Hull design variations

I was looking at the OK Malibu tandems, and noticed the bottom of the hull is like a roller coaster.  Maybe that's for stability, yet kayakers talk about glide and speed as a key component for a good ride...so why the swale in the Malibu?  I'd think a smooth hull with easy tapers would be the best design, but what do I know!  What do you experts know about the top 3-4 hull designs and their main characteristics (beyond "wide=stable, long=fast" basics)  I'm sure the manufacturers have put the big bucks into it, so if you could share what you know that'd be great.

god question.
 I don't know, but I would think it was for the varius weght distributrions that may occur on the larger boats/tandems.
 I'll wait for a more knowledgeable answer with ya

I think what you're getting at is the channels that run the length of the yak right? If so, those are added to help with tracking. Keeping the boat going straight as compared to side slipping. There's not a ton of manufacturers out there that use them so don't know how effective they are.

Z

No, not the channels.  Most hulls are like a banana, but the XL and XL 2, among others, are like bananas with big dents.  Then we have the pontoon tpye like the Escape that takes 100+ lbs before it stabilizes and sits low enough for secondary stability.  Then the flat bottoms, etc.
I was kinda thinking with all the computer design, there would be some ultra-turbo hull out there now, but it seems the different manufacturers just run with their own designs.  I know we're not talking about racing here, jsut more about efficiency through design. 

I used to work in a boat yard, mostly building new wood/composite boats from 8-50'. We were absolutely anal about hull shape, even below the waterline. By comparison, the PE kayaks and their hulls are amazingly soft and deformed. There are often major
deviations from ideal hull shape. Probably not much can be done, considering the material.

I know we're not talking about racing here, jsut more about efficiency through design. 

I can do 5-6 mph w/o really trying hard... is that efficient?? Really though, there's efficient hulls out there. Test paddle a lot and you'll see.

Z

I think what you're getting at is the channels that run the length of the yak right? If so, those are added to help with tracking.

Just wanted to add, the channels also provide needed rigidity. Decks have a lot of angles - some hulls, much less so, meaning they have to be added or they'd simply be too prone to dent.

No, not the channels.  Most hulls are like a banana, but the XL and XL 2, among others, are like bananas with big dents.  Then we have the pontoon tpye like the Escape that takes 100+ lbs before it stabilizes and sits low enough for secondary stability.  Then the flat bottoms, etc.
I was kinda thinking with all the computer design, there would be some ultra-turbo hull out there now, but it seems the different manufacturers just run with their own designs.  I know we're not talking about racing here, jsut more about efficiency through design. 

The math & physics around hull design are way beyond me, but Sea Kayaker Magazine always has a section about this stuff.

Alot of the plastic boats, especially sit on tops, have some odd shaped hulls, because the material itself get's soft with heat. alot of hard angles etc. help give structural stability.

i think with sit on tops, they do this more because there is nothing to support the shape except the scupper holes (no bulkheads etc, and you are sitting on top of the structure rather than the bottom as with a sit in.

There is a company called Tide Race that has been using computer's to design the most effecient & high performance hulls out there. I've paddled the only two boats in the US right now, and I have to say they are the most amazing kayaks I have ever put in the water. Stability, maneuverability, speed, & glide are absolutely amazing. the Excite is the perfect rough water/surf boat, and the Explore an amazing high performance expedition boat.

http://www.tideraceseakayaks.com/

In general, I go with length, width, rocker, waterline template, chine, & hull style (shallow v, flat, etc.) to get a guestament of how the boat will perform in various conditions, and then go paddle it to discern the finer points. Unless you are a physics guy, this is the best way I've found to figure it out.

-Jason