How does in-mast roller furling affect pointing ability?

[StuM]

Originally Posted by mstrebe

I did some tacking yesterday and was able to maintain speed across 80 degrees to true wind by my instrumentation, without taking into account tides, currents, leeward motion of the boat, etc. Winds averaged 10..12 knots and boat speed consistently averaged about half of true wind while pointing. Below that, speed definitely fell off but the boat was able to maintain course down to 60 degrees true without luffing, but performance fell off down to less than 25% of true wind speed. Below that it was in irons.

So I would say its useful range is about 75 degrees, 70 if you're willing to take the performance hit or have higher winds than you need.

Sorry about the kerfuffle caused by not paying close attention to my instrumentation, and thanks for calling it out!

I'll hold off on reporting anything more accurate until I sort out exactly how to be more accurate.

Why is pointing ability reported as the sum of both tacks across the wind rather than the angle of a single tack?

Matt

80° (40° either side) tacking angle at 6 knots in 12 knots TWS will give you 27° apparent wind. That's pretty good, but not exceptional.

60° (30° either side) at 3 knots with the same wind speed will give you 24° apparent wind angle. Your telltales would have been lifting like mad since the headsail would really be starting to luff - which explains why you slowed down so much.

Note that these figures are assuming zero windage. In reality, even with no currents, at 27° your track would be more than that 80° due to windage. Unfortunately, your wind instruments can't tell you how much that slippage adds to your actual tacking angle over the ground.

[Dockhead]

Originally Posted by StuM

80° (40° either side) tacking angle at 6 knots in 12 knots TWS will give you 27° apparent wind. That's pretty good, but not exceptional.

60° (30° either side) at 3 knots with the same wind speed will give you 24° apparent wind angle. Your telltales would have been lifting like mad since the headsail would really be starting to luff - which explains why you slowed down so much.

Note that these figures are assuming zero windage. In reality, even with no currents, at 27° your track would be more than that 80° due to windage. Unfortunately, your wind instruments can't tell you how much that slippage adds to your actual tacking angle over the ground.

By "windage" I think you mean leeway.

Without figuring leeway, you don't know anything about upwind performance. When you start to pinch, you lose boat speed and leeway goes up dramatically, and you lose your VMG to windward even though your instruments tell you you're doing a great job (they're wrong).

That's why it's meaningless to talk about angle to true wind by itself. If you want to know your tacking angle, you need to:

Choose a place and time with 0.0 knots of current. And a steady wind.

Sail up close to the wind, then find that angle with highest VMG to windward. Record your COG.

Tack, and repeat previous step.

The angle between the two VMG-optimized courses is your tacking angle.

Will not be less than 90 degrees for any but the hottest non-racing boats.

T

[barnakiel]

Originally Posted by Dockhead

(...) you lose your VMG to windward even though your instruments tell you you're doing a great job (they're wrong).

(...)

Not so if you switch your GPS thing to display VMG along with SOG.

Amazing so few cruisers do ...

b.

[Dockhead]

Originally Posted by barnakiel

Not so if you switch your GPS thing to display VMG along with SOG.

Amazing so few cruisers do ...

b.

Yes, correct.

I should have said "wind instruments" not "instruments".

The point is that angle to the wind is meaningless; you care about VMG to windward, which is never achieved at the smallest angle you can sail to.

[sneuman]

Originally Posted by mstrebe

To be frank, I'm skeptical of the wind instrument. The masthead vane is closer of course because it reports apparent wind, but as I rotate the boat around the true wind varies by more than the feel of it tells. I think I'll have to calibrate this new boat's sensors before I make firm statements.

But what will say is she makes 6 knots in 9 knots of true wind while pointing, and 2 knots in 3 knots on a broad reaching the stock jib and mainsail. I'm happy!


Sent from my iPad using Cruisers Sailing Forum

Actually, my Tayana 37 can do as well on appx. 10 knots of breeze and with some effort could eke out 2 knots in less than 5 knots of wind pretty easily on similar points of sail. So, I'm not sure how impressive that is.

[robert sailor]

Actually The T37 sails quicker than many might expect but it goes to windward like a straw bale.

