How Much Weight Can Aluminum Pontoons Support in Fresh Water?

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Discussion Overview

The discussion centers around determining the weight capacity of aluminum pontoons when submerged in fresh water, specifically addressing how much weight they can support when fully submerged and when half submerged. Participants explore the application of Archimedes' Principle and engage in calculations related to buoyancy and displacement.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant requests the weight capacity of three aluminum pontoons, noting their dimensions and expressing a desire for an equation to calculate this.
  • Another participant suggests using Archimedes' Principle to solve the problem, providing a link for reference.
  • A participant calculates the volume of one pontoon and estimates its weight capacity based on water displacement, suggesting that three pontoons half submerged could support about 30,000 lbs, while noting that the weight of the pontoons themselves must be included.
  • Another participant challenges the volume calculation, indicating a potential error in the initial estimate and providing an alternative volume calculation.
  • A subsequent reply questions whether the previous answer is incorrect and presents their own calculations for the weight capacity of the pontoons, differentiating between fresh and salt water capacities.
  • One participant acknowledges their earlier error in volume calculation and provides corrected figures for weight capacity, suggesting a total of about 9,500 lbs for three pontoons half submerged.
  • Some participants express skepticism about the nature of the problem, suggesting it resembles a homework question.

Areas of Agreement / Disagreement

There is no consensus on the exact weight capacity of the pontoons, as participants present differing calculations and interpretations of the problem. Disagreements exist regarding the volume calculations and the implications for weight support.

Contextual Notes

Participants note variations in calculations based on assumptions about the pontoons' dimensions and the properties of water. There are unresolved mathematical steps and differing interpretations of the results.

Who May Find This Useful

This discussion may be useful for individuals interested in boat building, buoyancy calculations, or those seeking to understand the principles of displacement and weight support in aquatic environments.

christoph8025
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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

Chris
 
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christoph8025 said:
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

Chris

You can use Archimedes' Principle to solve this one.

http://en.wikipedia.org/wiki/Buoyancy
 
elect_eng said:
You can use Archimedes' Principle to solve this one.

http://en.wikipedia.org/wiki/Buoyancy

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
 
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.
 
DaleSwanson said:
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.

[\QUOTE]

The diameter is 2 ft, so the radius is 1 ft. I get 103.7 cubic feet. It seems you have
an extra factor of pi.
 
willem2 said:
DaleSwanson said:
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.

[\QUOTE]

The diameter is 2 ft, so the radius is 1 ft. I get 103.7 cubic feet. It seems you have
an extra factor of pi.

So does that mean his answer is wrong? is it 30,000 lbs?
 
christoph8025 said:
willem2 said:
So does that mean his answer is wrong? is it 30,000 lbs?

I came up with 6150 pounds per pontoon, in fresh water, and 6312 pounds per pontoon in salt water. This is the total weight that a fully submerged pontoon could support. As mentioned, you need to figure in the weight of the pontoon itself, to know the additional load that can be applied.

Roughly, at about half submergence with 3 pontoons, you might get about 9000 lbs of loading.
 
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.
 
Sounds like a homework problem re-worded.

I'd like to see pictures of the pontoons.
 
  • #10
Norman.Galois said:
Sounds like a homework problem re-worded.

I'd like to see pictures of the pontoons.

Dale thanks for the re-working of the problem. I am going to stick 9000 lbs to be on the safe side for building and what not. Norman I am 29 years old haven't been in school in quite a while but if you want to 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.
 

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