User Tag List

Thanks Thanks:  0
Likes Likes:  0
Results 1 to 9 of 9
  1. #1
    Join Date
    Aug 2011
    Location
    Ontario
    Posts
    332
    Thanks (Given)
    0
    Thanks (Received)
    6
    Likes (Given)
    0
    Likes (Received)
    44
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    First time trying a chopper prop... now i have a few questions on how they run

    Yesterday I tried my first surface peircing prop on my Valero YT - wow!

    My previous best was 65 MPH GPS with two people and a full tank of gas aboard (18 gallons) spinning a 26 pitch Tempest Plus @ 5900 RPM with the motor about 4 inches below the pad. This is deep - i know; however any higher and the prop wasn't able to hold the bow up. The prop would loose grip, the bow would drop while at full speed and she'd throw a big spray off the prop. I'd have to slow/trim down a bit and then try again.

    Now running a bone stock Merc 28 pitch A5 big ear chopper with the propshaft at about 3" below the pad and the same weight aboard i'm able to hit 76 MPH @ 6100 RPM!!! You go up in pitch AND your motor gains RPM - I guess thats the beauty of a surface peircing prop!! Boy this is fun!

    My questions are:
    1) This merc chopper caviates pretty bad while trying to get onto plane.... I have to feather the throttle and it takes about 10 seconds to get her up. I this normal for an over the hub type prop? If not. What would cause this?

    2) While trying to get the last few MPH out of my rig I can reach a point where I trim the motor enough for the prop to cavitate (while doing about 75 MPH) and my RPM goes up to about 6500-6700 but i loose a few MPH. I'm not really over trimming the boat at this point, the nose isn't too high and the spray off the back is less than the height of the motor. Why is it doing this?

    3) I just got this prop, but it seems like my motor can turn it easily and I think i'm getting past its peak power at 6100 RPM. Should I be looking for something else?

    Further info:
    - The motor is an '81 crossflow 235
    - I have yet to put a nosecone on my gearcase (water pressure is fine so far)
    - I have 8" of setback

    Many Thanks.

  2. #2
    Join Date
    Aug 2009
    Location
    south ga
    Posts
    949
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    0
    Likes (Received)
    0
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Yea some big pitch props on heavy Rigs makes the prop struggle to get on plane.
    2. The prop is still buried and your over trimming the prop as you said until you put a nose cone on and get the prop shaft up it's gonna have a hard time carrying the bow with alot of positive trim it has a adverse affect on the prop of pushing the boat thur the water.Think of it this way your prop being level it is driving the boat forward the higher you get your motor the less trim it will take to carry your bow.So over trim your prop it points to prop in a upward angle the rpms goes up and the rooster tail goes up but your bow goes down.(get a lwp)
    .3 Peak power? Is there ever enough spin the prop to the moon rpm equals speed get u a lwp take the prop to the surface and 6100 you will be learning to drive the boat all over again 3in below is not of the surface I'm a half in above some guys are as high as 2in above there pad your setup is gonna be hard to fix without a lwp altho some guys have plugged off the top 2 holes on there lowers and ran them higher just go on and get u a cone lower and set it up right
    90 xr 2002

  3. #3
    Join Date
    Mar 2009
    Location
    Port Saint Lucie
    Posts
    2,485
    Thanks (Given)
    3
    Thanks (Received)
    31
    Likes (Given)
    6
    Likes (Received)
    237
    Mentioned
    0 Post(s)
    Tagged
    1 Thread(s)
    The over the hub prop will cavitate alot with all that exaust going through it when your getting on plain. I had to releive the exaust above the cavplate to get it to grip better. Now it'll jump right on to plain no prob, but its loud.

  4. #4
    Join Date
    Apr 2001
    Location
    I live in Prineville Oregon which is in the central part of the state
    Posts
    1,592
    Thanks (Given)
    0
    Thanks (Received)
    3
    Likes (Given)
    0
    Likes (Received)
    9
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Sometimes the amount of cupping in the trailing edge of the prop wll have a big effect on prop slippage in a surfacing prop. Adding additional cupping in the right place can really help get you on plane quicker and will also help hold the bow up as you get more into higher motor heights. If you are truly running 75-76 MPH in your current situation you will surely need to add a nose cone to be able to run higher speeds as you will eventually run out of water pressure as you raise the motor. You will also get very close to blowout conditions as you start to reach about 80MPH. A nose cone with low water pickups will allow you to accomplish what you are looking for!== Higher speeds, no blowout, and good water pressure. If you don't have a water pressure gauge get one soon.

    Best wishes, Carter Powell

  5. #5
    Join Date
    Apr 2001
    Location
    Windsor, Ontario
    Posts
    5,942
    Thanks (Given)
    1
    Thanks (Received)
    82
    Likes (Given)
    48
    Likes (Received)
    321
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    I cured the planing problems on my Virage with a Bob's true tracker foil. I guess lots of other foils would work. It was dramatic. 5000 rpm and wait before, just hop on a plane after.

  6. #6
    Join Date
    Aug 2011
    Location
    Ontario
    Posts
    332
    Thanks (Given)
    0
    Thanks (Received)
    6
    Likes (Given)
    0
    Likes (Received)
    44
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Thanks for the input guys.
    I think my season is about over anyways, I'm going to be putting on a LWP, solid mounts and a torque tab this winter. I'll start off with those mods and then begin raising up the motor in the spring to see what she'll do. My goal is 80 MPH solo and the ability to carry 4 passangers with the same prop/motor height.

  7. #7
    Join Date
    Aug 2009
    Location
    south ga
    Posts
    949
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    0
    Likes (Received)
    0
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I was gonna say your planning problem can be solved with a allison cav plate you have a pm
    90 xr 2002

  8. #8
    Join Date
    Sep 2010
    Location
    arkansas
    Posts
    139
    Thanks (Given)
    0
    Thanks (Received)
    8
    Likes (Given)
    18
    Likes (Received)
    30
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    What are you using for steering.

  9. #9
    Join Date
    Aug 2011
    Location
    Ontario
    Posts
    332
    Thanks (Given)
    0
    Thanks (Received)
    6
    Likes (Given)
    0
    Likes (Received)
    44
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I will be adding a cav/drag plate over the winter (michael m I'll likely go your route). As for steering I'm running the duel cable ride guide that came with the boat, its got some slop in it so i'll be adjusting that over the winter too. I just wanted to see what she'd do this fall and so far i'm pretty happy with 76 on GPS.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •