Variable pitch props. Worth it on small boat?

Discussion in 'Props' started by DennisRB, Nov 30, 2010.

  1. DennisRB
    Joined: Sep 2004
    Posts: 1,268
    Likes: 25, Points: 48, Legacy Rep: 228
    Location: Brisbane

    DennisRB Senior Member

    I remember reading a thread by Richard where he listed the positives of a variable pitch prop and how they are not expensive when you are starting from scratch since you don't need a gearbox etc. Also I cant see, to find the thread anymore. Anyone got a link? :D

    Somehow I think this article was meant more for larger boats/ships. Are variable pitch props still economical for smaller sailing boats? With smaller boats and higher engine speeds you would still need gear reduction wouldn't you? How small can you get these things and how much do they cost? Is it worth it on a 30-40 foot sailing boat?

    I just found this and have been reading... http://www.kastenmarine.com/CPprops.htm
     
  2. Brian@BNE
    Joined: Jan 2010
    Posts: 262
    Likes: 13, Points: 18, Legacy Rep: 151
    Location: Brisbane, Australia

    Brian@BNE Senior Member

  3. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    When you build new the cost of the CPP... controlable pitch props.. setup is competitive with conventional transmission shafting arrangements. When you refit...it becomes expensive. New shaft log, new P bracket, new engine coupling , new engine alignment, and a new control system. On small sailing yachts the size of the CPP prop hub is to your disadvantage due to drag. Most sailing applications use a MAX prop . Low drag...very efficient reverse thrust and able to be fine tuned . also expensive.

    Good article on general CPP for small craft. Interesting that I never see any liturature on a CPP lifecycle. How many forward reverse featherings are needed to produce a service interval ? The max prop will need service every year due to grease blow . Blade STOP wear is also an issue on MAX props.

    http://www.kastenmarine.com/CPprops.htm
     
  4. DennisRB
    Joined: Sep 2004
    Posts: 1,268
    Likes: 25, Points: 48, Legacy Rep: 228
    Location: Brisbane

    DennisRB Senior Member

    Thanks for the link Michael ;)

    I will take a look at the other thread again too. Thanks Brian.
     
  5. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    There is a trend to run motors at their optimal rpm - usually where max torque is made, and where fuel is the most economic. The motor iow sits on one rpm and stays there. In this case the CPP would be a good option since you can adjust speed best for the load of the vessel while remaining at best economy.
     
  6. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    VPP are so good that everyone should have one...only money keeps it this way
     
  7. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Yes, wouldn't mind having a few myself. Have plans for them ;)
     
  8. portacruise
    Joined: Jun 2009
    Posts: 1,114
    Likes: 32, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    Another approach is using 2 props on the same shaft, rather than a variable pitch. I have used a small prop in front followed by a large prop in rear. With a 2 speed gearbox or one speed electric drive you can select the two for maximum efficiency. Both are run at low rpm, high torque together and the rear prop is removed by quick release if needed for shallow running at high speed. That is one thing a variable pitch prop can't do, which is increase or decrease length for better efficiency. Has worked for me on very small boats anyway..


    Hope this helps,

    Porta

     
  9. BertKu
    Joined: May 2009
    Posts: 2,480
    Likes: 43, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Vic,

    That is interesting. Any pics for us ? Special on how you release the one or the other prop.
    Bert
     
  10. apex1

    apex1 Guest

    Don´t mix up that Max prop stuff with a CPP folks! It is a completely different animal and although it can be "adjusted" it is nothing but a folding prop.

    And please forget the term "variable pitch prop" we do not have them on boats. Those are rarely installed, and only on commercial craft to finetune the pitch when the ship is hauled out!

    Sabb is still providing a smaller unit for sailboats.

    The service life is much longer than that of a gearbox. I had a CPP on a 21 meter police boat which had never seen a hand touching it in 40 years of hard service. (and the service records were seamless)
    Another reason for the northern European fishermen to install CPP´s exclusively. No service. (except for greasing the hub every few years on haulout)

    Porta,

    I too would be very interested to learn how you do that!!! And more so, how you compare the efficiency of such setup with a CPP! (remember it is not a VPP, as you always like to name it)

    Regards
    Richard
     
  11. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    I can offer some real numbers on a small boat conversion. In my case I removed a 47 hp Perkins 4-107 from a boat displacing about 8,500 lb. The 4-107 was propped to top out at about 2,400 rpm where the engine was producing around 28 hp. I operated the boat at around 1,600 rpm and the fuel burn was about 0.8 gph at 5.8 knots. I replaced this setup with a Sabb 2H (18hp at 2,250 rpm) and 490 mm two blade controllable pitch propeller. Fuel burn at 5.8 knots dropped to 0.62 gph. This is an S/L of 1.25 and a savings in fuel burn of about 22% With that tremendous savings I could buy dinner out for four at the end of a season. :)
     
  12. TeddyDiver
    Joined: Dec 2007
    Posts: 2,578
    Likes: 120, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Not sure but last year (in a phone call) they stated that their gear don't turn the blades to feathering posion, only from ahead to astern. So it seems for sailboats it gotto be West Mekan http://www.westmekan.com/index.php?option=com_content&task=view&id=12&Itemid=14 .
    There's also one another company possibly, but haven't asked them yet..
     
  13. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    Well I know Sabb no longer offers the small engines built by them so maybe they no longer offer the full feathering sailboat prop. My manuals clearly showed both a full feathering sailboat prop and a controllable pitch reversing prop for the 2H engine so they are available out there at least used.
     
  14. TeddyDiver
    Joined: Dec 2007
    Posts: 2,578
    Likes: 120, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    They do have their gearboxes still.. can you throw a picture from your manual pages? Maybe it depends of the propeller instead?
    I have been looking around also a secondhand setup locally to see if there's a way to modify..
     

  15. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    I cannot easily throw a picture up here of the manual. Its in the boat and the boat is shrink wrapped. If my memory serves me right the only difference between the two props was the drive block in the prop.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.