Newb Multihull wind angle question

[longjonsilver]

Originally Posted by 44'cruisingcat

He said 13' apparent upwind, 19' apparent downwind.

Does 14' mean 14 minutes or 14 degrees??? Just to be clear.

jon

[44'cruisingcat]

Seconds.

[Training Wheels]

Impressive!

[longjonsilver]

So you just point the boat into the wind and off she goes!

[wcapital]

To add a couple more points to this already extensive discussion:
- optimum pointing angle (to maximize VMG) in a cat typically much more variable subject to sea conditions....as, the lighter the boat (of any design, all else being equal) the more it will be slowed by waves. Our 44' cruising cat might optimally tack thru 90 degrees in completely flat water, but only 120 or more with big, short steep waves.
- leeway is another important consideration - though perhaps not technically affecting pointing angle it certainly affects CMG/VMG. Hull shape and (not) having daggerboards makes a big difference
These considerations of course apply to monos as well, but tend to be more important with more pronounced variations with multis

[tomtriad]

I sail an unusually close winded multihull, a Newick trimaran, which sails at 2/3 windspeed at about 30 degress AWA and tacks through 90 degrees true. I trim for upwind by sheeting in the jib tight to my spreaders and sailing on the tell tales, getting them to stream on both sides. It helps to steer up and luff the inner slightly on occasion to be sure of sailing the tightest angle. If I bear off a bit to a close reach without touching the trim the boat will accelerate but the lee side tell tales on both the jib and main will start to luff; by easing the main a bit the boat will accelerate more, up to wind speed, and the AWA will creep forward again flying the tell tales on both sides of the jib. So, it's all about balance, keeping a sharp eye on the tell tales, and sensing when the boat is accelerating too quickly for a beat. Keeping a feel for an easier ride is also important for crew comfort, so pinching a bit in rough conditions will lessen the stress on both boat and crew while making good headway upwind. Most cats won't sail as well to windward, owing to more windage and a looser headstay, but a well designed light weight one will do quite well, maybe tacking through 100 degrees true.

[Paul Howard]

My first catamaran was a typical 38ft early 90's cruising boat, four cabins, two heads, fixed keels, etc., and the TWA and AWA going to windward was little different from when I sailed on monohulls. We did average many more miles per day with the catamaran, about 180miles per 24 hours, not pushing or being uncomfortable, as opposed to about 115miles we averaged in our previous monohull on long ocean passages.
I now own a Walter Greene design 38ft catamaran with half the displacement of the previous cat, daggerboards, etc. My wife and I did a cruise including Cuba and Bahamas and back to Toronto on that boat, with the longest passage less than three days, complicated by lots of current, the Gulfstream, etc., so I did not get a real sense of what the boat would average, though I felt that the boat was a champ to windward based on the AWA and SOG, as there were no tacking duels but lots of searoom.

I am now doing some club racing (Toronto Multihull Cruising Club) with other cats and tris and am struggling with the chasing of the streamers or heading up. My kevlar sails can flatten out well and the windex seems to point almost over the bow, lots of boat speed in the light winds of Lake Ontario, but tacking through 130degrees is not unusual. Heading up and speed drops. I am still learning how to get the best performance out of the boat trying to drive it to windward compared to my fellow members with Corsairs, Farriers, Newicks, Crowthers, etc.
So all I am saying is that, yes, that tight to windward AWA and SOG is a challenge when doing short tacking and racing, but for ocean cruising, it matters little.

[sailjumanji]

Originally Posted by Jim Cate

Phil, I came up with a kina silly question whilst reading your post: With opaque (ie carbon) sails, how do folks read their leeward telltals? i don't see clear windows let into such sails...

Jim

I have Dimension Polyant GPL Lite Skin sails. Black, carbon material. The jib has clear windows for telltales. The main has leech telltales, as well as some on the body of the sail lower, that don't have windows. For those you just have to walk to the other side and peek! Seawind 1160 Lite catamaran.

[Don C L]

Originally Posted by tomtriad

I sail an unusually close winded multihull, a Newick trimaran, which sails at 2/3 windspeed at about 30 degress AWA and tacks through 90 degrees true. I trim for upwind by sheeting in the jib tight to my spreaders and sailing on the tell tales, getting them to stream on both sides. It helps to steer up and luff the inner slightly on occasion to be sure of sailing the tightest angle. If I bear off a bit to a close reach without touching the trim the boat will accelerate but the lee side tell tales on both the jib and main will start to luff; by easing the main a bit the boat will accelerate more, up to wind speed, and the AWA will creep forward again flying the tell tales on both sides of the jib. So, it's all about balance, keeping a sharp eye on the tell tales, and sensing when the boat is accelerating too quickly for a beat. Keeping a feel for an easier ride is also important for crew comfort, so pinching a bit in rough conditions will lessen the stress on both boat and crew while making good headway upwind. Most cats won't sail as well to windward, owing to more windage and a looser headstay, but a well designed light weight one will do quite well, maybe tacking through 100 degrees true.

never sailed one, but good to hear my lust for Newicks is not misplaced!

[Just Another Sa]

Originally Posted by 44'cruisingcat

I dislike being accused of lying.

It's notable that the person making the accusation has, after being proven wrong repeatedly and running off wailing to the moderators, failed to answer any of the factual points I've made.

