posted 04-25-2005 08:44 PM ET (US)        

I have replaced my tongue with a longer one (added 2'5") and am not totally clear on where to mount the safety chains.

Here is the originating thread if you want the reason why I did this:

http://continuouswave.com/ubb/Forum3/HTML/006980.html

While the tongue came with predrilled holes for the coupler, attaching to the frame, wiring etc. None lined up with the coupler or the frame so I had to end-for-end it and rotate one turn to get clean sides.

The new 2" class 3 coupler is through bolted with 1/2 inch through bolts.

There are existing (unused holes) near the coupler but are partially covered by the coupler.

Questions:

How far back from the coupler should the chains be mounted? The bolts for the coupler are not long enough to add the chains here if this matters.

Does it matter if they are mounted on the bottom or sides?

Mount each chain separately or off the same bolt?

posted 04-26-2005 12:35 AM ET (US)            

Attach the safety chains to the tongue via bolts going through the horizontal sections of the tongue - or use a U-bolt attachment. I would not drill through the 'vertical' sides of the tongue as the strength of the tongue is provided by the vertical sides.

posted 04-26-2005 08:35 AM ET (US)            

Front - two holes on opposite sides for a coupler. Holes are less than 3/8. Spacing is 1 1/2 and 2 1/2 inches from the end respectively. They are about 1/2 way down the face.

Factory holes too low, too close to the end and too small for new coupler.

Single hole of same diameter on opposing lower face (trailer light wiring?)

End - One hole on each side of vertical for attaching to the frame. holes were too small, too high and too close to the end.

I went back outside and looked. If you took the tongue and set it down with the factory holes, I turned it upside down. (coupler holes still at front, just now toward the ground.)

The first new front coupler hole is 1" above 1" to the right of the forward most factory hole.

The second hole is farther away, say 2" to the right.

On the End, the new hole is 3 1/2 inches inward of end and centered, 2 + inches from factory hole.

I have extra length so if you think I should cut it clean of existing holes and redrill on fresh steel, I could do that.

I do not have a drag skeg on this tongue.

posted 04-26-2005 03:54 PM ET (US)            

The vertical sides provide most of the strength to handle the turning
of the trailer left and right, which is much less than the
buckling load of the the tongue weight.

All four sides provide the strength to handle accelleration
and braking.

This is freshman Mechanical Engineering (statics). I'd drill
the sides.

posted 04-26-2005 05:11 PM ET (US)            

That is why I am concerned or protective of the sides of a trailer tongue as that just weakens that section.

The dynamic bending loads (imposed by the road)are the most important and severe loads put on the trailer and tongue.

posted 04-26-2005 05:25 PM ET (US)            

Just kidding with you Chuck, but Jerry's right on. An "I-Beam" is a good illustration of this principle, the depth of the beam is what determines it's strength, not it's width (within reason of course).

posted 04-27-2005 09:20 AM ET (US)            

The top and bottom flanges help, but are really more of "stiffeners" to keep the web true from buckling and deflecting.

posted 04-27-2005 11:22 AM ET (US)            

With that said, if you were to double up on the top and bottom flanges, you would have section that is much more resistant to bending and deflection (in the vertical direction) than if you doubled up on the sides. It's a pretty common procedure in building construction to add a plate to the bottom of an I-beam to increase the bending capacity. The whole idea behind an I-beam is that the more material you have on the top or bottom flanges, or the farther apart those flanges are, the stronger the section is.

The beauty of a tube shape is that it resists bending in both directions and it resists torsional forces and it's easy to attach things to, but pound for pound an I-beam will be stronger in one direction only because the "meat" is at the top and bottom.

posted 04-27-2005 03:06 PM ET (US)            

You may be disagreeing with everyone else, but you're not disagreeing with me, at least insofar as the properties of an I-beam are concerned. You pretty much wrote the response I would have made to Chris, and I would have added that the other thing that is done to increase the strength of a given I-beam is to add web stiffeners, the idea being to reinforce the web so it does not buckle as it does it's job of connecting and separating the upper and lower flanges and keeping them in alignment under load. Just as in a tube, both vertical and horizontal elements are necessary in order for the beam to work, but the fact that strength is gained by increasing the depth of the section does not indicate that the web is the stronger element; rather the deeper section is stronger due to the the greater distance between the upper and lower flanges making it more difficult to compress the upper flange differentially against the tension of the lower flange.

posted 04-27-2005 03:19 PM ET (US)            

First - basics: The strength of a member to resist bending moments is dependent on the 'section modulus' of that member - and for a rectangular member, the section modulus in the plane of the load is calculated, in part, by multiplying the base X the heigth cubed. Therefore the heigth of the member is of much more significance than the width or thickness. In other words, the heigth of the member is really what determines the strength of that member.

