Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can someone please help me solve this problem?

  1. Feb 1, 2010 #1
    I am building a house boat. I have bought 3 aluminium pontoons. The pontoons are 33 feet long and they have a 24 inche diameter. Here is the two answers I need (1) How much weight can it hold at full emersion in fresh water? (2) How much weight will make the pontoons half emersed in fresh water?

    I am looking to keep the pontoons half way under water but it would be nice to know how much total weight it could hold just for the knowledge.

    It would be great if someone could give me the equation for this as well. You can not find anyhting that relates to this on the internet!

    Thanks for the help

  2. jcsd
  3. Feb 1, 2010 #2
    You can use Archimedes' Principle to solve this one.

  4. Feb 1, 2010 #3
    Yeah I really can not make anything of that! It would be awsome if someone could solve this problem for me. I am not good in math at all! Thanks
  5. Feb 2, 2010 #4
    The amount of weight it can support is equal to the amount of weight of water it displaces. If they are perfect cylinders 33 feet long, and 2 feet wide then the volume is:
    v = pi * r2 * h = 325 cubic feet.

    The weight of a cubic foot of water will change slightly with temperature, but 62 lbs is a good number to use. So one pontoon will support 325 * 62 = 20,125 lbs. If you want it half submerged you simply half that weight. So the three of them half submerged will support about 30,000 lbs. It is important to note that the weight it is supporting will include the weight of the pontoons. Even if they are half submerged you must include their entire weight.
  6. Feb 2, 2010 #5
  7. Feb 2, 2010 #6
  8. Feb 2, 2010 #7
  9. Feb 2, 2010 #8
    Yes I made an error figuring the volume. The formula I gave was correct, but I made a mistake (I squared pi instead of r). So the correct numbers are 103 cubic feet, and 103 * 62 = 6,386 lbs fully submerged. About 9,500 lbs for all three half submerged.

    Sorry for the error.
  10. Feb 2, 2010 #9
    Sounds like a homework problem re-worded.

    I'd like to see pictures of the pontoons.
  11. Feb 3, 2010 #10
    Dale thanks for the re-working of the problem. Im going to stick 9000 lbs to be on the safe side for building and what not. Norman im 29 years old havent been in school in quite a while but if you wanna see pics of the pontoons I can post them. Thank you guys for your help and quick responses it awsome to have a place like this.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook