Sailing simulator

[Jim_ME]

Last night some of us were chatting with one of our members who had just gotten a Sunfish and was about to try sailing for the first time.

I had seen this online sailing simulator in the Education section of the National Geographic website, and suggested it as one possible tool to help get a sense of basic sail trim for a given wind direction and various points of sail, and even rudder control for tacking and gybing, etc., so am also posting the link here, for others that might also find it useful. (or fun to mess around with...) [...the boat speed of 15+ knots may be a bit counter-SailFarish... ;)]

http://education.nationalgeographic.com/education/multimedia/interactive/sailing-simulator/?ar_a=1

[Edit: Just discovered that you can control the tiller motion using the keyboard L & R arrow keys, which is more natural feel than dragging the button with the mouse, and the up & down arrows control the sail sheeting angle. It does a good job of showing the sail luff and the boat speed stall, etc. ]

[Headcase]

    Alright, now i have something else to obsess over. Full disclosure, I only got 11Kt out of it BOTH times I tried. So why am I happier doing 2 in light air having a Beverage "live"?

[Jim_ME]

I'm finding that this sailing simulator is a great place to down a few virtual grogs...
Get into any trouble...just hit the reset button.   ;D

11 or 12 or more knots IS way too fast!
Nat Geo should make a SailFar version with a more reasonable speed...say, 6 knots max, so people won't get unrealistic expectations...and then have to go out and buy a big ocean racer to meet them... ;)

Also, under no circumstances should the boat be able to sail any closer than 45 degrees to the wind. We see how this elitist society organization is so biased against small old heavy full-keeled cruisers!  :(

Maybe it could also have a sheet-to-tiller setup for self steering to windward...and a built-in timer buzzer to wake you up to look around every 20 minutes...? [Then we could practice simulator sailing all night...]

[Captain Smollett]

Also, under no circumstances should the boat be able to sail any closer than 45 degrees to the wind.

Any boat can "point" higher than 45 degrees to the wind.

The question is, "how fast" and "how much leeway."   :P

The sails totally luffing and not creating any lift at all is Angle of Attack (aka, "trim angle" with respect to the wind) dependent, which has nothing to do with the hull per se.  And, it's quite high, which you may have noticed while tacking.

So, from an aerodynamic point of view, the question becomes "at what point does our drag (hull + sails) exceed our lift (nearly all sails)."  That can be seen on the boat's polar diagram (and is, of course, windspeed dependent, and to a lesser extent, rig tuning dependent which effects sail shape).  I've always found it quite interesting that the polar does not drop to "zero" boat speed until pretty high into the wind.

Sorry for geeking out for moment...been a long day.  I needed a break.   :)

So, make On Topic to the simulator, maybe it helps us think about things in a different way.

(And no, I sure ain't saying either of my boats will, in practice, point right along with say a J-24....).

[CharlieJ]

And then you get into apparent wind angle. The Tatan 41 Tall rig we delivered to Mexico could make good speed at 27 degrees apparent. And we held her to that for most of 6 days, Rockport to Progreso, Yucatan.

Tehani sure won't do that- I figure I'm doing fantastic tacking under 100 degrees.

Of course it also was a fin keel drawing 6  1/2 feet!!

And for the better part of six days, this was the attire on deck :o 

[Captain Smollett]

The Tatan 41 Tall rig

Yep, aspect ratio has a lot to do with "pointing."  But, adding luff length has a price...more heeling moment.

I've got a picture book around here of wooden boats, and there are some beauties shown: classics, mostly from the early 20th century. 

It always struck me how some of those older boats had incredibly small aspect ratios...short, stubby looking mast (by today's standards) and booms that hung way out over the stern.

I'll be those boats were stable as can be and stood up to wind that make the modern high aspect boat shudder in its sleep.  Those boats have low heeling moments with relatively high turning moment from the main, balanced by big headsails on a sprit...raw power.

