Waterline Length = Speed?

So I have this Dagger Callisto which is 13’8" long and 24" wide. It’s a very low volume boat and fast for it’s length. It has no rudder or anything hanging off the back. I also have longer, skinnier, and faster boats. I’m thinking if I took a piece of spruce 1 x 6 about 14" long and coped, shaped and sanded it to a bolt on fixed keel line match at the stern I would add that much waterline length to the boat. It would be fun to see (or imagine) if that would add a noticeable increase of speed to flatwater cruising which is mostly what I do when the fish aren’t biting. Of course being an accomplished “shop worker” this would be done right with marine Varithane, S.S. bolting and all. Any theories, input, laughs, etc?

Save the wood. Read up on kayak design in general, and more specifically hydrodynamics and naval engineering as they relate to displacement hulls.

Length of a displacement hull gives wave making speed (hull speed) and an idea of the potential top speed (not the same as hull speed at all).

Your thin board doesn’t change LWL anymore than putting a knitting needle on the nose of my kayak would. It would be more like a large rudder - and rudders generally do not count toward LWL.

There is a lot more too this - like displacement, beam, cross section shapes and coefficients - and the most important factor - power.

If you really want more speed, work on the engine. For that, splitting and hauling firewood would be a more useful sort of woodworking than shaping a 1x6!

Splitting Firewood
Thanks, I was just splitting a bunch of 1 x 6’s the other day when I got this idea. Your keywords sound convincing but I’m not sure you’re considering all the factors. Improved tracking certainly translates to increased speed without correction strokes, etc. Hull displacement would carry through the additional length. Enthusiasum would add speed. My engine is doing quite well and all this would just be for fun.

Enthusiasm would add speed
OK the part about enthusiasm I agree with, but none of the rest.

Better tracking will not improve the boats speed, but poor tracking/poor technique will rob it! A skinny board will not increase the effective waterline length. Not everything is an even give and take, or about the hull. Making adjustments to the paddler is more effective than making changes to the paddlee.

Have fun! Make a piece for both ends! Take pictures.

Might Work…
The added buoyancy would make you sit higher out of the water and you would need to factor in the increase in wind resistance. Usually they put lead in the keel to add stability, adding wood might make it want to float upside down.

Good “out of the box” thinking though… keep it up and keep us informed… GH

Swimmers now keep one arm
extended in front of the while doing mid distance and long distance freestyle. Seems that the added length on water makes a difference at low speed.

to use this technique simply keep one arm in front of you and then stroke with it when the other arm reaches it. Once you are in the right configuration is does not limit a non-sprinting turnover. Weird at first though. Triathaloners take note.

Never know about that board!

Put it in the front …
Fill and (longboard) fair w/ 2part foam or Balsa as far back as you have time for. Wax or put some tape on the hull before all this if you want to just ‘pop’ it off later.

Fish now keep one eye open
for strange looking watercraft. (Sounds like fun. Let us know what happens).

added length
there has recently been controversy in the sprint boat world about added boat length from overstern rudder. Van Dusen came up with a rudder that had extra length on thier mohawk design which now appears to be illegal via icf ttp://www.vandusenracingboats.com/index/index.html It is also sold by simon river sports. The thought was that this increased the water line length over standard length for sprint boats.

If you want to play with your boats this may give you some ideas. If you want to go faster work on forward stroke.


better address please …

I would like to see the rudder you are talking about, but address given does not work. www.simonriversports.com/ does not work either.

If rudder were large and buoyant it definitely would add to the wl.

Happy Paddl’n!




go to kayaks and they breifly discuss it

I had the same thought as Peter:
the “Total Immersion” approach to swimming suggests using a “front quadrant” stroke in which one arm is kept purposefully extended during almost the entire stroke cycle, in order to increase one’s personal waterline length. It’s very simple to verify at the pool that extending even a narrow arm increases your speed significantly. (I can measure specifically next time I’m at the pool, but I’d guess a 20-30% improvement in speed.)

Perhaps the best shape for an extension would be a bulbous thing something like the bulb keels that some freighters have.


Thanks! Foto interesting too!
Was a little smaller than I expected, but then the whole racing hull is a bit smaller than I imagined. Looks like it is breaking the speed limit just sitting there! ;^)

Happy Paddl’n!



Worth A Try
Well, based on what I’m hearing so far this might be worth an hour or two in the shop. I guess what I’d be expecting is more “glide” and ease of cruising effort as opposed to higher end speed. The hull configuration of the Callisto is interesting as it tapers severely to a narrow 3/4" wide keel. That is what has me visualizing an extension of that line. Onnopaddle’s idea of a bow extension is also interesting because the plastic bow is more blunt than the entry line of my fiberglass boat. Anyway, it’s a “gagiteer’s” concept and I might give it a try. Thanks for all the input, what a great website!

More Detailed Info
This is a great article/website. Thanks ice19


Great link!

Clearest of comprehensive explanations I’ve seen.