VMG - rhumb line vs. banging the corners

[Delancey]

Originally Posted by OldFrog75

It might seem like a weird argument but some on the team are adamant that Distances and VMG's are different while others argue that they are the same.

soooo, which side of the argument are you on?

[OldFrog75]

Originally Posted by Delancey

soooo, which side of the argument are you on?

Distances and VMG's are the same for both alternatives.

[goboatingnow]

Originally Posted by OldFrog75

Distances and VMG's are the same for both alternatives.

Don't see how that can be true


Sent from my iPad using Tapatalk

[jannw]

Problem is that it's never simple.

If you're harbour racing you need to consider the currents, lifts, and knocks.

off sore and in harbour you also need to consider your competition ... are they shitting in your air, or are you planning to **** in theirs.

In a perfect world you would lay your laylines perfectly, and the corners have less tacking inefficiencies. But that perfect world is only long haul open ocean racing, and then you are playing weather shifts, so again it's never a blank canvas.

[monte]

distance to sail with 1 tack - 10 miles
av SOG 10 knots
time to mark 60 minutes
speed lost per tack - av 3 knots/30 seconds
time over course with one tack - 60 minutes 10 seconds
time over course with 10 tacks - 61 minutes 40 seconds

* tacking curve including SOG directly upwind mid tack also included in above figures

[OldFrog75]

Originally Posted by jannw

Problem is that it's never simple.

If you're harbour racing you need to consider the currents, lifts, and knocks.

off sore and in harbour you also need to consider your competition ... are they shitting in your air, or are you planning to **** in theirs.

In a perfect world you would lay your laylines perfectly, and the corners have less tacking inefficiencies. But that perfect world is only long haul open ocean racing, and then you are playing weather shifts, so again it's never a blank canvas.

The debate assumes a perfect world with no wind shifts, no current, and no other boats on the water where one group thinks the VMG and distance for banging the corners is different from the VMG and distance for multiple tacks up the rhumb line, while the other group thinks they are the same in both cases. It's a theoretical argument.

[cal40john]

Originally Posted by monte

distance to sail with 1 tack - 10 miles
av SOG 10 knots
time to mark 60 minutes
speed lost per tack - av 3 knots/30 seconds
time over course with one tack - 60 minutes 10 seconds
time over course with 10 tacks - 61 minutes 40 seconds

* tacking curve including SOG directly upwind mid tack also included in above figures

What boat is your tack number for? A Tahiti ketch is very different from a racer/cruiser or sport boat or a dinghy. Racing rules say you can't leave a tack faster than you went into it for a good reason. Certain boats were tacking continually just to create their own wind and go faster than you could sail the course just using the wind.

OP's profile says club racers. Could be sport boats that can probably lose nothing in a tack.


Melges 20 roll tack

https://www.youtube.com/watch?v=Ct4mJZ2Kdtc

470 roll tack

https://www.youtube.com/watch?v=898erG59hPU

[thomm225]

With the conditions the OP stated, constant wind/no current, this thread could only last this long on a cruiser's website.

Most racers try to decrease tacking by just one to win in a buoy race. You lose time during a tack. It's as simple as that.

Think of it from the starting line. If you only tack once on the layline you will be at the top mark first if your competition started on the opposite tack since he had to do one more tack.

[monte]

" Racing rules say you can't leave a tack faster than you went into it "
that's a new one on me, who's rule is that?

[cal40john]

Originally Posted by monte

" Racing rules say you can't leave a tack faster than you went into it "
that's a new one on me, who's rule is that?

Section 42
http://www.sailing.org/tools/documen...6StudyVersion-[13380].pdf


42.2 Prohibited actions
...
(e) repeated tacks or gybes unrelated to changes in the wind or to
tactical considerations.

42.3 Exceptions
(a) A boat may be rolled to facilitate steering.
(b) A boat’s crew may move their bodies to exaggerate the rolling
that facilitates steering the boat through a tack or a gybe,
provided that, just after the tack or gybe is completed, the
boat’s speed is not greater than it would have been in the
absence of the tack or gybe.

[StuM]

Originally Posted by goboatingnow

Don't see how that can be true

Discounting time lost in tacks:

1. Same points of sail, so same boatspeed.
2. Same distance sailed.
Therefore total elapsed time must be the same
Therefore average VMG must be the same.

[monte]

Thanks John, As I read it the rule only applies to moving body weight in light airs.
It seemed odd that " Racing rules say you can't leave a tack faster than you went into it " as this would exclude tacking for wind shifts and the general purpose of racing..to go faster.

[OldFrog75]

Originally Posted by monte

Thanks John, As I read it the rule only applies to moving body weight in light airs.
It seemed odd that " Racing rules say you can't leave a tack faster than you went into it " as this would exclude tacking for wind shifts and the general purpose of racing..to go faster.

I think the rule is intended to prevent "artificially" improving boat speed like the rules against sculling or rocking. If you assume the points of sail are the same and the wind is steady within a very narrow time period it makes sense. You can't go from starboard tack to port tack and immediately back to starboard tack if when you leave the port tack to go back to starboard the intent (and result of the action) is for you to increase boat speed compared to what it was when you entered the tack to port from starboard in the first place.

[who_cares]

Question isn't even remotely close to being a realistic scenario. You're always going to different conditions across the course, it also depends on what kind of boat you're on. If you're on a 420, tacking doesn't cost nearly as much as if you were on a big slow keelboat that takes forever to build up your momentum, so tacking once might be better. Also depends on your competitors...

I heard someone say that banging the corner is like kissing your sister, it seems like a good idea at the time but after you do it you always regret it.

[Ex-Calif]

Distance is the same, speed out of tacks valid. More tacks slower.

However as noted conditions are never ideal.

Also a very experienced racer/teacher of mine in context of tactics said, "If you find yourself all the way to the left or right of the fleet you are either the smartest guy in the race or the dumbest."

If you are in front - Hey diddle diddle I control the middle...

If you are not in front you better do something creative.

(learned a valuable lesson about the middle - I covered #2 out to the edge of the course. #3 took us both up the middle.)