diff --git a/Dockerfile b/Dockerfile
index c0413b1..beb9c3d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,11 +2,13 @@ FROM ghcr.io/sdr-enthusiasts/docker-baseimage:base AS build
 
 RUN set -x && \
     apt-get update -y && \
-    apt-get install -q -o Dpkg::Options::="--force-confnew" -y \
+    apt-get install -q -o Dpkg::Options::="--force-confnew" -y --no-install-recommends \
         git gcc && \
     cd / && \
     git clone --depth=1 --single-branch https://github.com/sdr-enthusiasts/docker-vesselalert.git && \
     cd /docker-vesselalert/src && \
+    # make the output in meters instead of nautical miles:
+    sed -i 's|/ 1852.0||g' distance.c && \
     gcc -static distance.c -o distance -lm -Ofast
 
 FROM ghcr.io/sdr-enthusiasts/docker-tar1090:latest