There are very few days that I would not consider taking the jetskis out. When the lake is too choppy for the jetskis, it is similarly too choppy for my 27 foot bow rider. Those days are few and far between. The jetskis are a wetter ride and you can get cold on those early season/late season days when you can enclose the boat to stay warm. But, again, those days are few and far between.
The jetskis are simply more fun and cheaper to run. On an operational basis, my jetskis run less than 25% (often more like 10%) of the cost of the boat. I can do my own winterization/summerization and most of the service...there is no need for winter wrapping or storage as they can be put in a garage on their trailer. The insurance is less...
On a capital basis, a low end new jetski runs about $8k and a top of the line $16k. Of course, used is much cheaper. That puts them in a much more accessible position than most boats. For a decent size boat you can multiply that number by 10x.
I think that this economy is forcing everyone to re-evaluate their spending habits and boats are clearly quite expensive. Jetskis remain a cheaper and more fun option (IMHO). I expect to see the trend continue toward smaller boats and jetskis.
Jetskier
