Outer Limits 4x4 Board

IM going to start building a boat trailer with a difference shortly. going to have the boat on the bottam as usual and have a rack on top to hold tent,etc.

Main reason is all the boat ramps here are concrete and my cartopper is getting a flogging without a trailer, BUt when i go camping i still need a trailer to take all the extra shiat, esp up to 300kgs in extra fuel

Now what i wanted to use for the main chassis is 50x75x2mm gal. Would it be strong enough or will i need 3mm or should i use somehting else. Basic design will be a std "A" frame boat trailer with all the extra bits added on?

Also how low/high should i make the top rack above the boat. I was thinking as low as possible as long as i can launch and retreive the boat easily?

Id say total load weight would be close to 700kg full loaded with fuel,water, boat, etc.

Suggestions?

my trailer has 75x50 3mm wall on the pull and its bent.
for a frame it should be fine tho i guess

I might checkout whats on the box trailer and add 1mm for good luck i spose. It can carry a tonne and still pull ok and shows no sign of bending, although its got to have the shortest pull ive ever seen

Why not just put overhead racks on a box trailer to carry the boat on top ? It would be easier to get on and off and the gear will be easier to get to.

Loanrangie wrote:Why not just put overhead racks on a box trailer to carry the boat on top ? It would be easier to get on and off and the gear will be easier to get to.

cause it will make life easier to go fishing for a few hours, I used to leave my boat on the roof all the time when i had a smaller one. It also cops a floggin up here cause all the boat ramps are concrete, etc

Why dont you also make the top section removable, so when your at home fishing you dont need to take the whole thing to the ramp

Update........... Was thinking of using 75x50x2.5mmx8m

what do you guys reckon, I think would be plenty but am thinking that it may be a little light and will crack where she is welded eventually.


I do realise its more in the design, but with a std boat trailer setup rather than a box trailer and A frame, i think will be fine.

Cheers

mate that section is way strong enough. most 750kg trailers use 40x40x3 which is far weaker in bending than even 75x50 by 1mm.

lighter the better. just made a bike trailer suit 3 bikes out of 50x50 x 2 and i thought that was heavy! draw bar was 75x50 x2 so it looks like everyone elses! it has a 4th bike on the draw bar too. look at a decent trailer an you can see that the spring perches are never weled across and are joined to the draw bar. make it light!!!! also don't be tempted to use heavy springs use those that suit the load.

bru21 wrote:mate that section is way strong enough. most 750kg trailers use 40x40x3 which is far weaker in bending than even 75x50 by 1mm.

lighter the better. just made a bike trailer suit 3 bikes out of 50x50 x 2 and i thought that was heavy! draw bar was 75x50 x2 so it looks like everyone elses! it has a 4th bike on the draw bar too. look at a decent trailer an you can see that the spring perches are never weled across and are joined to the draw bar. make it light!!!! also don't be tempted to use heavy springs use those that suit the load.

bru21 is right on the money not sure how badger bent a 75 x 50 x 3 drawbar i build light duty 6 x 4's with 65 x 35 x 2 pulls without any problems
75 x 50 x 2.5 should do no worries
use allgal/duragal & paint it the welds with cold gal it will last 4 ever
weld the spring hangers & pull along the length not across otherwise it will crack
if you have more questions just ask

Greetings all

i have done my fair share of research into the strengths of steel sections Vs the weight & thought i would share some figures with you for all of the steel sizes mentioned in the posts above

75 X 50 X 3 = 5.42Kg / Meter #0.522

75 X 50 X 2.5 = 4.58Kg / Meter #0.450

75 X 50 X 2 = 3.72Kg / Meter #0.372

75 X 50 X 1.6 = 3.01Kg / Meter #0.305

65 X 35 X 2 = 2.93 Kg / Meter #0.204

50 X 50 X 2 = 2.93Kg / Meter #0.141

40 X 40 X 3 = 3.30Kg / Meter #0.0932

the above figures are the Weight Per Meter of the Tube & also the strength over the Major Axis

as you can see the 65 X 35 X 2 & the 50 X 50 X 2 weigh the same but the 65 X 35 can handle 1.5 Times the amount that the 50 X 50 can

if anybody need any specs on different size tube dont hesitate to ask

I am in the process of fabricating an 8 Meter & 2.4 Meter Enclosed Trailer & have lost more hair trying to do weight & strength calculations than i have lost building it

regards
rod

on the smorgon site there is a steel sectional properties pdf. about 100 pages. well worth getting. it has tables for spans and all kN loadings etc. I use it regularly for work.

cheers bru

My current 6x4 has a 65mmx35mm RHS draw bar and looks pplenty strong and has had over a tonne of gravel in it no dramas.


But if i go that little bit bigger, i should be ok. It will have some weight up high so the extra bit of strength should help. 2 lengths of 75mmx50mmx2.5 will only weigh about an extra 24 kg's. compared to 65mmx35mmx2 RHS which is bugger all. Ill go a bit lighter everywhere else to save it a bit.

I guess ill start this project next week if it stops raining. I want to build it and used it ASAP

AS for spring, i was planning on using some old MQ front leaves i have here and just remove a few leaves to suit. Cant see them falling apart on a corrogated rd, and if the one on the front of the patrol do, at least i can use a trailer one to get me home.


Is there any dramas using a shackle spring setup v's slipper spring ?


Thanks for the help, I appreciate it.

use shackles slippers r only 4 twice a year garden trailers & will flog out on corrigations

Not that you will need them but if for some reason the MQ springs dont work out I have some front hilux springs you can have for nothing.