Somebody Check My Math

Phillbo

Phillbo

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I want to determine what my tongue weight is ( I feel it's a bit light)so I contacted the Port of Entry at Page Az (Lake Powell) and they said it would be ok for me to put my truck on their scale.

Here is how I think I'll approach it:

-Get truck weight before hooking up the boat.

-Weigh truck only with boat attached (truck on scale and trailer tires off scale).

-Weigh Truck and Boat together

My thought is that the difference between the weight of the truck only and the truck only with boat attached is my tongue weight.

The full weight with both on the scale would give me the overall weight of boat and trailer while I'm at it.
 
It would just be a lot easier to put the tongue trailer jack on a scale and read the result.

George
 
It will work, but why not just jack up the tongue and put it on a scale like George indicates?

Just remember, trailer must be level otherwise you are skewing the weight one way or the other.
 
Both ways will work for tongue weight as long as TW isn't over the small scale limit, but I like Phillbo's truck scale method because it gives a lot more pertinent weight info too for a towing reality check.
 
Like Sandy said, I'd like to know the weight of the truck, the boat and both combined as well.
 
The weight of the truck is in the truck literature. The weight of the trailer is required to be on the trailer placard. The weight of the boat is in the boat literature. That's dry. Gas = ~6 pounds per gallon. Water wieghs 8.35 pounds per gallon. Figure you are going to be travelling with all liquids full on both boat and truck. Add another couple of thousand pounds for junk.
 
If you weigh the truck and trailer/boat together you will NOT get the tongue weight. Tongue weight should be approximately 10pct of trailer weight. If you weigh truck alone then weigh truck with trailer attached, trailer not on scale, the difference will be tongue weight.
Tongue weight can be adjusted by a) shifting load in boat on trailer or b) by sliding trailer axles on trailer frame. Slide axles toward rear to increase tongue weight or toward the front to reduce tongue weight. Tongue weight of 10,000lbs. boat, trailer and accessories combined weight should be about 1,000 lbs.
 
If tongue weight is less that 300# use a home scale. More than that if you have a 4X4 or such make a weight divider using the scale and a brick. Put the tongue 10% of the distance from the brick to the scale and the weight is 10% of the scale reading.
 
I do not like the idea of using the truck and trailer at the port of entry except to get the combined weight of the boat and trailer. I don't think it will have the granularity to measure a few hundred pounds accurately.
To measure tongue weight accurately you will have to measure at the ball receiver on the trailer otherwise you have to use potentially difficult calculations. You must ensure the receiver is going to be at the same height it will rest at on the ball and this will change as the trailer weight is imposed on the hitch. It ALL matters.
I am thinking you will get decent results by using a method Bruce outlines, but the tricky part will be keeping the ball hitch at the height of the receiver when at rest with the trailer load applied. I am thinking to be certain you will need to come up with a mini saw horse that fits on the scale other wise it might slip off. Make sure you chock all the trailer wheels on both sides!
 
BB makes good points. angle and correct position do matter.

David's post show exactly how to do it>
 
Port of entry scales are ridiculously accurate. Over a26 year driving career I paid tickets for being as little as 10 lbs over weight on an axle with the truck having combined axle weights of 80,000 lbs. I have stepped on truck scales into the truck and seen the weight change to reflect my body weight. Don't even go there.LOL Tongue weight will not change with height or angle. The only change that will cause a change is axle position, or load shift.
 
quote:
Tongue weight will not change with height or angle.
Click to expand...
Have to disagree. it will change by the cosine of the angle. Within a few degrees it wont make much difference but just to satisfy my pedantic nature I like to be correct.
 
quote:
Originally posted by pdecat

quote:
Tongue weight will not change with height or angle.
Click to expand...
Have to disagree. it will change by the cosine of the angle. Within a few degrees it wont make much difference but just to satisfy my pedantic nature I like to be correct.

Click to expand...


I think I would have to see the math on that.

George
 
I agree with Bruce . The effect of his math, on a single axle trailer, is raising the tongue will somewhat shift aft the center of gravity of trailer & boat.

However, with I believe stronger opposite effect, raising the tongue of a multiple-axle trailer will ...tend... to make the fulcrum/axis the trailer rear axle making tongue weight heavier , lighter when lowered to shift to the closer forward axle. Somewhat similar effect to positioning the boat farther forward or back on the trailer relative to a single axle .
 
Here ya go George. If the trailer and truck are parallel 100% of the weight is on the hitch. As the angle changes less weight is n the truck and more on the trailer tires until when straight up no weight in on the truck at all. Of course straight up is silly but it demonstrates the cos curve. As I said at small angles the difference is minor. cos 10 degrees is .98 so hitch weight will only be different by 2%.

http://programmedlessons.org/VectorLessons/vch07/vch07_5.html
 
quote:
Originally posted by gcolton

quote:
Originally posted by pdecat

quote:
Tongue weight will not change with height or angle.
Click to expand...
Have to disagree. it will change by the cosine of the angle. Within a few degrees it wont make much difference but just to satisfy my pedantic nature I like to be correct.

Click to expand...


I think I would have to see the math on that.

George

Click to expand...


It is common sense. If the item being weighed is not level, then the weight is artificail skewed in the opposite directions.

It is the same principal as if you are carrying something heavy with another person, and you lift your end up, you make theirs heavier.

Same concept as to why high caliber race scales have levelers built in - if the car is not level, then the lowe end is artificially skewed higher and the higher corners are artificially skewed lower.
 
Another option - hook up trailer and go to scale. Weigh truck with trailer attached, but DO NOT drive the trailer wheels onto the scale.

Now go unhook trailer and weigh truck by itself. The delta should be the tongue weight.
 
quote:
Originally posted by In the know

quote:
Originally posted by gcolton

quote:
Originally posted by pdecat

quote:
Tongue weight will not change with height or angle.
Click to expand...
Have to disagree. it will change by the cosine of the angle. Within a few degrees it wont make much difference but just to satisfy my pedantic nature I like to be correct.

Click to expand...


I think I would have to see the math on that.

George

Click to expand...


It is common sense. If the item being weighed is not level, then the weight is artificail skewed in the opposite directions.

It is the same principal as if you are carrying something heavy with another person, and you lift your end up, you make theirs heavier.

Same concept as to why high caliber race scales have levelers built in - if the car is not level, then the lowe end is artificially skewed higher and the higher corners are artificially skewed lower.

Click to expand...


Not common sense nor like two people carrying a load.

The ball and hitch are essentially a point load.
No directionality .

That is why I want to see your math. I have been knows to be wrong. It is rare, but it does happen.

George
 
It varies with angle
Just look at the extremes. If the trailer was pointed straight up in the air, i.e., perpendicular to the ground, there is zero loaad on the tongue. The othere extreme is the tongue pointed to the ground and trailer vertical up in the air, 100% of weight is on the tongue. It varies by cosine exactly as Bruce describes.
 
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