a skim board is for riding the surf on the beach isnt it? If so, then the estes rockets that are avalible to you arent powerfull enough. there are some but you have to have a special licence to buy them. you could try building a pulse jet. another idea would be to use a jetski impeller and a gas motor.
it might be an intertaining flaw. if the conditions where right. like when i got rolled down a large hill in an oil drum. that was fun, dangerous and entertaining. at leas i wore a helmet.