New Posts New Posts RSS Feed: New boat for the Americas
  FAQ FAQ  Forum Search   Register Register  Login Login

New boat for the Americas
 Post Reply Post Reply Page  <1 234
Author
  Share Topic Share Topic  Topic Search Topic Search  Topic Options Topic Options
Granite View Drop Down
Far too distracted from work
Far too distracted from work
Avatar

Joined: 12 May 04
Location: Scotland
Online Status: Offline
Posts: 476 		Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Topic: New boat for the Americas
    Posted: 04 Jul 05 at 1:20pm
Originally posted by SARSIPPIUS

Originally posted by Granite

Have a look at some of the video of 12foot skiffs in windy wether when they have short masts and long poles and you will see this effect.

12ft skiffs dont have short masts, they are 30ft long from the keel, compare that to an actual waterline length of 12 foot, that rather large.
I hope in your viewing of the 12 ft videos you notice that the skipper and crew are right down the back of the boat? Maybe that mass creates a moment around the center of effort?  its not all kite that dose everything!

The No1 rig may be 30 foot but I would imagine the No 4 rig is slightly shorter The poles may also be shorter but probably not to the same extent.

I am not saying the lift from the kite is huge but I think that there is some lifting effect.

The difference between a windy white sail reach and one with the kite up is significant in where you need to be in the boat and how much the bow goes down.

to me that says that the center of effort in the rig has moved and that movement is pushing the bow down less than without the kite.



Edited by Granite
If it doesn't break it's too heavy; if it does it wasn't built right
Back to Top
redback View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 16 Mar 04
Location: Tunbridge Wells
Online Status: Offline
Posts: 1502 		Post Options Post Options   Quote redback Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jul 05 at 10:57pm
I'm not sure if its lift from the kite or the top of the main being relatively eased but the 4000 definitely sails more bows up when the kite is up, but then the 4000 does have a very long pole so only a small upward force has a large lever.
Back to Top
Blobby View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 07 May 04
Location: Australia
Online Status: Offline
Posts: 779 		Post Options Post Options   Quote Blobby Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 05 at 2:02am

12 ft skiff masts - lets not argue big fish here.

From C-tech website:

No. 1 Mast (7.85 m; ID 63mm)
No. 2 Mast (6.90 m; ID 58mm)
No. 3 Mast (6.20 m; ID 56mm)

No. 1 Prod (up to 3.6 meters; 5 spreaders)
No. 2 Prod (up to 3.0 meters; 3 spreaders)
No. 3 Prod (up to 2.5 meters; 3 spreaders)

By my reckoning to changes in length are pretty much proportional so the angles don't change much.

From all the 12ft skiff video clips I have watched it seems that as the kite is sheeted on, the boat accelerates and the bow goes down.  The bow then bounces up off a wave.  Once the bow is up at 30 degrees to the horizontal and the transom is dropping out the front of the wave, the back end goes down and the bow stays up.

So it would appear to me that - when the boat is trimmed approximately level fore and aft, then the kite pulls the bow forward and down.  Once you hit a wave and the bow points skywards, all the force vectors change and then the kite can be perfectly capable of lifting the boat into the air!

I think Mr. Redback may have a very valid point though - when you are two sail reaching the drive is coming from the main and jib - very much forwards with little in the upward direction.  Once the kite is up and driving, the force from the main and jib is greatly diminished so for the same heeling force, you get greater forward drive but also a greater lift at the front of the boat. 

Based on this, I think you could conclude that the kite normally drives the bow down - but to a lesser extent than when sailing under main and jib alone.  The kite is capable of lifting the boat when the boat is trimmed massively bow up.
Back to Top
SARSIPPIUS View Drop Down
Newbie
Newbie


Joined: 27 Jun 05
Location: Australia
Online Status: Offline
Posts: 6 		Post Options Post Options   Quote SARSIPPIUS Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 05 at 2:31am
Originally posted by Blobby

12 ft From all the 12ft skiff video clips I have watched it seems that as the kite is sheeted on, the boat accelerates and the bow goes down. 

From my time SAILING 12ft skiffs, when you are hit with a gust you bare away and go with it, the bow dosent get dragged up or down.  This is on flat water tho.  When on the harbour there are, wait for it waves!!! and funnily enough they have the tendency to make the boats hobby horse (leap out of the water).  Thats right, being only 12 feet long even small waves mave a big impact on the stability fore aft.  The sails are only half the component of all the force vectors involved.  You guys are neglecting the other half, the boat and the live ballast that is aboard it.  Its not having big rigs that makes 12's great boats, its the guys sailing them!
Back to Top
Blobby View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 07 May 04
Location: Australia
Online Status: Offline
Posts: 779 		Post Options Post Options   Quote Blobby Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 05 at 6:12am
so you are arguing that real experience is a substitute for bar stool bull??  Why should we let reality & the facts get in the way of an entirely pointless argument that could rage for days??
Back to Top
Granite View Drop Down
Far too distracted from work
Far too distracted from work
Avatar

Joined: 12 May 04
Location: Scotland
Online Status: Offline
Posts: 476 		Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 05 at 8:58am

Originally posted by Blobby

so you are arguing that real experience is a substitute for bar stool bull??  Why should we let reality & the facts get in the way of an entirely pointless argument that could rage for days??

I agree I thought arguments raging for days based on false logic and wild statements were the whole point of forums like this?

If it doesn't break it's too heavy; if it does it wasn't built right
Back to Top
 Post Reply Post Reply Page  <1 234

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