Spare Paddle Weight and other Cost/Benefit Comparisons
Lets begin with thoughts about your spare paddle.
Many people consider low cost to be the most important factor when choosing a spare paddle. Unfortunately the less a paddle costs, the more it usually weighs. Yet you might be tempted to go cheap in this case since it is unlikely that you will ever need to use your spare paddle, and if you never use it, does the weight of a spare paddle matter? Actually it does matter since on trips you will often need to lift your kayak with the spare paddle on deck, and then every pound of extra weight makes carrying your kayak that much harder on your back. And speaking of pounds, many of the cheaper kayak paddles have their weight measured in pounds not ounces. Although generally less significant, the weight of your kayak plus gear also matters on the water. The heavier your total displacement, the deeper your draft (depth into the water), and the greater your draft, the more wetted surface area your kayak will have. Most of the drag that you are constantly working to overcome while paddling is due to the friction of water sliding past your kayak's wetted surface area. So the more wetted surface area, the more you work to hold a given speed and/or travel a given distance.
How light should a spare paddle be? If you were racing, every ounce would matter, but then in most races you wouldn't be carrying a spare paddle at all -- they'll have motor boats to assist you if you have an equipment failure. For sea kayak touring, the spare paddle isn't the only piece of equipment that affects our displacement -- even on day trips. We could save weight by investing in a lighter kayak, and on camping trips there are many buying decisions and camping lifestyle choices that affect the weight of our kayak when loaded. So perhaps it is best to look at the cost/benefit ratio for saving weight on your spare paddle vs. your kayak or camping gear.
Some of the cheapest two-piece (and a spare paddle will need to be two-piece) sea/recreational kayak paddles run about $40.00 retail and typically weigh a little over 5 lbs. (=80 plus oz.). For about $60.00 you could get a paddle in the low 40 oz. weight range. So for this extra $20.00, you would shave 40 oz. off the weight of your loaded kayak, or another words it only costs you $0.50/oz. saved. For around $180.00 you could get a paddle in the low 30 oz. weight range, but comparing this to the $60.00 paddle means your pay and extra $120 to save 10 oz., or another words this costs you $12/oz. saved. So we are fast reaching diminishing returns in terms of weight saved for extra dollars spent. If you took this to the extreme, for about $440.00 you could get an all graphite/carbon paddle in the 18 oz. range which compared to the $180.00 paddle would mean you were paying $16/oz. saved.
Now if you looked at a kayak that was available in a choice of fiberglass for $2500.00 or carbon/Kevlar for $3400.00, and weighed 55 lbs. and 50 lbs. respectively. Then you would be paying about $11/oz. saved.
So at $0.50/oz. saved, stepping up from the $40.00, 5 lb. spare paddle to the $60.00 one is your best bargain. However, at a premium of about $12/oz., the $180.00, spare paddle would make sense if you were buying a carbon/Kevlar kayak. Even with a fiberglass kayak, it would be worth going for the 30 oz paddle if you planned to use your spare paddle some of the time since then you would the duel benefit of paddling with a lighter paddle as well as saving total displacement weight when carrying it on deck as a spare.
When shopping for camping gear, it would be worth keeping these cost/oz. premiums in mind. However, when gear shopping, it might be easier to work with the reciprocal of this premium ... in which case the $11/oz. (cost per oz. saved) premium for the carbon/Kevlar kayak vs. the fiberglass one is the same as saying you save about 1 lbs/$200.00 extra spent on a similar but lighter item. So when comparing two similar tents (or any other choice of similar items that you will be packing in your kayak), if it costs you more than $200.00 per pound saved, you would be much better using the money toward a lighter kayak or paddle, but if it costs less that $200.00 per pound saved it would be a good deal as kayaking gear goes. Another case to consider is that if you already own a tent and think there is no need to buy a new one, but you find a new tent that is one pound lighter than your old one and the total cost of the new tent is under $200.00, then buying a second tent would be as good of an investment as going for a lighter kayak.
Some unrelated other thoughts about paddle blades:
Question: I have a new paddle that is easier to move through the water -- not as much resistance as my old one, but I noticed I have to paddle a lot faster (more strokes per mile) to keep up with the group. With the old paddle I can keep up better... it has more power per stroke, but requires more strength to move it through the water.
Reply: The goal is not to move the paddle backward through the water, the goal is to have a paddle that barely moves at all while the kayak moves forward past the paddle. If you want less resistance from your paddle, go slower. This can be done by changing to a paddle with a smaller blade, or simply not exerting as hard on a large bladed paddle. It is the resistance from the paddle that moves the kayak forward. Your forward power and speed are proportional to this resistance. Anything that lowers this resistance also lowers your speed.