pants Posts: 659 Officer
    I've got a Kenner 2103 Vision Tunnel w/ a 200 Optimax spinning a "HUGE" 19P Rev4 prop and plugs are in.
    Holeshot is ridiculous and literally a snap of the throttle and you're on plane "from a dead stop" or idle. If I'm running above 1500RPM's and snap the throttle, that prop spins and spins then suddenly catches as if the plugs were out, but they're not. That is the effect of the tunnel "bubbling" the clean water behind the transom.

    Trimmed up, and jack plate down, I spin 5300-5400 and run about 47mph loaded down for fishing, and literally "may" have lost 2mph by adding a T-top. If I keep the motor down, I feel like I'm bow steering, but as soon as you trim the boat free's up quickly and and becomes very "slippery" in the turns if you're not careful. I can gain about 4mph with the jack plate by raising 3" and spin up to n5700-5800, but any higher, and she "falls off" her sweet spot, drops about 5mph and the wake gets real wide with a fat rooster tail. Without the tunnel, this boat is way faster by about 4-5mph as it does not "squat".

    The "pitch" and the diameter" are very different beasts with propping. I've been reading forever trying to figure out the mechanics. From what I understand, diameter with "push more water" at said RPM of the same pitch. You can go down in diameter, up in pitch and obtain similar results, let alone prop models, rake, cup, etc. etc.... don't forget about 3 vs. 4 blades.

    My best performance comes from a jack plate, which is the only way to really appreciate and utilize the tunnel, combined with trim angle, and a prop that can run real high without blowout.
    Test you boat. Watch you speed and RPM's as you trim. It's VERY obvious where she wants to ride. Once she's there, that's when a jack plate gets dialed in.
  • VeroDDVeroDD Posts: 317 Deckhand
    Thanks. I've been on the www.propgods.com website and it was recommended I raise my motor.
  • FS DanFS Dan Posts: 2,353 Moderator
    VeroDD wrote: »
    Thanks. I've been on the www.propgods.com website and it was recommended I raise my motor.

    :grin

    didn't I say that in post #2. lol

    CMD
    Formerly Catmandew
  • VeroDDVeroDD Posts: 317 Deckhand
    Catmandew wrote: »
    :grin

    didn't I say that in post #2. lol

    CMD

    Yep, you did. Thanks again:cool:
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