Sail trim quiz question
- Thread starter Jackdaw
- Start date
That's why the smiley, there's always somebody in the way, even if no more than a party barge towing a blow up couch, locally renowned for their ability to spit off small screaming organisms directly in your path and allowing barely enough time to put the kite away before you run them over.
Can you tell I hated math?
Can you tell I hated math?
Indeed, pointing as high as you can can often result in slower speeds, and/or slide slipping due to stalled foils. A boats ability upwind can be tracked on it polars, like BlueJs. Most boats with a high aspect keel will look like this angle wise (Up.Bt), the speeds (Up.Vs) are a function of length. Note how it starts wide as speeds are low and the foils are not working well. But once the boat powers up, to the moon!
My Annapolis book of seamanship speaks of disk calculators to compute the vmg. Anyone have one on board still? Probably gives the cosine of angle on one wheel and speed on another.
Getting leveled up in sailing skills to be within 10 degrees of any course for more than 5 minutes is daunting.
Getting leveled up in sailing skills to be within 10 degrees of any course for more than 5 minutes is daunting.
So if this is the correct answer my, keel challenged, H25 is better off taking the long way home .
Yeah, but wait till you get the wind input to the AP fired up. Mr. Bill gonna be pissed.
Correct for some imaginary boat in a certain breeze. Every boat will have its own polar chart. But if you OBSERVE that, you will know what is faster if you do the VMG calculation. The trick for most small boats is knowing the True Wind Angle with that resolution. You need good instruments, as its hard to gauge.
And if you go to pay the park ranger the ramp fee and he says "You're dragging something.", and its your furled jib dangling off the top of the mast, your polars might be off.
Remember that upwind sailing, you are not sailing a constant course (compass bearing), but a (relatively) constant wind angle off the bow, guided by your tell tails. But that can be daunting too!
Don't forget, you need to be where the wind is. Sometimes taking the slower course is faster because wind is never evenly distributed across the water. It isn't a very reliable continuum.
As a kid in my opti program, I sat, along with everyone else, watching one girl sail easily to the finishline because she was 75' farther on the the outside line while the rest of us, "better positioned", had no wind at all.
- Will (Dragonfly)
As a kid in my opti program, I sat, along with everyone else, watching one girl sail easily to the finishline because she was 75' farther on the the outside line while the rest of us, "better positioned", had no wind at all.
- Will (Dragonfly)
Right. But you have to be able to separate boat-speed from tactics. Boat-speed discussions (like this) center on how to make your boat as fast as possible in your current conditions. Tactics discussions are based on where those conditions are going to be best when you get there.
Absolutely! I have noted in other venues, that sometimes a single element discussion leads participants to focus on that element in practice, forgetting about the meta-picture. It is good to pull out and look with a wide angle once in a while.
This discussion in very interesting. I used sailing to teach vector addition. It is helpful to use ratio (proportionality) of xy elements for given angles in addition to sine=o/h, cos=a/h, tan=o/a because it is easier to visualize it inn your head. For example: 45 deg has a proportion of 1 to 1, but 22.5 deg doesn't have a 2 to 1 angle, it's closer to 12 to 5. These images are easier to see in your head so you can use it while under way.
- Will (Dragonfly)
Oh for sure, at the end of the day you have to look at anything holistically if you want to do well. North uses a pyramid model in their teaching, and any given class will make very clear what they are going to be talking about. At the base of the model is boatspeed. Everything is predicated on you being able to sail your boat as fast as you can in the given conditions and direction. Nothing else matters if you cannot.
I'm not sure what difference between 2:1 and 12:5 makes on the water. Those images are NOT easier to see in my head....but 22.5 deg doesn't have a 2 to 1 angle, it's closer to 12 to 5. These images are easier to see in your head so you can use it while under way.
- Will (Dragonfly)
The best sailboat driver I ever knew didn't cloud his head with all this. He drove the boat to his instincts and was a name in racing before I was born. No instruments. He and his family are legends in winning races and I guarantee he would have no idea what this diagram shows.
Jackdaw asked about a trigonometric problem equating wind direction, speed and heading to best performance. I was offering another way of seeing the problem, not the only way. Instinct, trial and error or intuition are still other ways but can't be used, in jackdaw's example, to answer the question. They will only work from the deck of a boat.
Roofers and other trades that use angles don't usually express themselves in degrees, radians or trig expressions. Instead, they use expressions like 2 to 1 to better convey a working idea that allows them to pull out a tape measure and build the expression without calculation or table lookup.
I'm not trying to put down or take away any value from the ideas here. I learn best when I can see problems through multiple paradigms. I assume it can only be helpful to others as well.
- Will (Dragonfly)
Indeed, most great drivers develop a ‘feel’ for the right upwind angle. It’s impossible to try and watch it on instruments due to hysteresis induced lag anyway. So they are there to spot check, not lead.
Downwind however, steering at the correct angle based on wind speed is very hard due to the wide range of possible angles (180-135), and the fact the fastest boat speed is rarely the best downwind
VMG. Having good instrumentation really helps.
Theses images DO help... If you have actual polar diagrams they let you 'see' the best angles for sailing your boat upwind and down based on windspeed. The raw numbers show this too, but not in the same way. The 'ticks' are optimum VMG. You can see you really need to foot (44 TWA) in light airs, but when the breeze is on you can come up SEVEN degrees! Downwind the same... start wide to keep the apparent up, but as it builds turn down.. then back out as the boat starts to plane.