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Alan Stewart

Everglades Challenge 2019

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We were only able to use the spinnaker on the last bit of the run around the everglades when the wind turned more west. We cant use it dead down wind being an assymetrical spinnaker but it gained us 1-1.5 knots vmg downwind in about 10 knots of breeze i would guess. So maybe 5.5 knots wing on wing vs 6-6.5 vmg with it sailing maybe 20 ir 25 deg off ddw. You lose speed in the gybes though and the Highlander would catch back up during gybes since we were being very careful not too flip or get lines hung up. As the wind picked up and the boat jumped up on plane with the spinnaker the gains are substantially more i think we say 9.5knots a few times when we let her heat up but it was speed with little vmg gain.  9213.thumb.jpeg.9f5d97d33a7655ae08be4cca9a120635.jpeg

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VMG. Velocity made good. How fast you are getting towards your desired destination. Say you are doing 6 knots tacking upwind towards a destination. Your VMG would be far less. The higher you point the better it would be, but if you point so high your boat slows, your VMG suffers. In this case I believe downwind they couldn't go directly at the destination and gybing was costing them time.

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We were glad to have them and they defenitely made a difference. For cruising at this point i dont consider the added complication to be worth it but if you are a tinkerer its a fun project. They do make rigging a bit more complicated which goes very much against the grain of the simple cat ketch rig in some respects. Extra topping lifts for the front are needed and the snotter is a bit different. Overall it probably added 4lbs to the booms in added material of the booms and extra blocks and lines. 

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Yes, VMG means velocity made good, but good as in towards the wind.  VMC or velocity made course is the rate at which you are approaching your destination.  And closely related, and significant in giving meaning to the other terms is TWA, towards wind angle.  For any given boat their is an optimum TWA for getting the highest VMG possible.  This is the angle you use sailing to weather.

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18 hours ago, Hirilonde said:

Yes, VMG means velocity made good, but good as in towards the wind.  VMC or velocity made course is the rate at which you are approaching your destination.  And closely related, and significant in giving meaning to the other terms is TWA, towards wind angle.  For any given boat their is an optimum TWA for getting the highest VMG possible.  This is the angle you use sailing to weather.

 

Technically you are correct. Unfortunately, on modern (at least on two my Garmin) GPS if you pick a waypoint and then select VMG it gives you the speed to the mark with no regard to wind direction. Ironically, most of my testing has been to an upwind mark when beating, but it's also useful downwind.

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Interesting how you guys refer to it as VMG instead of what most Mariners at least on the west coast refer to it as SMG (speed made good) or CMG (course made good). As a licensed deck officer and 23 years as a Coast Guard rescue boat operator I had never heard of VMG. Anyways thank you for your explanation.  After looking the term up on google search it is a sailing yacht term to describe upwind sailing as you guys previously stated, which might be why I wasn't familiar with the term, even though I'm no stranger to sailing either. Learn something every day!

 

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11 hours ago, Mark Baumgaertner said:

Interesting how you guys refer to it as VMG instead of what most Mariners at least on the west coast refer to it as SMG (speed made good) or CMG (course made good). As a licensed deck officer and 23 years as a Coast Guard rescue boat operator I had never heard of VMG. Anyways thank you for your explanation.  After looking the term up on google search it is a sailing yacht term to describe upwind sailing as you guys previously stated, which might be why I wasn't familiar with the term, even though I'm no stranger to sailing either. Learn something every day!

 

Velocity and speed are not the same things.  Velocity has a direction component and speed does not.  Lots of engineering students have gone off track by confusing the two terms.  Therefore VMG means speed made good in a specific direction, which can be upwind, downwind or crosswise.  Neither SMG nor CMG are as well defined although CMG can be so defined if you wish.

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I've always been disappointed in vmg readings on instruments I've used. Maybe I need better equipment. 

 

For instance, when tacking to a mark, on the second last leg (tacking to the lay line), vmg gradually diminishes until it reaches 0 at the lay line. Then you tack to sail directly to the mark and the vmg jumps to boat speed and stays there until you reach the mark. In reality your progress to the mark was constant over both legs. Does anyone have a GPS that will give the constant reading?

 

When gibing downwind compared to running wing-and-wing, the instrument will usually say that vmg drops with gibing. But, as in the example of tacking above, the vmg bonus reading comes on the last leg. On legs prior to the last one the vmg will diminish as you go along. 

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15 hours ago, Reacher said:

 

For instance, when tacking to a mark, on the second last leg (tacking to the lay line), vmg gradually diminishes until it reaches 0 at the lay line. Then you tack to sail directly to the mark and the vmg jumps to boat speed and stays there until you reach the mark. In reality your progress to the mark was constant over both legs. Does anyone have a GPS that will give the constant reading?

