Trailers

Trailer types

There are many differant types of trailers for all differant sizes of boats from small tinnys to some as large as 30+ feet. The main ones used for baots are:

Single axle - These are genrally used for light boats and if the trailer and boat have a combined weight less than 2000kg you will not need to have brakes on this trailer.


Tandem axle - Used for heavier boats as it has 2 axles and 4 wheels which preads the load over twice as muchs which will put less strain on the axles and wheels and be easier to control.


Triple axle - These are for very large boats which are very heavy.

Trailer designs

There are 2 common designs for trailer chasis which both work really well. The two types are:

A Frame - This design has two front chasis rails that form a triangle or 'A' shape which has the coupling attached at thier apex like the one below.



Draw Bar - This design has 2 front rails meeting earlier and then a draw bar which extends from thier meeting point and then the coupling is attached to the end of the draw bar. Some of these trailers have a removeable pin and a hinge at its inner most point which allows the trailers to tilt on the draw bar which can make launching or retreving your boat alot easier. 

Trailer materials

Boat trailers are generally made from galvenized steel or aluminium with differant shapes and sizes of steel or aluminium used.

Galvanized steel - This is just mild steel but it will have been galvanized and all that means it has been dipped into a bath of Zinc. This is done as Zinc is a great coating to prevent the steel from corrosion. Above is a photo of the baths of zinc at a galvanizing plant.

Aluminium - This is a lightwieght durable and ductile metal which can have appreances ranging from silvery to dull grey. Aluminium is up to 3 times as light as steel and has a better strength than steel also but this is why it can be very expensive.

These metals come in all sorts of shapes and below are the used shapes for the trailer construction:

The most commonly used ones would be the round tube, rectangular tube, C channel and I beams. These are all used as the are the strongest. The ones used in New Zealand Are I beams but I believe the best type to use would be the rectangular as it will be strong also all the wires can be inside the steel which helps protect them from the weather and any damage.



Trailer designs for differant boat hulls

The most common forms of trailers tends to be the bunk type or the roller type. The bunk type consists of of 2 boards or rails that are covered with carpet where the hull will sit on. The roller type is a more modern where several sets of rollers support the hull and allow for easier movement of the boat when launching and retrieving your boat. There are also a few types of rollers. Keel rollers are the opnes down the centre of the trailer where the keel sits on. some off these rollers are self centreing for easier retrieving. Side rollers are the rollers that are on a steel bracket that pivots from the chasis so the boats weight can be distributed evenly on all the rollers. These rollers come in all shapes sizes and differant materials. They will range from collered plastic to rubber. This picture below shows you all the differants types. The last is a snubbing block which is in the centre of the trailer generally on the upright post where the winch is for the front of the boat to sit safetly and centre.

WOF regulations

Weight and dimensions - You can tow a trailer that's up to 2.5m wide, 4.25m high when loaded, and 11.5m long, as long as the combined car and trailer length does not exceed 20 metres. The load can overhang the rear by up to 4 metres - measured from the axle. If it overhangs by more than 1 metre it must be flagged. At night red lights must be fitted to the rear. In daylight you should attach a fluorescent flag (white, red, orange or yellow), sized 400 x 300mm. A load can extend sideways up to 1.25 metres from the centre line of the trailer, but must be flagged if it extends more than 200mm beyond the sides. At night, you need to mark an extended load with white or amber lights to the front, red to the rear. a maximum gross vehicle mass (usually specified by the manufacturer) of 3,500 kilograms or less. (The gross vehicle mass includes the maximum load that the trailer can carry.)

Tyres -  All tyres must have 1.5mm of tread all round the circumference of the tyre and across atleast 75% of the tyre width.

Suspension types

There are usally 1 of 2 types of systems used on boat trailers. These are the very common leaf spring or torsional rubber. The coil spring system isnt used often as cant locate the axle both front and back and side to side.

Leaf spring -  this is used on all 3 types of axle systems. They are mounted on a pivot at the front and have either a shackle or sliper rear mounting to allow for hte lengthening of the spring as it deflects under the shock. One advantage of the leaf spring is that it can locate the axle both front and back and side to side. If on a tandem or triple axle trailer you will find a component called a compensator in between the 2 or 3 sets of leafs. This is there to transfer the load from one axle to the other when hitting bumps on the road.

 Torsional rubber - The most used and known type of this system would be the Duratorque type. The basic design has the axle housed in a tube with rubber elements around it. When you hit a bump on the road the rubber will absorb the shock which therefore is self damping.

Wheels and tyres

The tyres are a key part of towing your trailer safetly. All tyres must be fitted with crossply or radial tyres. The radial tyre has softer more flexible side walls and heavily braced tread area. The crossply has siffer side walls and less heavily braced tread area. When in use the radial tyre will give you much better grip, less tread distortion, longer life and redueced fuel consumption. The disadvantages though would be that the softer side walls take alot less strain to become damaged. For your own safety all the tyres should be the same on the trailer. The wheels for sale are almost always galvanised as they are cheap and great for preventing corrosion.

Couplings

Couplings are so important. You have to always check that when you purchase a car or trailer that you will be towing, always check the size of the towball compared to the coupling. Towballs will come in 2 differant sizes, either 1'7/8" or 50mm. The couplings themselves that are used on boat trailers can be put into 1 of 2 differant catagories:

- couplings for non braked trailers, to fit towballs

- couplings for braked trailers, "overide coupling" to fit towballs 

Couplings for non braked trailers, to fit towballs

These couplings are pretty simple. They are a basic handle mechanism that you lift up to fit over towball which is spring loaded so once placed over the towball the coupling will tighten up on it. There is a pic that you put through top of the coupling as a safety so the handle doesnt jump back up which will un-hitch your trailer from your veichle.

Couplings for braked trailers, "overide coupling" to fit towballs

This has abit more to it than the first coupling. These have the same sort of system for the handle and locking onto your tow ball but they also have a braking system which is apart of it. These brakes are operated by a piston in the coupling that when the trailer is pushed toward the car when under braking the piston will shorten which in hand pulls cables connected to the brakes and allows similar braking to the car. 

Brakes

 

Disc brakes

http://www.youtube.com/watch?v=rgbDyJhBb4c&feature=related a short video explaining how these brakes work.

Drum brakes

http://www.youtube.com/watch?v=bnc3VnQ8kUY another short video on the basic operation of this type of brakes.

Some basic and easy things you should do to keep your braking system well maintained. Firstly from time to time always check for and wear on the linings, shoes and pads. Check that none of the cables or linkages etc have corroded and still working fine. Always have your hydraulic fluid top up in the master cylinder. To keep ontop of all this you should regularly grease any moving parts and external linkages, cables and adjusters etc. 

Winches

You really have few choices when it comes to winches. A manual winch with either a cloth strip for smaller boats or a steal wire for larger boats or an electric winch. Unless your boat very large and heavy over 8m roughly you can get away with a basic hand winch. All winchs are mounted on a vertical post at the front of the trailer.

Lights

Depending on the size of your trailer and boat on it will depend on how many lights etc you will need as talked about in the WOF regulations. All boats though will have your basic braking and indicator lights on the rear of the trailer. You can get either your old common standard light that you can open up and change the bulb or the new style fully enclosed LED lights which will last longer and wopnt corrode. Above is the basic wiring diagram for the lights to be hooked up to your veichle.


referances:
www.google.com/images
www.wikipedia.com
www.voyagertrailers.co.nz
www.youtube.com
Unitec book (the bible)