If you install a tiller steer outboard motor on your 13 foot Boston Whaler Sport, the first thing you are going to notice is that the tiller handle is too short. You have to reach way back to steer. You can move the rear seat back some but then there will be no room for a battery or gas tank. I solved this problem on my boat by installing a tiller extender. A tiller handle extender is a simple device that is actually made for electric motors but will work on outboards as well. (Note – this works great for me but it is up to you to determine whether this is a safe option for your motor) I purchased mine through amazon.com and received it in just a few days. I paid about $30. It was the Minn Kota brand. I recommend that you get the shortest one that you can. A long extender is going to be in your way and will bend too much. I would think the shorter the extender the safer it would be.
To install the outboard motor tiller extender you simply loosen the nut and slide it onto your tiller and then tighten it. Make sure to push it as far on as it will go. That is basically it.
If you look at the picture of my engine below you will notice a little red handle that slides side to side. This is made to increase and decrease friction so that your engine stays in one position while running. I have found that it works best to have this loose when running slow and tight when running fast. I keep mine tight at high speeds so that if the extender came off or broke the engine would not fly to one side or the other and flip the boat or throw me out. Just a precaution. Also, I recommend you clip yourself in to the engine so that if something does happen it will cut off.
I have a picture at the bottom of this page of an extender that I made my self using a PVC pipe and a hose clamp. The one I made is not pretty but is actually more substantial and safer than the one I purchased. I keep it on the boat as a spare.