Trailer frame flexing even when empty

[mirrocraft16]

I have two boat trailers, both are built the same way, with a single 3x3" tongue and two 2x3" side frame rails joined in the middle with a single 1/2" bolt and two U bolts through a piece of angle iron about a foot behind the first bolt.

If I put any weight on the rear of the trailer, empty or loaded, the tongue to frame joint flexes about 4". The one trailer is brand new, the other one a few years old. I can't tighten anything up anymore without crushing tubing. What I don't like is that it no doubt flexes going down the road.
It just seems that the tongue should have gone all the way to the first cross member not just 12" past the first bolt.
I have no doubt that with time and movement the 1/2" bolt will eventually cut through the tubing, its already starting to tear or distort the tubing where its forced to conform to the angle of the joint.

The pic here is the style frame and almost identical trailer: The boat don't weight much, its just a 14' aluminum boat on it but with the bow secured to the winch post and the transom tied to the rear cross member, the frame has to be bouncing up and down under the boat. It almost seems like there should be a triangle shaped plate bolted over that joint to tie everything together. Every trailer this size I looked at used this design.

 

[smokeonthewater]

Let's see pics of your actual trailer showing the area in question.... There are several methods of making a strong connection for that style but we need to see what you have.

I have several ideas on how to improve yours but again need to see what you are actually working with.


BTW if you look at the pic you posted you will see on of those methods... there is a small cross member attached to the bottom of the frame and tongue behind the main connection

 

[dingbat]

Trailers flex by design.

When it come to trailers, rigidity is not your friend. The more stiffness, the more likely hood of stress crack developing. Properly secured, your boat stiffens up the assembly in use.

 

[mirrocraft16]

I don't have a camera to take a pic, but the trailer is identical to the one in the pic I found online.
Yes, there's a crossmember just behind where the tongue is through bolted, but its attached with three u bolts from the top. One U bolt is over the tongue tube, the others are over the two side tubes. That connection is secure. The issue is at where the two tubes bolt to the tongue with a through bolt. The through bolt deforms the end of the tubes since the angle there is about 60 degrees or so, this bolt is not very tight, if made tighter, it would no doubt collapse the tongue tubing, or tear through the side tubes.

With the boat on the trailer, pulled snug against the bow stop, and still resting on the mid roller and both bunks all looks fine. But if I shake the rig I can see the mid roller move up and down under the boat.
Without the boat on, if I put weight on the rear of the trailer the trailer flexes at the tongue connection about 4" each way, that's 8" total movement with just a foot on the back of the trailer. If I grab the tongue and lift, I can pick the tongue up off the ground and watch that connection flex.
If the crossmember wasn't so close to the through bolt it wouldn't be such a flimsy mess. The old trailers had longer tongues, the tongue tube went all the way through to the first crossmember but on these new trailers the tongue stops only a foot past the through bolt connection.
I looked at a few brand trailers but all were the same style, brand doesn't seem to matter.
The bolt going through the tongue is only 1/2" by 4" long with two big washers and a nylock nut.
The U bolts are all 1/2" diameter. The tongue is 3x3" the side tubes are true 2x3" tubing. The trailer is rated at 1550 lbs. Both carry open 14' boats, I went with the next longer/ heavier model trailer to get the 12" wheels and longer tongue. For $700 each I'm a bit disappointed in these trailers.
What happens on the road is the mid roller is bouncing up and down against the keel as the trailer flexes in the middle. Its fine on smooth roads but there aren't any smooth roads on the way to the ramps here, in fact many of the roads near the ramps aren't even paved, which is one of the reasons I went with a heavier trailer.
When I called the dealer they said the only fix was to buy a welded trailer for double the money.
I think the fix is a longer tongue and longer cross brace which would spread the torque being applied to the tongue over a greater area.
I have little doubt that if left alone either the side tubes will wear or tear free of the bolt or it'll wallow out the bolt hole through the tongue.
As it stands now, I highly doubt that it would survive even me jumping on the tongue with my 340lbs without bending something.
On the old trailer, which got retired due to rust, the frame was solid, with no flex, at least none that I could impart with my hands or feet.

I agree a trailer should have some flex but when a 500lb aluminum boat makes the tongue joint sag several inches there's a major design flaw.

