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Kinny

Determining Trailer Tongue Weight

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I had access to a tractor trailer scale today so I wanted to check the tongue weight of my boat/trailer.  I pulled my boat onto the scale and stopped as soon as my truck rear tires left the scale.  I recorded that weight, chocked the trailer tires, and used the jack to lift the tongue of the boat just off of the ball, and recorded the weight again, which is also the total weight of the boat/trailer.  My tongue weight should be the difference in the two, correct?

Thanks in advance.

 

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I am not sure if that would give you an accurate tongue weight. 

Typically, you weigh just the truck with the trailer attached, so the weight shows the combined truck plus tongue weight. 

Then younweigh just the truck with the trailer not attached.  

Take the first weight - the second weight and that is your tongue weight. 

 

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I always measure the squat of the tow vehicle, by comparing the before and after distance in inches to ground from a duplicate place on the bumper. I then remove the boat trailer and pile 50# bags of softener salt upon the ball until I duplicate the squat. Mine is about 645#. Rule of thumb seems to be 10% of total trailer weight.  W

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Just take the trailer while off the truck and put the jack under the ball and weigh.  Simple.

What am I missing?

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22 minutes ago, WaterDR said:

Just take the trailer while off the truck and put the jack under the ball and weigh.  Simple.

What am I missing?

For me, a 1,000# capacity scale.

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If you don't have access to a scale to do what dsmacey mentioned, you can still use a bathroom scale. We tested this with a heavy construction trailer once vs a CAT scale and it was darn close.

You take a 2x4 and lay one end on a bathroom scale and another end on a brick of the same thickness so the 2x4 is level. Put the trailer tongue on the 2x4 1' from the brick (I don't know why we used a foot but you apparently just have to) but then 2 or 3 feet from the scale. Take whatever the scale reads and multiply it by the feet from the scale to the brick (so x3 or x4). The number you get is the tongue weight.

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Thanks for the replies. I’ll verify the tongue weight with the method suggested by dsmacey tomorrow.  From a mass balance standpoint, I think the way I measured it should be valid, but that’s why I asked the question.  Thanks again...

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14 hours ago, watson524 said:

If you don't have access to a scale to do what dsmacey mentioned, you can still use a bathroom scale. We tested this with a heavy construction trailer once vs a CAT scale and it was darn close.

You take a 2x4 and lay one end on a bathroom scale and another end on a brick of the same thickness so the 2x4 is level. Put the trailer tongue on the 2x4 1' from the brick (I don't know why we used a foot but you apparently just have to) but then 2 or 3 feet from the scale. Take whatever the scale reads and multiply it by the feet from the scale to the brick (so x3 or x4). The number you get is the tongue weight.

Yup....you have to use a FT just to make the match easy and have the correct ratio.

This method will be nearly perfect so long as you are close to level and have the distances correct.   In many ways, you are doing a larger version of the internal scale mechanics.

This is why all you really need is a bathroom scale.  Naturally, if your tongue weight is in the range of the scale you don’t need the board or the brick.

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It turns out the method I used was accurate, as verified with the scale / 2x4 method listed above.  Thanks again to all that responded.

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I set mine exactly as Watson 524 described above.  I also have a 700lb bathroom scale that I bought from Amazon that helped.

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I purchased a “Weight Safe” drop hitch several years ago that has a built in scale gauge.  A little expensive, but I tow several different trailers that require different heights and this makes life easy.  Comes in 4-6-8” drops design, all billet aluminum and stainless steer with interchangeable ball sizes, sweet unit if you tow a fair amount or various trailers.

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51 minutes ago, Wak'in said:

I purchased a “Weight Safe” drop hitch several years ago that has a built in scale gauge.  A little expensive, but I tow several different trailers that require different heights and this makes life easy.  Comes in 4-6-8” drops design, all billet aluminum and stainless steer with interchangeable ball sizes, sweet unit if you tow a fair amount or various trailers.

I got a rapid hitch, best purchase ever,  always have a 2 and 2 5/16 ball at all times with it and I think it drops up to 6in.  All aluminum so it wont rust.  Its good for up to 10k lbs.

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6 hours ago, soldier4402 said:

I got a rapid hitch, best purchase ever,  always have a 2 and 2 5/16 ball at all times with it and I think it drops up to 6in.  All aluminum so it wont rust.  Its good for up to 10k lbs.

I got the same. My tongue weight is 300lbs on my 21’ H2O. 

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On 5/5/2018 at 3:06 PM, dsmacey said:

I am not sure if that would give you an accurate tongue weight. 

Typically, you weigh just the truck with the trailer attached, so the weight shows the combined truck plus tongue weight. 

Then younweigh just the truck with the trailer not attached.  

Take the first weight - the second weight and that is your tongue weight. 

 

I think that gives you the weight of the boat and the trailer, not the tongue weight.  The tongue weight is the amount of downward weight placed on the hitch.

 

 

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This is not rocket science. Go to a truck scale and get a rear axle weight. Hook up the boat and get another rear axle weight. The difference is your tongue weight. 

