This issue John and Meg (Harry) Kennedy tell their story of building a DIY trailer especially for Cape York adventures.
After trying our luck at barra fishing along the banks of remote Cape York rivers, my wife and I decided next time we headed north we’d take a punt and enjoy a more relaxing fishing trip.
Having seen the effects of the northern roads on boats and their trailers we also decided that a standard punt and trailer was not the answer. Purchasing a standard trailer and then strengthening it just wasn’t practical when we saw how flimsy they were.
It’s no wonder the dirt highway to Weipa is lined with tangled, wrecked trailers. The typical urban environment trailer just can’t stand up to these rugged conditions.
No - instead we’d buy some steel and do the whole thing ourselves, so we would have a trailer that would do the job.
The punt itself was a much easier proposition. All it took was a visit to Cairns Custom Craft, and a talk to Marcel the boss to have a sturdy punt on the drawing board.
Personally, building the punt was out of the question since I didn’t have the right gear, the skills or the know-how. However, we did ask Marcel to add 50mm to the gunwale height as we wanted to make the craft suitable for the occasional open water trips.
Meg (Harry) wanted to add a metre or two to the gunnels to “croc proof” it, however, everyone assured her that crocs just don’t jump into boats.Those jokers who run photos of crocs jumping up out of the water to advertise Northern Territory tourism have a bit of explaining to do, if I ever meet them!
Meanwhile, we would do all the hull fitting out ourselves, to keep the overall price down substantially.
DESIGNING THE TRAILER
Having a little engineering knowledge, I felt confident about creating a really tough, go any-where trailer for travelling along tight, winding bush tracks. Nevertheless, I sought advice from Marcel as well as one of the local off-road trailer experts.
My original concept was to build a trailer made from “C” section steel. The idea being that a C section wouldn’t hold water in it so if it got a submersion in seawater, the water would drain away and I could hose the whole surface easily. Whilst a good idea, the problem of distortion under load meant that the C section would need to be quite thick and braced in many of the stressed points. This would result in a relatively heavy trailer, which would be a hassle to build. Even though the weight was not a prime concern, it still had to be thought about because an excessively heavy trailer needs heavier springs, heavier axles etc and so the whole weight issue begins to spiral upwards.
An aluminium trailer, whilst ideal in many ways, was going to cost a lot more for the materials and since I have no experience in aluminium welding, the cost of manufacture would put that out of reach.
The other issue with aluminium is that it does work harden and this can cause cracking. Our Hysocat has an aluminium trailer under it and has never cracked yet but then it doesn’t get dragged along rough, potholed tracks either. Also there simply isn’t alloy welding available in these out of the way places.
The decision to go for box section (RHS) steel was almost made for me when a local steel merchant put on a sale of galvanised steel at almost half the normal price. The eight-metre lengths on sale were 70mm x 30mm and 4mm thick and double galvanised. Talk about overkill!
While this heavier section steel would add about 20-25kg to the trailer weight, the increase in strength was amazing to say the least. Plus a mug welder like me could crank up the amps on the welder and really melt it into a good, solid weld without the risk of blowouts.
Having the steel section sorted, the next step was to determine the width of the trailer axle. This might seem trivial to the bitumen bound trailer boaties but think about it - if the tow vehicle is going through sand or mud, you really want the trailer wheels to follow in the same ruts.
You don’t want the tow vehicle to dodge a pothole only to have the trailer wheel plough into it because it is tracking a little wider, or narrower.
The local trailer parts distributor was very helpful and quickly worked out the exact width of axle required to match that of the Nissan Patrol. We also decided to make the wheels on the trailer the same as the Nissan as this reduced the number of spare wheels and tyres needed to be carried.
In the worse case scenario you could always pinch the wheels off the trailer if you have a few blowouts on the vehicle.
Admittedly, the cost of manufacturing the custom axle proved to be a little sphincter puckering, but worth the cost in my opinion.
The frame would be a conventional rectangle and triangle style and here is where the first problems cropped up. The axle width determines the frame width so you either need to do some very precise measurements and hope you make no errors or, you do as I did, accept that I’m a klutz and set the axle/springs and wheels up in the workshop and work it all out from the ground up.
