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Old 08 September 2014, 13:12   #1
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Trailer Build / Conversion

Hi guys, the previous trailer we had was just too short and not wide enough for our 4.5 sib, so I now have a caravan chassis to use instead.

It is an aluminium Al-Ko chassis.

The original frame shown on the photo was 19ft, however to fit in our garage the tail ends have been cut off now making it a total length of 16ft.

So the sib being 4.5 meter / 14.5ft, should fit much better on this trailer.

The flooring has been completely removed leaving just the frame, the frame itself right now is not very strong so it will need reinforcing somehow....

Could you guys give your thoughts on how you would go about strengthening the frame to support the weight of the boat ?



Also - the lower welds have cracked on the inside lip where the frame bends to the A shape. See photos !

How is best to resolve this ?

Should i drill a small hole to prevent the crack running, and then bolt on some short lengths of mild steel angle section to add rigidity ?, or is there a better solution ?
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Old 08 September 2014, 14:06   #2
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I would want that crack welded and then a strengthening plate welded over the top.
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Old 08 September 2014, 14:33   #3
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What concerns me Camelgas, is that those bends are the weak points on the frame ( the same weld on other side is also cracked ) and i worry that welding the cracks and even a small plate will still have a high risk of cracking again unless long lengths of steel ( or whatever material ) is used as a doubler on those weak sections.

I'm thinking that the aluminium will tend to be brittle after welding and wont flex as much as a bolted/riveted type repair, which would be better suited to a trailer driving over speed bumps etc and constantly being stressed and twisted?
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Old 08 September 2014, 15:07   #4
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I'd find another donor van and give that one a good send off
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Old 08 September 2014, 15:45   #5
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Hi Bedajim, even if i get another donor chassis, the frame will still need reinforced in those bent sections ?

So, wouldn't strengthening the current chassis make more sense ?
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Old 08 September 2014, 16:33   #6
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No. Welding weakens aluminium far more than it does steel. Welding your one isn't going to help much.

Find a steel donor chassis
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Old 08 September 2014, 16:47   #7
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is there no way to strengthen this trailer to use for our sib ?
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Old 08 September 2014, 18:05   #8
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The crack just needs to be welded and plated with a fairly long plate to fix it. The SIB should weigh far less than the caravan that was on top. Some X bracing will keep it rigid since you will be removing the box above. You would need to setup a balance point around the funky axle setup though. Does that thing have enough wheel travel? I would assume it is an internal spring inside the axle?
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Old 09 September 2014, 01:07   #9
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There is nothing wrong with a properly prepared and welded joint on aluminium, use ali for your reinforcing plates !. As steel and ali plus salt water will corrode rapidly, and the ali will loose !.

As caravan base's seem to change hands for between £50 and £100, once you factor in the cost of getting a fabricator to repair it for you , replacement may be better (weighing in the old one for scrap)
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Old 09 September 2014, 04:12   #10
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The wheel travel should be fine - there is around 6 inch gap between tyre top and mudguard.
The axle has a triangle shaped shaft with 3 rubber sections, 1 in each gap, if that makes sense !

What size plates would you fit on those bends ?

I have access to some steel sections, and friend who is a competent welder.

I'm thinking to use a length of 6mm angle iron ( 100cm or so, placed central on the bend giving 50cm on either side of the bend ) and bolted to the frame with a thinner gauge backing strip plate on the outside.

The left sketch on the photo - Black part is the existing chassis section.
Red parts are the angle iron and backing plate.

An X brace would then be added between both sections.

Would this be a suitable repair using just mild steel and bolts ? ( I don't have TIG welding gear )

Also, will the steel be ok against the aluminium if not going into water, or would it need coated?


The sib will just be pushed into the water on transom wheels.
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Old 09 September 2014, 05:31   #11
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100 mm is a waste of time IMHO, it's Knackered
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Old 09 September 2014, 05:33   #12
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Hi Bedajim, 100cm / 1 meter lengths,

6mm thick, 100mm x 50mm angle iron.
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Old 09 September 2014, 13:16   #13
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Any other thoughts on this repair guys ?
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Old 09 September 2014, 17:17   #14
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Yes, bin the aluminium.

As Camelgas said aluminium and steel don't mix so I wouldn't bother trying to fix it if you can't weld aluminium.

I'd be inclined to keep the axle/hitch and make a new (steel) trailer.
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Old 10 September 2014, 01:40   #15
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(A quick search will enlighten anyone who doesn't get the reference and lead to hours of interesting reading. )
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Old 10 September 2014, 03:36   #16
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Quote:
Originally Posted by HighlandR View Post
( I don't have TIG welding gear )
Your done!

I assumed you had some kind of metal shop setup.

Shop for a trailer in the classifieds. With probably a few minor adjustments you boat should be fitted to the trailer.
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Old 10 September 2014, 04:36   #17
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If I were to get the aluminium welded, would that solve the problem ?
the frame would still need strengthened, right ?

Let's assume for moment that the frame gets welded, would it then still not make sense to strengthen it, rather than bin it ?

It also doesn't make sense why the manufacturer has the axle bolted directly to the aluminium , why would they do that knowing that it will corrode?


Before i bin this chassis or whatever, could anyone explain why it shouldn't / couldn't be strengthened enough to use?

How about a full length ( from hitch to back ) steel box section A frame welded up, and simply bolted on top of the existing chassis and welded to the axle brackets ?

It just seems a shame to bin it when all there is are 2 little cracks that i see could easily be repaired with some plates.
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Old 10 September 2014, 08:28   #18
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You have bought a pup bin it!
Or if you want to bodge it stick the floor back on as this will give it back a lot of rigidity and make up a cradle or bunks to screw to the top of it
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Old 10 September 2014, 09:00   #19
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Dunno why all the doom & gloom talk on this thread the caravan probably weighed 16-1800kg the sib probably 400kg at most
Just make up whatever frame arrangements you need to carry the boat & bolt them on, keep an eye on the cracks when your using it if they get worse get them welded & overplated
With regards the ally to steel corrosion problem look at all the 30 year old landrovers around! ok they do rot but don't fall apart driving down the road just keep an eye on it
If it starts to corrode or fall apart find another galvanised chassis the same dimensions & bolt the boat cradle straight on to that
Nothing lost that way as you won't have wasted money on bits you won't use as they can be easily transfered to another chassis
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Old 10 September 2014, 17:03   #20
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Quote:
Originally Posted by beamishken View Post
look at all the 30 year old landrovers around!
Yeah but they didn't make Landrovers with an aluminium chassis and a steel body.

That chassis will flex all over the place without the rest of the caravan to support it so it'll need plenty of reinforcement as well as the cracks repairing.

If the OP is going to do that with a steel frame then he might as well just knock up a new trailer using the hitch and axle. I don't see the point in keeping the aluminium bit.
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