Cruising cat - sub 90 degrees tack upwind

[arsenelupiga]

Originally Posted by Dave_S

I'm never sure if your pulling our legs about the results you are getting with your boat, they seem too good and I think maybe the tide was with you and not against you . There is a boat the same as yours on my arm at the marina. It looks very fat and not really made for sailing but it all makes for interesting conversation.

i am not making it up. To my argument adds ex member Monte that claimed better results than me with his L 400 at 90 over ground. Django's results are even better but he is a bit of racer and L 380.

I have achieved now same results in what i believe no current or even against current 3 x. even if there was a current here, cant be in all directions. I have avoided squall here.

Originally Posted by Dave_S

One thing I have noticed is the top of the polars on the more luxurious boats are flatter than mine. If I sail at 30° I might drift between 28 and 32 which is ok but if I hit 26 it's like putting on the brakes. I noticed in your video you lost speed but not as dramatic as my boat and you drifted way passed the top on some swings. I suspect your best VMG maybe a little passed the the top of the polar just because it doesn't cost you much on speed but the extra degree or two will make a difference possibly more than the windage and drop in speed,.... Only one way to find out

sorry no video from me. GRIT has done it but his boat is really fast 50 footer. Yeah, i cant do what he did. That discussion was really intended for keeled boats, promoting new technique.

[44'cruisingcat]

Originally Posted by arsenelupiga

maybe at lower speeds ? Unless i was every time in favourable current, which i try hard to eliminate, how else i could produce these tracks ? We point up to 30 app in low to medium winds, say 4 kn in 10 kn true. How could possibly be leeway 10 degrees? or even 5? Maybe 3 or 4, according to this calc.

A VMG calculator can't give any idea about leeway.

Looking at heading compared to COG on both tacks gives some idea, but doesn't account for tide.

[arsenelupiga]

Originally Posted by 44'cruisingcat

A VMG calculator can't give any idea about leeway.

Looking at heading compared to COG on both tacks gives some idea, but doesn't account for tide.

angle of tack from track over ground = 90

angle of true wind sailed from excel = 41

Therefore leeway = (90 - 2x 41) / 2 = 4 degrees.

[arsenelupiga]

Originally Posted by Dave_S

There is a boat the same as yours on my arm at the marina. It looks very fat and not really made for sailing but it all makes for interesting conversation.

i know what you mean. Our boat is quite light and aerodynamic compared to other l 400. It took me a while to balance it. Largest issue was 160kg of gel batteries pushing down port stern, replaced by 56 kg of lithium. We also do not have 240 V on board except thru honda. No diesel gen. We probably 10 cm higher than average L 400. That is plenty of wetted surface ~ 5m2 out of 43m2.

Then it took me a while to learn to sail upwind up to the point i am now.

Will try more and report back, ideally in zero-current environment if i can find one.

[44'cruisingcat]

Lake Macquarie is probably the only dependably current free sailing venue I can think of on the east coast.

Of course, being a lake, the wind can be a bit shifty....

[arsenelupiga]

Originally Posted by 44'cruisingcat

Lake Macquarie is probably the only dependably current free sailing venue I can think of on the east coast.

Of course, being a lake, the wind can be a bit shifty....

ok, sounds good. I think we will make it there somewhere mar/april. Good place to dive and hull clean. Will do more tacks, so shifts should cancel out more or less.

Will report back even if proven wrong. Good data point so one can gauge true impact of weight on fat cat like L 400 is.

[Dave_S]

Originally Posted by 44'cruisingcat

A VMG calculator can't give any idea about leeway.

Looking at heading compared to COG on both tacks gives some idea, but doesn't account for tide.

It makes you wonder why all VMG calculations aren't made on plotters by using COG and SOG.


As you were, I figured it out.

[arsenelupiga]

Originally Posted by Dave_S

It makes you wonder why all VMG calculations aren't made on plotters by using COG and SOG.


As you were, I figured it out.

My speedo stopped working due to growth, when I had my raymarine AP set to true wind (not apparent) windwane, noticed it used SOG to calculate true wind.

Maybe what you want is available when one uses true wind (at least raymarine)?

[Factor]

Interesting - I tried to make mine use SOG, but couldnt achieve it, spent some days going back and forth with Raymarine and they couldnt assist. Mind you that was 5 years ago.

[django37]

The L380 and 410 have relatively deeper and shorter keels than the newer Lagoons and therefor less induced resistance going to windward. As Arsenlupiga says: Good sails, folding props, lightly loaded, but first of all a lot of sailing praxis is needed. Whether the hulls are deep and narrow or wide and flat is not important. My 380 is my 7th cruising cat, and the first I have not designed myself

[arsenelupiga]

Originally Posted by django37

The L380 and 410 have relatively deeper and shorter keels than the newer Lagoons and therefor less induced resistance going to windward. As Arsenlupiga says: Good sails, folding props, lightly loaded, but first of all a lot of sailing praxis is needed. Whether the hulls are deep and narrow or wide and flat is not important. My 380 is my 7th cruising cat, and the first I have not designed myself

Very interesting statement from someone with real design experience ! So you basically saying narrow hull shape does not add any benefits, compared to lagoon like hulls, for upwind work, apart from standard narrow hulls being bit faster. That is quite against accepted norm but from my experience, that could as well be right.

[django37]

Have designed many cats having a Master of Science degree in Naval Architure from the Tecnical University of Denmark, designed and built my first cat in 1971, and have sailed round the world in our L380. The accepted norm about of high length to beam being faster comes from high length to beam normally means the boat is lighter. But if we fix length and displacement, many cats would be faster with more beamy hulls at the waterline. Best relation between waterline beam and depth of a hull is around 2.5 to 1. This because it doesnt sink so much between its own waves at speed and get more wetted surface as the narrower hull.

[Dave_S]

Originally Posted by django37

Have designed many cats having a Master of Science degree in Naval Architure from the Tecnical University of Denmark, designed and built my first cat in 1971, and have sailed round the world in our L380. The accepted norm about of high length to beam being faster comes from high length to beam normally means the boat is lighter. But if we fix length and displacement, many cats would be faster with more beamy hulls at the waterline. Best relation between waterline beam and depth of a hull is around 2.5 to 1. This because it doesnt sink so much between its own waves at speed and get more wetted surface as the narrower hull.

I'm having trouble following this. This is really a question, I don't mean this as a dispute but this would be my understanding.

If displacement and length are equal and one boat has 2 to 1 hulls and the other 2.5 to 1 hulls and each boat is sailing on flat water the 2 to 1 hulls will be narrower and deeper but with a more efficient displacement to wetted surface ratio. Then surely with less wetted surface and a smaller silhouette when viewed from the front this will have less drag.

If the sea state increases and the boat starts to hobby horse then the broader hull will submerge less in distance but almost equal in volume submerged, it seems hard to imagine that the difference would be enough to close the gap between the two boats.

[Training Wheels]

The fatter hulls would have less wetted surface for a given displacement.

[django37]

Waterlinebeam to depth of a semicircular (Ratio 2:1) underwater section has the min. wetted surface at rest, but as speed builds up, a flatter section has less wetted surface. Basicly, the water doesnt care if it has to moove to the sides or down as the boat passes - again length and displacement fixed.