Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Design > Multihulls
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read Most Recent Posts Gallery Images Search

Reply
 
Thread Tools Search this Thread Display Modes
  #151  
Old 03-24-2012, 03:38 PM
garydierking garydierking is offline
Senior Member
 
Join Date: Sep 2004
Rep: 174 Posts: 107
Location: New Zealand
Here's some real world experience with an Oceanic lateen sail used on Pacific proas. These are sometimes called crab claws.
http://homepages.paradise.net.nz/garyd/walap.html
Reply With Quote


  #152  
Old 03-24-2012, 04:37 PM
rapscallion rapscallion is offline
Senior Member
 
Join Date: Oct 2006
Rep: 132 Posts: 455
Location: Wisconsin
Quote:
Originally Posted by DIY Tri Guy View Post
The sail on my little boat is definitely not a crabclaw, though it bears a slight similarity to one. First, my sail has battens -- radial ones. Crab claws have no battens. Second, my sail has a pronounced roach. Crab claws don't have any roach, or are cut hollow.
My sail is what I have come to call a "fan sail" -- the general shape being inspired by various Asian designs, and the construction loosely inspired by the batwing and sliding Gunter sail.
In reality, it works perfectly "as is." If I were having a pro make one (and I probably will be), I would not change the cut one bit. I gave it a bit of luff curve and a bit less foot curve, trying to anticipate how much the C/F mast and the alum. boom would bend. Amazingly, I got it right on the first try. Hey, sometimes you just get lucky!
Could be your design performs better than a traditional crab claw! I figured you might be interested in the wind tunnel research on crab claw sails, it may help explain the performance you are seeing.

There is a lot of interest in low aspect ratio foils in the aerospace industry. The facetmobile is a nice example of this.
__________________
http://janetcg32.blogspot.com
Reply With Quote
  #153  
Old 03-24-2012, 04:56 PM
DIY Tri Guy DIY Tri Guy is offline
Junior Member
 
Join Date: Jan 2012
Rep: 90 Posts: 68
Location: FLORIDA, USA
I do have one of Marchaj's books -- Sail Performance, I think. It's a bit over my head, but I really enjoy reading it. Brilliant guy.
I wish there were some way to objectively quantify the performance of my little "fansail," but for now all I have is my seat-of-the-pants experience.
Does it outperform a similar sized crab claw? I'll probably never know. But I'm willing to bet that it sails closer to the wind.
- Frank
Reply With Quote
  #154  
Old 03-24-2012, 05:07 PM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 459 Posts: 1,459
Location: Ft. Worth, Tx, USA
Quote:
Originally Posted by garydierking View Post
Here's some real world experience with an Oceanic lateen sail used on Pacific proas. These are sometimes called crab claws.
http://homepages.paradise.net.nz/garyd/walap.html
Gary,

Thanks for the article, it is very interesting detail about the "radical" hull. Pity there was no description of the rig - area, height, length of the "booms" or "yards" (I don't know the proper term).

Was the hull representative of a working boat from the Marshals? Or was this designed as a racer?
Reply With Quote
  #155  
Old 03-24-2012, 06:10 PM
garydierking garydierking is offline
Senior Member
 
Join Date: Sep 2004
Rep: 174 Posts: 107
Location: New Zealand
This was an Enewetak design and was a little different from most Marshallese models. The hull was very narrow and it carried less sail in proportion to its length than most.
I have a 150 page PDF (6 Megs) I can send you describing the design and construction.

gary.dierking (at) gmail.com


Quote:
Originally Posted by upchurchmr View Post
Gary,

Thanks for the article, it is very interesting detail about the "radical" hull. Pity there was no description of the rig - area, height, length of the "booms" or "yards" (I don't know the proper term).

Was the hull representative of a working boat from the Marshals? Or was this designed as a racer?
Reply With Quote
  #156  
Old 03-24-2012, 06:14 PM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 459 Posts: 1,459
Location: Ft. Worth, Tx, USA
Gary,

Thanks for the offer. Please send to upchurchmr@yahoo.com.

I guess I didn't read well enough about this being Enewetakest.

Marc
Reply With Quote
  #157  
Old 03-25-2012, 10:35 AM
rapscallion rapscallion is offline
Senior Member
 
Join Date: Oct 2006
Rep: 132 Posts: 455
Location: Wisconsin
Quote:
Originally Posted by DIY Tri Guy View Post
I do have one of Marchaj's books -- Sail Performance, I think. It's a bit over my head, but I really enjoy reading it. Brilliant guy.
I wish there were some way to objectively quantify the performance of my little "fansail," but for now all I have is my seat-of-the-pants experience.
Does it outperform a similar sized crab claw? I'll probably never know. But I'm willing to bet that it sails closer to the wind.
- Frank
I have been reading a lot about the low aspect ratio foil airplanes recently, because it seems all of the newest fighter planes, stealth planes and stealth bombers are moving in that direction for various reasons...

One of the things I read was the large angle of attack the low aspect foils can create lift with out stalling, it is an interesting feature. Its true a high aspect foil has a better lift/drag ratio, but maybe at a certain scale (smaller boats and planes) the angle of attack advantage outweighs the L/D loss in terms of overall performance, and especially upwind performance.

At any rate I love your design! Even if a traditional rig would perform better, I would prefer your configuration because of it's ease of setup and tear down. A version of your rig would be great on an everglades challenge boat.

