New Posts New Posts RSS Feed: dinghy design questions
  FAQ FAQ  Forum Search   Register Register  Login Login

dinghy design questions

 Post Reply Post Reply Page  <1 23456 7>
Author
gbrspratt View Drop Down
Posting king
Posting king


Joined: 26 Sep 11
Location: Felixstowe
Online Status: Offline
Posts: 170
Post Options Post Options   Quote gbrspratt Quote  Post ReplyReply Direct Link To This Post Topic: dinghy design questions
    Posted: 09 Oct 14 at 7:06pm
You brought the plusplus Jim? What was it like? Does it need the modifications talked about on the website?

So for waterline length is key for upwind does but does hull shape effect pointing? And how?

What hull shape is fast down wind? If we say in ten knots of breeze.
Back to Top
getafix View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 28 Mar 06
Location: United Kingdom
Online Status: Offline
Posts: 2143
Post Options Post Options   Quote getafix Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 7:10pm
Hull shapes are out there already IMO, ok I'm sure refinement with materials and weight distribution could add a few % here and there but the big gains are to be had with the foils above and below the "waterline" as ably demonstrated recently in the AC and with Moths... Can't wait for the "trickle down" as I can't afford one of those foiling cats .... yet!

Edited by getafix - 09 Oct 14 at 7:11pm
Back to Top
Medway Maniac View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 13 May 05
Location: United Kingdom
Online Status: Offline
Posts: 2788
Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 7:50pm
Originally posted by gbrspratt


So for waterline length is key for upwind does but does hull shape effect pointing? And how?
People like to say it does, but in reality the lift provided by the hull is tiny compared to that generated by the foils, which moreover generate lift with a lot less additional drag than the hull, which when you think about it is a very low aspect-ratio foil!

As an example, I'd cite the Fireball - no bow to dig in but goes to windward like stink.  Good foils and a very well-developed rig.  As getafix says, the 'foils' above and below the waterline are what count.
Back to Top
Jim Mitch View Drop Down
Newbie
Newbie
Avatar

Joined: 04 Jun 07
Location: United Kingdom
Online Status: Offline
Posts: 7
Post Options Post Options   Quote Jim Mitch Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 8:12pm
I always thought Blue Arrow looked interesting. The ultimate "long and thin" design? Given the advances in foil and wing technology, would it work better today?

http://www.americas-cup-history.at/english/blue.htm
Back to Top
JimC View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 17 May 04
Location: United Kingdom
Online Status: Offline
Posts: 6662
Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 8:46pm
Originally posted by gbrspratt

You brought the plusplus Jim? What was it like? Does it need the modifications talked about on the website?

Well, I would say so [grin]

Originally posted by gbrspratt

So for waterline length is key for upwind does but does hull shape effect pointing? And how?


Not really in the sense of affecting leeway. Foils are so much more powerful and efficient than the hull. But indirectly, well hull shape affects drag, and drag affects pointing ability.

Originally posted by gbrspratt

What hull shape is fast down wind? If we say in ten knots of breeze.

Very hard to make hard or fast rules. But all else being equal a long boat will still be better than a short one unless you can get into a real planing mode with very little wave generation, and there are precious few dinghies that can manage that.

Originally posted by Jim Mitch

I always thought Blue Arrow looked interesting.

Certainly interesting. The thing about it though was that it was primarily a rule beating boat but most of the rules it had to beat were unwritten. They had to work up a boat that would meet the Deed of Gift rules (not too difficult), be faster than the Yanks catamaran (pretty challenging) but, when the principle dimensions were put on paper, sight unseenm make the Kiwis and Yanks think it couldn't possibly be faster than the big Kiwi monohull so they'd be allowed to play (very difficult and in the event they failed at that). So it wasn't necessarily the boat they'd have built for maximum speed round a track.

My understanding was that they were not allowed to play, and so with the last of the money they went sailing faster and faster in more and more wind, and then one day... bang.

Edited by JimC - 09 Oct 14 at 8:59pm
Back to Top
Rupert View Drop Down
Really should get out more
Really should get out more


Joined: 11 Aug 04
Location: Whitefriars sc
Online Status: Offline
Posts: 8956
Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 9:38pm
John Claridge was involved with Blue Arrow, as a sailor of narrow Moths. He had some interesting tales to tell. Surprised the idea hasn't been revisited without the rules.
Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
Back to Top
andymck View Drop Down
Far too distracted from work
Far too distracted from work


Joined: 15 Dec 06
Location: Stamford
Online Status: Offline
Posts: 397
Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 10:31pm
[QUOTE=gbrspratt]

So for waterline length is key for upwind does but does hull shape effect pointing? And how?

Scam

Hull shape can be changed to affect pointing ability. N12 and Merlin designs have since the 70's had fine deep bows as they improve upwind performance by giving lift off the bow. The DCB was a big move away from this, the winged rudder helps overcome the need along with the trim tab. This of course is used to overcome other constraints, in boats that are designed to plane downwind, and go at displacement speeds upwind. Of course for a displacement boat I would agree with a u shaped cross section with a banana rocker like the americas cup boats, or look at the modern radio controlled hulls like the 1m britpop. These attempt to reduce wetted area in light winds then go to maximum waterline once healed like the old J's and metre class boats.

Going downwind designs over the last 15 years have also changed. In the N12 wide flat sterns had already been tucked in with the planing surface sometimes more forward. The winged rudders have changed the trim angle again, with the boats planing less bow up. The stern waves have as a result got smaller. It feels more like the way a motor boat planes. Of course the skiffs are different, so again depends on power to weight ratio.

Andy
Andy Mck
Back to Top
gbrspratt View Drop Down
Posting king
Posting king


Joined: 26 Sep 11
Location: Felixstowe
Online Status: Offline
Posts: 170
Post Options Post Options   Quote gbrspratt Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 10:35pm
Originally posted by andymck



Scam




Its not scam. Its Matt. But close! Just trying to get my head around a few things.
Back to Top
JimC View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 17 May 04
Location: United Kingdom
Online Status: Offline
Posts: 6662
Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 10:38pm
Originally posted by andymck

...as they improve upwind performance by giving lift off the bow.

Has to be a myth. There's not a chance that the lift/drag you'd get off the hull could contribute anything useful compared to what the foils are doing. The reduced wave impact of a fine deep bow might be another matter. Just because something works doesn't mean people know *why* it works.
Back to Top
andymck View Drop Down
Far too distracted from work
Far too distracted from work


Joined: 15 Dec 06
Location: Stamford
Online Status: Offline
Posts: 397
Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 14 at 11:12pm
Sorry matt
Andy Mck
Back to Top
 Post Reply Post Reply Page  <1 23456 7>

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.665y
Copyright ©2001-2010 Web Wiz
Change your personal settings, or read our privacy policy