Civil Air Patrol and JROTC are Superior to Sea Cadets
I have been and active duty Air Force and Naval Officer. I was trained to fly by the US Navy at NAS Pensacola and NAS Whiting Field. I currently fly in C-17 aircraft for the Air Force Reserves. I attended an Army military academy in high school. My son was in the Sea Cadets, but has switched to the Civil Air Patrol (CAP).
CAP is a much larger and more robust organization then the Sea Cadets. They outnumber the Sea Cadets by the tens of thousands. JROTC programs (Army, Navy, and Air Force) outnumber the Sea Cadets by the hundreds of thousands.
As you might expect, that means the organization and support infrastructure is much more solid for CAP and the JROTC programs. The Sea Cadets might have fun during their summer trainings, but they do not emphasize the true traits of a military officer. Those are things such as integrity, unselfishness, anti-fraternization, tact, and respect for actual military rank.
The Sea Cadets wear their uniforms sloppy and do not march as well, relative to CAP cadets. I would think the Young Marines probably march better than Sea Cadets. Close order drill (marching) is vitally important for discipline later in life, and in the actual military. For example, when they say left face, and you turn right - that could mean you turn the wrong way in an Army convoy in Iraq and run directly into superior enemy forces. That is how Jessica Lynch's convoy got captured. So the lack of close order drill discipline of the Sea Cadets could establish bad habits for any future military person, no matter what branch you eventually wish to serve in. The very strict discipline that CAP imparts even during routine weekly drill is one of the reasons Lieutenant Colonel Malachowski attributes to her ability to qualify as a USAF Thunderbird pilot.
Furthermore, I have seen a Navy Sea Cadet adult officer disrespect and say four letter curse words at an actual high ranking military officer. Of course that Sea Cadet officer was almost beat up by a military person who witnessed the incident. That incident epitomizes Sea Cadet culture. Many Sea Cadet officers have never served in the military as officers. Yet they wear naval officer uniforms and all of a sudden think they are Admirals. They are bossy, lack tact, and are condescending even to actual military personnel. The Sea Cadets highly favor their friends, and you will see Commanding Officers favoring their own kids for awards. Fraternization is present in the Sea Cadet program.
All the sail boating and submarine building in the world will not replace the discipline, integrity, in-depth science education, and respect taught in CAP and JROTC programs. CAP officers actually have a real-world mission (Search and Rescue, similar to the land version of the Coast Guard). JROTC Commandants are typically retired military officers who have served our nation for 20 years. In contrast, Sea Cadet officers might be civilians who have never served a day in the military. The difference is night and day.
If you want to go to West Point, the Naval Academy, the Air Force Academy, be a pilot/aviator, or become an astronaut, I highly recommend CAP or JROTC. For those aspiring to be a naval aviator, go Navy JROTC AND CAP (yes you can do both). If you want to be a ground infantry fighter or be an airborne paratrooper, go Young Marines or Army JROTC. My son is so much more refined and disciplined now that he is in CAP.
Don't let the Sea Cadets fool you into thinking they can prepare you to be a Navy SEAL. They may have Navy SEAL camp, but that will not prepare you for the real thing. I have met at least 5 Navy SEALS in person and have spoken to an Undersea Medical Officer (physican for the SEALs). They will drown you in training until you are almost unconscious, or until you actually pass out underwater. Then they will revive you. There is no training for that, you either have that in you when you are born, or you do not. Some little SEAL-wanna-be camp for a few weeks will most likely not make a difference.