Keep up the good work Frank! I enjoy reading about your experiments, thanks for sharing.
__________________
http://janetcg32.blogspot.com
Reply With Quote
  #158  
Old 03-25-2012, 01:38 PM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 459 Posts: 1,459
Location: Ft. Worth, Tx, USA
Rapscillion,

Low aspect foils on a jet are only one part of what makes the high angle of attack work. Just fwd of the intersection of the wing and the fuselage is extremely critical to formation of a vortex that spreads out over the wing. For this you need a lot of power (jet engine).

Sailboats have neither the geometry in front of the wing, nor the outside power to get what you are talking about. Poor application to a sailboat.

B2 and B1 bombers have high aspect wings.

But I still like the fan sail, except for adding more area in light wind.
Reply With Quote
  #159  
Old 03-25-2012, 02:54 PM
DIY Tri Guy DIY Tri Guy is offline
Junior Member
 
Join Date: Jan 2012
Rep: 90 Posts: 68
Location: FLORIDA, USA
Just took the folder-boat out today for 3 hours. First really good shakedown with the new hull. Wind, weather, and water were all just perfect. I don't rate many sailing days a "10," but this was one of them. Cloudless sky, well, you know...
The boat handles and rides like a dream with the new hull, and is really quick, but I found some unexpected weather helm on the way back. Not sure how I'll tackle that...
Overall, I'd say that 90 sq ft of sail is just about perfect for this boat IF the sail is really optimized -- which this fan sail seems to be. I'd swear it pulls better on all points of sail than my 102 sq ft leg-o-mutton.
This hull also comes about on a dime and jibes with zero drama. Once I get that weather helm straightened out, it might just be the perfect little tri!
- Frank
Reply With Quote
  #160  
Old 03-25-2012, 02:55 PM
DIY Tri Guy DIY Tri Guy is offline
Junior Member
 
Join Date: Jan 2012
Rep: 90 Posts: 68
Location: FLORIDA, USA
PS - and as I may have noted in an earlier post, both the folding aka-amas and the lowerable sail rig were inspired by the EC.
Cheers - Frank
Reply With Quote
  #161  
Old 03-25-2012, 03:18 PM
rapscallion rapscallion is offline
Senior Member
 
Join Date: Oct 2006
Rep: 132 Posts: 455
Location: Wisconsin
Quote:
Originally Posted by upchurchmr View Post
Rapscillion,

Low aspect foils on a jet are only one part of what makes the high angle of attack work. Just fwd of the intersection of the wing and the fuselage is extremely critical to formation of a vortex that spreads out over the wing. For this you need a lot of power (jet engine).

Sailboats have neither the geometry in front of the wing, nor the outside power to get what you are talking about. Poor application to a sailboat.

B2 and B1 bombers have high aspect wings.

But I still like the fan sail, except for adding more
area in light wind.
Nothing to despute there, I'm interested in the facetmobile and the similarity of that design to the new experimental low aspect ratio low cost (if there is such a thing) stealth fighters and bombers...

The stall angle at low speeds of the facetmobile is well within the apparrent wind speeds experienced by a multihull. You could be right though, maybe there is nothing there to gleen that would apply..
__________________
http://janetcg32.blogspot.com
Reply With Quote
  #162  
Old 03-25-2012, 03:35 PM
DIY Tri Guy DIY Tri Guy is offline
Junior Member
 
Join Date: Jan 2012
Rep: 90 Posts: 68
Location: FLORIDA, USA
What, if I may ask, is the facetmobile?
- Frank
Reply With Quote
  #163  
Old 03-25-2012, 03:52 PM
rapscallion rapscallion is offline
Senior Member
 
Join Date: Oct 2006
Rep: 132 Posts: 455
Location: Wisconsin
Quote:
Originally Posted by DIY Tri Guy View Post
What, if I may ask, is the facetmobile?
- Frank
http://www.facetmobile.com/

It was rightly pointed out that jets and sailboats are very different animals. What I find interesting is the efficiency of this particular low aspect ratio airplane, as well as the low speed stall angle of plane. I saw the fx-4 when it was in Oshkosh.. and I was amazed how much it reminded me of the first generation stealth fighter. But what is even more interesting is the current experimental stealth planes follow the facet construction approach (cost savings) and are low aspect ratio wing forms.
__________________
http://janetcg32.blogspot.com
Reply With Quote
  #164  
Old 03-25-2012, 04:04 PM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 459 Posts: 1,459
Location: Ft. Worth, Tx, USA
Rapscallion,

Thanks for the reference I had not seen this. He still has power to keep it flying at high angle of attack. High AOA also "always" means high drag. perhaps the low aspect would work for downwind - but we already know that. See Marchaj.

What "current experimental stealth planes" are you talking about?
Reply With Quote


  #165  
Old 03-25-2012, 04:50 PM
DIY Tri Guy DIY Tri Guy is offline
Junior Member
 
Join Date: Jan 2012
Rep: 90 Posts: 68
Location: FLORIDA, USA
Wow, what a totally cool airplane! I'm totally impressed!
I'm not sure that anything from that plane translates meaningfully into anything I can do with a sail, but it's sure an amazing piece of technology in its own right.
In any case, low aspect seems to work great downwind. And the small upwind advantage of high aspect sails evaporates very quickly and even becomes a liability as you turn farther away from the wind.
- Frank
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes



All times are GMT -4. The time now is 09:49 AM.


Powered by: vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2014 Boat Design Net