I didn't post the brand, but I looked at about 7 brands and all look identical other than brand name. The dealer who sold me these sells three brands, both of these are different brands but both are identical other than the brand decals.
If I had a local source for galvanized 3x3" tubing I think I'd just go buy two new tongues about 4' longer each and fine a way to attach the rear end of the tongue to the first crossmember like on the older trailers.
Also, these things are way heavier than the old trailers, the gauge of steel is heavier. The old trailers were maybe 210lbs, these are both marked as weighing 338lbs each. They have the same GVWR but less capacity overall. My thought was that the heavier frame would take longer to rust through but with all the flex, I suppose the first failure will be due to torn metal. Both are galvanized to I really don't want to weld on them and break the galvanized coating either.

 

[Scott Danforth]

its not a design flaw, it is simply a light-weight trailer. Trailers are made to flex.

 

[Maclin]

Trailers flex by design.

When it come to trailers, rigidity is not your friend. The more stiffness, the more likely hood of stress crack developing. Properly secured, your boat stiffens up the assembly in use.

^^^^ This ^^^^

plus what Scott wrote.


If the trailer is setup for the boat then no worries. Perhaps yours needs some more setup attention.

 

[dingbat]

The 1/2" x 4" lg. bolt that your complaining about is not load bearing. You could tighten that bolt till you crushed the tubing with no affect on deflection.

I have a #7K, 28' lg. trailer of a similar design built with 4" x 3" tubing. The tongue is over 12 ft. long. Center bolt to tie plate maybe 18". The deflection is easily under 1.5". I suspect our trailer is set up wrong.

I suspect the rear axle too far from the center of the load. What is your current tongue weight?

 

[mirrocraft16]

The tongue weight is less than 100lbs, the axle is set as far back as it'll go to give it more tongue weight. The boat is light, maybe 900lbs with the motor, 1100lbs tops fully loaded. If I walk up to the empty trailer, grab the rear most part of the tongue where it clamps to the frame and lift, I can lift the frame up 4 1/4" before lifting the tongue jack or axle off the ground. I can't do this on any of my old trailers. The bunks attach only to the cross members, the majority of the weight is on the transom, so while sitting still, the leverage off the rear is forcing the middle up against the hull. The boat is tied down with two straps in the rear, from the rear handles to the rear cross member on each side and with a strap at the bow. The middle of the frame has nothing keeping the front and lone roller against the hull.
I have little doubt that the through bolt will eventually tear free or wallow out the hole in the tongue, there's just no support there. I've already had to run a separate wire for the tail light grounds because that junction will not maintain a good ground. It would be better if they had welded a tub through the frame to allow that bolt to be tightened but as it stand now, it can't be more than just snug. Just rolling the empty trailer around the yard that bolt squeaks and squawks as the trailer flexes.
On my old trailers, the basic design was the same but the tongue went all the way to the first cross member which was a C channel. The tongue was attached inside that channel with a vertical through bolt. It didn't rely on a short cross brace and U bolts to support the connection.
Flex in a trailer is fine but the last place you want to see flex is along the center line of the keel, it should at least keep all the keel rollers against the hull and supporting weight. What I have now is the front roller being able to sag away from the hull as the tongue bounces up and down.
The actual flex is the two side tubes distorting when force is applied, the end of the box tubing goes out of square as its pulled on.

 

[roscoe]

Your trailer is completely defective.
Cut it up and scrap it before someone gets killed.

Or give it to me and I'll take care of it.

So what do you want to know?

What do you want to do? Firm it up?

Get 2 pieces of steel and either weld, or bolt them on.
One on the top, one on the bottom, of where the tongue and side rails meet.
Should only take you an hour, once you get the 2 pieces of steel.

 

[mirrocraft16]

Here's a quick drawing with some measurements to show how these are built, there's simply not enough space between the cross member and the through bolt.
I've been calling around to see where I can find a longer tongue, I want to install a longer tongue that reaches back to the first cross member, a connection there plus the u bolts to the short angle iron and through bolt should stiffen up the frame. The simple fact that they also rely on only 3/8" U bolts to attach a tongue on a trailer this size doesn't make any sense either, they used 1/2" U bolts for the bunks, yet 3/8" U bolts for the frame and suspension?

 

[reelfishin]

If you want to reinforce that set up your on the right track by making the tongue longer and extending it to the first cross member.
There are many brands that use that very same arrangement and they hold up fine, but the distance between bolts on yours seems shorter than most.
If its galvanized, welding on it is out of the question if you want to preserve the zinc coating.
Either run a new tongue back to the first crossmember or just get a longer piece of angle and make a longer tongue support a bit further back.

