sail question

I have limited resources so I was wondering...if I could make a spinnaker and have my boat just have the spinnaker as the mainsail if the mast is 35 in and the spar is 2 ft.

 

To start with, a 35 inch mast won't let you carry much sail. Secondly, a spinnaker is for downwind only; broad reach at most. If you only want to sail downwind, then it would work, but as a head sail. Mainsails are attached to the mast and that is not possible with a spinnaker.

 

thx... well I was thinking about making a lateen rig with the mast being 2 ft and the spar being 35 in...would that work for a 5 ft catamaran?

 

A lateen rig has three spars. The mast is one of them. The five foot catamaran must be a model or for use by small children. Otherwise it's questionable whether a boat so small should have two seperate hulls.
No one will be able to help you figure out sail area based on the length measurement alone. Length alone tells little about what kind of force would be required to move a hull along through the water. Displacement matters, intended use, and a multitude of lesser details, but no single factor such as length has much meaning alone.
Before asking a lot of basic questions here you should read a book about boat design (look up "Dave Gerr").
What is the boat intended to do?

 

go on a lake

 

Will it go on a lake and be an RC?