Building a super new boat trailer, but on the cheap!

[willk]

Pikey Dave got it right in his Signature line

[Anchorhandler]

Originally Posted by Downhilldai

See post 1: 80x40x3 RHS

Feck me DHD.... Did you actually read all that?.. :-)

I was waiting for the 'Jeepster's trailer for dummies' to be published. :-)

Simon

Sent from my iPhone using Rib.net

[jeepster]

Originally Posted by Anchorhandler

Jesus....if ever we needed (more) proof that you have no idea what your talking about then ....HOW AM I SUPPOSED TO CALCULATE THE MAXIMUM POSSIBLE LOADING ON YOUR SIDE RAILS WITHOUT THE DIMENTIONS (AND THICKNESS) OF THE SIDE RAILS THEMSELVES.

Duh!...If you took the time to read through my original post on this thread you would have noticed that I already gave you all the dimensions and thicknesses of the materials used to build the trailer

[Downhilldai]

Originally Posted by Anchorhandler

Feck me DHD.... Did you actually read all that?.. :-)

I was intrigued...

[Bigmuz7]

Originally Posted by jeepster

Er, it only a 9.9hp!

Holy shit .. is it ? ..... I thought they managed to get loads of power into really small spaces these days ? .. maybe someones fitted the wrong cowling on your engine ?

[Anchorhandler]

Originally Posted by jeepster

Duh!...If you took the time to read through my original post on this thread you would have noticed that I already gave you all the dimensions and thicknesses of the materials used to build the trailer

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

[Anchorhandler]

Edit: I haven't included the strength of the angle bar used where the axle ties into the rails as i didnt know the length and thickness of said bar. This will have a positive effect on the loading reducing the stress in the rail.

If i get time i will re-do the simulation but considering i havent included a safety factor into the calculations (by increasing the loadings proportionally), i would estimate it will be very similar to the results shown above.


Simon

[chewy]

Simon, if your up my neck of the woods I'll get you a pint too!

[Pikey Dave]

Originally Posted by Anchorhandler

Edit: I haven't included the strength of the angle bar used where the axle ties into the rails as i didnt know the length and thickness of said bar. This will have a positive effect on the loading reducing the stress in the rail.

If i get time i will re-do the simulation but considering i havent included a safety factor into the calculations (by increasing the loadings proportionally), i would estimate it will be very similar to the results shown above.


Simon

Ahh! but don't forget to allow for the holes

[jeepster]

Originally Posted by Bigmuz7

Holy shit .. is it ? ..... I thought they managed to get loads of power into really small spaces these days ? .. maybe someones fitted the wrong cowling on your engine ?

Well is it a four stroke.

[Bigmuz7]

Originally Posted by jeepster

Well is it a four stroke.

I dunno ? .. hey I thought you were the wordsmith

[gasman]

Originally Posted by jeepster

You obviously haven't studied structural engineering then!...The holes in question, called lightening holes (because they lighten the structure), do not weaken the structure, they actually increase the strength to weight ratio...Which is why lightening holes are applied to RSJ's whichare required to span very large gaps between supports, such as in modern open plan warehouses with the minimum of support pillars.
They would also give me convenient access to the inside walls of the RHS for ease of painting.

Is that why they put holes in some types of Dutch cheese?

[Anchorhandler]

Originally Posted by jeepster

Before building the trailer I closely studied the materials used by commercial boat trailer manufacturers in their boat trailers, and where possible, copied what they used, going on the assumption that if its good enough for them, its good enough for use on my trailer.
In particular, I spent a fair bit of time closely examining an Indespension "Hallmark" boat trailer with a gross weight of 1300kg, in the car park of a local marina.

like these Hallmark 1300kg trailers maybe?
John McAleese Marine - Halmark Trailers Specifications

Or this one maybe?
Indespension Boat Trailer for sale , New Indespension Roller Coaster 1300kg trailer - Boats And Outboards

Or how about this Extreem 1300kg trailer?
Extreme Boat Trailer for sale , New Extreme 1300kg HD Galvanized Boat Trailer - Boats And Outboards

Perhaps it was similar to this Snipe 1300kg trailer?
A Boat Trailer for sale , NEW Snipe 1300kg swing beam roller boat trailer - Boats And Outboards

I'm not being funny here Jeepster but can you spot the common theme with these 1300kg trailers? (ladder type side rails, much stronger than simple rectangular box section on its own.)

As i said earlier, you've done a good job building your trailer, but its a shame you didnt do more research as to how much your boat weighed and how this weight is transfered down to the axle. Oh, and listen to the advice you get on this forum, I listen to it all the time and have found it very reliable.

Simon

[martini]

Originally Posted by jeepster

You obviously haven't studied structural engineering then!...The holes in question, called lightening holes (because they lighten the structure), do not weaken the structure, they actually increase the strength to weight ratio...Which is why lightening holes are applied to RSJ's whichare required to span very large gaps between supports, such as in modern open plan warehouses with the minimum of support pillars.
They would also give me convenient access to the inside walls of the RHS for ease of painting.

Nor have you obviously, they're called cellular beams and they haven't just had holes cut out of them. Google it.

[jeepster]

Originally Posted by Anchorhandler

like these Hallmark 1300kg trailers maybe?
John McAleese Marine - Halmark Trailers Specifications

Or this one maybe?
Indespension Boat Trailer for sale , New Indespension Roller Coaster 1300kg trailer - Boats And Outboards

Or how about this Extreem 1300kg trailer?
Extreme Boat Trailer for sale , New Extreme 1300kg HD Galvanized Boat Trailer - Boats And Outboards

Perhaps it was similar to this Snipe 1300kg trailer?
A Boat Trailer for sale , NEW Snipe 1300kg swing beam roller boat trailer - Boats And Outboards

I'm not being funny here Jeepster but can you spot the common theme with these 1300kg trailers? (ladder type side rails, much stronger than simple rectangular box section on its own.)

As i said earlier, you've done a good job building your trailer, but its a shame you didnt do more research as to how much your boat weighed and how this weight is transfered down to the axle. Oh, and listen to the advice you get on this forum, I listen to it all the time and have found it very reliable.

Simon

I found a pic of the VIN plate on that particular trailer and it was actually 1100kg gross weight, not 1300kg (my bad)....Here is a pic of the trailer:
http://imageshack.us/a/img62/2443/in...ntrailer1c.jpg

See, no ladder type side rails, just a single rectangular box section on its own.

[jeepster]

Originally Posted by Anchorhandler

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

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:

[BogMonster]

^

I think you'll get a vibration problem with those triangular wheels

[jeepster]

Originally Posted by BogMonster

^

I think you'll get a vibration problem with those triangular wheels

[Anchorhandler]

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:

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.

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.

Simon

Sent from my iPhone using Rib.net

[Boats&Outboards]

Originally Posted by Anchorhandler

Jeepster.....

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.

Simon

Sent from my iPhone using Rib.net

Simon - At last. Why didn't you just admit you were wrong in the first place :ROFL:

Peter @ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007