Show Ski Prop Size Question

Discussion in 'Drivers Corner' started by 78Hydrodyne, Jun 3, 2008.

  1. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,321
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    Both RiverRat and Must-ski have extensive show team experience. I would listen to them for a show team prop.

    It sounds like the four blade is a good prop. If you are looking for a little more rpm and low end I would be tempted to have the tip cup (or some of it) removed and leave the trailing edge cup alone. This would decrease the effective pitch a little and also decrease the effective rake.

    This should give you a little less bow rise, more static thrust, and more RPM. Opti's have rev limiters so you really can't over rev one.

    jim
     
  2. Dyna-Kid

    Dyna-Kid Boat of the Month

    Joined:
    Oct 19, 2007
    Messages:
    203
    Location:
    Lake Metigoshe, ND
    Boat Model and Year:
    74 18 Hydrodyne 150 / 06 17.6 Dyna-Ski 150 Merc FS
    Ski Team:
    Club de Skinautique
    Took off my merc 4 bladed 15"X18p prop last week and put on a standard 3 bladed merc aluminum 15"X17p prop. More testing to be done this week coming up but this is what I've discovered so far.

    The 3 bladed prop only runs the boat about 2 mph faster at the top end and the 3 bladed "blows out" almost every time coming out of the hole on tight turns. The 4 bladed prop seems to have more bite starting from a dead stop but I haven't tried a heavy pull yet.

    I will try and have some of the cup taken out of the 3 bladed prop this fall but so far I'd have to say I favour the 4 bladed prop for my applications.

    On a side note, in turns out that our 17.6 is much more versatile than I could have imagined. Not only does it do a nice job pulling skiing acts, but it also works well as a safety/pickup boat with the open bow (just more room to put skiers and skis). I only wish that the gas tank was up front.

    Airguide speedo goes in next week and a wedge installed this fall.

    Kevin
     
  3. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,321
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    Maybe I should try the four blade. Is it a Merc aluminum prop?

    I had a bow rider many years ago and I was able to shoe horn a tank under the front bow seat. It was not a Dyne and there may not be room for one in your boat. Maybe two small tanks--one on each side.

    jim
     
  4. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,321
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    If the prop is ventilating in turns, taking the cup out will probably make that situation worse. Props are black magic, so it might be worth a try.

    I have to really lay my boat on its side to make it ventilate, but it is a foot narrower than yours.

    Moving the tank to the front might make it ventilate worse also.

    jim
     
  5. Dyna-Kid

    Dyna-Kid Boat of the Month

    Joined:
    Oct 19, 2007
    Messages:
    203
    Location:
    Lake Metigoshe, ND
    Boat Model and Year:
    74 18 Hydrodyne 150 / 06 17.6 Dyna-Ski 150 Merc FS
    Ski Team:
    Club de Skinautique
    Hi Jim,

    I'm 99% sure my four bladed aluminum prop is a merc prop. I will double check when I get out to the lake tomorrow.

    I never had time to check the rpm / speed ratio's and will most likely wait until my airguide is installed.

    Cheers,

    Kevin
     
  6. Dyna-Kid

    Dyna-Kid Boat of the Month

    Joined:
    Oct 19, 2007
    Messages:
    203
    Location:
    Lake Metigoshe, ND
    Boat Model and Year:
    74 18 Hydrodyne 150 / 06 17.6 Dyna-Ski 150 Merc FS
    Ski Team:
    Club de Skinautique
    Jim,

    The four bladed prop I have IS a Merc Prop. It's an Alpha 4 aluminum 14.5"x18p prop and Mercury lists this prop as being designed for ski boats.

    Interesting to note that both the 3 bladed 15"x17p and the 4 bladed 14.5"x18p run the exact same numbers at 3500 rpm and 4500 rpm (on this boat). At 3500 rpm I do 29 mph and at 4500 rpm I do 37 mph with either prop.

    For moving the boat from one location to another, I have the kids run it at 3500 rpm as all the boat review stats I looked up for the 150 Optimax have 3500 rpm providing the best fuel economy.

    I would still like to try one of the high performance stainless steel 3 bladed props before the end of the summer. I'm wondering which one to try first.

    Kevin
     

Share This Page