Hull displacement

I was beating myself up over the weight I put on since fall and started to think about hull displacement.

Follow me in this line of thinking:

Kayaks are displacement hulls.

Weight of water displaced = boat weight +paddler weight+ gear weight. (ref: Archimedes)

Therefore I am displacing (splitting?) approximately 300 lbs of water for each waterline length I travel.

If I lost 50 lbs, I would only displace 250 lbs of water for each waterline length. Less weight displaced results in either greater speed or reduced effort.

Is this a correct assumption, or the musings of a clueless marine architect wannabe?


Less Weight
translates into a lower displacement/length ratio and less wetted surface which improves speed and reduces effort. A 50# reduction in weight on a 17’ waterline boat with a ppi (pounds per inch immersion) of 100 could mean 1.42 square feet less wetted surface which could be as much as 7%. The decrease in disp/length is the biggest factor though as it directly relates to wave making resistance.

Yeah I could lose some weight too

– Last Updated: Jan-18-04 10:57 PM EST –

Also inertia is a factor. Always in a kayak there is acceleration and deceleration. Less weight: less to re-accelerate.

Do not beat yourself up! Nobody says what the defiention of success in kayaking is, except for coming home with all your buddies (if you are not paddling alone) all alive and healthy.

sounds good to me
but improving hp/lbs is always a good idea unless you’re a slow moving truck.

Flat vs deep
but you still displace the same amount of water with a wide, shallow hull as you do with a long narrow one. The difference is how far you have to move the water. Poor analogy: Would you rather split wood with a wedge or a piece of pipe?

My point was that it appears that the lighter the paddler, the less the displacement and possibly less effort in moving water aside.


point taken
trying to clarify short ,shallow draft comment. also see my friend who is in a similar boat but is30 lb. lighter glide over shallow spots I scrape bottom.

Lighter folks
Dang, that bugs me too. I was thinking of helium in the fore and aft compartments.