This post and video is a continuation of the previous post. However, it is also much more. By calculating the lift of a partially submerged barrel we can estimate how high our raft will float in the water and how much we can load the raft. To do these calculations we need some way to determine how much the volume of water the submerged part of the barrel will displace. We could probably look up in books and or the internet and find a formula, but that is no fun. We develop our own way of determine it using the trigonometry we have just learned. (Yeah there really was a reason we learned it!)

That is the first part of this exercise is figuring out a way to figure out the problem. The first picture shows the method. We need to figure how how much of the barrel is under water. This is shown in light blue in the diagram. We do that by determining the angle from the center of the barrel to the water line and then from that angle we can determine how much area is in the “pie slice” of the yellow and blue areas. We can then subtract the triangle area represented by the yellow to determine the area. submerged. The second picture shows the values we need to determine and our need for the trig. we have just learned.

The final thing I am showing in the post is how to use a spreadsheet to solve a problem. Because I made a mistake in the video and had to troubleshoot it, you also get to see in detail the difference between pointing toward a fixed cell location and a relative cell location. (I planned it that way! Believe that and I have a bridge to sell you also.)

If you want to download the spreadsheet file it can be found here: Spreadsheet flotation_2.

The dxf file of the diagram of the problem is also available for use with LibreCad. BarrelCalcs1.dxf

If you do not have a spreadsheet program available on your computer you can download a free version of LibreOffice on their website. It works with Linux, Windows and Mac operating systems.

The video associated with this post is embedded below.

As always I hope you learned something and was at least somewhat entertained as I stumbled through making the video.

Gary

“A Plastic Barrel Pontoon Raft – Part 2” by Create-and-Make.com is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

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[…] calculations are very similar to the previous calculations. We have to again calculate the area of the “pie slice” and the triangle part of the pie […]