Someone mentioned that the side sections were in shear - whereas in fact, those members are subjected to bending moments. The bolts connecting the coupler to the hitch are subjected to shear loading - but that is about it for shear.

Someone mentioned that any one element is not more important than the other - whereas for a trailer tongue, the vertical members are far more important as those members withstand the dynamic loading, the bouncing of the load on the trailer induced by the road.

Now, if we are talking about the lateral loading - the top and bottom sections are more important than the vertical members. But the lateral loads are relatively minor.

Many have used an I-beam in their discussions - and yes, the flanges (top and bottom) play a part - but look at the real heavy I-beams which have relatively small flanges compared to the height of the web. Those beams are built as they are for a reason - the section modulus of the web and the separation of the flanges - i.e. the height of the web!

And Chris is right - the I-beam flanges, in part, 'restrain' the web. If it were not for the I-beam flanges, the web would flex out the way.

Ever wonder why trailer tongues are not built of I-beam sections?

And now - back to Whalers and related equipment! --- Jerry/Idaho

posted 04-27-2005 05:14 PM ET (US)            

Take a square tube section and weld an additional plate on the top and bottom. Set the modified tube on two supports and load it up. Measure the deflection. Now take the same tube and rotate it so the extra plates are on the sides. Load it up and measure the deflection.

posted 04-27-2005 06:10 PM ET (US)            

Thanks for the responses, I got my answer and one small concern resolved.

I think the conversation has reached the end.

Put the throttle in neutral and turn the key to off..LOL

posted 04-27-2005 07:14 PM ET (US)            

But - run the test yourself - with wood strips, the old fangled computer cards, foam-core - anything. They will all show the same relative test results. Let us know what you find out.

posted 04-27-2005 08:35 PM ET (US)            

Phil, sorry for the semi-hijacked thread. I sure am glad my structural engineer doesn't follow some of the advice given here or I'd spend more time in court than I do in my boat.

posted 04-27-2005 10:02 PM ET (US)            

The distance between the flanges is what most greatly impacts the strength of the beam, not the flange thickness.

I think we actually MAY be in agreement more than it seems. My analogy to an I beam was probably not the best for THIS argument but again (in simplistic terms) if you double the width of a beam you get approx. double the strenth; if you double the depth, you get approx. 4x the strengh.

Again, I'm not sure we are disagreeing as much as it seems. The concept Jerry and I are trying to illustrate is perhaps best seen with a common 2x6 used as a beam. It's placed on it's "2x" side (actually 1.5"), not it's "6" side (actually 5.5"). Double the width of that beam (use a 4x6) and you will get a minimal increase in strengh. Double the depth (2x12) and you get a much greater increase in stregth.

posted 04-28-2005 08:55 AM ET (US)            

The real question is where to drill. The sides are taking
less of the load than the top and the bottom. In fact, the
middle of the sides is under almost no load (neither
compression nor tension). So drill the sides.

Take a look at couplers. They take bolts on the sides.
See above for why.

I just checked my Shorlandr'r tongue. The chains are attached
via their own bolts, about even with the back of the
coupler. I figure the Shorland'r folks know what they are
doing. I also flipped through the pictures in the trailer
part of the refrence section, and I didn't see any where
the the chains were attached to other than the sides of the
tongue.

posted 04-28-2005 09:25 AM ET (US)            

Under loading, the top surface of the beam (or trailer member in this case) is shortened due to compression, and the bottom surface of the beam is elongated due to tension

At a location between the top and bottom surfaces of the beam there is a surface whose lengths are the same as the original lengths of the straight (unloaded) beam.