[Ex-Calif]

I sailed with a Skipper who was having trouble racing. Not that experienced - nice boat, all the gadgets.

Was trying to sail wind angles, vmg and gps speeds and blah, blah, blah - none of it calibrated not even his speed log.

I tied tell tales on the shrouds and made him do two races with instruments turned off. Dramatic improvement...

Also taught his crew how to trim sails... now he is a consistent top 3 contender.

Forget the instruments until you can make the boat go as fast as possible on all points of sail.

Once you figure out your speeds, sog and vmg are useful to figure out what kind of currents you are in and may need to get out of...

[s/v Beth]

Originally Posted by Dockhead

That's why it's meaningless to talk about angle to true wind by itself. If you want to know your tacking angle, you need to:

Choose a place and time with 0.0 knots of current. And a steady wind.

Sail up close to the wind, then find that angle with highest VMG to windward. Record your COG.

Tack, and repeat previous step.

The angle between the two VMG-optimized courses is your tacking angle.

Will not be less than 90 degrees for any but the hottest non-racing boats.

T

Where I currently sail this is an impossible exercise. There is no zero current anywhere, even offshore. And steady winds are not steady for more than an hour. Maybe this is why this spitting contest does not seem so important to me.
At least there is wind, and lots of it.

[savoir]

Originally Posted by Dockhead

By "windage" I think you mean leeway.

Without figuring leeway, you don't know anything about upwind performance. When you start to pinch, you lose boat speed and leeway goes up dramatically, and you lose your VMG to windward even though your instruments tell you you're doing a great job (they're wrong).

That's why it's meaningless to talk about angle to true wind by itself. If you want to know your tacking angle, you need to:

Choose a place and time with 0.0 knots of current. And a steady wind.

Sail up close to the wind, then find that angle with highest VMG to windward. Record your COG.

Tack, and repeat previous step.

The angle between the two VMG-optimized courses is your tacking angle.

Will not be less than 90 degrees for any but the hottest non-racing boats.

T

Are you sure you didn't really mean 80 degrees ?

[Ex-Calif]

Originally Posted by Dockhead

Sail up close to the wind, then find that angle with highest VMG to windward. Record your COG.

Tack, and repeat previous step.

The angle between the two VMG-optimized courses is your tacking angle.

Will not be less than 90 degrees for any but the hottest non-racing boats.

T

You need to actually lay a rhumb line DDW from the mark and perform tacks across the rhumb line. Record VMG at various wind angles as you approach the rhumb line.

VMG is constantly decreasing as you move away from the rhumb line until it ultimately reaches zero (90 degree bearing to the mark)

I've had skipper's chase VMG heading away from the rhumb line by heading up until they are pinched and slowing - which of course makes it all worse.

You should know your boat speeds at several apparent angles 30 (if you can get there) 40, 45, 50. 60...

You should be aiming to nail boat speed every time.

VMG is interesting but not as important as tactics and currents. However, boat speed is fundamental.

[StuM]

Originally Posted by Ex-Calif

You need to actually lay a rhumb line DDW from the mark and perform tacks across the rhumb line. Record VMG at various wind angles as you approach the rhumb line.

VMG is constantly decreasing as you move away from the rhumb line until it ultimately reaches zero (90 degree bearing to the mark)

I've had skipper's chase VMG heading away from the rhumb line by heading up until they are pinched and slowing - which of course makes it all worse.

You should know your boat speeds at several apparent angles 30 (if you can get there) 40, 45, 50. 60...

You should be aiming to nail boat speed every time.

VMG is interesting but not as important as tactics and currents. However, boat speed is fundamental.

One way to compensate for the decreasing VMG when moving away from the rhumb line is to set a waypoint 100 miles or so upwind of your mark and read the VMG to that point.

[Dockhead]

Originally Posted by Ex-Calif

You need to actually lay a rhumb line DDW from the mark and perform tacks across the rhumb line. Record VMG at various wind angles as you approach the rhumb line.

VMG is constantly decreasing as you move away from the rhumb line until it ultimately reaches zero (90 degree bearing to the mark)

I've had skipper's chase VMG heading away from the rhumb line by heading up until they are pinched and slowing - which of course makes it all worse.

