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Cracked Trailer frame repair ideas

Posted: Sun Oct 07, 2018 9:57 pm
by Tfitz
The last fishing trip of the season I noticed a crack in the frame of my boat trailer at bend in front of the axles where the crossmember bolts on. The roads in Alaska are terrible and trailers take a beating. I have my own ideas how to fix it but was wondering if anyone else has successfully dealt with this problem before? Any info anyone could share would be greatly appreciated. These are last year brand new axles, tires and brakes so I'm not ready to give up on the trailer and buy new yet.

Re: Cracked Trailer frame repair ideas

Posted: Sun Oct 07, 2018 10:08 pm
by Tfitz
Crack in frame

Re: Cracked Trailer frame repair ideas

Posted: Sun Oct 07, 2018 10:12 pm
by Tfitz
Location of crack

Re: Cracked Trailer frame repair ideas

Posted: Mon Oct 08, 2018 5:55 am
by gandrfab
Just a guess, that cross brace is holding the bulk of the hull weight and only has 2 bolts on each side holding it in place.
If so and as fun as it does not sound. I would through bolt the inside of the I beam to the cross beam.
Then jack up the front bunks some to help even the weight out.

If those assumptions are all wrong I would grind the crack and weld, add a plate at least the thickness of the I-beam fit it so it touches the whole width of the top,bottom flanges and height of the web. Weld all around in between the bolts.

Just grinding out and welding the crack would cover the problem but not correct it.

Re: Cracked Trailer frame repair ideas

Posted: Mon Oct 08, 2018 8:26 am
by welder
Yep, stress crack due to the bottom flange rolling, the cross member is causing the flex and repeated flexing will cause cracks. I would contact the trailer manufacturer 1st to see if they have a fix for you. If they don't then I would look at plates and stiffeners to beef up the areas where the crossmembers meet the rails.
Welding on the frame could weaken it if not done correctly.

And of course make sure the trailer is completely level and supported all the way around before attempting any repairs as you don't want to build in a warped frame.

Re: Cracked Trailer frame repair ideas

Posted: Tue Oct 09, 2018 11:17 am
by Tfitz
Thanks for the ideas! I did talk to the manufacture and they said anything i do to fix the frame would just be a band aide and would happen again sooner or later. Bottom Liine was they were more interested in selling me a new trailer.
So I think I'm going try and fix this by getting the widest C channel that will fit in the web of the I - beam, bend it in a press to match the bend in the trailer frame on the inside AND outside, then through bolt the inside AND outside C channels to sandwich the cracked frame. Then use the bottom leg of the C channel to through bolt the crossmember too from the bottom. No welding. Other than welding over the crack. Just bolts sandwiching everything together. I'm worried welding across the I beam will weaken it to much.
I know about crevice corrosion and overlapping aluminum is bad but I think the moisture will drain from behind the C channel and it will last a long time. What do you think?

Re: Cracked Trailer frame repair ideas

Posted: Tue Oct 09, 2018 11:19 am
by Tfitz
Bunk and inside crossmember

Re: Cracked Trailer frame repair ideas

Posted: Tue Oct 09, 2018 11:50 am
by kmorin
Tfitz,
the top of the bent beam is flexing in and outward (reference the centerline of the trailer) or the break failure wouldn't be at the bottom of the inverted T of the I beam.

So, gouge out- weld and then put a gusset from the box cross beam up to the top flange with a or a V brace (looking down) - one in front of the bend and one aft- to help the I beam remain in column- not to flex in and out at the top flange.

Also widening the top flange will stop this type of failure- using a plate of the same thickness as the flange- and making a bolt on replacement/reinforcing flange that is 2x the width of the I's flange, then using small bolts (or welding at the flange to replacement flange lap joint) you'd also create a flange that will keep the web from flexing in and out- which is what caused this crack.

It possible the alloy (6061?) and shape at the web to flange extrusion curve (cross section of beam at the transition) was bent at a too small radius for this particular beam's section? don't know where to find that info- but cold working an I is somewhat better than hot work in regard future stiffness.

