To Point or Not To Point

[RangerTim]

Watching the last America's Cup I was exposed to Velocity Made Good [VMG]. My better half Swampgirl, who introduced me to sailing and sailing kayaks, had already explained the concept but I had been unaware of the term.

So, let's assume that my destination is directly into the wind. Am I better off pointing as close to the wind as I can and still have the boat moving at say, 3.3 knots, or should I fall off a bit where I can achieve, say, 3.8 knots? At what point do I maximize VMG?

I can say that sailing at 3.8 knots is more fun than sailing at 3.3 knots and often I have no particular place to go so I choose the greater absolute velocity over seeking to maximize VMG.

A pretty big deal in the small-boat-racing world, Stuart Walker, was an acquaintnace of Swampgirl when she was much younger. He gave her a copy of a 1960 book he edited called THE TECHNIQUES OF SMALL BOAT RACING. Swampgirl retrieved this book after a discussion of when using two leeboards would be better than using just one.

In the chapter on sailing in strong wind, the author points out that at faster speed the boat side slips less. This would be a vote for falling off a bit.

Elsewhere in the chapter the author talks specifically about small catamarans. For these boats in strong wind, the author claims describing a scalloped pattern maximizes VMG. Fall off the wind a bit to gain momentum, then point up until the boats slows significantly, perhaps even pinching a bit. Then fall off once again to regain momentum.

For those of us who use akas and amas, aren't we trimarans? Perhaps this method might work for us. Then again, it would seem this method assumes the boat can glide. Most folders do not seem so good at this.

Anyway, just food for thought on a day when the water is still too cold for me to want to go out.

[JohnSand]

An interesting question for any sailboat, I've often mentally debated it underway. The answer depends on the math: how far do you have to bear off and how much speed do you gain. My simple answer is to buy a handheld gps, or install an app on your phone which wil give you speed over ground and velocity made good. Warning: trying to sail a very small light boat and consult electronics can result in swimming lessons.

[gbellware]

Thanks for this very interesting topic, I had no idea how much time and how many words could be devoted to VMG...just ask google! I look forward to digging in to learn more but Tim, you have the key issues teed up for us. Yep, speed over ground will be faster on a tack off the wind, and it also results in better VMG as opposed to sailing as close to the wind as our boats will go. How much off the wind makes optimal VMG? Stay tuned, or chime in, because I have not found the answer yet! There are so many factors, even with a single sail. Introduce a headsail or mizzen and, well, oh my. But Tim's assumption that we (with amas) are really trimarans is correct, and the importance of that is related to the amount of heeling we do/don't do. And then there is the issue of rudder angle, which provides both lift (who knew) and drag (I DID know that). The trimaran aspect (minimal heeling) and the rudder issue are both factors that go into the weather vs. lee helm, which also varies depending on wind strength and tack angle...and so on! And these both factor into VMG...somehow. Oh, and btw, the hydraulic drag (caused by hull moving through water) that needs to be overcome is LINEAR with respect to speed, which is completely different that the drag in air, which increases exponentially with speed. This is important because you get to "keep" all of the increase in speed you get by sailing a bit off the wind. If that was not the case one would experience diminishing benefit from falling off the wind to increase ground speed, as some of that speed would be spent overcoming the non-linear drag you would experience sailing through a sea of air.
Well, I'm no physicist but I am intrigued by the sailing geeks I have begun to read on the sailing blogs. If anyone is interested in a deeper dive from one of the better sources I found you can look at this string: http://www.cruisersforum.com/forums/f48 ... 02231.html

Best,
g

[DLee]

Hi Guys!

I had been doing a lot of Radio Control sailboat racing at Noroton Yacht Club in Stamford, CT, this winter. These guys live for sailboat racing and are apparently quite competitive and quite good. I can tell you this; none of these guys are headed straight for the pylon or finish line. They're all making the best speed they can while considering the reciprocal tack angle they will have for the run to the pylon or finish line.

I'll ask about philosophy next time I see these guys.

I don't see how a vertical rudder (kept vertical by outriggers) can offer any lift to a Blue whale, lol.

My philosophy is to take the fastest, most fun, route that is most direct and will hopefully have a nice reciprocal course to the destination... or home.

Really looking forward to getting out this year.