 

Your GPS is correct.  What is deceiving is that the read out you are getting is really VMC.  VMG is much more complicated to measure as it requires the winds speed and angle as well as your speed and angle to the wind.  Keep in mind that I am using the terms a sailor uses, GPS don't have a clue what the wind is doing nor do they care.

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15 hours ago, Reacher said:

I've always been disappointed in vmg readings on instruments I've used. Maybe I need better equipment. 

 

For instance, when tacking to a mark, on the second last leg (tacking to the lay line), vmg gradually diminishes until it reaches 0 at the lay line. Then you tack to sail directly to the mark and the vmg jumps to boat speed and stays there until you reach the mark. In reality your progress to the mark was constant over both legs. Does anyone have a GPS that will give the constant reading?

 

When gibing downwind compared to running wing-and-wing, the instrument will usually say that vmg drops with gibing. But, as in the example of tacking above, the vmg bonus reading comes on the last leg. On legs prior to the last one the vmg will diminish as you go along. 

 

The problem is that you put the mark in as your way-point. If you have an instrument with apparent wind, eyeball in a waypoint a few miles upwind of your mark. This assumes your mark is directly upwind. Adjust as necessary.  This is difficult on our small boats with a crew of one. Some chart-plotters make this easier than others. On my hand held Garmin, I just have a lot of way-points entered to pick from. Once you figure a good tacking angle, and get used to the adjustments needed for wave size, the dependency on it goes down.

 

Dave is correct in that the VMG function on your GPS isn't too sophisticated, but it can be very useful. I crewed on a 40' boat with a skipper that was always pinching. It was maddening.  It was the VMG function on his chart-plotter that gave a few of us the data to show him fast......

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Im not sure how that would be useful for navigating. That is vmg to a direction but sure you could just set a go to point that is very very far away in the desired heading and vmg will show essentially your speed toward that heading. We are always trying to go to a destination. And i am constantly updating the next destination i want to reach along my course to avoid things. Vmg to those coordinates is the most relevant info to have because you know right away if you've overstood (crossed the layline, vmg=0) and i always show the "turn" field which tells you how many degrees to turn L or R to be on course. Vmg and turn together allow me to identify shifts by watching for changes in how far off course i am from one tack to another and i can identify current with or against by noting my tacking angle with each tack. The turn display field also prevents overstanding and missing the layline. If i get a 20 deg shift ill see it right away on my turn to angle without needing to be looking at a compass. We just try to keep the turn to at zero. Without this tool (handheld gps, and "turn to" feedback) navigating florida bay at the speeds that have been done would not be possible at night. 

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It's not useful for navigating. It would allow you to figure out what TWA yields the best VMG (to wind).  Though you're waypoint far away idea would work Alan if you could ID a point way off in the exact direction of the wind.

 

BTW, when you reach "VMG" = 0 according to GPS you are 90° from approaching the mark.  This means you have reached the lay line only if your boat does 45° TWA, which a B&B cat/ketch won't do. So your GPS doesn't  find the lay line.  And if you sail a really weatherly boat you will have crossed the lay line before "VMG" = 0. Yes, the "VMG" still helps keep track of the next way point, but when you tack on 0 you still won't fetch the mark.  

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I loved seeing Southern Skimmer flying her chute.

 

Alan, presumably as you sail away from the rhumb line, your VMG decreases, and your 'turn field' values increase. I haven't raced. Using these values, what's your rule of thumb for when it's time to tack? And when you say you're often entering or changing waypoints to avoid obstacles, are those obstacles things like sand bars, etc that weren't on your chart?

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Mark, 

For years we've used the GARMN MAP76 and 76CX (color version with charts and magnetometer). They have always served me well and garmin always fixes them and sends them back when we send them in for repairs. I think our family has about 6 of them between us and we carry multiple spares although we've rarely had a breakdown with them. They do have a tendancy to shut off when the battery gets disconnected such as if they bang against the cockpit seats and the battery squeezes the spring and momentarily loses contact. I keep the gps in my PFD pocket on my kokatat misfit pfd with the screen facing my chest. i can slide it up for a quick check very easily. at night i typically leave it clipped to something and sitting on the seat in front of me with the backlight on the dimmest setting. That way i have a hand free to use the spotlight and can just look down to check our course. This year we took the newer MAP 78 which is a bit different but i still like it fine but don't have nearly as much time on it. 