By 'trapping' the top flange's in and out movement the web is stabilized at the lower flange and the beam will probably be fine.

Cheers,
Kevin Morin
Kenai

Re: Cracked Trailer frame repair ideas

Posted: Tue Oct 09, 2018 5:03 pm
by Tfitz
You can see the dip in the I beam at the crossmember attachment point. I believe it's the weight of the boat bouncing that is making the I beam crack and separate. By doubling up the crossmember attaching point and stiffening the I beam with 6061 C channel and bolting it all together it should hold. The weld you see in the photo was a last minute temporary fix just to make it work for one last fishing trip. And it looks like it held with out cracking again on the 700 mile round trip Valdez goat trail.

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 10, 2018 4:55 am
by gandrfab
Tfitz wrote:
Tue Oct 09, 2018 11:17 am
Thanks for the ideas! I did talk to the manufacture and they said anything i do to fix the frame would just be a band aide and would happen again sooner or later. Bottom Liine was they were more interested in selling me a new trailer.
I would be a little pissed off about that. Not going into detail, but I would mention something along the lines of trailer life and not buying a new one from them.

What ever you go with I would still look into taking some of the weight off that cross beam by putting more weight on other load bearing points.

Good luck.

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 10, 2018 10:50 am
by Tfitz
The trailer IS 14 years old. And the load IS right at the trailers rated limit. And the frost heaves on Alaska roads ARE really bad. So I don't really have a problem with the trailer manufacturer. And I should take some blame for this too. The week before I had a fuel pump go out mid trip. We got back to port on the kicker but I still had 75 gals of gas onboard. I trailered the boat home like that and that's when this problem happened. I really should get a heavier trailer for this boat but I would like to get a few more years out of these new axles, tires and brakes I installed last year. I think if I keep the boat light as possible, slow down and make some minor changes how I strap the boat down it will still work for now. My next trailer will be galvenized steel.

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 10, 2018 1:54 pm
by kmorin
Tfitz, the point-load on the bottom flange would also be reduced by the cross member-to-top-flange bracing as that would re-load the I-beam in the full section- not solely the bottom flange. By triangulating the load- so the cross member pulls down on both top and bottom in a fixed triangle- the flex- in an out- of the top flange and web base goes away. Same as building connectors- load I beams uniformly in section or from the top- not the bottom.

Just a note about carpeted bunks! evens sloped as well as yours appear? they are a notorious source of 'bunk rot' or corrosion of the aluminum by holding a thin film or water against the hull-as the carpet can't dry out very well when its compressed by the bottom onto the wood bunk.

Plastic bunk covers are worth the time, they drain fully and they don't contribute to de-areated water film held to the hull.

Cheers,
Kevin Morin
Kenai

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 10, 2018 5:25 pm
by Tfitz
Based on past experience I've come to realize that MOST of the time when I don't listen to what you are telling me to do....I regret it later. SO I will try to incorporate a gusset or V brace into my C channel design. Since I just bought a 25' piece of 4" 6061 C-channel for this repair. I think the channel will distribute the load and stiffen the beam, and the gusset will reduce flexing. I don't won't to weld on the I beam though, I'll bolt things together. And yes the carpet bunks were on the list to be replaced with plastic covers as soon as I locate some good ones

Re: Cracked Trailer frame repair ideas

Posted: Sat Oct 13, 2018 11:50 pm
by Tfitz
Got the trailer out to where I can work on it now! I have a plan and it's going to be Beluga strong when done!!

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 17, 2018 12:25 am
by Tfitz
Whats the best way to weld this crack and make this area strong again? I could mig it and grind it smooth but I think it won't have much strength. I'm adding the two 1/4" × 4" C channels and support the crossmember off the C channel legs so I'm thinking that will add the strength.

