Cruising cat - sub 90 degrees tack upwind

[arsenelupiga]

Originally Posted by arsenelupiga

at 35 app in 10 kn of wind, max possible VMG is 3.66 kn at 7.2 kn boat speed, assuming no leeway.

Our L 400 does in 10 kn wind with main and jib 4.0 kn at 31 app, which is 2.93 kn vmg. This is only 20 % less than best VMG at 35 app. At 35 our boat would have to go 4.6kn to achieve same but i dont think we can increase .6 kn with 4 degrees more.

sorry that is wrong. reversed formuals and best VMG is 3.86kn at 8.6 kn boat speed. in 10 kn true at 35 app.

[44'cruisingcat]

Originally Posted by arsenelupiga

if you too slow there is a drag. IF 10 deg drag, you need to point 25. Especially draggeboards boats that work better at higher speeds. Keels are different. Remember seawind 1250 chasing me upwind at larger angle. Still beginners back then, we were doing 38 app and he was left behind. So drag of keel boats at slower speeds is less. Speed at all costs for keel boats may be wrong receipe. At 6 kn and 30 app we seem to be doing very little leeway.

The Seawind 1250 is a minikeel boat.

[fxykty]

Originally Posted by arsenelupiga

if you too slow there is a drag. IF 10 deg drag, you need to point 25. Especially draggeboards boats that work better at higher speeds. Keels are different. Remember seawind 1250 chasing me upwind at larger angle. Still beginners back then, we were doing 38 app and he was left behind. So drag of keel boats at slower speeds is less. Speed at all costs for keel boats may be wrong receipe. At 6 kn and 30 app we seem to be doing very little leeway.

I think you’re mistaking drag (both form and wetted surface) for leeway.

A mini keel catamaran will almost always have wider hulls and more wetted surface. Further, mini keels do not have, by their actual physical attributes, a clean NACA foil shape as they are too long in the cord for their height, so they also have shape drag. Each of these factors are not issues for properly designed daggerboards - there will always be less drag for a daggerboard cat.

But of course, the greater surface area of the mini keels will help reduce leeway at slower speeds, as long as you’re applying sufficient power to overcome the greater drag. With your optimised sail plan it seems to me that’s what you’re doing and why you’re successful with your slow and high strategy.

A daggerboard cat will need higher speed to maintain flow over the daggerboards and to overcome the smaller area, hence high and slow don’t work well for optimum VMG.

Note that this works the same for monohulls - full keeled boats can point very high, while fin keeled boats will need to go lower to maintain flow on their smaller (surface area) keels and avoid excess leeway.

90 degree tacks are a fetish as it’s not an absolute number that everyone should aspire to.

[jmh2002]

Originally Posted by fxykty

...the greater surface area of the mini keels will help reduce leeway at slower speeds, as long as you’re applying sufficient power to overcome the greater drag. With your optimised sail plan it seems to me that’s what you’re doing and why you’re successful with your slow and high strategy.

Originally Posted by fxykty

Note that this works the same for monohulls - full keeled boats can point very high, while fin keeled boats will need to go lower to maintain flow on their smaller (surface area) keels and avoid excess leeway.

A nice simple explanation and comparison about the relative "grip" (lateral resistance) that different designs are able to exert in the water

[arsenelupiga]

Originally Posted by 44'cruisingcat

The Seawind 1250 is a minikeel boat.

exactly my point. he used possibly wrong strategy to compete. Not all keel cats are the same, but it is worth a try.

i have noticed that polar of l 400, although understated, curved up even at sharp angles so sharper upwind producer better vmg. Normally cat polars max VMG at around 60. Maybe this ability is property of this type of boat ...

[arsenelupiga]

Originally Posted by jmh2002

A nice simple explanation and comparison about the relative "grip" (lateral resistance) that different designs are able to exert in the water

[44'cruisingcat]

Originally Posted by Dave_S

But it reduces VMG. To increase VMG you need to increase the angle between AWA and TWA.

Yes, slowing the boat to reduce tacking angles will generally not be optimizing VMG. As I said, you could do this if achieving sub 90' tacks was important to you.

[Dave_S]

Originally Posted by 44'cruisingcat

Yes, slowing the boat to reduce tacking angles will generally not be optimizing VMG. As I said, you could do this if achieving sub 90' tacks was important to you.

I knew you understood, it was you guys who started me on this path of all things VMG years ago when I asked for help with it I just wasn't sure it was clear to arsenelupiga that the quest for tight tacking angles wasn't the same as best VMG.

[Factor]

Originally Posted by Factor

The laws of physics have finally been bent.

I should also clarify, my comment wasnt in response to dave S. It was in response to the suggestion that LAR minikeels can achieve a higher angle to windward than a daggerboard, all other things (sails etc), being equal

[Factor]

Originally Posted by arsenelupiga

if you too slow there is a drag. IF 10 deg drag, you need to point 25. Especially draggeboards boats that work better at higher speeds. Keels are different. Remember seawind 1250 chasing me upwind at larger angle. Still beginners back then, we were doing 38 app and he was left behind. So drag of keel boats at slower speeds is less. Speed at all costs for keel boats may be wrong receipe. At 6 kn and 30 app we seem to be doing very little leeway.

Which 1250, I know most of them - huge difference in skill and sail cloth

[arsenelupiga]

Originally Posted by Factor

Which 1250, I know most of them - huge difference in skill and sail cloth

couple of years ago. i think extra pics on hulls. pittwater to harbour. Boat looked liveaboard. No special sails.

[arsenelupiga]

Originally Posted by Factor

I should also clarify, my comment wasnt in response to dave S. It was in response to the suggestion that LAR minikeels can achieve a higher angle to windward than a daggerboard, all other things (sails etc), being equal

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.

[arsenelupiga]

Originally Posted by arsenelupiga

couple of years ago. i think extra pics on hulls. pittwater to harbour. Boat looked liveaboard. No special sails.

First after Seawind 1000 was Seawind 1160. Nice boat on our list but was too pricey at the time. Then after that Seawind introduced Seawind 1250 that was enlarged copy of 1160. That is the model. It is also possible 1160 but when we were close i estimated boat longer than ours.

[arsenelupiga]

Originally Posted by Dave_S

I knew you understood, it was you guys who started me on this path of all things VMG years ago when I asked for help with it I just wasn't sure it was clear to arsenelupiga that the quest for tight tacking angles wasn't the same as best VMG.

i get that tightest angle may not be best vmg angle. That is something i am working on. New technique (for me) i use - tighten jib halyard - improves pointing and do not know where best VMG is. Although suspect may be the sharpest angle boat can handle comfortably - hulls glued to sea and sail working properly - in given conditions.

[Dave_S]

Originally Posted by arsenelupiga

i get that tightest angle may not be best vmg angle. That is something i am working on. New technique (for me) i use - tighten jib halyard - improves pointing and do not know where best VMG is. Although suspect may be the sharpest angle boat can handle comfortably - hulls glued to sea and sail working properly - in given conditions.

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.

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