Build log - 10m tour boat

Discussion in 'Boat Design' started by yodani, Nov 12, 2015.

  1. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    HI THERE I HAD A GOOD LAUGH, without a sense of humour, this forum will be dull. Bert
     
  2. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 1, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Hi everyone:) I am sorry for the upside down pictures. I have posted straight from my iPhone and I had no idea how they will look on the forum. Will be away from a real computer for a while so they stay that way for now.

    As I have mentioned before the prop is a bit too big abd I plan to reduce its diameter. Do you have any experience with that? Prop calc reccomends a prop 21X15" and I have a 22x17" now. The engine achieved a max of 2000RPM when it should go up to 2700 RPM. Do you have any suggestions on how much dia should be taken out?

    By my calculation I should reduce the diameter with 2" so that will give me a 20x17" prop. Is that correct? Or should I reduce 1" and try again to see how it works?

    Cheers,

    Daniel
     
  3. BertKu
    Joined: May 2009
    Posts: 2,498
    Likes: 43, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Daniel, Don't worry anymore, the moderator has kindly rotated the pictures for you.
    Why don't you ask Daiquire to help you with the pneumatics, he is an expert in that field.

    There are programmes on the internet which gives you some idea for the pitch and propeller info. the program is propcalc and if you google Castle Marine in the UK, you can download the program at no cost. Bert
     
  4. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 1, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Thank you Bert.

    As i said in my post- I have calculated the prop and I knew the prop I have is a bit too large but now thw question is how do I proceed with the modification? I have read that one inch in diameter removed will give you about 400 RPM MORE ON THE CLOCK. Any experience with that? As I can not modify the pitch of the prop easily by my calculations I need to take off 2 inches.

    Any advice ?

    Daniel
     
  5. BertKu
    Joined: May 2009
    Posts: 2,498
    Likes: 43, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Regret, but my knowledge is very limited. In any case in my case I made my own propeller from scratch. Daiquiri was so kind to give me a lot of advice and I am happy. But in my case I am not worried about speed or efficiency. My advice to you? Download that program from Castle Marine ad the various prop diameters in them and with the wrong pitch and see what the result is. One piece of advice. As soon you change a value go total back, otherwise you result is not accurate Bert
     
  6. BertKu
    Joined: May 2009
    Posts: 2,498
    Likes: 43, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Here some pictures how I made the prop. I first made 2 pieces within 1 gram each with the same shape from 3mm 316 SS. Then I bought a piece of round bar + a piece of aluminium 2 mm + a 25 mm shaft (round SS 316 bar) I have a small lathe and welded it all together. It seems to work (with some help from Daiquire, when I placed it in the wrong way) and it works reasonable well , I have no idea whether it would have worked better with the shape slightly different. I made it in a 2 blade, because it was easier to balance for me. Next time I will make a 4 or 3 blade.

    Most of the time I used a big hammer and the vice and the metal vile.
    Bert
     

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  7. BertKu
    Joined: May 2009
    Posts: 2,498
    Likes: 43, Points: 58, Legacy Rep: 223
    Location: South Africa Little Brak River

    BertKu Senior Member

    Daniel, I would not reduce the prop at all. I have been playing with the propcalc program from Castle Marine and if you reduce the power to your prop, i.e. you throttle back you need a different size of prop in anyway. What means do you have to accurately measure your power to the prop in anyway. You cannot change the adjustment needed on the pitch. We both are stuck in what we have.

    Thus my conclusion is. Don't reduce it, but first get it all finished and see how your boat performs at max. rpm and at a lower rpm, with the same weight on board. In my view there are so many variables, like full fuel tank, empty fuel tank, two passengers less or more, lower engine speed, etc. You cannot change your pitch in anyway. Why removing something, which you may need at the end of the day? You cannot weld it back !! However I am not an expert, my knowledge is just common sense logic. Bert
     

  8. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 1, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

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