Chances are however it'll survive just fine the way it is. Have fun getting that first through bolt out though, I've run across a few that were assembled in halves with the bolt ending up trapped in the tubing. Meaning that the bolt cannot be removed with the side tubes in place. They build the frame with the bolt first inserted through the inner wall of one frame rail, then its placed into the tongue and through the second frame rail. You would have to remove at least one side frame tube to get the bolt out.
This means removing the springs from the frame on one side, and unbolting all cross members on that same side.
Its normal for the outer tubes to distort as the bolt is tightened.

I've had both this style frame and a few with this union welded in place with a top and bottom plate. All three welded trailers I've had rusted out in that area due to debris and salt collecting in that area. At least with the bolted type frame a rusted member can be replaced.

 

[minuteman62-64]

I see lots of galvanized trailers that are used to launch in salt water and have been welded, for post-manufacture alterations, in areas that get submerged. The welded area is coated with the cold galvanizing spray can stuff (hopefully after good prep.). Nowhere near as good as the original galvanizing, but seems to hold up reasonably well with occasional maintenance.

 

[reelfishin]

I don't think I'd be welding on a brand new trailer though, especially in a saltwater area like NJ.
I've used that cold galvanizing spray and it does work but it doesn't really bond with the metal, its just a sacrificial coating.
I'd be more apt to to a proper prep job then paint well with a good paint, then maybe coat with the cold galvanizing spray.
If it were mine, I'd be going the same route by adding a longer tongue, it will do wonders for the overall strength of the trailer.
But keep in mind that if buying galvanized tubing commercially, chances are it will have to be cut to length, leaving at least one end or edge of the tubing unprotected. This edge will need to be properly painted or treated to avoid corrosion from starting there. I'd also put this edge at the coupler if possible.

 

[minuteman62-64]

I don't think I'd be welding on a brand new trailer though, especially in a saltwater area like NJ.
I've used that cold galvanizing spray and it does work but it doesn't really bond with the metal, its just a sacrificial coating.
I'd be more apt to to a proper prep job then paint well with a good paint, then maybe coat with the cold galvanizing spray.
If it were mine, I'd be going the same route by adding a longer tongue, it will do wonders for the overall strength of the trailer.
But keep in mind that if buying galvanized tubing commercially, chances are it will have to be cut to length, leaving at least one end or edge of the tubing unprotected. This edge will need to be properly painted or treated to avoid corrosion from starting there. I'd also put this edge at the coupler if possible.

Based on my observations at local launch ramps, and the trailer we had at last job, it is not unusual to weld after market brackets, etc. to galvanized trailers. The key is, you don't just spray the cold galvanizing stuff on - you prep the area as you would if you were painting bare metal - wire brush and/or grind, clean, etch and then spray. Again, agree nowhere near as good as actual galvanizing - but, if you need to modify ............

 

[Lou C]

No Title

When I put a longer (9' vs 7') tongue on my old Load Rite I was concerned that it would flex more so what I did was add a second cross bar similar to the OE one, out of angle galvanized stock that I got from Champion Trailers. A lot of drilling but it came out pretty well...

 

[Frank Acampora]

That is a similar design to the trailers used on the smaller Bayliner boats. Yes, the 3/8 U bolts are sufficient but you are correct in that the tongue to frame should not flex. The problem is the long 1/2 inch bot used to secure it. It simply can not be tightened enough. The correction is to remove that bot and replace with two shorter bolts inside either frame member and securing the tongue to them. You get a long wrench and reach inside the tongue with the nuts. Then you can tighten the bolts until the frame members do bend enough to contact the tongue tube fully. The bolts can be tightened to 55 foot pounds and the tongue will no longer move.

 

[reelfishin]

A better fix yet would be to insert a cross tube inside the tongue, and maybe even increasing the size of the bolt to 5/8".
I'd have some concerns using two separate bolts in that it changes the structural property of the tubing. By using a through bolt it maintains the strength of the tubing. With two bolts, there could be a risk of tear out of the bolts on each side. Each bolt would only be as strong as the single wall thickness of the tongue.

Take a length of 3/4" water pipe and cut it to fit up inside the tongue, then bolt up the joint tight with a larger diameter bolt. This will allow you to apply proper torque without crushing the middle tube. Make sure the washers used on the through bolt are larger than the OD of the tubing used inside.