A plastic molded, sit-on-top kayak of unique size and shape is disclosed with various components which provide multi-purpose usage. The kayak is especially useful for multi-purposes such as sailing kayak surfing, scuba diving, paddling, touring and electric motorized usage. The kayak has attachment points integrally molded that provide for these multi-purposes. An important component of the invention includes a removable backrest that additionally provides secure waterproof storage of the operator's personal items. The backrest can be easily removed and reattached securely in place when desired. The ability to easily remove a backrest or backpack option also enables a desirable compact capability for transportation and storage by a user. Additional benefits of this feature provide for a smaller profile for packaging and commercial transportation. The kayak as disclosed may be formed for the most part, typically by blow molding, rotational molding, injection molding, rim molding, fiberglass and thermoforming, and by using a wide variety of polymer materials that may be suitable.