Deck sweeping sails

[usa2]

im not sure if you exactly understand what im attempting to state here..

I guess the thing to point out,if necessary, is that the flow over the windward edge of the hull when it is heeled going upwind does not blanket the lower portion of the sail; on the contrary it forms a vortex which interacts positively with the flow at the bottom of the sail.
Without spending a lot of time researching exact quotes the best reference that comes to mind is Marchaj 's "Sail Performance" at the bottom of page 184..

[CT 249]

I thought about doing the same thing in one of my classes, but some leading skiff designers who are also involved in rigs said it's not worth it, compared to shoving the available sail area up high.

It's been tried many, many times before. Miss Nylex, the C Class in 1975 IIRC, and some Nacras I think. Plus some other C classers; Helios? Frank Bethwaite noted the movement of spray over a Tasar in Australian Sailing magazine about '81 and queried whether the deck sweeper was worth it; the spray indicated very little flow over the deck but of course that was ignoring the end plate effect. 18' skiffs have moved to higher booms and become faster. Windsurfers talk a lot about "closing the gap", but the rig and hull configuration means that many other effects occur when you close the gap and therefore it's hard to see how much effect the end plate has.

The endplate effect seems to come and go. The Dashews like it, but the speed increase they talk about is totally out of kilter with the proven impact (or lack of it) in other classes and if the Dashew boats are such great performers, they wouldn't be slow according to their PHRF ratings. Certainly in boards we can easily futz around with the height of the foot off the deck and while it's perhaps important in terms of gaining a few boatlengths, it doesn't seem all-important in terms of being a breakthrough.

249, seems to me that nobody in this thread has claimed a deck sweeping sail is any form of breakthru only as you yourself mentioned:that "it might be worth a few boat lengths" which on a race course, of course, could be a solid margin of victory.
Seems appropriate to consider a decksweeper or any other detailing of a rig in the same or similar manner to be a small but potentially important contribution to the overall aerodynamic effectiveness of a sailboat rig.
Whether or not it is beneficial in a specific class depends on what the tradeoffs are....

[CT 249]

Re "249, seems to me that nobody in this thread has claimed a deck sweeping sail is any form of breakthru"

Well, the Dashew link you posted makes some pretty damn big claims; "This is five to seven degrees closer than before, at a speed improvement of around two percent. That is a huge difference."....."more increase in performance for less cost than anything else you can do.".... "a good seal was worth at least five degrees in tacking angle with no loss in boat speed."......"huge" increases in speed sound a bit like a breakthrough considering how a few boatlengths can, as you say, change a race. There were also other claims for 5% more efficiency which may well translate into a "breakthrough".

[yokebutt]

Hey hey hey Chris, you're getting you're knickers in a twist again, what kind of an Australian are you?

Yokebutt.

[CT 249]

Aaaahhh, yeah mate, ya may well be only too right, I admit I get my knickers in a twist faster than a goanna going up a gum tree. Only on the web, though. :-)

[yokebutt]

Well, Chris, if you and your buddy Lorsail doesn't soften up soon, I'll tow you both behind my ute on a rope down a gravel-road 'til you do.

That's not a threat, that's a promise.

Yokebutt.

CT, what a load --whups- I better soften up a bit so I don't get to find out what a ute is...