Messing around with this highlighted the first scary moment. The trailer dealer had mentioned, in passing, that my axle was a bit narrower than the standard boat trailer and “would the tinnie still fit on it?”
When I told the trailer man that the tinnie was going to have a width of 1.2m he raised his eyebrows, whipped out a calculator and said, “Hmmm, it’s going to be close”. Now suddenly, I realised the full significance of his question.
The space between the tyres looked a lot less than the width of the tinnie. With my shoulders sagging, heart pounding, my brain racing with potential excuses and explanations for Harry as to why we were up for the cost of a new axle assembly, I measured the space between the tyres.
Relief, it was exactly 1.3m and we were home and hosed. However, this little exercise was a good warning to think about EVERY DETAIL before you launch off into a project. This oversight would come back to haunt me later.
A few practice welds (and some tutoring from a professional welder friend in the fishing club) and the frame was tacked together.
HINT 1: NEVER fully weld up any joints until the entire frame is assembled. Half an hour on the grinder with a cutting wheel fixed that little oversight. I had no idea the frame would distort like that.
Time-wise it took me all day Saturday and half of Sunday to get the frame fully welded up to the point where the front “A” frame could be welded on to it.
Macka (our welder mate) took a long hard look (as well as a couple of beers out of my fridge) at every weld I’d made and pronounced them as “OK”, but what happened here?
HINT 2: Make sure you grind off ALL the zinc when welding galvanised steel, zinc causes welds to bubble and generally stuff up. More time on the grinder and cutting wheel.
Why is it that I spend hours getting everything dead straight, cleaned up and manage to warp the steel and yet Macka can waltz in, have a few stubbies and weld the whole joint perfectly and without any warp at all without even trying? Another unsolved mystery of life.
The important thing to remember with an off-road boat trailer is that it must support the boat in as many places as possible. The normal set of rollers just won’t do it. By the time you reach the Hann River road house you will have broken all the rollers in half and the boat will be resting on the steel rod supports instead.
The continual pounding on a dirt road can actually crack a tinnie open. So, to all those people considering towing a trailer boat up north, get some advice on the whole rig before you set out.
HINT 3: NEVER think of the trailer boat as a great place to store the kids’ bikes, tents and heavy gear. If you do, you’re really asking for trouble.
With this in mind, I stepped away from the normal convention and, instead of a set of rollers down the middle of the trailer, designed a channel that runs down the entire length of the trailer and pop riveted a strip of Teflon into it.
The Teflon also sits on the side of the channel and the whole assembly grips the keel of the tinnie very closely. The idea is not only to provide support for the tinnie along the entire length of the keel, but also to connect all the cross members of the trailer together, (giving it longitudinal strength), and at the same time prevent the boat moving sideways across the trailer. The result is pretty good, even if I say so myself!
Once the frame was welded I decided to go right over the top and weld gussets on all the joints. Considering the wall thickness of the frame and the full welds all around each one, these gussets are most likely redundant. After sitting behind my computer and calculating the force that could (theoretically) be applied to the frame at 80kph if a single wheel dropped into a really deep pothole, I found the safety factor was only two, so the gussets are there for the absolute worse case scenario only.
While I was at it, I decided to modify the design, yet again, and weld all the openings shut. This would allow me to put a cupful of oil in the frame and prevent internal rust from starting.
Most trailers rust from the inside out because that’s where it’s the most difficult to flush salt water away. The oil in the frame would also alert me to any cracks in the frame should this happen. This meant drilling and tapping filler holes in every frame member but what the hell, it’s only my time.
BOAT MEETS TRAILER
With the frame ready, the punt was dragged on to the Teflon keel channel and Harry and I got a very pleasant surprise, the whole hull just slipped on with barely an effort at all, it was almost as if the hull wanted to leap on! I had anticipated a real struggle since there was no winch up front but the Teflon provided an almost frictionless surface. More advice from people in the know indicated that when fully winched in, it is essential that the winch applies a significant downward pressure on the towing eye on the bow otherwise the boat could actually jump off the rollers. Some experienced off-road boaties use a turnbuckle to achieve the same thing.