And, those powerful rigs (not optimized for pointing, but for driving through seas) on a hull with waveform shapes and the net result is ... well ... a sea boat.  Form follows function, and boats of that era were typically designed around work boats that had to get a job done.  They did not have the luxury of 'staying in port' just cuz it was blowing 20 knots.

As I said...beautiful.   :D

[CharlieJ]

Yep- that Tartan was definitely a race boat. And for many years now, being a race boat meant being optimized for going to windward. Gotta make that windward mark in as few tacks as possible. But off the wind, they MUST add extra sail area, because the regular rig is woefully short aft of a beam reach, with regular sails. Thus Spinnakers, Assymetricals, Bloopers, ballooners, Code zeros, etc

An example from  a BEER Cruise. I was in Necessity. A 21 foot sloop, originally a swing keel but converted to longer keel. Still  fairly high aspect ratio, compared to older designs, and better at windward work. We were sailing with, passing actually, a 21 foot gaffer, sailing hard on the wind. And passing him we were for sure.

Then we rounded a corner, came off the wind, he was able to start sheets, and that big old gaff main started to work. And he ate us UP!!

Now I COULD have run up the big genoa but usually it just ain't worth it

[Jim_ME]

Also, under no circumstances should the boat be able to sail any closer than 45 degrees to the wind.

It took me a little while to find it, but here is the chart...

[Captain Smollett]

That wind speed is 6.7 knots...so...

What's the polar look like for 15 knots?

I mean, that polar does not even reach hull speed on a reach.   ;)

And, I'm sorry, I've never seen a polar with a sharp corner like that before.  They usually turn to zero pretty quick above about 45, but it is more of a smooth transition.

Edit: Another point.  In real measurements taken from nature, NOTHING ever comes out at "precisely" an even, pat number like 45 degrees.

Do you know who published this polar?

[Jim_ME]

...

And, I'm sorry, I've never seen a polar with a sharp corner like that before.  They usually turn to zero pretty quick above about 45, but it is more of a smooth transition.

Edit: Another point.  In real measurements taken from nature, NOTHING ever comes out at "precisely" an even, pat number like 45 degrees.

Do you know who published this polar?

Yup...a definitive chart from...um, let me check...

Small Old Slow Heavy Full-keeled Boat Magazine

a highly reliable and prestigious source...  ;)

[Captain Smollett]

But it actually does not make sense either aerodynamically or for other reasons.

The lift-drag function of the sail does not abruptly change, and since the drag function of the hull does not vary with angle to the wind, it makes no sense that the polar would have a sharp corner like that.

There are other problems as well.

But, the bottom line, and the trump card, is that it is not consistent with real world experience.

Are you telling me that your Typhoon fell to 0 knots at precisely 45 degrees, every single time?

Because...well, let's suppose that the polar DID fall to zero abruptly just for the sake of argument.  The angle that it did so would depend (rather strongly and noticeably) with rig tuning...specifically forestay (er, really jib luff) tension.

So, the precisely 45 degrees claim is easily debunked...sag your forestay a bit and watch that angle change.

Since I can change the "no longer drives" angle (even if I assume its onset is sudden) with fore stay tension, the claim that all Alberg boats fall to 0 kt at precisely 45 deg is clearly...not true.

Now, I recognize that there may be some element of humor here that I am missing.  It's been a busy week and I am...exhausted.  So...mea culpa if the key bit is flying over my head. 

[Captain Smollett]

Yes...good humor went right over my head. 

Grog for Jim!

[Jim_ME]

Yep, Once I made the proclamation that our cruising boats hit the wall at exactly 45 degrees...I had no choice but to tweak the data graph to support that claim. It soon seemed very convincing, even to me. If this isn't true...well it should be!  ;D [The simulator boat shows high speeds at wind angles way closer than most of our boats can sail, and I was poking fun at how that did not represent our experiences so much...]

Thanks John. As I said...geek humor. Grog to you, for being a good sport. This will no doubt now be reused as an authoritative source from now on...will see where it shows up in the future...many traditional boats may be abandoned and scrapped as a result...