Cheers!

d

[gbellware]

Dennis,
Great to hear from you, glad you are still on (if not sometimes in!) the water. Hope you can make it to one of the group sails, we are in Cupsuptic in Maine in August.

I had the chance to play around with VMG at our last sail in Virginia a couple of weeks ago. Using my GPS with a VMG window open next to a mph window (I know, I know, real sailors use knots). What I found was entirely consistent with TIm’s “I just go fast” scientific method of finding VMG.

My Klepper A1 does not track very well, that is to say that I slip a lot, especially in heavier wind and close hauled. But I track OK as long as I am making +3.5mph through the water. Taking tidal current out of the mix, what I found was that I achieved best VMG by taking a tack that is considerably off my best pointing angle, and surprisingly so. Pointing as high as I am able, while still making over-the-water speed but dropping below 3.5mph, takes away the tracking help I get from my leeboard and I slip like crazy. So even though I can point to, maybe, 20 degrees off the wind…where it seems like I should achieve best VMG…I do not. Pointing away at least 5 and maybe 10 degrees from that tack my speed-over-water and VMG both go up considerably. Tacking even farther off from that, all the way to a broad reach, I pick up a few tenths in speed but loose VMG.

Throw current into the equation and I am completely lost.

Oh, and BTW, when I said that the rudder gives lift I totally mislead. An experienced sailor corrected my use of the term “lift”. In this case, “lift” just means that applying windward rudder causes the boat to point into the wind. Duh.

And that’s all I know about that.

g

[DLee]

Greg that 'lifting' issue is pretty funny.

So if I'm reading you correctly you're saying 25-30º off the wind is the best tack for speed and VMG. I think my experience concurs with that pretty closely with or without current although I wouldn't be surprised if I fell off even further at times.

I doubt I can make Maine this year but it sure would be great. I'll go back and check your email on the dates. Billy's going to College this fall, so things are a changin'. We'll see what happens.

[DLee]

I forgot to add that your comments about the AE1 not tracking well made me think back to posts a long time ago where guys spent a lot of time talking about ballasting the bow when sailing. Remember that? I never found it necessary, but it could be that is what the AE1 is asking for. ?

Glad to hear you're sailing that boat, remember, Howard Rice did sail an AE1 around Cape Horn.

BTW, what kind of speeds are you making when you have all three sails up on the double? Are we planing yet? lol.

At what section of the boat are you placing your outrigger? I'm thinking I'll reluctantly revisit outriggers this year so I can start venturing further without so much fear. So, I'm gathering data and spinning molecules in the ole' hat stand.

d

[RangerTim]

Hey Guys,

Greg, I confess that I did not investigate VMG at the sail gathering. I was having too much fun just plain sailing. Your comment about increased side slip when close-hauled intrigues me.

Let's say you are close-hauled. The boat is pointing 55 degrees off the wind, a reasonable point for many folders with just a mainsail. The direction of travel, with side slip, is, say, 70 degrees off. Let's assume that side slip decreases as you move away from the wind. Would you be better off pointing at 65 degrees off, with a direction of travel of the same 70 degrees off? The numbers I am pulling out of a hat, but you get the idea. This seems to be what Greg discovered.

As you know, Klepper sail rigs and the old Folbot sail rigs have twin leeboards. I believe these are shorter than the Balogh leeboard. I have been told that Balogh only requires the one, longer leeboard. This eliminates the necessity of raising one leeboard and lowering the other with each tack/jibe.

Tidal current can be strong on the river near home. Even when close-reached, when near the shore I can discern considerable side slip. One day I went out with two Balogh leeboards. While deploying two leeboards simultaineously slowed the boat, it reduced the amount of side slip. I wonder, would two leeboards when close-hauled, assuming adequate wind, increase Velocity Made Good?

I really must be scientific the next time I go out. I tend to enjoy sailing on a visceral level.

[DLee]

I'm sticking with the theory of maximum speed wins.

As far as the two lee boards on older Klepper and Folbot systems, I believe it's customary to leave both down in the water at all times. I've always kept both down and find it works pretty darn well.

Pretty anxious to get out. Need to re-glue my hull on the AII a bit before I can sail it though, and it just won't stop raining up here.

There's an itsy bitsy teeny weeny infinitesimally small possibility of a chance that I might be able to join you guys in Maine for a couple minutes. Man, would that be great.

d