Originally Posted by jeepster
Are you 100% sure you inputted the correct figures?...80x40x3 has a permissable bending stress of 141 MPa but with MITcalc I calculate the maximum bending stress from the rear swing beam to the axle, when the trailer is carrying a 950kg boat (its maximum payload capacity)is only 14.4 Mpa? Perhaps I have made an input error somewhere, or simply misinterpreted the results?
It would certainly appear at first glance that my load model is much closer to reflecting the true loading situation on the trailer than yours appears to, but if you spot any errors let me know.
For those not familiar with MITcalc load models...The two red arrows are the load on each swingbeam, the black triangle to the left is the axle and the one to the right is the towhitch.
Note that the swingbeam loading is not symetrical...The load is heavier over the rear swingbeam because it is further away from the axle, and because the boat is heavier at the stern than at the bow.
I calculate the split to be about 68.6% over the rear swingbeam and 31.4% over the front.
Assuming the trailer has an unladen weight of 150kg, and a maximum gross weight of 1100kg, thats allows for a maximum payload of 950kg. That is split to around 651.7kg over the rear swingbeam and 298.3kg over the front.
If I read the results correctly the trailer is well within structural limits even when fully loaded. Of course my boat only weighs about 750kg (currently), so there should be no issues at all.
...See the following screen caps for the results:
I have remained quite polite throughout this thread but you really are testing my patience now ...
Uf your going to try and use something like Mitcalc the at least try to learn fundamental mechanics beforehand.
In simple terms, the weight of your trailer is being transferred down to the axle through 4 seperate points, the connection points where the swing beams meet the rails.... Follow me so far?
This force then gets added to the downward force that the weight of the trailer is also generating on the axle.
Now for the important bit..... Listen carefully
FORGET YOUR FECKING TOWHITCH!!!!!!
I have worked out the stress on the longitudinal rails as this is quite obviously the most heavily loaded part if your trailer. Your just going to have to take my word for it as its quite clear that your unable to grasp this but the the weight of the boat is trying to bend the side rails over the top of axle. As your now infamous towhitch can only take 50kgs so its hardly worth subtracting this from the downward thrust created by the forward swingbeam. ( plus i would have to calculate the moment based on the distance to the forward swingbeam itself anyway)
Now look carefully at what you tried to simulate on Mitcalc....
WHY HAVE YOU SIMULATED AN UPWARDS THRUST RIGHT AT THE END OF THE TRAILER?
How many fecking axles does your trailer have?
Also you need to learn a bit more about steel grades also.
If your going to jump in at the deep end, FFS learn how to swim first!!.
To give you a bit of background, i'm a mechanical engineer. I run a small engineering workshop in my spare time and when im not doing that i subcontract full time for a multi-national oil company..... Wait for it.... As a chief engineer.
Oh and i also have an HGV2 ticket and run a DAF LF55 crane lorry as part of the workshop.
The picture of the trailer i built i posted earlier is ( i think) the 6th trailer i have built to date. (four of which were braked trailer with at least a 2000kg gross weight)
Now if you still don't trust what im saying ithen fair enough but i have shown you 4 other examples of other trailer manufacturers pridung a 1300kg trailer and each shows a reinforced side rail.
Why am i wasting my time here?
You know what,,,, go ahead, your trailer IS perfectly safe in fact your right about drilling holes down the side of the rails and your right also about loading up the towhitch too.
Good luck to you (and to the other road users who are following you down the road.
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