Collision issue on gazebo 9 ?

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Hi everyone,

I face some trouble to place a boat on a step to study its motor and steering.

This occurs from both sides of this catamaran-like boat

Seems that the hull is inside the step, is it an issue with the physic engine (default ODE) or the mesh ?

I launch gazebo through a roslaunch file and a test world.

Here is the part of the URDF file describing the hull :

<link name="boat_link">
    <inertial>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <mass value="38.718"/>
        <inertia ixx="16.283" ixy="0.008" ixz="0.458" iyy="19.728" iyz="0.0" izz="33.013"/>
    </inertial>

    <collision>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <geometry>
            <mesh filename="package://aquanaute_description/models/meshes/Assambly_aquanaute.stl"/>
        </geometry>
    </collision>

    <visual>
        <origin rpy="0 0 0" xyz="0 0 0"/>
        <geometry>
            <mesh filename="package://aquanaute_description/models/meshes/Assambly_aquanaute.stl"/>
        </geometry>
        <material name="gray"/>
    </visual>
</link>