 

Fred, 

Dead down wind (with main and mizzen on the same side) the chute is hanging lifeless behind the mainsail which is when you would hoist or recover it if it were bag launched from the cockpit. As we head up, we sheet it in to get it "started" and the leading edge catches the breeze and it quickly fills and we let the sheet way out so it can billow out to it's proper trim (leading edge just starting to curl). We head up to say 10 deg off ddw and the chute stays filled but the boat does not accelerate much this is where I found the best angle to be for the lighter winds we had (about 8 knots). Heading further up to say 20-30 deg off the wind the leading edge collapses as the apparent wind rotates further forward so you sheet in to keep the chute trimmed and the boat accelerates. As it accelerates apparent wind moves further ahead and you have to sheet in even more to keep up with it OR bear away. With an asymmetrical chute you are constantly playing it. rounding up to "heat" the boat up sheeting in as you do and then bearing away in the puffs to bleed off speed and gain progress downwind. VMG initially goes down but then back up once the boat gains speed. Whether or not VMG is better than it was when going ddw is what you're looking for. It's tough because you are constantly playing the chute and heading up and down a bit to keep it in trim. We didn't play the chute nearly as much as you would if you were buoy racing so with the chute cleated off it's up to the helmsman to keep it in trim with changes in course instead of constant sail trimming. heading up until it just starts to curl on the leading edge and then bearing away in the puffs. We did this a lot sailing in the tybee 500 especially when conditions were very steady state (flat water and constant breeze) and the crew can take a break from "sawing" on the spinnaker sheet. 

 

With a following swell you can head up to heat the boat up, catch the swell, bear away (sheeting out as you do to keep the chute powered up if needed) or if you caught the swell (yay) and are now surfing you might be sheeting the chute in hard to keep up with the apparent wind shifting forward. You just have to have your eyes glued to the leading edge of the spinnaker and do whatever it wants. If we'd had a bit more wind which we did a couple of times then the boat pops up on plane and as soon as it does you have to sheet the chute in again to keep up with the apparent wind (keeping the chute trimmed properly all the time). And then you can bear away now on plane and let the the chute out a bit as you do keeping the boat powered up and you can now drive the boat down on plane and make lots of good speed more toward ddw and if you lose speed you head back up to find it again. wash rinse repeat. 

 

I kept the mainsail in about where it would be when sailing upwind which is where it wanted to be and also helps act as a back-stay. Of course the running backstays were pulled in as well. On the spinnaker catamarans, if you don't have the main sheeted in tight when you're flying the chute the mast won't stay up very long.  The mizzen is a different story, I kept it out more like i was on a broad reach or even a bit deeper because it has a lot of leverage over the boat and when the boat heats up and heels over there is weather helm generated from the lift of the sails being to the lee of the boat. To de-power the boat while flying the spinnaker you bear away toward ddw and you don't want anything to prevent you from doing that. The mizzen can easily overpower the rudder input in that situation. Many times when you want to bear away you have to make sure the mizzen is let out a touch. Also if you're sailing upwind hard and the boat is trying to sail on her ear too much it will cool right off if you just crack off on the mizzen just a touch. 

 

As for knowing when to tack or gybe in this case it was really just when we felt like it. We were following the leader so as a rule you don't want to get too far from them so you get about the same air as they have and you get about the same shifts and puffs. In our case we were also trying to minimize gybes which are slow so we would sail out until we though we can sail "in" back toward cape sable and have a nice long run. We're trying to sail the shortest path so like for sailing around cape sable we set a go to point down at the farthest point out that we'll have to turn at. When we reach that point we set a new point and so on. So the gps is always telling me to turn to that course that is the shortest straight line course. If you tack through 100 deg and you're sailing upwind on a port tack and the gps says turn 50 deg to port to be "on course" then you know you're doing just as good on that course as you would do on the other tack. If you get headed (wind shift causing you to bear away or fall off) then you can switch to the favored tack for a slightly higher vmg. Some boats sail waaay out away from the beach but i don't like that because most of the wind is usually right there near the beach and also i can't tell you how many times i've been farther off the beach and watched boats closer to the beach pull away and rarely is it the other way around. As you approach a "go to" point you're navigating to on your GPS then you get close to the laylines and the "turn to" number changes faster. You know when you've reached the layline when your turn number equals your tacking angle (assuming there is no current). the gps is a super handy tool and invaluable at night but during the day i'm focused just as much on where other boats are, looking for current as we pass markers and making sure the boat "feels fast". Also, we probably kicked our rudder up 30 or 40 times along the course and pulled the CB up all the way occasionally during a tack to make sure we weren't dragging an ocean of seaweeds around with us. Usually you see a nice clump of them float away behind the boat whenever you do. 

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Wow - thanks Alan. That is a ton of great information. I'm going to copy the whole reply to my OneNote notebook.  You set up most or all your waypoints before the race, don't you, so you're just selecting the next point along the route, or are you actually creating new points as you sail the course?

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