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I need help in making a boat for a project!

  1. Apr 12, 2010 #1
    There's a project i have to do where i would be testing different kinds of propeller blades on the boat. Its just to test the effect of different blades so nothing has to be all high-tech. Apparently i know how i can make Propeller blades but i have no idea how to make the boat.

    I just need to create a small boat as a model for my experiment. I need ideas on how to make one so that i can attach and detach propellers to it to record its varying performance.

    I know this sounds like something really weird to ask but any help will be highly appreciated. Try toe xplain stuff as if u were explaining to a highschooler.

    Hope i make sense
    CHEERS:)
     
  2. jcsd
  3. Apr 12, 2010 #2

    berkeman

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    Do you actually have to make the boat part for the project? Or can you just buy one from a hobby store?
     
  4. Apr 13, 2010 #3

    rcgldr

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    You can't just buy or rent a real boat with a motor? One of the issue with a boat propeller is that it operates within the wake of a boat, so the boat has an effect on propeller design.
     
  5. Apr 13, 2010 #4
    @berkeman
    see im not much of boat geek. I have never bought toy boats so i kinda' dont understand how thier system works. the thing is if i buy a boat from outside, will i be able to attach and detach home-made propellers or not?

    Also, i believe my english is not that great so thier might be a misunderstanding in my descriptions. when i say small boat, i mean a small one like an RC boat. Not a big one. Just a small working model.
     
  6. Apr 13, 2010 #5

    sophiecentaur

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    Very non-trivial. You have to deliver the 'drive' to the propellor underwater. This can be done with a very long straight shaft at a shallow angle over the stern (like the canoes on the Amazon), a 'stern gland' to take a straight drive to a propellor just under the hull or a right-angled drive (like on a regular outboard motor).
    These three approaches suit different hull types (for instance, where the rudder goes).
    As far as I can see, you should buy / borrow an existing boat with an engine and just stick to making and testing a few of your designs of propellor.
    Mind you, if I had to do it, I'd go to the lake or pond where you plan the tests and get chatting to an enthusiast with a boat. He ( I assume) could be very keen and furnish you with details of shaft and thread size for his boat. You could offer him the best version of propellor from your tests, if it works better than his existing one. This approach involves minimum of non-prop work and maximum time for the actual project.

    and
    "Its just to test the effect of different blades so nothing has to be all high-tech."
    Hah! Tell that to a powerboat enthusiast or oil tanker designer! :biggrin:

    The pitch of the propellor, the revs and power of the engine and the hull design speed are all vital to match together, if you are to get the best design for each boat.
    Just how long do you have for this proj?

    btw, was it ever suggested that you might do static tests in a tank with no boat? You can measure force and water speed very easily when everything is within easy reach.
     
  7. Apr 13, 2010 #6
    @sophiecentaur

    so here it goes. My aim in the project is to find out the distance traveled by a boat in a particular period of time when a) there is a change in diameter of the propellers and b) there is a change in the number of wings of the propellers. So i need to do a bunch of trials attaching and detaching different propellers. now the problem here is that I DONT HAVE A BOAT.

    try and help me what sorts of design i can do to conduct an experiment like this finding out the effect of different kind of propellers.
     
  8. Apr 13, 2010 #7

    berkeman

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    I agree with sophiecentaur's point, that you may be better off *without* a boat for these experiments. It would be much more scientific for you to just use a force measuring device (like a spring balance) to measure the force generated by your propellers in still water. A swimming pool or pond would be fine, as long as you can position the propellers far away enough from the bottom and sides so that there is no interaction with the prop's water stream flow.
     
  9. Apr 13, 2010 #8

    sophiecentaur

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    A HUGE factor in marine propellor design is the Pitch of the propellor. When it is running properly, it will act exactly like a screw, through the water with very little slippage. If it is too coarse or too fine it will just thrash around in the water generating bubbles and no thrust. I should say that is almost the major factor in the choice of design - as long as the blades aren't too long or too short. Number of blades is only a choice between 2 and 3; more than 3 is unlikely to make any difference (or make it worse) - but your project should show that, I suppose.
    Ask anyone who has had proper advice about changing their propellor and they will say it was equivalent to a real increase in power.
    Presumably your propulsion will be from a 12V motor. Use a meter to check the current - it will give a good indication of the power being delivered. You will need a gearbox to get the revs something like right or the screw may just thrash around uselessly - do some sums and look up marine propellor design on Google to get some ideas. There are many links at all levels of sophistication.
    I am even more of the opinion that you need to collaborate with a local enthusiast or your whole time will be taken up in boat construction and design. Else you'll need to buy something (arrrrrgh!).
    But it all depends on what the project is for. If it's something that has been suggested by a supervisor then you may be better to re-think and go for the berkeman solution. Not as flashy but it would give some much more worthy results. Why do you want to get into boats all of a sudden?
     
    Last edited: Apr 13, 2010
  10. Apr 13, 2010 #9
    I want to know who the hell is making a highschooler do this?! If the internet were not around, this wouldn't even BE a learning experience!

    @chirag.rk93: Another approach could be to look at the efficiency of the prop design for a given boat. Then you can choose ONE hull type and pitch, and instead of measuring force with a gauge you probably don't have... you could check to see how many revoltions or how much current applied to different prop configurations while maintaining the boat at a constant speed.

    To do that, just have water flowing at a steady rate, and try to keep the boat "stationary" (think of a swimming pool that jets water at you against which you swim). An Ohmeter (with the bells and whistles), a couple of fishtanks and you're halfway there.
     
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