what does "tacking through 75-800" mean

[mattonthesea]

Crewed on a sigma ( 38- 40 ish) set up for racing. Wind indicator said 29 degrees apparent on both tacks, and we were flying.
Downside was that entire crew felt sick!

Edit: forgot "apparent"

 

[Daydream believer]

Crewed on a sigma ( 38- 40 ish) set up for racing. Wind indicator said 29 degrees on both tacks, and we were flying.
Downside was that entire crew felt sick!

That would be apparent wind, which would be different to the true tacking angle.

 

[flaming]

My target upwind angles in “medium” conditions, ie 12-15 knots true, are 41 degrees with carbon sails and inhaulers and all the rest. Very little out points us. If you see a 70 degree tacking angle claim in a cruising boat review, that reviewer is talking out of their backside.

 

[AngusMcDoon]

It depends on the type of boat / rig - and where the jib sheets go gives...

It also depends on how fast a boat can sail through the water as a proportion of true wind speed. When this boat speed proportion of true wind speed increases tacking angle also increases - higher boat speed gives diminishing returns sailing upwind for performance boats. This affects trimarans, windsurfers and foiling boats particularly as they sail with a boat speed a higher proportion of true wind speed than other boats. The ultimate high speed sailing craft - ice yachts - suffer from this immensely to the point where they have to sail extremely close to their apparent wind to get upwind, for example the Skeeter - it's 6 degrees to apparent wind. Less close winded ice yachts have to slow down to get upwind at all.

Here are some figures. For all examples leeway is ignored, true wind speed remains 10 knots and the angle the boat can sail to the apparent wind remains 32 degrees...

Speed through water	Tacking angle degrees	VMG upwind
50% - 5 knots	94 degrees	3.4
80% - 8 knots	114 degrees	4.3
100% - 10 knots	128 degrees	4.4

Increasing the boat speed from 8 knots to 10 knots has almost no effect on VMG upwind in 10 knots of true wind speed - it mostly just increases the tacking angle. The best way to make good progress upwind in a trimaran is to wait for a stiff breeze. For example a boat speed of 10 knots at 32 degrees to apparent wind with a true windspeed of 20 knots gives a VMG to windward of 6.8 knots.

All boats have a boat speed a higher proportion of true wind speed in gentle winds compared to stronger ones, and so the tacking angle of all boats will vary depending on this proportion. Don't be surprised if your tacking angle is pants on a day of 5 knot wind.

 

[Chiara’s slave]

My target upwind angles in “medium” conditions, ie 12-15 knots true, are 41 degrees with carbon sails and inhaulers and all the rest. Very little out points us. If you see a 70 degree tacking angle claim in a cruising boat review, that reviewer is talking out of their backside.

Sounds about right. I’d tend to disbelieve a J70 as being capable of 33 degrees true. That too must surely be apparent. Our pointing is similar to yours. Main is sheeted til the leech appears on the centreline, flat cut 110% jib is sheeted 40cm off the centreline.

 

[Refueler]

I think mine (Parker 31) might manage 40 degrees off the wind on a good day, but like you say, at the cost of slowing down a bit. Boat has new sails and I keep bottom as clean as possible.

I’ve always assumed when they say 35-40 degrees (usually on modern racey types) they mean without slowing down a great deal to achieve that angle.

I hope OP doesn't mind this discussion ?

My Tallin race boat seen here winning the 2003 Balt Regatta in Pirita (just passing a carter 30 !!) was helmed by the 3 yrs running Laser Champion ... I'm tactics ....

She could tack to about 100 deg total and then pinch back to about 40 off the wind ... and keep good speed ... she could pinch to ~35 but you lose out ... better to accept the few deg off wind and gain speed.

It will be interesting

 

[Daydream believer]

If you cannot overtake a Carter 30 you may as well not race

 

[Refueler]

If you cannot overtake a Carter 30 you may as well not race

You don't know much about Carter then ...

