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Author Topic:   Predicting Tongue Weight
mustang7nh posted 05-24-2004 03:28 PM ET (US)   Profile for mustang7nh   Send Email to mustang7nh  
I like my current tongue weight on dual axle galvanized trailer for my 1991 Outrage 22. However, I need to move the boat forward by 14". To keep the weight the same, is it a simple one to one relationship- meaning I just move the axles forward 14"? Thanks
greyg8r posted 05-24-2004 05:11 PM ET (US)     Profile for greyg8r    
By moving the axle forward, there would be more weight of the trailer aft of the axle, but because the weight of a trailer is usually a fraction of the wieght of the boat, I think this would be relatively minor.

If it were me, I would try moving the axle 80% of the distance i move the boat to account for the shift in the weight of the trailer.

Note: This answer is not as good as empirical or experimental data but is better than a wild a-- guess.

Richard

jimh posted 05-24-2004 06:18 PM ET (US)     Profile for jimh  Send Email to jimh     
A method for calculating trailer hitch loads (tongue weight) is presented in the Reference Section.

This article presents an engineer's analysis of boat trailer weight distribution performed by Jerry Townsend, a fellow Boston Whaler owner who is a mechanical engineer (M.S.M.E) with considerable experience in modelling of tractor-trailer dynamics.

See:

http://continuouswave.com/whaler/reference/trailering/trailerCalculations.html

jimh posted 05-24-2004 09:09 PM ET (US)     Profile for jimh  Send Email to jimh     
Jerry Townsend also wrote a DOS-executable program to perform all the calculations needed to predict the tongue weight. This will be of great assistance to those not intimidated by numerals.
kamie posted 05-25-2004 06:09 AM ET (US)     Profile for kamie  Send Email to kamie     
I used the DOS program mentioned to help in repositioning my Outrage on it's trailer. I moved it forward 12 inches and had to move the axle forward 12 inches to keep the same relative tongue weight. I will know on wednesday if it actually worked.
Chuck Tribolet posted 05-25-2004 12:42 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
There will more trailer weight aft of the axle, but the
tongue will be a shorter lever. Without actually running the
numbers, I'll bet they about balance out. My first try would
be to move the axle 14" and see what happens. If the tongue
weight is off, run the numbers and move the axle again -- it
doesn't take that long, less than an hour on my single axle
trailer, by myself.

Mark where everything is on the trailer before you start. If
you end up having to move it back 1" (after the initial 14"),
measure 13" from the original marks. This will avoid
cumulative error.


Chuck

gimcrack225 posted 05-25-2004 03:52 PM ET (US)     Profile for gimcrack225    
Great information. I have to do this soon - the tongue weight is too heavy on tandem trailer with a 21' footer. The tongue jack is sinking into the asphalt.
QUESTION- Is there a problem with maintaining wheel alignment? Do I take the trailer to get it aligned after I move the axles?
Thanks
Karl
Jerry Townsend posted 05-25-2004 08:09 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
gimcrack225 --- Realigning after moving the axles may not be necessary - but take a few precautions. When moving the axle(s), make sure that the axle is square with the frame by having the same dimension between a point on the center of the hitch and an identical point on each side of the axle.

Periodically closely look at the tires to see if there is any abnormal wear - on either side of either tire, or cupping, et.al. Should you notice abnormal wear - it's time to have the trailer axle aligned.

Now, if one is moving the boat forward X inches, a good first shot at the axle(s) movement is to move the axle X inches. You will still have to move the axle(s) again because the distances have changed. --- Jerry/Idaho

kglinz posted 05-25-2004 08:48 PM ET (US)     Profile for kglinz  Send Email to kglinz     
One thing that I have never seen mentioned on a tongue weight thread is "ball height". On a multi axle trailer with torsion bar axles, correct ball height is critical. On a multi axle trailer with leaf springs the springs are linked together through a bell crank, but with torsion bar axles the axles are completely independent. This means that the trailer frame must be parallel to the road surface or the axles will not carry equal weight. If the hitch is high the tongue weight increases. If the hitch is low the tongue weight is less.

Kemp Lindsey

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