To get to Yalova from Istanbul you need to take a ferry.
Ferries live only few times a day so schedule your trip early.
You will live from Yenikapi Ferry Terminal.
To reach this terminal take a tram to Aksaray. From there you can walk south or you can take a bus to Yenikapi Terminal.
Terminal is really nice. It is more like an airport than a boat stop :-)
Your ticket will cost 15 YTL one way if you want to seat in front of the boat. Or around 10 Ytl for back seats.
Boat is very modern (catamaran if I remember) and very fast.
Ride is a pleasure.
Yalova port is very active because
Boats from KARTAL
Ferry boats from PENDIK
Ferry boats from YENIKAPI
TOPCULAR-YENÝKAPI link is the main link for the transportation to Anatolia
and its situated 9 km far from Yalova
Yalova is in the center of Istanbul-Bursa highway
Yalova-Bursa: 69 km
Yalova-Gemlik: 43 km
Yalova-Orhangazi: 21 km
Yalova-Karamürsel: 30 km
Yalova-Gölcük: 50 km
Yalova-Kocaeli: 63 km
Yalova-Ýstanbul: 174 km