The Balt Regatta was for 'classics' of the 80's .. my Saaremaa was one of the 12 that gave demo race during 1980 Olympics in Tallinn ... in fact mine was the Prototype ... built on the island of Saaremaa specifically for that .. and then sold ...
Sadly - I've mislaid the original Tallin Bay chart with the race areas marked out that she used ...

The Saaremaa is still a quick boat today ... pine on elm and oak frames.... but I would be surprised if she's still around .. she had keelson rot when I sold her - guy wanted to strip and replace ..... so I let him have it for small sum ... knowing it was going to good owner ...

 

[dunedin]

Sounds about right. I’d tend to disbelieve a J70 as being capable of 33 degrees true. That too must surely be apparent. ….

Well the link I gave in Post #11 was to the site of a top J70 team, and the file claims to be official ORC polars - and you can see it differentiates the apparent on the left and True wind angle on the right, the one I used.
Seems pretty definitive.

 

[jamie N]

Carter 30, the new Anderson 22 I reckon.......

 

[Chiara’s slave]

Well the link I gave in Post #11 was to the site of a top J70 team, and the file claims to be official ORC polars - and you can see it differentiates the apparent on the left and True wind angle on the right, the one I used.
Seems pretty definitive.

I appreciate that. But if it were true, how come our rating gives 20% to a J70, and how come we’d bately notice if one were chasing? 7kn at 33 degrees is bonkers.

 

[dunedin]

I appreciate that. But if it were true, how come our rating gives 20% to a J70, and how come we’d bately notice if one were chasing? 7kn at 33 degrees is bonkers.

I might ask the J70 European champion or the World champion next time I see them

 

[Chiara’s slave]

I might ask the J70 European champion or the World champion next time I see them

It’s the only way.

 

[Daydream believer]

You don't know much about Carter then ...

Well I have beaten Carter 30s boat for boat in my Stella back in the 70s. Obviously it depended on the sailors but they were EAORA races & local port to port races. Different with the Carter 33 though.

 

[Chiara’s slave]

https://www.quantumsails.com/en/sails/one-design/documents/j70/j70_perftargets_june2020.aspx

seems a bit more realistic.

 

[Daydream believer]

I hope OP doesn't mind this discussion ?

My Tallin race boat seen here winning the 2003 Balt Regatta in Pirita (just passing a carter 30 !!) was helmed by the 3 yrs running Laser Champion ... I'm tactics ....

She could tack to about 100 deg total and then pinch back to about 40 off the wind ... and keep good speed ... she could pinch to ~35 but you lose out ... better to accept the few deg off wind and gain speed.

Surprised you get anywhere with all that lot stuck in the stern.

 

[AngusMcDoon]

https://www.quantumsails.com/en/sails/one-design/documents/j70/j70_perftargets_june2020.aspx

seems a bit more realistic.

To achieve the first entry in the upwind table (4 knots TWS, 4 knots boat speed, 45 degrees TWA) from solving the vector diagram it would require the boat to sail with an apparent wind angle of 22.5 degrees, and that's ignoring leeway, so likely to be less than 20 degrees apparent wind angle taking that into account. Is that realistic? I've never sailed a boat that can do that.

The figures can be calculated here...

Triangle Calculator

Enter boat speed on side b, TWS on side a and 180-TWA for angle C and press calculate. On the result angle A is AWA and side c AWS. Does anyone else do vector diagrams, or am I talking to myself here?

 

[Chiara’s slave]

That one is way less radical that the polars Dunedin quoted. Yet still as you say, still optimistic. What is it about the J70?

 

[flaming]

That one is way less radical that the polars Dunedin quoted. Yet still as you say, still optimistic. What is it about the J70?

Angle slightly better than us, speed 1-2 knots slower. Seems about right to me.

 

[Chiara’s slave]

Angle slightly better than us, speed 1-2 knots slower. Seems about right to me.

My boat is radically quick, but it won’t do 4kn at 45 deg true in 4kn of wind. I might do that at 100 true with the kite up.