User:Vincecate/Models/Multispar

This model was sponsored by Joep. His support is greatly appreciated.

Model design

This multispar has 4 spars each with its own ballast that are loosely connected to a platform. This is a bit like Versa Buoy. There are 4 legs of 4.5 feet each made from 2 inch pipe. The X-shape platform is 1-inch pipe with each piece 1.5 feet long. Elastic cords connect the 4 legs to the platform. Each elastic cord has a knot inside the cap and also a knot on top of the platform pipe. So the legs are held to the platform but they can flex. There is a small balsa wood platform held on with rubber bands. The cup has a thumb tack inside it holding it to the balsa wood. Used an orange highlighter pen to put a little color in the water in the cup.

July 15, 2008

Tried 2.5 lbs steel weights from a weight set and these were too small, the legs floated out. Then tried 5 lbs steel weights (so 20 lbs total) and it floated too low in the water (picture above). It was very stable, just that the platform was hit by some waves. Plan is to use sand in plastic bags so that we can adjust the amount of weight used till it is right.

July 16, 2008

Today we used grocery bags of sand tied to the bottom of the spars instead of steel weights. I think a solid weight tied with a short rope works better, but I did not have the right sized weight. Used some red washable paint from my children's craft supplies to color the water in the cup, which works better.

Video below starts with the view from the pier and then shows the view from the multispar. Biggest waves are in the 8 to 12 inch range. Winds are 20 to 30 MPH. For a 1:25 model this is like modeling 100 to 150 MPH winds, or a strong hurricane. The model does lean some and is moving downwind.

This video should be slowed down by a factor of 5 to show the movement of a full sized version. I have not done this because the video mostly just takes longer to watch.

<youtube v="oZz1wCWbO10" />

July 17, 2008

Cut 2' 1" lengths of 1/2 inch rebar and put 2 on each leg with big rubber bands. This was both easier than bags of sand and worked better. It meant that all the legs had the exact same weight so it floats level now.

<youtube v="mliXEhUMu-4" />

Only remaining problem is heave, the up and down motion. Might be able to bend the re-bar so that it offered some resistance to up and down movement but have not tried that yet. If we cut a 2-inch hole in a 2 lbs plate of steel and put it over the bottom of the leg instead of the re-bar it would work better.