As we use the trailer for hay hauling, company deliveries and collections and even engine moving occasionally, we get a fair bit of use out of our existing unit, which we built three years ago. The limitations of the existing trailer are more related to domestic use, as we cannot get a large hay load on it without going more than four bales high and having the back flap down as a deck extension. Even then we can only safely carry 42 bales if we empty the Midi completely out and fold the internal seats against the sides. If we have tools or anything else in the van, we loose about 3 bales capacity.
For engine carrying it is nigh on perfect, as we never have had anything on it approaching its 1.9 ton capacity. We can get six railway chargers at a time without lowering the back, and as they go 5-6 cwt each, that is quite enough !
I have a leaning to build a drawbar trailer this time, not for any particular reason other than it is less strenuous on the towing vehicle, it stands on four wheels without need for extra supports, even with a full load, and there is no problem with an unevenly distributed load (within reason) It tows better, goes round corners (tracks) better and generally does away with jockey wheels and the associated drama when you have too much on the front of the trailer and have to move it.
Reversing is a bit of a pig, as you now have two joints in the system instead of one, but if you watch the Scandinavian truck drivers with an artic followed by a drawbar trailer (60 metres plus) it obviously can be done. I remember watching a Danish meat truck, a Scania LB140 V8 being reversed the length of Reigate station goods yard with the trailer on the back of the artic, and thinking to myself that it made us look absolute beginners. The truck had been pulled off the M2 with broken synchro rings in the gearbox, and we had towed it and the trailers with our old Gardner 6LW engined Scammel 6X4 to Reigate. After repair, I followed it for a while out of Redhill on the old A25, but it lost me on the hills !
The generic drawbar trailer has a turntable bearing ring on which the front axle pivots. This is usually a 'fifth wheel' plate and the underside of the trailer on artics, but a proper ring is available from Jost GB Ltd., who live in Heywood, Lancs. Jost are Europes' largest trailer accessory manufacturer, based in Germany. You see their products everywhere in Europe, and they have a very good reputation.
Looking at their drawings, a 500mm diameter bearing ring (0500N) will support 1.8 tonnes axial loading in either direction, which gives a maximum trailer weight on two axles of 3.6 tons gross. (Indespension have axles rated at 1.9 tons each, so that will match up quite nicely) One ton = 2240lbs One Tonne = 1000Kg - 2200lbs (or thereabouts)
This bearing ring is the smallest in the range, and has a RRP of £192.00 (which we should be able to cut by about 30%) There is a 650mm dia ring which has an axial rating of 2.5 tonnes if we want to get extreme ! The 'proper' truck rings go up to 16 tonnes radial capacity.
If we cannibalise the existing trailer for axles and couplings etc, we would be able to build the new one quite cheaply. We can get box section tubing direct from Parker Steel, and would probably use 50X90X5mm for the chassis runners, plus 50X50X3mm for the deck supports.
Because we do not have to support tension loading from the front drawbar, and because the cantilever bending effect of wheels in the middle and loads hanging out each end is eliminated, the trailer chassis can be quite light, although we will be over-specifying as usual to make sure we have something in hand.
Side raves will be folded channel of 10 swg steel, and we will make sure we have enough rope hooks this time ! Finish in powder coat as before.
If we build new, we would obviously keep the existing trailer which has proved to be very useful, both domestically and for our company, better still, we could sell it to the company and get some money back.
Body length would be about 4metres, and I would probably incorporate the folding deck arrangement which is fitted to the existing trailer, thus making it easier to park up. Decking of aluminium chequer plate over 18mm ply as before would be more than adequate for the occasional 15HP Ruston that I may just chance upon :-) and does take a fair bit of punishment without looking too tatty.
On the existing unit we have the wheels outside the deck, so the deck height can be kept low. This we have found to be quite convenient for all purposes, except that the width of your trailer deck is limited by the width between the wheels and mudguards. On the new trailer we would go for under-mounted wheels, and if we use the small diameter wheels and tyres, we should still be able to get a low deck height. There is a small advantage that you do not need mudguards with under-deck wheels, although you would need mudflaps as a courtesy to other road users.
Drawbar mechanics are a bit involved, especially with trailing arm suspension beams. The weight loading of the front axle is not put into the drawbar frame in the centre, and is offset by about 9". As long as the mounting frame for the front axle and bearing ring is sufficiently rigid, this should not be a problem. The trailing arm imparts a twisting moment to the frame which must in turn be strong enough to resist this force.
I will be drawing this up in the next week or so, and if anyone is interested I could supply a drawing if they send me a large SAE (Prepair Ltd., Unit 11, Flowers Ind Estate, Latimer Road, Luton, Beds, LU1 3XA) It will be an A0 plotted drawing, so don't send an ordinary letter envelope ! No charge for the drawing, but please only ask for it if you are genuinely interested.
Tyres and brakes are well enough covered by the Indespension beam ratings, and a gross weight of 3.5 tonnes will squeeze into the existing trailer regs without too much hassle.
The only item to cause some thought is the handbrake/overrun brake cables to the front axle, as the turntable will rotate indefinitely, but the cables most definitely will not ! Thus we will have to ensure that this part of the design is thought out carefully. The load balancing bracket for the cable brakes usually goes on the front of two close coupled axles, but when they are four metres apart, we will have to think again !
Don't forget the new regulations on the Driving Licence side which came into effect in January 1998. New max limit for new drivers is only 500Kg without a separate trailer test.
For those interested, I hold a Class 2 HGV licence, and under the old regulations I could drive up to a four-axle rigid vehicle or a four wheel truck with drawbar trailer. These reg's of course enabled anyone with a Class 3 HGV to drive a 16 ton vehicle with a drawbar without needing to take a Class 1 artic test.
Now, I cannot drive a commercial truck/trailer if the trailer exceeds 500Kg. I can however still drive under the old C&U regulations and on the car section of my licence, a vehicle and trailer combination which exceeds the new figures, but only privately, and it does not include large horseboxes and coaches etc. I may just take the trailer test, just to have it under my belt. (Since been changed by the UK Govt, old 'grandfather rights' have been restored)
If anyone has had experiences with drawbar trailers big or small, please drop me a note, or any constructional advice or queries would be welcome as always.