i want to build one rc boat from foam, Suggestions with plan, electronics and calculation like weight thrust and all.

1. Understanding Boat electronics.
2. Understanding Boat dimensions (Ratios).
3. Boat controls.

As far what we do in plane is weight calculation, wing-loading and then based on this parameters we have all ratios wherein fuselage and other parts dimension can be calculated.
So whats is boat, how to start?

First decide the model...
BOats are relatively more simpler than planes....
See some of Roopesh sir's (now Krishna Madam's) boat build logs...
They are very simple to very complex...
Start with something like...
http://www.rcindia.org/boats/make-a-simple-boat-and-rcyit-in-three-hours/

As far as controls go,
Two controls are there...
Throttle and rudder..

Electronics are one motor and 1 servo

That thread is awesome, starting from same. Need to built same boat as shown in the link. But slight big.

http://www.rcindia.org/boats/neptune-(scaled-up)-from-available-plans-in-sunboard/

after dgca notice i should stop building airplane ,so now i will also go grounded respect law
next build could be simple boat with a motor and rudder servo , a flying boat

Should be simpler to build an air boat if you have some aeroplane electronics laying around.

http://www.rcindia.org/boats/my-first-boat-build/

How to control boat speed.?