Aftmast rigs???

Optimized Foil Shape

For years I've always understood that an ellipitical or parobolic shape to the head of the sail was best for limiting 'induced drag', which can represent a considerable amount of the total drag of the sailing rig. I found this forum discussion, and this referenced paper that gives the subject more detailed response:

Square-Top Mains
http://www.boatdesign.net/forums/showthread.php?t=9668

Minimum Induced Drag of Sail Rigs and Hydrofoils
http://www.tspeer.com/Planforms/Planar.htm


I've even ask Tom to reply to my possible mis-quote;
"Very interestingly the overall profile of this sail plan almost perfectly matches that of the idealized semi-ellipital/parabolic planform shape. The lift/drag factors for this optimized shape are so much superior to those for the triangular sail-shapes of the Bermuda rig."

 

Sorry Brian, my description was not good. I was referring to the camber and twist of the sail. I am wondering how important these factors are, relative to the Dynarig sail plan. How much control do you intend to have over sail shape?

 

I am a laymen...please excuse me if I am using bad terminology

 

The camber on the DynaRig can not be controlled, but was rather optimized at a 12 degree arc.

And the twist one might wish to incorporate as the impending wind varies up the height of the rig was also disregared in favor of KISS.

You could read more about the Dynarig on there site, thru google, and on these two forum discussions:

http://boatdesign.net/forums/showthread.php?t=12459

http://www.yachtforums.com/forums/perini-navi-yacht/2487-perini-navi-maltese-falcon-sailing-yacht.html

 

square rigged clippers delivered 6000 sail hp now burning half a million liter fuell for an atlantic crossing
here some more background and links http://www.windschiffe.de/theorie.html

 

Aft-mast and kite rigs seem to get more drive by giving the sail luffs clean air. Even rotating masts and wing masts do it, but with complexity. I can see kite rigs in open water, but I can't see sailing it into a slip or thru a draw bridge. I've seen aft mast designs with a bipod mast and 1 or 2 backstays, and Brian Eiland's with a single mast and 2 backstays. The simplest I've seen had a single mast, one shroud and no backstays.

Richard Atkin's comment about no mast and no stays brough it to mind. Imagine a jib and main on stays with no mast. Both would have clean air and could be roller furled easily. This was done on a multihull without a backstay by canting and raking the mast. The mast was stepped at the third point of a line at about the two-thirds of the way from stem to mainluff. The single shroud is outboard on this same line. The forestay strain is balanced by the vertical mainsail stay, which acted as the backstay. Since there is no actual backstay, the mainsail could have a broad head and a generous roach.

I'm modifying my Hobie 16 to place the mainsail on a vertical stay bridled from the shroud chainplates and the mast stepped in the same place on the cross arm. The aft shift in the center of effort may require a larger rudder, or just a shift in crew placement, or not. I'm also trying to use as many standard class parts and as few custom parts as possible. I'm still working out the numbers to see if it is even possible. If so, I hope to get the NA association to let me race against other 16's, even if my time is not eligible for trophies.
Larry Modes

 

Hi Larry, any chance one can have a peek at your new setup ?

It seems the only problem one have with the aft mast is the mast bending hence aft stays. I was actually thinking in the lines of having the forestay connect to the aft stays via a mechanical lever that would pull the aft stays as the forestay pulls, but so the aft stays have the advantage of the movement to put more pull on the forestay. Just an idea though, haven't thought it through yet.

 

Half A-frame mast

Here are beam and headon views of the half A-frame I mentioned.
There is no backstay to limit mainsail size of shape.
In a gust or as wind increases, forestay and mainstay tension automatically increase and balance each other.
The is only one shroud. Forestay and mainluff stay provide lateral support.
Sails may be roller furled.
The mainluff stay may rise vertically from or near transom.
Additional stays may be added in plane of stays for smaller sail areas. Usefull on large boats and cruisers.

On my Hobie modifications, the mast head is moved aft, so I may need to add a skeg or enlarge the rudder, or something else to move the CLR.
Larry Modes

 

now i see what you mean but how to tack with a one side shrouded lateral canted mast, downwind forges on the main sail stay may be another concern

 

Half A-frame mast

The attached file BtFm3.xls shows 3 lateral views of the half-A-frame with mainluff stay.
1) as an aft-mast rig with a mizzen-like main,
2) with a mid-boom mainsheet to the transom, and
3) similar to a sloop rig.

It should tack like a rig with a staysail and swept-back shrouds. But, with less chaffing during tacking, no running backstay, and little possibility that sail will chaffe or boom will rest against a shroud while running.

One of the criteria for the strength of the mainluff stay is the forces while running.

Larry Modes

 

WoW

I doubt that Tom has discouraged any well researched and documented rig design, even from a newbie.

New rig designers get discouraged and sometimes surly when their pet idea or claim cannot pass the reality test.

This forum is full of such ideas. Some of them get repeated fairly regularly (golf ball dimples for hulls comes up at least twice a year).

When I see a claim that seems obviously wrong, I question it. I do the math to try to prove it one way or the other. Sometimes I learn, other times I point out the flaws. Sometimes I get into heated debates with zealots ...

Anyone that is going to design a rig, would do well to read Brion and Skene before they post their latest greatest rig idea.

