How To Weigh Your Boat and Trailer Part 2 PDF Print E-mail
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Monday, 10 August 2009 01:57

How to Weigh your Boat and Trailer Part 2

  This article is Part 2.  If you haven't yet read part one,  please go to here.


Step 4 - Weigh Yourself

Weigh Yourself

 The plan is to weigh yourself.    Then you will press down on the end of the beam, while still still standing on the scale.   The scale will then read your weight minus how hard you are pressing.   I weighed in at 214 pounds.


Step 5 - Lift the beam up a tiny bit while still on the scale

Weigh the Empty Beam


While still on the scale, lift up the beam by the end, and read how much your weight goes up.   The weight of the beam itself is contributing to lifting the boat too, so it must be considered also.  While lifting the beam as pictured, the scale read 232 pounds, meaning that the end of the beam weighed in at 18 pounds.


Step 6 - While still on the scale, push down on the beam


 While still standing on the scale, push down on the end of the beam until the wheel of the trailer lifts a tiny bit off the ground.  It make take a few tries to get the scale positioned right so it reads accurately while you are pushing.   If your weight isn't enough to lift the trailer, you will need more leverage with either a longer beam, or with a fulcrum which is closer to the point of contact on the trailer.

Safety Note:  Note that in the picture my fingers are not wrapped under the beam.  At any time, your beam might break or fall.  You do not want to mash your fingers against the scale or the pavement!

Safety note:  The scale is not under the beam, and neither are my feet.   If the beam breaks or slips, I don't want to hit my feet.

With the wheel lifted off the ground, my scale read 70 pounds.  I tried it a few times in slightly different positions until I was confident I was getting consistent results.

So how much force was required to lift my boat wheel?   I was pressing with 214 - 70  = 144 pounds.   The end of the beam was also pressing with 18 pounds due to its own weight.  Therefore, it took a total of 144 + 18 = 162 pounds to lift the wheel.


Step 7 - Measure the Distance from your hands to the fulcrum

Measure Long Measure Long Also


 In this example the distance was 71 inches from the fulcrum to the center of the spot where my hands were pressing down.


Step 8 - Measure the distance from the contact point against the trailer frame and the fulcrum

Measuring the short distance

This measurement should be as accurate as you can make it.   Being off by an inch here can result in an error of 10 or 20 percent in your accuracy.  It might be a good idea to use a marker to mark the fulcrum position.  Make sure you measure from the point of contact against the trailer, which might not be exactly at the end of the beam.   In this example the distance was about 10.5 inches.


Step 9 - Measuring the Tongue Weight

Measuring the Tongue Weight

 This is pretty easy.  For an accurate measurement, make sure weigh it at a point as close to the actual tongue as possible.   This boat had a tongue weight of about 140 pounds.  If you like, you can weigh the block of wood separately, and subtract it from the tongue weight, but as far as the total boat weight goes, this is a trivial amount.

Safety Note:  Put the trailer jack (The front post with the wheel on it) down for this.  If the tongue falls off the scale, you do not want it to mash your foot!


Step 10 - Doing the Math

 OK, we've already done some math to figure out how hard the end of the beam had to be pressed to lift the wheel.   In step 6, we calculated 162 pounds of force was needed.  That includes the dead weight of the end of the beam.    Now we make a ratio of our leverage distances to get the amount of upward force on the other end of the beam which lifted the wheel off.

Weight on One Side = (downforce from step 6)  X  (Distance from hands to fulcrum) / (Distance from trailer contact point to Fulcrum)

In our case

 Weight on One Side =  162 * 71 / 10.5 =  1095 pounds


Now we assume that the weight on the other side of the trailer is about equal, so the total weight of the boat plus the trailer is:


(Tongue weight)  +   2 * (weight of one side) 

 140 + 2*1095 = 2330 pounds


So now you have an approximate weight of your trailer.   I was very happy to learn that my boat was well under 3000 lbs, and that I could get a smaller SUV to pull it.



 In Conclusion

     It only took about 20 minutes to do, which is a lot less time that dragging it to a weighing station, although admittedly this is less accurate.   But it was fun.   If you do decide to try this yourself, remember to keep safety in mind with every step.








Last Updated on Monday, 10 August 2009 03:25

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