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Old 15 September 2012, 06:26   #111
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Originally Posted by Anchorhandler View Post
Jeepster.....

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.
Are you sure you know how to use MITcalc? Your model would imply that you don't.

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Originally Posted by Anchorhandler View Post
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?
Are you just being dense on pupose? If you look at my MITcalc model it clearly shows the exact positions of the "4 connection points", relative to the axle ie: The swingbeam pivots, where the the force is being applied to the siderails.
Being two dimensional, of course it only shows a single beam, but this beam is of course made of two seperate 80x40x3 RHS rails, so you can double the strength of the beam...Or perhaps you failed to realise that?

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Originally Posted by Anchorhandler View Post
This force then gets added to the downward force that the weight of the trailer is also generating on the axle.
Just as my model takes into account!

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Originally Posted by Anchorhandler View Post
Now for the important bit..... Listen carefully

FORGET YOUR FECKING TOWHITCH!!!!!!
Its not going to happen...Its part of my model so it stays.


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Originally Posted by Anchorhandler View Post
I have worked out the stress on the longitudinal rails as this is quite obviously the most heavily loaded part if your trailer.
So have I, but your model looks nothing like mine and therefore you have different results.
And just FYI, after the axle, the rear swingbeam is the most heavily loaded part of my trailer, not the siderails!

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Originally Posted by Anchorhandler View Post
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.
And which part of my model, that clearly shows exactly that, didn't you understand?

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Originally Posted by Anchorhandler View Post
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)
That 50kg is part of the equation, so I am not simply going to ignore it.

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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?
...Its called the towhitch!

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Originally Posted by Anchorhandler View Post
How many fecking axles does your trailer have?
...I told you it only has one axle, my photos clearly show it only has one axle and my MITcalc model only has one axle...Which part of "one axle" don't you understand???


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Originally Posted by Anchorhandler View Post
Also you need to learn a bit more about steel grades also.
I have included the steel grade in my model, have you?

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Originally Posted by Anchorhandler View Post
If your going to jump in at the deep end, FFS learn how to swim first!!
I am wearing my life jacket, so I am not too worried.

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Originally Posted by Anchorhandler View Post
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.
With that in mind, I'm glad I am not one of your clients!

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Originally Posted by Anchorhandler View Post
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. .
...Please read my previous posts before you reach for your keyboard...In one of my recent posts I clearly state that mine is actually based on a 1100kg Indespenion trailer, and they do not have reinforced side rails!
I even showed a photo of the trailer in question.

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Why am i wasting my time here?
Amen!

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Originally Posted by Anchorhandler View Post
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.

Simon

Sent from my iPhone using Rib.net
They had better not get behind an 1100kg gross Indespension trailer either, because according to you they aren't structurally sound!
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Old 15 September 2012, 07:05   #112
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Out of interest when trailers fail (from being overloaded) is it the vertical force that actually kills them or perhaps the roll/yaw/cornering force? It strikes me that a trailer could survive being overloaded sitting in the yard but the dynamic load going over a speed bump or the g force going round a corner will be much higher and less predictable. Of course if it fails in the yard its possibly expensive and inconvenient. If it fails at 40mph on a corner its possibly manslaughter.,
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Old 15 September 2012, 07:10   #113
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Originally Posted by Poly View Post
Out of interest when trailers fail (from being overloaded) is it the vertical force that actually kills them or perhaps the roll/yaw/cornering force? It strikes me that a trailer could survive being overloaded sitting in the yard but the dynamic load going over a speed bump or the g force going round a corner will be much higher and less predictable. Of course if it fails in the yard its possibly expensive and inconvenient. If it fails at 40mph on a corner its possibly manslaughter.,
Particularly if you are daft enough to build it without knowing what you are doing!

Ignorance is no defense under the law. Much better to leave these things to people who know what they are doing, and carry public liability insurance, and prepared to give it a certificate.

I would suggest that after jeepster finishes cutting all his holes he takes it along to a VOSA center and see what they think of it. (without his boat on I would suggest!)
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Old 15 September 2012, 07:15   #114
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Particularly if you are daft enough to build it without knowing what you are doing!

Ignorance is no defense under the law. Much better to leave these things to people who know what they are doing, and carry public liability insurance, and prepared to give it a certificate.

I would suggest that after jeepster finishes cutting all his holes he takes it along to a VOSA center and see what they think of it. (without his boat on I would suggest!)
I didn't say I was going to cut holes in my trailer, it was just a suggestion. You have got the hole thing mixed up!
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Old 15 September 2012, 07:20   #115
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In the spreadsheet Jeepster seems to have point loads and continuous loading muddled up and the beam dimensions (breadth and depth) the wrong way round. How about we ignore the weight of the beams for now (getting rid of the continuous loading)?