I was not going to respond to this post until I noticed a post from 2006 (IIRC) that your MainStay rig was described. It is now 2008 and you are still talking about it. You mention using a Hobie as a test bed, have you built and sailed the rig yet?

If you pay yourself minimum wage for all the time that has been put into the idea, you could afford a working example.

Hobie 16's are cheap, rigging wire and polytarp are cheap too ... I would guess that you could have an answer for $500-1000. That is pocket change to R&D the basic concept.

Spending the time to read a couple of rigging texts to get a grasp of the loads involved might lend some credence to the idea too ... if you can show the numbers.

If you are not comfortable with the math, think about the standard rig on your Hobie. Does the leeward shroud go slack when sailing upwind? Can you put enough tension into the rig so the leeward shroud does not go slack?

In your MainStay rig, the mainstay is the windward shroud on one tack and the leeward shroud on the other tack. Just how much tension will the rig have to be under to keep the mainstay under tension when it is on the leeward side?

Headstay tension is the least of your concerns with the rig as you have drawn it.

What you are doing is trying to set a sail on a shroud that is not under equal tension on each tack. That does not sound like such a great idea to me.

Cheers,

Randy

 

I have to smile. In a post dated March 2008, you say you are modifying your Hobie to a Mainstay rig ...

Would you be:

Title:Mainstay rig
Document Type and Number:United States Patent 6250242
Link to this page:http://www.freepatentsonline.com/6250242.html

Abstract:The mainstay rig is an improved standing rig system for wind-powered vehicles that travel on water, snow, ice, land, or rail. Mainstay rig uses a mast at a rake and uses a vertical mainstay to support mainsail luff, which gives less disturbance of airflow at mainsail luff and greater driving force. Mainstay rig can use jib-furling mechanisms for mainsail furling. Mainstay rig eliminates backstay and gives a greater choice of mainsail shape which allows more efficient energy extraction from wind because sails can be shaped with larger roach or be shaped closer to an ideal elliptical shape. Additionally, mainstay rig can use one shroud, which reduces windage.

Inventors:Modes, Larry (Houston, TX, 77062)

Application Number:09/547410
Filing Date:04/11/2000
Publication Date:06/26/2001

Patent filed for in April 2000?

And in March 2008 you are going to see if it works?

Amazing, and to think some people think that patented ideas have to work.

I notice in another thread where someone is trying to get a patent on the bumps on whale flippers. Is it time to find the absurd patent thread and start adding to it?

I have to give Mr. Modes credit. He did not come in and brag about the patent, he made it sound like a new amateur rig design. People offered comments and provided feedback ... all the time the rig is patented. Is Mr. Modes trolling for customers/investors? Nice try.

 

Mast Compression Spreadsheet

RHough
Your condescending attitude is inappropriate in this forum.

The name of my patent is my screen name. Perhaps its other meaning was lost. But having a patent does not mean it is a viable idea, only that is it's new and original, and not previously patented.

So don’t do the vector diagrams. Here is a 2D trigonometric comparison of the Bermuda, mainluff stay and aft-mast rigs.

It is set up to have the same forestay sag, the same jib halyard tension, the same main halyard tension (it can be different than the jib) on all three rigs. It compares the 3 rigs with the same sailplan, on one boat, on your boat, or on any boat you choose. Enter data in the 6 boxes: I, J, L, forestay tension, and halyard tensions. The SS does the rest. The cells are not protected, so you can mess it up quick if you do anything else. The formulas are in the cell, for anyone to check their accuracy.

There are numerous aft-mast rigs each with a different mast step. For this comparison, the step is located so the mast bisects the main triangle. Likewise, the mast of the mainluff bisects the foretriangle.

The numbers I entered show an increase of less than 10% in compressive mast loads in the mainluff stay rig. It is the aft-mast (with the same sailplan) that has a 2x increase. With your help I would like to use loads that have some semblance of reality to them, and to expand the analysis to include shroud and sail loads.

Are you are willing to continue to dialog with a sailor who thinks outside the box, but who holds a patent?
Larry Modes

 

One of these boats is next door!

I am so pleased to have stumbled across this thread. While it may look like I'm a first time poster, I believe (but I can't say for certain because my Alzheimer's disease is so bad!) that I have posted previously as AndrewDavis or AndyDavis or ADavis...I'm the same guy, I just keep forgetting my user name and password.

I am a naval architect in Richmond, California, and I have started to keep a blog:
http://www.tallshipdesigner.blogspot.com/

Essentially, I just rant about what I had for breakfast or what they're doing in the yard, and what does any of this have to do with this thread? Well, my last entry was about just this subject...one of these aft mast things is next door to my office and, in my ignorance, I thought it just had to be unique. But lo, I see there has been a whole world of energy devoted to this rig.

In the blog I pleaded for information about the vessel. Does anyone know it? Could one of you knowledgeable (and honorable) persons look at the pfotos and post anything you may know about the boat. Or you can post to the blog (even if you don't know the boat, feel free to post just to say what a waste of electrons the blog is!).

Hey, keep up the good work. I'm going to stayed tuned to this forum (and try to remember my user name).

 

Hi andrew, and do what I do, have the browser remember the password & username stuff and also set up the site in your favourites, then it is just a couple of clicks & the first letter of the user name (for you "A") and click away. All my regular sites have the same username and password...