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Old 08 September 2014, 14:12   #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, 15:06   #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, 15:33   #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, 16:07   #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, 16:45   #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, 17:33   #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, 17:47   #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, 19:05   #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, 02:07   #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, 05:12   #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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