You should know your boat speeds at several apparent angles 30 (if you can get there) 40, 45, 50. 60...

You should be aiming to nail boat speed every time.

VMG is interesting but not as important as tactics and currents. However, boat speed is fundamental.

Yes, that's a useful clarification. Obviously, in order to calculate VMG to windward, you need a windward mark. You can just set a waypoint which is dead upwind or nearly so. If your instruments are reasonably well calibrated, you can just read off the wind direction and put a mark bearing that. Some error will not have a big influence, because anyway you are trying to achieve the highest possible rate of advance towards a mark you can't lay in one tack, so you will be sailing as close to the wind as you can on boat tacks, that is, with max possible VMG to windward on both tacks, even if the mark is not dead to windward.

And yes, you are also correct, of course, that achieving maximum VMG to windward is not at all all there is to racing. But we weren't talking about racing per se, but about tacking angles. My point was that the meaningful tacking angle is the one on which you are getting to windward fastest; not the narrowest angle you can theoretically sail to. And that this angle is much wider than many people think, at least on cruising boats.


And yes, in my experience, it's not less than 90 degrees. I spent two weeks on a friend's Swan 90 with brand new laminate sails, mostly at the helm hand-steering (the pilot was broken), during which we sailed several hundred miles upwind. That's probably just about as hot a cruising boat that exists; the same boat routinely did 300 mile days crossing the Pacific a few months later. We cracked 90 degrees only in absolutely perfect conditions, despite professional crew on board, every hydraulic control known to man, etc., etc.. But we were, of course, sailing to max VMG to windward, not minimum angle to the wind.

Another thing to remember is the influence of current, which opens up or closes down your tacking angle. In bodies of water with strong tides, like the English Channel, you are always either getting a big lift or a big knock from the current, and it's hard to tell (as Newt mentioned) what your real tacking angle is. If you have to sail upwind, you for damn sure wait for a fair tide, because a foul tide creates absurd tacking angles which kill your ability to go upwind. A fair tide makes it a piece of cake. Unless the wind is such that the wind-over-tide required by this makes the sea conditions untenable.

In places like the Baltic, where I am now, there are no tidal currents, but the surface of the water tends to move with the wind, around a knot in a F4 or F5. This gives you a permanent knock going upwind which is really frustrating. You need a lot of boat speed to overcome that. It's no wonder that Baltic sailors mostly motor upwind.

[Ex-Calif]

Originally Posted by Dockhead

<snip>


And yes, you are also correct, of course, that achieving maximum VMG to windward is not at all all there is to racing. But we weren't talking about racing per se, but about tacking angles. My point was that the meaningful tacking angle is the one on which you are getting to windward fastest; not the narrowest angle you can theoretically sail to. And that this angle is much wider than many people think, at least on cruising boats.

I agree we are not talking about racing but best VMG is the same either case.

Originally Posted by Dockhead

<snip>

Another thing to remember is the influence of current, which opens up or closes down your tacking angle. <snip>

I am not sure it Closes down tacking angle - if lifted on one side you are knocked on the other.

Clearly there will be a favorable tack on a current, if it is at an angle to the mark. But when you do tack I think you still tack thrugh 90 (or whatever)

Hmmm...

[StuM]

> I am not sure it Closes down tacking angle - if lifted on one side you are knocked on the other.

It closes or opens tacking angle if the current is from ahead or astern, it lifts/knocks one side or the other if it is from abeam,

[Phoenician]

Back to the OP's original question (not that the ensuing discussion was not interesting, far from it!):

As regards pointing, the main difference between furling mast and a "normal" mast, is that the mast rake (or pre-bend, whichever the case) with in-mast furling must be significantly less than in normal masts, for the simple reason that with less bend in the mast, you minimize problems with the internal foil when furling in the main. (jamming etc.)

So all other things being equal, the furling mast will have less rake than the regular mast, and this, IN THEORY, will affect pointing ability.

That said, I fully subscribe to what's been said above, ie, no noticeable pointing difference in similar boats with different mast profiles - if we're talking production, cruising boats