# Pls explain drag prediction graphs

I have read a couple of online essays on the subject. I still don’t completely understand how a drag prediction graph can show you the predicted hull speed. Also how many lbs does an average paddler exert with each stroke?

I would suggest
looking for that information elsewhere. Contact Chris at Sea Kayaker directly, or search for Broze brothers. Matt and Cam have written some excellent information on this. Winters as well. Likewise George Gronseth, author of Deep Trouble. Some people here such as bnystrom have an excellent understanding. I’d also reference anything Greg Barton has written, as it’s excellent information. There’s lots of tradition out there and some of what these guys say will be controversial. Good luck.

Following Larry as he slid along really

– Last Updated: Aug-21-06 4:53 PM EST –

got to you and now you want to slide along effortlessly too? ;^) In your own designs? :^)

>:^)

Mick

Drag values are much more useful.

“Hull Speed” is just a formula related to wave making. Speed in Knots = SQRT(LWL) * 1.34.

This predicts the speed where the wavelength of the wave generated by the hull is the same as the waterline length.

“Hull Speed” (S/L 1.34) is not a speed limit - especially not with narrow shallow draft hulls.

Making longer waves takes more energy (simple physics) - and is why the drag curves sweep up once wave drag becomes predominant. Wave drag is more exponential - skin drag is more linear. Hull Speed tells you nothing about the actual effort needed to paddle at that speed. You need total drag numbers for that.

If you’re looking for relations of Hull Speed to actual paddling, I’ve observed the following: Cruising speeds are typically 60-80% of hull speed (roughly S/L

“Hull speed” isn’t my only concern

– Last Updated: Aug-22-06 10:54 AM EST –

but it seemed like a good place to start.

I'd like to know how a drag prediction chart relates to the paddlability of a canoe. Frictional and residual coefficents, cwp, clp, cx, cb. I read the numbers but don't know how they relate. I am having a hardtime trying to figure it out.

hey mick
better to make mistakes on paper than in 3d, less expensive.

Seat time
IMO engineering and analysis are of limited value when evaluating boat design. That’s why so many sucsessful designs are the result of incremental changes over a few seasons.

Again IMO, boat design is as much if not more art as it is engineering.

Wetted surface affects efficiency, length and beam affect top end but they also affect stability and handling and you can not separate those.

The Osprey I’ve been paddling for the last few seasons is a real eye opener for me. It handles so differently from my other boats that I wasn’t sure I’d like it at first. But it does so many things so well that I’ve decided to stay with it. While I respect Winters engineering I think this boat at least speaks more to his art.

But hey, if you come up with a good 50/50 paddle sailing design, I’m certainly interested!

yes that is the quandary
a sailing canoe is a compromise. Mine sails very well, but under paddle is a “dog”.

Stitch & glue Osprey II
I bought plans for the Osprey II from Green Valley with the idea of building a fully decked version. Havn’t got to it yet.

But if I decide the Osprey is not too tender as a sailer I’m going to build the Osprey II as a 50/50.

Osprey
I set my Osprey up to sail a year ago but have never used it for that purpose. Definitely seems like I would have to remove the seat and sit in the bilge to keep it upright.

Wouldprobably haveto make a smaller sail also. 35 sq ft seems about right fro the Osprey without hiking out.

Osprey Wing
I’ve got a 40 sq ft sail on my Osprey since last week. I’m kneeling on the seat.

Started out with a 2" x 13’6" mast but didn’t like the weight up high. So I went back to my 1.125" x 12’ setting pole.

Up on the Sheepscott River in Maine last weekend it sailed pretty good. Steady wind! But I was nervous because the water was cold and I’m not completely confidant of my ability to self rescue.

So I’ll work on my self rescue and see how often I need it!