Design Challenge: Ultimate Downwind Destroyer

For sizing, you should be looking at the Carbonology Atom or Stellar SES. These are the right size boats for us skinny guys. Length is not that critical actually, 20' plus or minus.

If you're going to try a centerboard, yes, make it elliptical, I would say about 4"/10cm base chord, maybe 8-12"/20-30cm long. Somewhere in the region of a smallish windsurfing slalom-racing fin. You might want to just get a standard windsurfing fin box (Tuttle or Powerbox, whatever is most common in your area) and glass it right into the hull, that way you can either swap in different windsurfing fins to try, or just cut off an old one and make a flush plug to fill the box if you want nothing in there at all. You can also use the old-style surfboard-type fin box, which has the advantage of not having a bolt coming down from the top, but it's also significantly more drag.

I agree Kestral, early on I was going to suggest get a Stellar SES but broaden the area behind the paddler, to say 45cm, this would move it into the intermediate category. Don't really need to do much else in my opinion. Trim is important and I find my SES gets onto a wave more easily than my SEL. With broadness adding to the stability and also encouraging more lift from the rear it would be an ideal downwind ski for someone of the OP size.

Redfrog - great to see someone thinking outside of the box!
I was mulling the replies you`ve had over in my head whilst outside looking at my spec ski with one of those `hammerhead` type waveys on the front. Then it struck me - it`s only in the water when you need it. So, what if you had a ski that looked like an up-side down Concord from the seat back? From behind the seat the top deck could widen into a triangle shape until it got to the tail. This section should be buoyant and should be well above the normal water line, so that beneath this the usual narrow shape is kept. Swells hitting the back end would lift up and push the ski along much more than they do at present, so theoretically, everyone could catch waves they would normally have difficulty catching, especially in small conditions.
It would have to be light and not too wide at the tail, so as not to interfere negatively when riding across big waves.
It could even be removable, a bit like the Huki Gulwing design.

Like this:

Imagine catching an edge on that!

Ah Owen... great minds stink alike!LOL I thought of that one last week. But, possibly a little flare on the aft sheer would have the desired effect? Thank you for the contribution. Good to hear from another outside the boxer!

Started playing with Kfoundry tonight. Did not come up with ultimate downwinder but, something that might be fun. Don't know if it will even work. Probably too much for me to power up with the extra beam. Tear it apart Kestrel/Robin. Maybe I will figure out something by process of elimination. Regardless of what I start with on paper, I know the finished product will be different when I get done with it!

Too much time in front of this computer but, I am enjoying the conversation and learning a lot.

Thanks

Hope this is the right file!

Hey Redfrog, won't you please email it to This email address is being protected from spambots. You need JavaScript enabled to view it.... I'm out of town on business, but tonight I'll add the file type to the allowed list...

Yikes, I'd love to see the video when a 3/4ing breaking wave comes over the back of that.... Things back at the tail are more complex than you might think at first, given the circulation within the water and all. I think back to my days in whitewater kayaks and how strangely (and unpredictably) some of the playboats with hard hull angles and flat tails behave in difficult water, compared to the traditional downriver kayak shapes. Bottom line: if you give angry water something to grab onto, it will.

Greg's idea of a subtle widening of the tail is a good one, but if you decide to put a real whale tail back there, I hope you're a good rough-water swimmer....

Interesting point Kestral. THAT is something I have yet to consider.

Looking at it this morning, looks like a better flatwater boat than anything...if that. Curious what you think of the bow sections though.

Looked at FlyingLow's design on Blue Heron [A New Surfski]. Thinking I might head in that direction. Maybe pare it down a little.

Thanks Robin. Will do. Might be good for a laugh!

Here's Redfrog's .yak design file... (also inserted into his message above.)

(.yak files may now be uploaded!)

fun to dig out old threats ...

> or get a downwinddestroyer next year from Boyan

OK, so seems silly to reply to such an old post, but, this one is near and dear to me. I grew up with Avon Redstart and Redcrest inflatables and still use a Redcrest as a tender to my 30' powerboat. Of course being the old cantankerous waterman that I am, mine is powered with oars and cervezas. Anyway, I use a one piece floor constructed from 3/8" x 4' x 8' plywood. I set my mate up with the same floor on his Redcrest powered with a 4 hp
Yamaha. He flies around the harbor at around 15mph with no wake. Pretty dam good for a boat desinged to cruise around at max speed of around 4.5 mph.
So what is the definition of planning vs displacement?
Might be some exceptions to the rules eh?

Google "planing-is-bunkum-myths-about-planing-displacement"

(I can't get the link to post)

“Planing” is Bunkum – Myths about Planing, Displacement and semi Planing

I have magic powers

But there is some argument about the article on Reddit...

"Planing is Bunkum" article is Bunkum

Cheers Robin.

Ain't it always the way. Though I'm not quite sure I buy his theory either. Bunkum all round perhaps?