Between May and October each year in New England, the sum of the water temperature in the Charles River plus the daytime air temperature exceeds 100 degrees, reducing the risk of hypothermia in the case of submersion. For me, that's kayaking season.
At least 3 times a week, on my way home to western suburbs of Boston, I stop at the Charles River Canoe and Kayaking building on the Charles River where the Mass Pike meets 128. I have a season pass and can take any kayak out on the river for my typical 8 mile paddle through the Lakes district to the Moody Street Dam in Waltham. The Lakes district is the site of the former Norumbega Dance Hall, home to the big bands of the 1940's and a very popular wide and shallow canoeing spot for the past 100 years. Of historical note, the local native americans called the region Norumbega after it was visited by the "Norumbegians" in the 1300's. The thought is that Leif Ericson or his Viking compatriots may have navigated up the Charles from Boston Harbor to this location, many years before Columbus 'discovered' America.
The Charles is relatively calm flatwater with few currents. How do you choose a kayak for river kayaking?
Kayak designs are a tradeoff between directional stability and maneuverability, and between stability and speed.
For river travel in flatwater, I choose a highly maneuverable, fast kayak with limited primary stability but good secondary stability. These terms are explained below. The primary boat is a use a the Epic V10 Surf Ski , an 18 inch wide kayak that performs like an Olympic racing kayak, but is slightly more stable. I'm able to maintain 8 mile per hour rowing speeds on the Charles without difficulty. On very windy or choppy days, I choose the Epic 18X , a 20 inch wide kayak with greater stability, that I paddle about 7 miles per hour.
Primary stability refers to the initial stability a paddler feels when they sit in the boat. High primary stability feels very comfortable and reassuring. Wider kayaks with more buoyancy away from the centerline will present more resistance to tipping and thus feel less likely to capsize than a narrow one with less buoyancy away from the centerline. Although wider kayaks are more stable, they are also much slower. A 26 inch kayak is easy for a beginning to use, but challenging to paddle more than 6 miles per hour.
Secondary stability refers to the stability a paddle feels as the kayak approaches capsizing. They may feel initially a bit tippy, but are in fact challenging to capsize. My experience is that a relatively narrow kayak with low to moderate primary stability but excellent secondary stability is the most seaworthy in challenging conditions. Since the Charles is rarely that rough, I'm happy to trade stability for speed.
Longer/narrower kayaks are generally faster but a shorter kayak may be turned more quickly. Olympic K1 racing kayaks are 17 feet long and 16 inches wide. They are so unstable that only an expert paddler can use one, but they are very fast.
The shape of a kayak is defined as
* Symmetrical: the widest part of the boat is halfway between bow and stern.
* Fish form: the widest part is forward of the midpoint.
* Swede form: the widest part is in back of the midpoint.
Kayaks are very personal and I'll recommend you try many types in many conditions. For me, a season pass to a kayaking center is the most cost effective approach because I do not have to store or transport the boat, I can use a new state of the art kayak every year and test many different designs. Since the kayaks I like best - ultralight Kevlar racing kayaks, are $3000-4000 each, the $250 per year for a season pass to use one as often as I'd like, really works.
One last note about kayaking. Keeping a pace of 8 miles per hour for a sustained paddle up and down the Charles burns a lot of calories. When I first became Vegan 7 years ago, my first sustained exercise was kayaking. My 70 pound weight loss was the result of diet and kayaking. I highly recommend paddling as low impact, high cardio, mentally stimulating exercise. Especially if you use a very narrow, slightly unstable, and fast boat. That certainly keeps your blood pumping!