# GPS and VMG



## TSOJOURNER (Dec 16, 1999)

One of our sailing club Bards presented a very detailed description of generating and using Polar Diagrams to improve preformance on the race course. I had put together a similar presentation for our local Multihull association on how to use your inexpensive GPS to maximize windward and leeward performance without needing to generate Polar Diagrams. It won't necessarily help you win races but it is a very simple way to improve your upwind and down wind speed. A complete description is on my web site: www . wingsailor . com by clicking on the "VMG & GPS" tab.


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## sailingdog (Mar 19, 2006)

Wingsailor-

What boat do you sail??? Also, recommend you read the POST in my signature to help you get more out of your time here. Also, believe a fellow Telstar owner sails out of Punta Gorda, do you know him??

Here's your link: *CLICK HERE*


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## TSOJOURNER (Dec 16, 1999)

*Ocean Catamaran*

Dogsailor,

I sail an Ocean Catamaran 49 out of Charlotte Harbor SW Florida. The web site containing the VMG GPS page has a lot of other information on it including some of the wing sail stuff I am working on.

The description of the set-up and use of an inexpensive GPS to generate a consistant windward or leeward speed monitoring VMG anywhere on a race course seems to be easy to understand and use but I haven't yet talked to one of our racers that has tried it since I made the presentation several months ago. Hard to believe racers are not interested in improving upwind and downwind performance.


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## tommays (Sep 9, 2008)

In this area Polars are very common and used all the time even the 1970 C&C 35 i race on has a set that was made for it when the original owner put on a new keel and light weight mast


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## sailingdog (Mar 19, 2006)

I don't race, so it isn't of much interest to me. 

As for wing sails, I'm not a big fan, as they're a considerable hazard on most cruising boats, since they create a sail that is not reefable or removable.


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## paulk (Jun 2, 2000)

VMG is certainly of interest to racers. If they have GPS sailing units, they're likely to get them with the VMG software programming already installed.


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## SEMIJim (Jun 9, 2007)

paulk said:


> VMG is certainly of interest to racers. If they have GPS sailing units, they're likely to get them with the VMG software programming already installed.


Yes, except VMG to the mark really doesn't give you what you want. The point is to sail to weather at best VMG, which is what wingsailor's method gives you. It's kind of like polars for free, with the advantage of auto-adjust for current conditions. All is explained in wingsailor's article.

Jim


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## tommays (Sep 9, 2008)

I have a limited abilty to express my thoughts in text  

I dont do a lot of sailing outside of racing and feel like we have allways used the GPS VMG in combo with the polars

The polars exist to tell us if we are trimed well enough to hit a target speed in a known wind speed and course 

One of the problems is we offen have to cover other boats as staying ahead of them is how we win, this is not allways the best VMG 

In are shorter races the legs are offen only 1 mile and there is really not any time to even use the GPS when your doing a short race with 40 boats in 7 divisions

In longer races the Long Island Sound current chart becomes a key tool as to were we decide to go (the short ones also as we do get a wicked current inside the harbor also)

And it has been proven that the odds on wind shifts favor sticking to the middle of the course unless there is something way out of normal 

I see what else come to mind as i ponder this complex stuff 

I will say that on Zooom(35') we win a whole lot of races and only use the GPS here and there to get fixes and kind of wing it based on what the GUT says to do


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## TSOJOURNER (Dec 16, 1999)

*VMG & Wings*

sailingdog,

Your statement regarding wing sails seemed a little unusual for a guy with a trimaran for an avitar. Don't you know those things break up and flip over [;^) ?

I came over to the "Dark Side" 20 years ago because, after doing a lot of research, reading designers books, sailing with friends with large cruising/racing catamarans and several charters on Multihulls, the design concept and life style just made more sense. A lot of my friends who sail lead mines, never set foot on a catamaran and have little understanding of the world of multihulls always brought capsizing up early in any conversation about sailing. My usual response is "upside down on top of the water beats right side up on the bottom". As I am about to start the last phase in this wing thing (building time and money involved) I would be interested in the basis of your comment:

"As for wing sails, I'm not a big fan,
as they're a considerable hazard
on most cruising boats, since they create
a sail that is not reefable or removable."