Or, if the scale can not weigh each axle separate then you need to weigh just the truck with no trailer hooked up and then weigh just the truck with the trailer hooked up. The difference is your tongue weight. Weighing how much the trailer weighs when hook and unhooked from the truck does not give you the tongue weigh. The weight of the trailer will not change much as the axles do not care what is carrying the weight of the tongue.  

 

What were the numbers you got when you did it in the OP?

 

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If you do it Phills way.

Get the tow trucks wheels on the scale. With the trailer attached. record that weight.   But make sure you have the trailer jacking wheel  OFF  the scale and over solid ground.  Crank up the trailer off of the truck. Record the weight.

The difference is tongue weight. Simple & safe. If you can afford a few trips.

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Or do it with the trailer only on the scale. Either way will work.

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As cyclops stated, either method works, but only if your trailer jack is properly positioned.

If looking at the difference in the tow vehicle weight, the tow vehicle axles must be on the scale, the trailer axles and trailer jack must be off the scale.

If looking at the difference in the trailer weight, the tow vechile axles must be off the scale, the trailer axles and jack must be on the scale.

In my case I was more interested in knowing the weight of the loaded trailer as well as the tongue weight, so the latter method was how I proceeded. Scale read 5140 when trailer was supported by trailer jack and axles, all of which were on the scale. Scale read 4880 with the trailer hooked up with only trailer axles on the scale. Difference was 260, which I later confirmed with a smaller scale measuring the tongue weight directly since I knew it would not exceed the limits of the smaller scale.

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1 hour ago, Kinny said:

As cyclops stated, either method works, but only if your trailer jack is properly positioned.

If looking at the difference in the tow vehicle weight, the tow vehicle axles must be on the scale, the trailer axles and trailer jack must be off the scale.

If looking at the difference in the trailer weight, the tow vechile axles must be off the scale, the trailer axles and jack must be on the scale.

In my case I was more interested in knowing the weight of the loaded trailer as well as the tongue weight, so the latter method was how I proceeded. Scale read 5140 when trailer was supported by trailer jack and axles, all of which were on the scale. Scale read 4880 with the trailer hooked up with only trailer axles on the scale. Difference was 260, which I later confirmed with a smaller scale measuring the tongue weight directly since I knew it would not exceed the limits of the smaller scale.

sometimes they are hard to find, or can be faded, but every trailer should have a data plate that provide unladen weight. 

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  Hopefully it has both weights stated.  I just call the trailer company .

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On 5/5/2018 at 2:39 PM, Kinny said:

I had access to a tractor trailer scale today so I wanted to check the tongue weight of my boat/trailer.  I pulled my boat onto the scale and stopped as soon as my truck rear tires left the scale.  I recorded that weight, chocked the trailer tires, and used the jack to lift the tongue of the boat just off of the ball, and recorded the weight again, which is also the total weight of the boat/trailer.  My tongue weight should be the difference in the two, correct?

Thanks in advance.

 

Makes sense. If you add the 2 numbers you should come close to the boats and trailer weights. Just to double check. 

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On 5/8/2018 at 1:32 PM, Kinny said:

As cyclops stated, either method works, but only if your trailer jack is properly positioned.

If looking at the difference in the tow vehicle weight, the tow vehicle axles must be on the scale, the trailer axles and trailer jack must be off the scale.

If looking at the difference in the trailer weight, the tow vechile axles must be off the scale, the trailer axles and jack must be on the scale.

In my case I was more interested in knowing the weight of the loaded trailer as well as the tongue weight, so the latter method was how I proceeded. Scale read 5140 when trailer was supported by trailer jack and axles, all of which were on the scale. Scale read 4880 with the trailer hooked up with only trailer axles on the scale. Difference was 260, which I later confirmed with a smaller scale measuring the tongue weight directly since I knew it would not exceed the limits of the smaller scale.

You want a tongue weight about 10% - 15% of the total trailer weight. Therefore, with a 5140 lb trailer you should be around 500 - 550 lbs, not 260. You risk instability with too light of a tongue weight.

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Most places I looked at have recommended boat trailers be 5-8% for the tongue weight to total weight percentage, vs 10-15% for travel trailers. 

Venture says 5-7%.

http://www.venturetrailers.com/Weight_Distribution.html

Depends on boat size and configuration, but for our stern drive boats the 5-8% would be appropriate, I think.

I just had my trailer adjusted a bit, and they set the tongue weight at 7% since the boat only had 1/8 tank of fuel.  Since the fuel tank sits basically on the axles, it should drop the tongue a bit when full (80 gallons).

It is not just about tongue weight with a boat trailer as it is how it is loaded.  Boat trailers typically have the axles farther back than travel trailers, because so much of the boat's weight is in the stern.  It is more important to get the boat load distributed on the axles properly than it is the tongue weight.  Too much forward weight, and you are loading up the front axle, too little and you are loading up the rear axle.  So it really depends on your boat, trailer, and where the center weight line of the boat is.  Which is why trailer specs for boats include that information.  Longer tongue, less tongue weight, shorter tongue more tongue weight if you want to adjust it.  That is better than moving the boat load around on the axles.

http://forum.chaparralboats.com/applications/core/interface/file/attachment.php?id=2926

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