Most boaters who do not have a year-round berth in a harbour (dry, on a dock or afloat) must move their boat from its storage location to the launch and back again, using a boat trailer.
This trailer is usually worth several thousand euros, the price varying according to the number of rolls they have ( facilitating the loading of the boat ), the quality of the metal it is made of ( especially its anodization against the effects of sea water ) or the method of launching ( fixed or breakaway trailer ).
Consider insuring the trailer against theft
The first precaution is to insure the trailer. Although insuring the trailer does not guarantee that it will not be stolen, it does provide some peace of mind in the event that it is stolen.
This insurance will allow you to cover the acquisition of a new trailer in case of theft but also, depending on the contract, to allow you to find a quick solution when you notice its disappearance ( loan of a replacement trailer, transportation of the boat by truck, compensation of the pontoon costs ).
The company that covers the transported boat or the towing vehicle will be able to inform you about the possibilities of insuring the boat's trailer.
For a few hours or a weekend, keep it simple
For a limited time ( sunday morning or weekend sailing ), you have to think easy and fast.
A chain looped around the trailer frame and attached to a parking hitch is the first precaution. For this method to be effective, the link ( chain, antivoleuros ) is of good quality and resistant to the ravages of time and salt water. Hooking up a trailer that is subject to spray will have to be done at several points on the trailer and, above all, in a place that cannot be easily removed.
It can be doubled by a hitch lock that covers the female part (on the trailer) of the hitch. This device is locked with a key or a padlock.

The latter models, equipped with a padlock, are the most reliable. They let the user choose the type ( key, code, stainless steel ) of padlock used.
These hitch locks are the easiest anti-theft items to use. They can be stored in a boat's locker and installed in an instant.
The immobilization of the trailer wheel can also be done by using shoes. Simply put three hooks around the wheel, on each side. The shoe will hit the trailer, disabling the rotation and, thus, the movement of the trailer. To install these shoes, you must consider that you will have as many manipulations to realize as during the change of a wheel. It is a rather dirty task that requires training.
Prevent the trailer from moving for the long term
When launching for a longer period of time, it may be useful to spend more time preventing theft.
The first and foremost precaution is to prohibit the movement of the trailer. There are two schools of thought, the first considers that the trailer will necessarily be towed in order to be stolen, the other that it will be moved in one way or another ( crane, manualeuros ).
Obviously, no method is absolutely foolproof to prevent theft. A motivated person will not be prevented from committing his act!
To prevent the trailer from being towed, the first thing to do is to remove the coupling head. This requires a minimum of tools ( flat key in particular ) and will demotivate the opportunistic thief. The disadvantage is that it is necessary to think of re-greasing the coupling each time it is reassembled and to find a place to store the head away from the trailer. Indeed, keeping it on board the boat that remains on the trailer is a very bad idea!

Others suggest removing the wheels from the trailer. Again, you need to be equipped for this and store the wheels somewhere. Leave a anti-theft nut in place on each wheel, so that the installation of one wheel is not sufficient to steal the trailer.
The method is simple. We mount the trailer with a jack. We put down logs ( especially not a cinder block that will hurt the metal ) under the trailer structure and lower the trailer.

The weight of the trailer must not rest on the hub, which is not designed for this purpose and may become deformed.
The major disadvantage of this solution is the loss of elasticity in the movements of the trailer due to the wind. It risks to rip and fall from its supports. It is also necessary to think about the storage of the removed wheels.
Some people suggest locking the trailer brake, but the idea seems ill-advised. Effective against displacement, this method will damage the brake shoes and discs, which are not designed to remain tight together at all times, especially in a salty environment. And the method used on purpose ( locking of the cable by a clamp, holding of the coupling head in braked position ) always consists in putting a mechanism in a position that is not initial, generating fatigue on this mechanism.
Other options exist, such as removing an axle or completely disassembling the wafers. Although effective, these methods require a lot of effort to be considered simple and applicable to everyday life. Indeed, they require tools and means of action that are beyond the effective and easy reach of the yachtsman.
Track the trailer in the event that it is stolen
If it is stolen, it will be useful to be able to track its trailer. The idea, like boat trackers, is not to go to the location where the trailer was seen or spotted, but the beacons can be useful to investigators.