This surface is theoretically in neither tension nor compression and is called the Neutral Axis

this diagram shows generally what I'm talking about:

www.princeton.edu/~humcomp/bikes/design/desi_63.htm

The reason this is theoretically true and not absolute is the hole you are cutting has a diameter, and therefore will pass on either side of the zero force line to some degree so it will have SOME impact on the strength; however given what you are looking to do and the size of the members, you wouldn't have a problem.

Hope this helps clear it up (in case you were wondering). I also hope it makes sense.

Again I apologize if I drifted this topic a bit. Phil, are you still with us buddy?

:)

posted 04-28-2005 10:17 AM ET (US)            

No one here is arguing that a steel I-beam of greater depth, everything else remaining equal, will typically have greater strength; (I *am* arging that the web serves more to stabilize the flanges than the flanges serve to stabilize the web). I discussed the reasons for that in my comments above, and Chuck's analogy of a mythical webless beam is exactly right; the web is there to serve the flanges. If you spend some time studying the AISC Steel Construction Manual tables (listings of real life steel sections and their design criteria and characteristics), you'll see that as any I-beam of a given depth increases in weight and strength, the thickness of the flanges increases at a greater rate than does the thickness of the web, implying just what Chuck said: the flanges are taking the load.

The strength of any given beam to resist applied loads comes from the inherent EFFECTIVE *differential* between the compression of the top flange and the tension of the bottom flange. Increase the distance between the top and bottom flanges and that differential increases. If the two flanges are actually in contact with one another (no web) they almost have no differential and they deflect very easily. If they are held apart and stabilized or braced in some way (like by a web), the upper flange must compress and the lower flange must expand, both to a much greater differential degree to one another than if there were no web between them. An I-beam web would then have to compress or buckle near the upper flange and it would have to stretch or tear near the bottom flange, in order to allow either flange to succomb to the applied load.

A wood 2x12 acts just like an I-beam: it has more strength to resist applied loads vertically (and *only* if it is adequately braced) than horizontally, because of the greater differential required between compression the top edge (like the top flange) and tension of the bottom edge (bottom flange) in order to allow deflection.

All my comments were ever intended to convey here was said in the two sentences of my first post to this thread; I am more than a little chagrined that I helped lead this thread astray, and for that I apologize, but I didn't want my remarks to be misconstrued.

posted 04-28-2005 11:38 AM ET (US)            

Seriously, I'm sure all of us would be interested in your experiment's results.

I'll admit defeat if I have to, but don't suspect I will.

posted 04-28-2005 12:57 PM ET (US)            

> A rectangular tube section is strongest for vertical
> bending moments when the long side is vertical. Adding
> thickness to the bottom and top increases the bending
> moment capacity more than adding thickness to the sides.
> This is why an "I" beam, with top and bottom flanges and a
> single web, is an efficient section for bending

posted 04-28-2005 01:55 PM ET (US)            

I think the confusion was probably due to MY introducing beam "depth" into the equation vs. "thickness". That's another argument and not really relevant to the situation here. Sorry for the confusion.

I guess that's why I hire out structural consultants - good thing, huh? :)

Sorry all. Newt, you can keep your boat. I'm gonna crawl under my desk now and cry. :)

posted 04-28-2005 02:05 PM ET (US)            

It's all about getting the mass (additional plates) as far away from the neutral axis as possible. This goes a little back to beam depth, but I won't open that can of worms again.

Hopefully we all learned a little something. I know I did. I was really looking forward to that Outrage too.....darn it.

posted 04-28-2005 06:33 PM ET (US)            

I took a hypothetical square tongue 4 inches square with 3/16" wall thickness and calculated the section modulus of the horizontal and vertical sections. Those calculations showed that the vertical sides only contribute about 29% of the total section modulus while the horizontal sections contribute the remaining 71%. While the horizontal sections contribute little to the section modulus - the separation distance of those horizontal sections is, by far, the controlling factor - and this effect is much more significant that I had guessed.

And I laugh - because a few minutes ago, I started a response commenting on Chris's giving up too early - and then thought that it would be a good idea to make a few calculations. And now Chris - I'll crawl under that desk with you.

While the discussions regarding the various sections, the 2x6, et.al. were right - the controlling factor is, again. the separation distance of those horizontal sections.

My apologies for getting this tread off track - and it rekindled a thing I've known for a long, long time - put your mind in gear before opening your damned mouth (fingers). ---- Jerry/Idaho