[Rhodes22-list] Trailer Measurements

[Jerry Duke]

For Slim,
Adjusting the Tongue Weight

The tongue weight of the trailer seemed excessive, and with the aid 
of a household scale proved to be 280 lbs.!!! Although this was still 
within the 5-10 % of total weight guideline; considering I had an 
extendable trailer tongue, I felt like it was too much. In order to 
extend the tongue of the trailer, and avoid buckling the extension 
bar, the trailer tongue weight should be kept to a minimum. At a 
tongue weight of 280 lbs., I was running the risk of buckling the 
extension bar.

I wanted to bring the tongue weight down more towards the 5% range. 
Considering the total load (boat & trailer) is about 3100 lbs., I 
wanted to shoot for a tongue weight of 160 lbs. (+/-). The tongue 
weight would be reduced by moving the axle assembly slightly forward.

Outlined below is the formula I used to determine how far to move the 
axle assembly.

  Diagram of Trailer Weight & Balancing




Adjusting Tongue Weight:

1) Measure weight at ball/coupler

2) Measure or estimate total weight of load (boat + trailer)

3) Measure distance from ball to rear axle. (use mid-point between 
axles on tandems). Call that distance "C".

4) Find the Center of Gravity by solving for "A" and "B".

Assume the trailer is not moving, therefore all forces must be equal. 
Therefore, we know the following to be true. . .

(280 * A) = (2820 * B) and (A + B) = C=180 inches ('cuz we measured it)

Solving for A and B, we get . . .

A = ((2820 / 280) * B)     or "A" is about 10 times the distance of " B ".

A = 10 * B   and    (10 * B) + B = C     so,    (11 * B) = 180 inches

B = 16 inches , A = 164 inches

Adjusting (reducing) the tongue weight will be done by moving the 
axle forward, i.e. shortening "B".    "A" will stay the same, as we 
will not be moving the C. G. (note that the overall measurement "C" 
will be reduced as well). Pluging in our target tongue weight (160 
lbs.) and solving for the new "B" measurement . . .

(160 * A) = (2940 * B) or (160 lbs. * 164 inches) = (2940 lbs. * B inches)

B = 9 inches  So, the axle needs to be moved forward 7 inches (16 - 9).
------------------------------------------------------------------------

  The final results, as checked by my household scale, was 155 lbs. 
(exactly 5%). If I needed more tongue weight (which I did), I could 
store the rudder assembly in the V-berth, bringing the tongue weight 
to about 190 lbs.
------------------------------------------------------------------------
JD






>Bill,
>
>Here's my situation at this point:  When landing Fandango, I can't get it
>far enough forward on the trailer.  Many attempts, various ramps,  various
>depths,  etc. but always the same result.  At least it's consistent.  If
>only the balance were right, it'd be nearly foolproof!  That part gives me
>hope.
>
>This spring I bought a pair of WM boat stands and a floor jack.  And I have
>trailer jacks on the rear corners of the trailer, and together with the
>tongue jack, I raise the trailer as high as it will go on its 3 jacks. This
>raises the trailer wheels off the ground. Then I put the boat stands under
>the stern quarters and can even raise the hull up some more by cranking the
>screws on the boat stands.  Then I pull the tongue extension out of the way
>and put the floor jack under the bow, jack it up as high as it will go.  At
>this point, you can lower the trailer jacks and the boat is perched on the
>floor jack at the bow and the two boat stands in the stern--a nice, sturdy
>tripod. Even if one of those stands were to fail, the trailer bunks are only
>inches below. 
>
>Now I go to the trailer's bow winch clipped to the bow eye of the boat and,
>with the boat on the hard, I winch the trailer backwards--farther under the
>boat.  I have to lift the boat off the trailer in this way in order to
>position the trailer under the boat at the correct balance point, i.e., to
>get enough tongue weight.  Needless to say this is a royal PITA, albeit
>doable. 
>
>Roger's not the only one to modify a trailer.  Rik posted his changes too.
>I saved their recommendations as well as Todd's dimensions,  and I'm just
>gonna have to go for it.  But when it comes right down to it, I'm going to
>have to guess at how far to move the axle back.  Is there a formula for
>this?  I'm thinking about 6".
>
>Slim
-- 
.../)_JD