Have you sailed on any vessel using a wing or Aerorig or large cord wing mast and if so what was the problem/hazard? Have you seen any reports of problems/hazards caused by wing sails on cruising boats? Also, is there a forum or thread somewhere on this site where wing sails are discussed?

Wingsailor


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## sailingdog (Mar 19, 2006)

Basically, if you get caught in a heavy storm with very strong winds, the wing mast becomes a serious issue. 

I have been on a trimaran that had a wing mast that did become a problem... and the problem was solved when the wing mast broke and fell overboard... causing other problems. Generally, cruising boats shouldn't have a sail that they can't remove. A wing mast is effectively a sail that can't be removed. 

If you're going to use a wing mast, it would probably be wise to make it less than 10% of the total main sail area in size. Then you could probably get away using it as a storm sail.  

The reason I doubt you'll find much on using a wing mast or wing sail is that they're very limited purpose and fairly rare, mainly due to the expense of building them and maintaining them and the dangers involved in sailing a boat with one. 

On one of the video websites, probably Youtube.com, there was a video of a wingsail shredding itself during a speed record attempt... really not pretty to watch.


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## TSOJOURNER (Dec 16, 1999)

sailingdog,

A distinction needs to be made between wings/foils/sails in the air that are restricted in rotation (Rotating tear drop masts, rotating wing masts, aerorigs - the sort of rigs I think you are referring to) and freely rotating rigid wing sails (360 degree full rotation weather vain wings). My Ocean Cat has a (hydraulically controlled) aluminum tear drop rotating wing mast. The cord is a little over a foot. Most large ocean racing multihulls have "rotating" wing masts with a very large cord. They do make good storm "sails" but have standing rigging and "rotate" 45 degrees or so side to side. They also "hunt" when at anchor. Soft sails on these rigs would need to be reefed or taken down. All these rigs have excessive windage because of stays, halyards and foller furled sails. I am talking about the fully (360 degree) rotating wing sail such as the one developed/built by Walker Wing Sails (only a much simpler version). Walker crossed the North Atlantic and got a glancing blow from a hurricane, no problems, nothing fell down. The windage is less on a feathered wing than on a similar vessel with a stayed mast. Pictures of these wings are on my web site. The problem I am having is that most rigid wings are build for very high performance speed record attempt machines (that usually crash because water over a foil moving at 50K tends to vaporize and they loose traction, spin out or go airborn) and few cruising boats have been fitted with them. I feel like I am a guy looking at multihulls in the 1960s with all the lead mine "conventional wisdom" sailors saying they are dangerous, they won't work, they will flip and they will break up. The early multihulls had their share of problems but there are a lot of us sailing them now.
Aside from the "Little America's Cup" sailed by catamarans with restricted rotation wings there is not much action for these devices in racing. This is a racing thread so a discussion of wings should probably go to another Forum. Any suggestions regarding where to look (what forum) for help with this project?
Wingsailor


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## sailingdog (Mar 19, 2006)

The Boatdesign forums would be a good starting place.


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## llissenden (Aug 30, 2001)

Polars are great for target speeds in the absence of wind shifts and wind speed changes. GPS will tell you speed over ground and course made good taking into account wind and current and your boats' movement across the face of the earth - not just through the water. We always punch in the leward turning mark at the start (usually the pin, sometimes a separate mark just upwind) to look at VMG-to-the-mark coming back downwind. At the top mark, we punch in again if doing multiple laps. VMG readings tell you not just best angles but can tell you when to tack/jibe when the number starts to drop. It's a great racing tool! Covering competition must always be weighed, especially in onedesign or bigger multiple race regattas..but being on the right tack and at the right angle will get you around the course faster in most cases.


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## sasbibic (Nov 30, 2010)

*Personal Sail Computer*

Small Software can give You helping hand with VMG, sailing speed towards target point, polar diagrams, speed diagrams and many more. Personal Sail Computer is FREE with statistic information for last 30 minutes.


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