New Cnt Pts
There is NO rudder so it won't turn - that is the problem. Try these cnt pts I modified. I gave it gear so it can taxi on land (you won't get 'stuck' in the mud). But you can comment out the gear if you're a 'purist' (ie: use 'slew'-ha).
Hans Wuhrmann uploaded a 'fix' at FltSimCom (Name: do24_config.zip: Size: 989 Date: 03-25-2016 . ''FS2004 Update For Dornier Do24 (DO24T3_FSX.ZIP). With this change the Do 24 by Shessi/Erwin Welker water lands, stops and takes off without crashing''). But he forgot the water rudder. I like my cnt pts better. Enjoy.
Chuck B
Napamule
Edit: Here is a short video of DO-24: Link:
https://youtu.be/gMCQOdLzuJE 
3:42)
[contact_points] //cb mods
//Floats
point.0=4, 18.60, -0.56, -1.12, 2600, 0, 0.45, 0.00, 0.100, 4.5, 1.000, 0.0, 0.0, 4, 0.0, 0.0
point.1=4, 18.60, 0.56, -1.12, 2600, 0, 0.45, 0.00, 0.100, 4.5, 1.000, 0.0, 0.0, 4, 0.0, 0.0
point.2=4, -12.00, -4.00, -1.22, 2600, 0, 0.45, 0.00, 0.100, 4.5, 1.000, 0.0, 0.0, 4, 0.0, 0.0
point.3=4, -12.00, 4.00, -1.22, 2600, 0, 0.45, 0.00, 0.100, 4.5, 1.000, 0.0, 0.0, 4, 0.0, 0.0
point.4=5, -16.65, 0.00, -1.30, 2600, 0, 0.65,40.00, 0.100, 4.5, 1.000, 0.0, 0.0, 4, 3.0, 3.0
//Gear
point.5=1, 18.80, -1.00, -2.42, 2600, 0, 1.45,60.00, 0.200, 2.5, 0.900, 2.0, 2.0, 0, 0.0, 0.0
point.6=1, 18.80, 1.00, -2.42, 2600, 0, 1.45,60.00, 0.200, 2.5, 0.900, 2.0, 2.0, 0, 0.0, 0.0
point.7=1, -11.00, -4.30, -2.42, 2600, 1, 1.45, 0.00, 0.400, 2.5, 0.800, 2.0, 2.0, 1, 0.0, 0.0
point.8=1, -11.00, 4.30, -2.42, 2600, 2, 1.45, 0.00, 0.400, 2.5, 0.800, 2.0, 2.0, 2, 0.0, 0.0
//
max_number_of_points= 11
static_pitch= 1.0
static_cg_height= 1.400 //o=1.0
//tailwheel_lock= 0 //Do Not Use
//gear_system_type= 4 //DO NOT USE
//always_use_avg_surface= 1 //Do Not Use - Unknown (?) source/spec