If we kept it simple, would Simon and Jeepster agree that the loading might look something like this?

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Shear force and bending moment like this?

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And work it out from there?

Second moment of area of the beam is (40 x 80^3) / 12 - (36 x 74^3)/12

(My university days were more than half my life behind me now!)
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Old 15 September 2012, 07:54   #116
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Yeah....

I wasnt going to reply anymore as its pretty clear there is nothing on this forum that you either dont already know or dont want to hear but since the safety of other road users comes into it i figured i better post these pictures....

They both show the computer simulation of the loading on each side of the trailer based on forces being applied at the points you have indicated. Picture 2 follows from the bottom of picture 1.
As you can see, the first shows a simple forces diagram showing the current set-up of your trailer....
I have allowed for a 6" landing area where the axle meets the side rails.
I have also set this up on the assumption that you have used a 50B grade steel or similar.
I have simulated a 200kg force forward and a 210kg force aft (at the points that the swingbeams connect to the rails.

This gives you a total loading of (200x2)+(210x2)= 820kgs

If you loook at the second picture you can see that in your case you are on the absolute limit of the permissible stress allowed in the steel. (Highlighted red, 208Mpa out of 207Mpa m, ax). Beyond this you risk deforming the steel leading to possible failure. Incidentally It also shows a maximum deflection of 18mm

Keep in mind that i havnt subjected the loadings to any safety factor either.

Your best option to render this safer is to move the rear swingbeam further forward thus reducing the bending moment on the side rails.


But of course... you already knew all this didnt you?

Simon
I just had another look at your MITcalc model...Oh dear!
You appear to have the load equally distributed at either end of the beam, and two axles! Plus you only calculated the bending stress for a single 80x40x3 beam, not for two as is the case with my trailer!
And you call yourself a chief engineer?
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Old 15 September 2012, 08:55   #117
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Quote:
Originally Posted by jeepster View Post
I just had another look at your MITcalc model...Oh dear!
You appear to have the load equally distributed at either end of the beam, and two axles! Plus you only calculated the bending stress for a single 80x40x3 beam, not for two as is the case with my trailer!
And you call yourself a chief engineer?
No, but you are by your own admission an unemployed toy lorry driver...
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Old 15 September 2012, 09:00   #118
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Originally Posted by jeepster View Post
I just had another look at your MITcalc model...Oh dear!
You appear to have the load equally distributed at either end of the beam, and two axles! Plus you only calculated the bending stress for a single 80x40x3 beam, not for two as is the case with my trailer!
And you call yourself a chief engineer?
Yes actually, i do call myself a Chief Engineer....

The load is equally distibuted at both ends because, as i mentioned, i'm only intrested in calculating the stress in the side rails at the area they connect with the axle. This is the most critical part of any trailer.

Re-read post number 86 and you will see that i mention a 150mm area where the rails connect to the axle....this is represented in the drawings by the two black triangles....funny enough, spaced 150mm apart.

If you also look at the calculations i have given you in the same post (200 X2)+(210 X2)=820Kgs, i thought it would have been obvious that the calculation was for one rail only considering i'm multiplying the loadings by two to account for the whole trailer.

I gave you an estimated maximum loading for your design of trailer at 820Kgs....based on my calculations. Have you actually checked what an Indespension 1100kg trailer is rated to carry? Funny enough i just have a few minutes ago... 800Kg max!
So not only are my calculations correct, it means that this fantastic trailer you've constructed is very nearly on the absolute limit for what your boat weighs....better not think of uprating that engine for a while then!

I also suggested you move the rear swingbeam forward to make it safer.....Look at the bending diagram and shear force diagram HughH has kindly uploaded and pay rarticular attention to the high bending/Shear force at the rear of your trailer (P.S. Thanks for taking the time to do this Hugh).

Finally, look at the calculations YOU have used and exoplain to me what is wrong here....Where did you get a 440 odd tonne load from? and, as Hugh also questions....where has the uniform loading come from?

Both myself and others on here have genuinly tried to give you sound advise but you have chosen to refute it each and every time....

Before i bid farewell to you one final time......remember this.

"We are all born with two ears, two eyes and one mouth....and we should always try to use them in that proportion"

Good luck to you Jeepster

Simon
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Old 15 September 2012, 09:35   #119
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"We are all born with two ears, two eyes and one mouth....and we should always try to use them in that proportion"
Ah, but the he had ten fingers (although apparently none of them could find the return key in his OPs!). So that lets him type a lot...
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Old 15 September 2012, 10:23   #120
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(P.S. Thanks for taking the time to do this Hugh).
They were a "finger in the air", "not to scale", "the value of your investment can go down as well as up" type bodge I hasten to add!
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