Just looking at the pics, you would think, not much. Both made by Boeing, the 46 discontinued in 1971. The 47 is a little over twice as long as the 46, hauls twice as many people, and carries twice the cargo. The engines on the 47 develop 3750 hp each, while the 46 engines are only 1870 hp. To top all that off more than two times as many 47s made as 46s and are still being upgraded.
They look similar, but that's just a family resemblance. They're actually completely different machines. Once you become familiar with either one, you'll be able to tell them apart easily. As other readers have pointed out, the Chinook's much bigger and heavier. The CH46 is designed to operate in tight flightdeck environments.
Check the web -
The CH46 is about half the gross takeoff weight of the CH47, has three wheels instead of 4. The USMC uses the CH46, the US Army uses the CH47
Boeing/Vertol makes both the CH46 and 47
There are many... the first would be that the Chinook is made by Boeing Vertol and the Sea Knight was made by Sikorsky.
The Chinook is larger and more powerful.
I would ride in a Chinook but will never ever get in a Sea Knight again !
Although there are differences under the skin of the aircraft, the noticeable differences include:
The Sea Knight has three wheels, the Chinook has four. The Sea knight has Sponsons, the Chinook doesnt! Simple!