Tim H16 wrote:
If you wear a properly sized water ski/wake board vest with 3-4 cross-chest straps, you are not going to slip out of it nor will it ride too high on you while your in the water.
I agree, a proper fitting and properly worn life vest/ski vest will not allow the person wearing it to slip out. The chest straps should be snug, and the vest overall should fit like a glove. No way would I ever prefer a crotch strap! It would be far too uncomfortable, make it that much more difficult to get into and out of, could potentially get tangled up with a harness and/or snagged on things as you're crawling around a trampoline.
It appears that a type iv is not required, see below from the USCG website. But I think it's a good idea to have one handy anyway.
1.Q: What life jackets are required to be carried on my recreational boat?
A: In general, Federal law requires that you must have a Coast Guard-approved wearable, life jacket (Type I, II, or III) for each person onboard your vessel. In addition, boats greater than 16 feet in length must carry a Coast Guard-approved throwable device (Type IV). A throwable device is not required on canoes or kayaks regardless of length. For more information on exemptions and the proper use of life jackets, see A Boater’s Guide to the Federal Requirements for Recreational Boats.
That was exactly the requirement I was referring to. The H18 is greater than 16 feet in length and therefore technically must carry a USCG approved type IV throwable device. The coast guard usually will also tell you that it should be readily accessible in case of emergency (they'll ticket you for it on a power boat if they're tucked away somewhere that is difficult to get to). The problem is, your only options are underneath the trampoline or on top, where it'll take up a lot of space and have to be well secured - probably not all that accessible. I usually don't bother with one, I was just curious if anyone else does.