Chulachomklao Fort

To get to the boat you will enter through a market. The enterance on the map is directly across from the art piece that is in the middle of the intersection. You will enter the market and proceed straight to the back. The walkway makes a left turn, but continue straight past the supermarket which will be on your left side ( you will see the turn styles ahead). The boat fee is 5 baht per person. Sometimes the boats will go around the island and you will get to see the temple on your way to where the boat will be docking on that side of the river. When you get of the boat, simply walk straight to the front of the market. Here you will need to get a taxi to take you to the fort.
If the driver doesn't understand you when you mention the name of the fort, you can simply show the driver the name of the fort, or show him the Google Map picture. He will know where to go. Taxis will come to the fort looking for people that need their service, so you will have no problem getting back to the boat.

To make your way to Chulachomklao Fort from Bangkok you will first find the nearest BTS station (also known as the skytrain). There is a kiosk with an automated tickey machine and on the kiosk is a map, you want to head towards the BTS station "Bearing" this will get you going in the right direction. There is also a ticket counter, if you would feel more confident making your purchase there (prices depend on where you get onto the skytrain, but no more than 52 baht per person). Look for the sign "Bearing" and go up those stairs. 
NOTE: You can get off at the Bearing station or the Samrong station. The Bang Nam station will be open in the future, you may ask the attendent at the ticket counter if the Bang Nam staion is open. If it is open, purchaase a ticket for the Bang Nam station. If you are able to take the BTS to the Bang Nam station, make sure when you leave the station that you are on the  south side (right side) of the street. Simply walk down the sidewalk and follow the rest of the instructions. It is not far to where you will be getting on the boat.
When getting off at the Bearing of Samrong stations, make sure you exit to the northside of the street (left side) so you can get the bus or taxi going in the right direction. NOTE: At Bearing you should be opposite of the 7 Eleven, at Samrong you should be opposite of the Imperial shopping center. 
The yellow buses are airconditioned and the bus numbers you can take are: 536, 511, 508, 142, 102.
If you decide to take a taxi just simply tell them Bang Nam market or show him the picture of the map and point out where you want to go. 
If you take the bus, refer to the map for walking directions.