Trailer tongue

[Empty]

I am in the throws of building a trailer, squaredrop camper. 8 x 4 braked will be IVA tested to 1300 KG.
I am using 75mm x 50mm x 3mm for the main frame. Cross bearers 50 x 50 box. Axle are knott independant units. I need advice on the tongue I have purchased 100mm x 50mm x 3mm it looks out of proportion ( to big) I would like to use 80mm x 40mm x 4mm. Is there any structural engineers that could confirm this would be ok.

 

[addjunkie]

Most amateurs over engineer….I built a few ski boat trailers, axles and main leg used to be 50x50x5 much longer than your mini caravan and much heavier.

Go to a caravan place and look whats under them.

 

[colnerov]

Most amateurs over engineer….I built a few ski boat trailers, axles and main leg used to be 50x50x5 much longer than your mini caravan and much heavier.

Go to a caravan place and look whats under them.

Yes, I call them IRN-BRU builds, made from girders.

 

[tom2207]

Yes, I call them IRN-BRU builds, made from girders.

most of the ones I see look like starved whippets ,,,, bog all under them worth talking about ,,, that looks like a very long drawbar in relation to what its doing in your picture.

 

[jsf55]

I've only ever used 50x50 for the tongue and chassis and 50x25 for the floor supports, all 2mm wall

 

[Bornfree]

1300kg is a decent weight, I would stick with the 100x50 if you have already bought it.

 

[jo1010]

To summarise....you've got the weight of a small car on a single box section drawbar with 3mm wall thickness...I'd see that kind of design as suited on a 750kg camping trailer. For 1.3 ton I'd have thought an A frame arrangement would have been better - with your 4mm wall thickness you could probably use 40mm box section then - and no problem with the length of the drawbar then either (short drawbars can make reversing a twitchy pita )

 

[addjunkie]

Wheres the 1300kg figure come from, seems a fair bit for a small caravan.

 

[tom2207]

To summarise....you've got the weight of a small car on a single box section drawbar with 3mm wall thickness...I'd see that kind of design as suited on a 750kg camping trailer. For 1.3 ton I'd have thought an A frame arrangement would have been better - with your 4mm wall thickness you could probably use 40mm box section then - and no problem with the length of the drawbar then either (short drawbars can make reversing a twitchy pita )

thats not strictly true ,,, you will prob have 15/20kg on that box as a ow hitch load ,,,, the load transfered down the tow bar is a product of speed and weight , depending on braking set up , draw bar loading is not just about total weight , yep a long bar makes going backwards handy , but storage becomes a pain , take a closer look at caravan proportions , that will tell you all you need to know ,,, if in doubt take a tape rule to a Brian James ,,,

 

[pedrobedro]

8 x 4 braked will be IVA tested to 1300 KG.

Are you filling it with concrete blocks ? We bought a little Eriba Puck last year a bit bigger than what you are building and unladen weight is 500kg approx. I built a little trailer many years ago using 40mm box with 3mm wall and it was thoroughly abused by BIL who was putting 500kg of concrete slabs in it till I saw what he was doing but it is still in one piece. I wouldn't worry about reversing, just unhook it and push, it's not that heavy.

 

[8ob]

I am in the throws of building a trailer, squaredrop camper. 8 x 4 braked will be IVA tested to 1300 KG.
I am using 75mm x 50mm x 3mm for the main frame. Cross bearers 50 x 50 box. Axle are knott independant units. I need advice on the tongue I have purchased 100mm x 50mm x 3mm it looks out of proportion ( to big) I would like to use 80mm x 40mm x 4mm. Is there any structural engineers that could confirm this would be ok.

Not a structural engineer but would put my name to the 80x40x4 being strong enough for what you are trying to achieve, I personally wouldn’t go any smaller. Its also a good platform to bolt a jockey wheel to the side of without compromising the integrity of the drawbar.

Bob

 

[minimutly]

To summarise....you've got the weight of a small car on a single box section drawbar with 3mm wall thickness...I'd see that kind of design as suited on a 750kg camping trailer. For 1.3 ton I'd have thought an A frame arrangement would have been better - with your 4mm wall thickness you could probably use 40mm box section then - and no problem with the length of the drawbar then either (short drawbars can make reversing a twitchy pita )

I built a small car transporter with inch and a half box a frame. With the mini in tow you could feel the a frame flexing - like a rhythmic pulsing. A third bracing section up the middle solved it, but lesson learned -make the towbar (tongue)? Plenty stiff enough!

 

[jo1010]

... Plenty stiff enough!

A stiff tongue is always good

 

[jo1010]

Are you filling it with concrete blocks ? .... I wouldn't worry about reversing, just unhook it and push, it's not that heavy.
View attachment 523365

... if its still full of concrete blocks unhitching can be (an embarrassing) pain

 

[PhillipM]

Not a structural engineer but would put my name to the 80x40x4 being strong enough for what you are trying to achieve, I personally wouldn’t go any smaller. Its also a good platform to bolt a jockey wheel to the side of without compromising the integrity of the drawbar.

Bob

A lot of motorhome towbars are only that and hung laterally with the towball in the centre - a design as stiff as wet spaghetti, they cope fine with 1500kg tow limits.

 

[zzr1200]

45+ years ago I built a 6ft x 4ft 10cwt box trailer (for camping) with Indespension units.

The A frame drawbar was 50 x 50 x 6 angle, from the front cross section of the box frame to tow ball centre was 32 inches, over the years in my ownership it WAS WELL tested, 1 yard of ballast on several times, sold it a mate 15 years ago and I believe it's still going strong today.

The trick to having a well balanced trailer with low stress is axle and load positioning layout to maintain correct nose loading weight.

 

[8ob]

My experience of 50mm box drawbars is not good, we have a Dory that doesn’t weigh half a ton, the trailer it came with had a 50mm drawbar. That buckled and bent to the point it was dragging/bellied out driving down the road, a guy in the marina had to bodge it so we could get the thing home.

Bob

 

[zzr1200]

My experience of 50mm box drawbars is not good, we have a Dory that doesn’t weigh half a ton, the trailer it came with had a 50mm drawbar. That buckled and bent to the point it was dragging/bellied out driving down the road, a guy in the marina had to bodge it so we could get the thing home.

Bob

Agree 100 x 50 in a vertical configuration should be ok.
Introducing a welded on winch post won't have helped imo, a bolted on version would be my preferred choice.

 

[Empty]

Probably missed a couple of things in my original post. It is a A frame I am using. The reason for the 1300kg is I am fitting a handbrake. So it will have to be IVA tested. All the calcs for the hitch and brakes were suited to 1300kg as these need to be supplied fir the IVA test.

 

[minimutly]

My experience of 50mm box drawbars is not good, we have a Dory that doesn’t weigh half a ton, the trailer it came with had a 50mm drawbar. That buckled and bent to the point it was dragging/bellied out driving down the road, a guy in the marina had to bodge it so we could get the thing home.

Bob



View attachment 523385
View attachment 523383

But how much water was in the Dory @8ob