With this in mind Harry and I came up with a combined stopper and clamp. A hard plastic “V” piece prevents rubbing on the very front of the bow, while Teflon lined angle iron prevents the boat jumping up.
The winch cable exerts downward pressure as well. As this is a custom-made trailer, none of the fittings are adjustable and so I could weld everything in place.
Although the keel was now gently but firmly gripped, the hull could still rock left to right so it needed support there too.
I had originally planned to make up some more Teflon skid plates but by now, after a couple of weekends of welding and grinding I had collected a number of small burns, so the decision was made to support the sides with large plastic rollers.
This job was much easier; you can buy the right angle supports and rollers off the shelf and there’s no need to make anything up. Propping the hull up on bits of steel and timber the roller brackets were welded in place.
The result is brilliant, the hull no longer is able to slide around on the frame or rock sideways and is a nice, tight fit when winched on the trailer.
Now the time had come to weld the mudguards on.
Oh, disaster. I’d forgotten that boat gunnels don’t just come straight up - they lean out quite a bit (duh).
After a few choice Aussie oaths we tackled the problem head on. The only solution was to remanufacture a wider set of guards and mount them at an angle which was going to look really amateurish. But who cares, I AM an amateur so it’s OK!
Sure it’s not a slick professional trailer but the guards actually DO what they are supposed to do. They stop stones flying up from the tyres and protect people from the wheels. And they don’t look too bad either.
After cutting the guards to shape I also mounted a set of rollers on the top of the guard itself to protect the hull. With movement on rough roads I reckoned the guards could have worn a hole in the side of the hull in no time at all.
I also added some side rollers near the transom to assist in retrieving the boat onto the trailer.
We also welded some massive lugs with towing eyes onto the back and sides of the trailer so that the whole trailer/boat combo could be winched out of any bog without risk. I have several secure points so it’s possible to recover the entire unit from any direction.
HITCHES AND SPRINGS
I had planned to weld an off-road, fully swivelling trailer coupling directly to the trailer when, by chance I came across an even better idea. I was telling a mate at work about it when he came up with the following solution - make the towing hitch slide out of the draw bar.
This way you can use either the 50mm tow ball, or the Treg hitch as needed. This is a great idea, because when the trailer is sitting at home the drawbar hitch can be removed completely and that makes the outfit just that much harder to steal.
This took quite a bit of stuffing around getting the right box section steel, which fits inside the main drawbar, however, by welding two 2mm plates to either side of the hitching bar, I came up with a very snug fit with just enough clearance to allow the hitch in and out but with very little movement.
Of course, this meant building two hitching bars but, after all the other work I’d done, this seemed like peanuts. A useful side benefit is you can remove the hitching bar and put in a snatch strap, using the same link pin. Now that’s handy!
My obsession with strength and functionality became obvious when the whole rig was finished, the outboard on and all the gear stowed in the boat ready for its first trial. You could jump up and down in the boat and the springs did not even look like flexing.
In fact, we had overdone the springs and needed to put smaller size springs. The fact is the trailer would be all over the road if you don’t have some flexing.
By now, of course, Harry and I had coated the springs with a thick layer of Lanacote so pulling the pack off again was going to be a filthy, grubby job.
Worse, the trailer man wouldn’t trade them in as I had packed grease into them. The only way out was to remove a single leaf from each pack, reassemble them and try that.
The difference was immediate, my overalls looked like they had been dragged through a grease pit and Harry declared them as condemned and consigned to the rubbish. More expense! Still, removing the extra leaf made the difference. Now rated at 800kg, the springs flex nicely and we are all set for our first big trip north to Cairns to see how it all works.
Next issue we’ll share the story of the punt.
Related Boating Articles -
Beach Launching - The do's and don'ts of beach launching
Buoy Your Anchor - There is an easy way to anchor when you are in open water, the float buoy method.
Crossing A bar Safely - Steps and Procedures needed to be taken in order to cross a bar safely.
Radio Distress Procedure - In-depth article describing how to approach emergency situations.