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 17, 2018 2:42 am
by kmorin
Tfitz,
the weld shown is cold lapped. the lower edge is not fused to the flange top surface- but the top is fused to the vertical web surface; although the start and stop need work. I'd suggest grinding this out, gouging the weld metal out and using run-in blocks. This is a piece of 3/16" or so plate about 2" x 2" to start on- and to stop on- these would be bend outward when done and the weld's start and stop wouldn't have a cold start or a crater point stop? If your new 4" channels will not interfere or lay on this weld (?) THEN; its not nearly as important. However if the channel will overlap the weld- meaning you'll be taking the head or crown of this weld off??? then it become important that the root (remaining after flattening/sanding) becomes more fused on all sides: start, top, toe and end.

to my eye the lower edge of this MIG weld shows a cold 'curl' or beading up not the line of fusion seen at the top. If I were using MIG to do this I'd preheat to 230-250 F using a temp crayon to reduce the fusion issues trying to weld to a huge cross section. The beam's thickness is greatest at this particular spot- where the vertical web curves into the flange shape; the two elements are radius-ed and that makes this cracked area thicker so MIG is very hard to adjust.

MIG depends on uniform thickness- AND a voltage setting that is adequate compared to the wire feed speed to deposit a fully fused weld on both (all) edges. That is very tough to adjust due to the thickness of this area of the beam. Temp crayons or temp sticks are wax crayons that melt at a given temp. However using temp sticks/crayons to get a targeted preheat will make a MIG weld SO much more reliable in this area. I do realize that heating the beam (a heat treated alloy) to get a good weld is a compromise- but.... the lower edge shows its needed.

To repair the flange, I'd cut a V along the crack with a burr, or a U shaped gouge. Then I'd add a flange doubler the entire length of the curve of the beam's bend. So a 12" to 18" long strip, cut to the width of the bottom flange plus 1/2" (width so a 1/4" inside and out) of 1/4" or 3/8" material. I'd prefer to use 5086 over 6061 due to the increased tensile of that alloy.

I'd weld a lap joint along both outside flange edges; after grooving into the bottom of the flange. This weld would only contract along the line of the weld seam- so the flange would not be weakened- but stiffened and the tension load on the bottom flange would be reinforced by the added flange thickness which will distribute to the new, lower, flange doubler of 5086.

When the crack is welded up- with a V or U shaped groove all the way through to the flange doubler - that weld would 'pick up' or fuse to the new added doubler flange. So the bottom flange would be welded to a doubler below and that material would be edge welded (outer edge lap welded) to the flange.

So; both directions this failure point would be reinforced. I'd re-drill the holes in the bottom flange after all the welding was done. The new bottom flange doubler will lower the cross member by it's thickness- but I don't see that being critical to the re-install of the bunk mount? If it is- re drill the vertical mount plate into the bunks.

Hope this make sense without sketches?

Cheers,
Kevin Morin
Kenai

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 17, 2018 3:46 pm
by Tfitz
When i made that weld on the frame i could barely see and was out of position because the boat was still on the trailer. I knew i would be doing it over. It got me there and back on my last fishing trip so it worked out ok. You really think I need to add a doubler on the bottom of the frame to stiffen it and add strength to support the crossmember? Remember I'm adding 2 ea 1/4" C channels to do that very thing. I'm going to through bolt the crossmember to the lower leg of the new C channel so the new C channel will be carrying most of the crossmember weight. I am hesitant to do allot of welding on the trailer frame when I can double the strength by bolting channel on

Re: Cracked Trailer frame repair ideas

Posted: Wed Oct 17, 2018 8:08 pm
by kmorin
Tfitz wrote:
Wed Oct 17, 2018 12:25 am
Whats the best way to weld this crack and make this area strong again?
you asked, I just replied to that question. The crack completely compromises the side to side (lateral moment resistance) of the beam's lower edge. So the doubler is to address that- alone.

Yes, I realize you're sistering/fishplating/sandwiching the original web with both new web and added flanges- I was addressing a single question not the overall repair.

Cheers,
Kevin Morin
Kenai