one day in Yokohama

could anyone suggest a route for a one day trip on how to see some of the sights in Yokohama maybe using short local transport or just walking

I recommend to walk from Sakuragicho Station through Minato Mirai and then along the waterfront to Yamashita Park to Chinatown. If interested you could also include the Yamate and/or Motomachi area near Chinatown and Yamashita Park.

If you like ramen, you could also include the ramen museum (open 11:00 to 23:00). Or if you like gardens Sankeien (open 9:00 to 17:00). Or if you have another special interest any other of Yokohama's other sights:
http://www.japan-guide.com/e/e3205.html

Check the weather forecast before you go
We went there on Sept 2
Our first stop was Seaside Paradise because I wanted to take my daughter to see the animals there.
Nice collection: seals, beluga, walrus
It was raining on and off, just a drizzle, so it was fine.
But then it rained harder when we arrived at Sakuragicho Station. We waited for like 30 minutes but it didn't stop. So our plan for the Minato Mirai was ruined.
I only managed to take few pictures of the area
(if interested, you can check my photos here: http://www.flickr.com/satoosoft

So if I were you, I'd make a back up plan as to where to go in Yokohama just in case it rains.
Good luck!

Take the 100 yen bus from outside Sakuragicho Station , it will bring you along tourist stops and you can get off and on at any stops you fancy. The whole loop takes about 2 hours I think.