CPP a Practical Option?

Discussion in 'Props' started by We're Here, Aug 1, 2011.

  1. We're Here
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    We're Here Junior Member

    Let me preface my question by saying that I wanted to go directly to one of two forum contributors for advice but I've since found that neither are members so there is no way to message them. My fear is that my question is so specific that the overall membership might be bored to tears and for that I apologize.

    I am discussing a build with the builder of a FRP Maine lobsterboat. This is a planning hull with dimensions of 28' 6" LOA, 27' 2" W/L, 10' 6" beam and a draft of 2' 10". Finished weight unknown but it will be heavily built. Power is a Cummins QSB intermittent rated at 350 BHP. Propeller estimated to be 22". Estimated cruise speed of 26 kts with a 32 kt top speed (sorry but I am metrically illiterate).

    As it stands, I would probably spec a TD 5050 or 5061 with a ratio of 1.75 or 2.0. I'd want a dripless system in place of a stuffing box and I'd need a trolling valve to slow it down to trolling speeds.

    Now the question (and I've read nearly all of the CPP threads here), is a CPP system a practical option? I know CPPs are near universal in parts of the world but they aren't in the US. First and foremost is whether I could put one in for what I'd pay for the system mentioned above (whether or not the builder would touch it is another unanswered question). A principal concern is support - are these available in New England and is there an experienced repair facility here (I looked at the Helseth website and saw nothing in the US - perhaps this was just a website omission)

    I'd appreciate any thoughts on the matter.
     
  2. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Yes it's practical, but remember it depends of the kind of use you have as you know.. They aren't too comlicated for any of the NE facilities to repair.. and any part you need comes flying where ever you need it.
    If you wan't I can forward your question to Richard just PM me your email..
    BR Teddy
     
  3. FMS
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    FMS Senior Member

    Does anyone have an idea why controllable pitch propellers have been so slow to be adopted in the USA for recreational boats? I was impressed by Michael Kasten's article and cost comparison 10 years ago: http://www.kastenmarine.com/CPprops.htm
    But now 10 years later controllable pitch propellers are still not popular here like in Europe.
     
  4. Adler
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    Adler Senior Member

    Fact

    Dear,

    CPP was designed for a particular reason and special conditions that faced on tugs and trawlers often; where we need high thrust at low hull speed . On such cases that is succeeded when the Propulsion Engine's Speed increased and the Propeller's Pitch is regulated at Low value.

    Through a general point of view the CPP system affords the ability to use the Total Power of a Propulsion Engine to produce High Thrust at Low Speed or the Opposite where is needed.

    CPP system for example has much better effect on Crash Stop Test on Sea Trials which is very important in Navy Applications.

    Based on that CPP system is installed only in ad hoc applications - if you consider the cost criterion.
     
  5. Willallison
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    Willallison Senior Member

    I'm curious... Richard (asTeddy suggested) is surely one of the uncontactables.... but who is the other...?

    My only experience with CPP's is on low speed craft... I don't ever recall seing one in a planing application. I would imagine that the mechanism for controlling the pitch would create rather a lot of drag / turbulence at higher prop revolutions.
    Why not contact the manufacturers.. they'll soon tell you if they have anything that's applicable
     
  6. baeckmo
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    baeckmo Hydrodynamics

    You might check with the Servogear people in Norway; they have a lot of medium-speed applications running.

    And how the h.... can anybody suggest the performance without a decent figure on final weight?????!!!!! Propeller dimensions and gearing are strongly connected with the weight, and likewise is the critical hump drag. Before you do anything further, have someone qualified to check displacement, otherwise you will end up with a disappointment and fighting everybody previously involved in the project!
     
  7. We're Here
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    We're Here Junior Member

    Hhmmm ... Well, considering the fact that the boat exists only on paper at the moment, an accurate weight isn't readily available. On the other hand, I was able to venture an educated guess as to speed and wheel size because that's what earlier builds of this design delivered. I appreciate your suggestion about Servogear and will look into this.

    I've followed our local (Maine) lobsterboat racing series for more than twenty years now and I agree that with similar power and similar hull design, the lightest boat will win every time.

    With your questions hopefully explained, I'd like to point out that your keyboard seems to be sticking when you hit "!" and "?".
     
  8. FAST FRED
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    FAST FRED Senior Member

    Does anyone have an idea why controllable pitch propellers have been so slow to be adopted in the USA for recreational boats?

    Cost and a lack of demand by initial purchasers.

    Heck mfg. of million dollar bucket don't even install a fuel tank with a sump to solve water and therefore bugs in the fuel problem.

    AS the owners don't ask.

    On a black iron tank it wouldn't be $25. and you ask why no $10,000 props that require some understanding to operate?

    FF
     
  9. TeddyDiver
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    TeddyDiver Gollywobbler

    Valid points :(
     
  10. We're Here
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    We're Here Junior Member

    I met with the builder yesterday and he estimates the weight at just under 8000# with tanks dry (total fuel capacity expected to be 160 gallons so the displacement then becomes about 9100#).
     
  11. Submarine Tom

    Submarine Tom Previous Member

    No water tanks to fill?

    Any other undocumented weights to add on?

    -Tom
     
  12. Willallison
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    Willallison Senior Member

    A preliminary weight estimate is something that should be produced during the very early stages of any design - and particularly in a powerboat where higher speeds are part of the objective. As the design is refined, so too is the weight estimate... failure to do so as Baeckmo quite rightly points out will almost certainly end in disappointment.
    Producing an accurate weight estimate is a long and tedious task... for a relatively simple boat like you are talking about, it will likely only run to a few pages in length. Everything needs to be accounted for - right down to the number of beers you want to have on board.
     

  13. We're Here
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    We're Here Junior Member

    Other than the contents of an MSD holding tank, none.
     
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