My idea is to have a whitewater rafting sim like thing were you start in the boat of your colour (launching point) and can bombard any of the starting positions. The entire map has neutrals of 1 (except portages).
I want to have 4 obstacles where there is an alternative to portage around it on land - if you take the portage you go around the obstacle but have to defeat a (reverting) neutral of 3. If you go through the obstacle you will lose 2 (or random if possible - to simulate getting through clean or hitting a rock).
Its a race to the bottom, and once you get to the bottom you can take the shuttle back to the top to defeat any of the launching points. This will allow people to go through at different paces, you can only attack forwards down the river and you have the objective of defeating all others to rule the river. The interesting idea is all about when you take the shuttle to hit someone as you then have to allow that the others around can take their spots. Is it too complicated?
Here is a rough drawing I did. I will probably end up taking out a portion of the spaces before the first bend to streamline it. But I like the bulky spaces at the front, and fewer spaces throughout. The idea I want is for people to rush forward. I guess I have to give them incentive to do so. I was thinking of having 'check points' which once passed it would give a bonus of x (5?). Then again cards do that don't they.
Thanks in advance