gooseneck coupler bracing

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I've been running a converted gooseneck to 5th wheel coupler for years on my camper , first an adapter, then an extended kinkpin job that someone else made, never had any problems with any of them, but I put a huge bed tank in and I wanted a different type coupler that I could back into , ( an Atwood) so I bought one of those to make a new coupler to poke out front and all the literature says to use 3/8 plate connecting the thing. Now that seems lika a bit of overkill for a 10,000lb 5th wheel, the factory pinbox was only 3/16  and the thickest pinbox I see sold is 1/4" I'm wondering if that requirement of 3/8" is onlyto get the max rating on the coupler ( it is a 25k rated coupler ) in which case I would certainly not use any less than 3/8" but on a 10k trailer if 1/4" wouldnt  be more practical. I've seen LOTS of goosenecks running around with 1/4" necks  that weren't hauling heavy equipment  so I must not be crazy here. I've got no problem making the thing out of 3/8", it just seems a but redundant when it's better than twice as thick as the pinbox on the trailer I'm going to attempt to get ahold of atwood tech support, but I only got through to them one time  and the wait can be hours and one time after waiting for a couple hours I got put through to a voicemail that never got returned, The one time I actually did get through the guy was  a design engineer and was helpful, but I'm not counting on that ever happening again, so in the mean time,  I'm open to opinions on thickness here. Not on whether gooseneck couplers are a good idea or not.ThanksPanasonic Gunslinger 261Mig/Stick, Hypertherm Powermax 30 Plasma
Reply:If the lit says use 3/8" plate, then use it.  Yes, it may be that thick so you can get the max load capacity.  But, the material thickness might also be specified at 3/8" to keep stress levels in the assembly below the point where fatigue will occur.  In mild steel, if the stress is less than ~1/2 the yield strength, then fatigue from cyclic mechanical loading will not occur.It should go without saying, but do your job carefully and with the utmost attention to detail.  Sound welds with good penetration, adequate size, proper weld cross-sectional profile, and no undercut.  Any deficiencies in welding will reduce the capacity of the assembly to carry the load and resist fatigue.Suppose you did use 1/4" material instead?  What happens when you sell this trailer to somebody else?  You may not use it today at max capacity, but someone else might....Regardless of where the legal code stands on your liability, how would you feel if someone was hurt because you skimped on steel when you fabricated the hitch components?  In the face of the unknown, just assume that someone had a good reason for specifying 3/8" plate and follow their recommendations.Just my $0.02.Last edited by A_DAB_will_do; 07-01-2010 at 08:54 AM.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:If it is the king pin plate you are talking about there is a reason. The length of the king pins are made for a specific plate thickness.
Reply:What gets me is everywhere I look I see most goosenecks are made with 1/4 including my 32 ft Cargomate Qualifier  carhauler that came with one of those Atwood couplers from the factory, and I saw another 3 axle trailer today very nicely done, well braced, 1/4"all aroundThe instructions were going for a 3/8 to the side, not the base, I'm not attaching it to the kingpin setup, I'm making a whole new attachment to bolt to the pinbox I saw a similar setup another fella made and it was less cobbled, much stronger than rigging an adapter to the bottom of a kingpinPanasonic Gunslinger 261Mig/Stick, Hypertherm Powermax 30 Plasma
Reply:I don't see what is the big opposition to using 3/8?  It's not a huge amount of metal and cost difference isn't that much for small plate sizes (sq ft).   Just go with the 3/8 and know that it's done right, by the book and you have nothing to worry about.   Go thinner than designed and now you're the engineer.  Are you qualified for that duty?MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:No big opposition, it's just going to get heavy as heck when it gets all together and I'll have to either drag the cherry picker over or fire up the tractor and chain it to the boom arm to mount the sucker  . All the previous nose pieces ( including the factory one ) that were made from 1/4 or lighter , my son and I could wrangle up there easily  by hand with some blocks under it. Just trying to think of all possible options.Panasonic Gunslinger 261Mig/Stick, Hypertherm Powermax 30 Plasma
Reply:I don't like the baby fifth wheel arrangements............so now that's out of the wayThe leverage generated above the plate, along any vert members, etc. is phenominal.I run a standard gooseneck with a high ball for clearance.  Braking, the possibility of a rear end collision, etc. tells ya that you need some meat in the coupler or the hitch.Ever run over uneven lousy highway, or have a weird load??  The rocking action you feel in the pickup is stress flowing thru the hitch.  Makes ya really want to have a good solid hitch able to withstand the flex without fatigue"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Static load, shock load, and repeated flex load, are all different things.  Flex can kill you over an extended period.  Bend a beer can repeatedly, and see the results"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammStatic load, shock load, and repeated flex load, are all different things.  Flex can kill you over an extended period.  Bend a beer can repeatedly, and see the results
Reply:In actuality the instructions were very poorly written ( as my late father , an engineer, said about 40 years ago, "technical writing is a lost art"... it's been going downhill for a while now) I went over my designs with my metal man who is also a custom trailer builder  and turns out the spec was for 1/4" all along with only requirement being a set of 3/8" side gussets. I went ahead and designed the thing for 3/8 for a bit of overkill and essentially it's many , many times as strong as specification requires for the full 24k load limit by the time it's all said and done, and I'm only pulling a 10k 5er, plus I reinforced the pinbox on the 5er with the 3/8 as well and ran it all the way out to the frame rails. Only place I used 1/4" was on the top and bottom fill plates as those just kind of help keep the twist out and the forward plates are 3/8" so basically the entire trailer is going to twist in half before that thing is going anywhere. My metal guy actually talked me into  cutting back in a few places. I had OVER designed the thing way too much. After all the trouble my boy and I  had mounting that heavy sucker, I could just about kiss his ugly hide for that   The length of the thing is a bit of an optical illusion due to the design, it's only about 1.5" longer than a factory type long kingpin that was on the thing ,  it's just the straight rails of this thing make it look longer than one that goes down to a point I have a factory built enclosed carhauler with an identical coupler and the setup I built is roughly 6 times as strong as what the factory built one  is, I have no concerns whatsoever about this thing...aside from possibly having to take it off to lubricate the crank mechinism on that heavy monstrosity Attached ImagesPanasonic Gunslinger 261Mig/Stick, Hypertherm Powermax 30 Plasma