Engine Stops

If you crash head on into a heavy bouy or the bank your engine will spring forward on the rubber mounts, especially heavy 15cc engines. If this is happens you can damage your linkages or servo gears. If you use a two piece coupling as most of us do, this can separate, and whilst the engine is still spinning the two ends can hit together and ruin the coupling, there is also a good chance the shaft end in the boat will be bent. You now have a big job trying to get the bent shaft out of the tube.
All this damage can be prevented by fitting simple engine stops. Two ideas are shown below.

In example 1, the rubber mountings are enclosed by a metal "cups", this leaves the rubber mount still free to move in normal use, but in the event of a crash it is prevented from stretching too far forwards.

Example 2 shows some brackets fitted between the gearbox and the side mountings, in a crash these will hit together and stop the engine shooting forwards.

These are just two ideas, but anything that will restrict the forward movement of your engine in a crash is well worth fitting.