A strange question

Discussion in 'Props' started by BertKu, Dec 29, 2020.

  1. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    I am busy building my 2nd dual electric motor system. We all know that the one must turn the opposite way then the other. But before I make a mistake, although my gut feeling is it does not make matters. Is there any rule on which side, Port side is left handed or right handed. Thanks for your reply. Bert
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 1,204
    Likes: 273, Points: 83
    Location: Colorado

    Blueknarr Senior Member

    Port is left. (Same number of letters)
    Starboard is right. (Both have many letters)
     
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,153
    Likes: 958, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

  4. RAraujo
    Joined: Apr 2010
    Posts: 129
    Likes: 22, Points: 18, Legacy Rep: 114
    Location: Singapore

    RAraujo Senior Member - Naval Architect

    I think usually the right (starboard) propeller will rotate to the right (clockwise) and the left (port) to the left (counter-clockwise) (supra-divergent). See below as seen from aft.

    [​IMG]
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,153
    Likes: 958, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    That certainly would agree with common sense, in terms of reducing aeration.
     
  6. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Thank you RAraujo
    But my problem is that I have my rudder between those two propellers. Thus maybe I should have it the other way, so that the water gets pushed more to the outside and not against the rudder. That is the reason why I wrote: Strange question. Bert
     
  7. gonzo
    Joined: Aug 2002
    Posts: 15,408
    Likes: 999, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The water will be pushed to the outside either way. One rotation on the top, and the other on the bottom. With two propellers, the usual setup is to have two rudders.
     
  8. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Thank you for your reply Gonzo, but I am not so lucky that I can lift my 2 propellers and 2 rudders out of the water. I started with 1 rudder which I can lift out of the water when trailing the boat on a trailer and I am able to lift the 2 propellers out of the water and can sail with the sails and rudder , without drag of my propellers. I am not so clever that I have been able to master reverse energy into my batteries from my propellers when sailing ( on a lake as my electric power is limited to 2 Hp and limited battery capacity) . Bert
    P.S. Actual I can go to 5 Hp, but it means short battery duration
     
    Last edited: Dec 30, 2020
  9. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    RAraujo, I have decided to go with your reply. Should it be later on better to do it the other way, it will make a plan. Thank you very much.
    Bert
     
  10. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    One more question I have on the 2 propellers. Should they be pure parallel pushing the boat OR should they be slightly push to a center point , let say, center point about 3 meters behind the boat OR should they push slightly outwards? Bert

    The attached photo is the old system, motors parallel . I am now building a different new system and although, for the professional, it is a strange question, but for me better safe than sorrow. I assume parallel is the best, because if one propeller falls out, the boat still steers straight. Should I make it to a center point, then the steering is changed. Your view is greatly appreciated. Bert
     

    Attached Files:

    Last edited: Feb 7, 2021
  11. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Keith, just to illustrate what I have made in the past few years and now my 3rd last design. The first motor was too heavy for me to lift when I got older. The motors I have a question on is the 3rd motor, lifted totally up out of the water and the last one totally motored down. Bert first engine.jpg 3rd double engine.jpg
     

    Attached Files:

  12. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Keith, here the photo of the 90 degrees bevel gears I made. They are from 316 Stainless steel and in closed with gearbox oil. Also my problem is that I only have prop software program's for Diesel and petrol boat engines, thus I have decided to make the props myself. Brushless Motor has torque from the 1st revolution to the max speed and thus non of the programs are actual valid for brushless motors, It is logical, as the current at 1 RPM is unbelievable high, due to the fact the no inductance has at that moment build up. I measured currents up to 300 Ampere for some of my brushless motors. Thus I experiment now with it, by making my own propellers. The balancing I do when I have bend all the blades to what I think it should be. Bert
     

    Attached Files:

  13. gonzo
    Joined: Aug 2002
    Posts: 15,408
    Likes: 999, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Have you compared the performance to that of an off the shelf propeller?
     
  14. BertKu
    Joined: May 2009
    Posts: 2,521
    Likes: 46, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Gonzo, No, it does not make sense for me to buy lots of propellers and try to see whether I will go 1/10 knots faster or slower. It would be a different issue when I need to win a first place. I am quite happy with my propellers made by myself. I fully agree with you that a profesoional propeller would do maybe a lot better maybe not. But which one? I googled and I have a choice of a few hunderd makes and shapes and sizes. But Gonzo I am 80, speed is no longer an issue for me. I wonder whether soon propeller software would come out special for electric motors. Thanks Gonzo, Bert
     
    Last edited: Mar 3, 2021

  15. gonzo
    Joined: Aug 2002
    Posts: 15,408
    Likes: 999, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    A propeller is calculated for the power input, RPM, hull resistance and other parameters. It is irrelevant where the input power comes from.
     
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.