The fact was and still is, that the AC50 boats sailed downwind at TWA=155 degrees in 8 knots of truewind with boatspeed of 24 knots. All that data comes from real world measurements made public by AC35 organisation, and is far more accurate and precise than anything recorded before on sailboats. The data monitoring system they used was truly at the very top level in every way.

What the AWA was at those times is not a matter of opinion either, but a mathematical fact.
What some sailor of SAILGP team said to you is and will remain as an unproven opinion at best, not a fact. A big difference, and have nothing to do with the irrelevant fact I have not sailed sailGP catamaran. That was just your way of attempting to confuse the followers of that discussion.

Unfortunately you seem to be unable to distinguish fact and opinion. Therefore I concluded there was no point in continuing to discuss this issue with you until you have calmed down.

Of course there is far less true wind down low near water, like at the end of prodder, which means that AWA at that height will be even less, perhaps just 50% of the value calculated from the facts mentioned.
So less than 14 degrees AWA at mast top, and most likely in the order of 7 degrees at the prodder altitude at optimum downwind VMG point of sail with 8 knots of true wind.

With awa 19 degrees and twa 155 degrees and TWS 8 knots, boatspeed would be less than 17.1 knots. That is so far off the real world measurement of 24 knots of boatspeed AC50 catamarans were capable of in those conditions that the claim is really not even worth responding to.
The only explanations making any sense at all from such claim is either lying or instrument error. I suggested the latter, and you kept insisting that is not the case, leaving only the former possibility. And of course you now seem to indicate my original thought was correct and such claim was not made regarding those conditions, but in some other conditions. Like I already wrote long ago, awa will not remain constant in those kind of boats, but change significantly with windspeed. 42...43 knots of boatspeed in 20 knots of true wind would lead into 19 degrees apparent. But still far less than 12 degrees apparent at prodder height due to much less truewind down there.
19 degrees apparent will not happen at prodder height for those boats when they are up to speed at any point of sail. With the level of performance those cats are capable of, it is simply mathematically impossible.

You have not made any factual points in this matter and you have not proven anything I wrote wrong. I haven't wailed to moderators either, ask them if you don't believe me.
Or keep making absurd claims like that if that is what you really want to do.

[Training Wheels]

Just curious, am I the only one here who doesn’t care?

[Tillsbury]

Originally Posted by Training Wheels

Just curious, am I the only one here who doesn’t care?

To my surprise, I find that I *can* actually care less...

[44'cruisingcat]

Originally Posted by Just Another Sa

The fact was and still is, that the AC50 boats sailed downwind at TWA=155 degrees in 8 knots of truewind with boatspeed of 24 knots. All that data comes from real world measurements made public by AC35 organisation, and is far more accurate and precise than anything recorded before on sailboats. The data monitoring system they used was truly at the very top level in every way.

What the AWA was at those times is not a matter of opinion either, but a mathematical fact.
What some sailor of SAILGP team said to you is and will remain as an unproven opinion at best, not a fact. A big difference, and have nothing to do with the irrelevant fact I have not sailed sailGP catamaran. That was just your way of attempting to confuse the followers of that discussion.

Unfortunately you seem to be unable to distinguish fact and opinion. Therefore I concluded there was no point in continuing to discuss this issue with you until you have calmed down.

Of course there is far less true wind down low near water, like at the end of prodder, which means that AWA at that height will be even less, perhaps just 50% of the value calculated from the facts mentioned.
So less than 14 degrees AWA at mast top, and most likely in the order of 7 degrees at the prodder altitude at optimum downwind VMG point of sail with 8 knots of true wind.

With awa 19 degrees and twa 155 degrees and TWS 8 knots, boatspeed would be less than 17.1 knots. That is so far off the real world measurement of 24 knots of boatspeed AC50 catamarans were capable of in those conditions that the claim is really not even worth responding to.
The only explanations making any sense at all from such claim is either lying or instrument error. I suggested the latter, and you kept insisting that is not the case, leaving only the former possibility. And of course you now seem to indicate my original thought was correct and such claim was not made regarding those conditions, but in some other conditions. Like I already wrote long ago, awa will not remain constant in those kind of boats, but change significantly with windspeed. 42...43 knots of boatspeed in 20 knots of true wind would lead into 19 degrees apparent. But still far less than 12 degrees apparent at prodder height due to much less truewind down there.
19 degrees apparent will not happen at prodder height for those boats when they are up to speed at any point of sail. With the level of performance those cats are capable of, it is simply mathematically impossible.

You have not made any factual points in this matter and you have not proven anything I wrote wrong. I haven't wailed to moderators either, ask them if you don't believe me.
Or keep making absurd claims like that if that is what you really want to do.

Good heavens! You completely make up a load of numbers, guess at a bunch of others, then go on about no facts!

By the way, how did they get the precise true wind angle without using any onboard instruments?

[44'cruisingcat]

TWS 7kts.
AWA 14degrees.
Boatspeed 21 kts.

VMG to wind 10.33kts
TWA 60.5 degrees.

= NOT sailing downwind.

[StuM]

Originally Posted by 44'cruisingcat

TWS 7kts.
AWA 14degrees.
Boatspeed 21 kts.

VMG to wind 10.33kts
TWA 60.5 degrees.

= NOT sailing downwind.

True. But this IS sailing downwind

TWS 7 kts
TWA 148°


AWA = 14°
Boatspeed = 21kts