Cruising cat - sub 90 degrees tack upwind

[jmh2002]

Originally Posted by Factor

If its not speed through water then its all a bit pointless

And it needs to be 'accurately calibrated' speed through the water too

[Tin Tin]

Originally Posted by Factor

If its not speed through water then its all a bit pointless

When does SOG = Speed through water?

[arsenelupiga]

Originally Posted by Factor

If its not speed through water then its all a bit pointless

i think it is more accurate actually. We know there is no current. so speed thru water = GPS speed.

I proven the point that leeway is less than what is commonly believed, at least for Lagoon 400. Speed in this case is not that important. I will do another test with gennaker. Now I know that leeway will not be large so see what we can squeeze out with this old gennaker. White sails in 6-8 kn true are not adequate.

[arsenelupiga]

Originally Posted by jmh2002

And it needs to be 'accurately calibrated' speed through the water too

yeah, and wind gauge as well !

there is lots of error possible going that route. Going GPS and no current is more accurate approach.

[arsenelupiga]

as my geenaker will soon be retired, I plan and in process of design new one that will be upwind oriented. ~ 10 % smaller. So that is one reason for these tests. And then i think will get large assym. And current smaller sym will be for stronger winds.

[Paul L]

Originally Posted by Tin Tin

When does SOG = Speed through water?

No currentand, no leeway and same averaging period.

[arsenelupiga]

anyone outside AUS: east coast australia went recently thru 1 in a 100 years flooding and waters are still very polluted. Visibility in lake say 0.5m. Swimming not advised, on top of that corona found in waters. So I am behind my hull cleaning schedule and will be so for a while.

Speeds will be slightly to considerably less due to hull growth but dont see why tacking angles would be affected.

[arsenelupiga]

The fact that fixed keels produce excellent results regarding leeway one is forgiven to ask :

WHY BOTHER WITH DAGGERBOARDS?

they cost you 600kg in carrying capacity including properly reinforced hull

they cost extra space

extra gear required and deck space cluttered.

then can break, and cause hull damage if unlucky

You can push them all the way down when sea running and sailing upwind, this is when bad seas and uncomfortable drive. You get better angle. But if you do not like beating in such conditions then this argument not valid.

You can also pull them up and have less drag downwind.

Is it really worth it? How much would Outremer 55 be slower with fixed keels overall ?

[fxykty]

Originally Posted by arsenelupiga

The fact that fixed keels produce excellent results regarding leeway one is forgiven to ask :

WHY BOTHER WITH DAGGERBOARDS?

they cost you 600kg in carrying capacity including properly reinforced hull

they cost extra space

extra gear required and deck space cluttered.

then can break, and cause hull damage if unlucky

You can push them all the way down when sea running and sailing upwind, this is when bad seas and uncomfortable drive. You get better angle. But if you do not like beating in such conditions then this argument not valid.

You can also pull them up and have less drag downwind.

Is it really worth it? How much would Outremer 55 be slower with fixed keels overall ?

Your first fixed keel statement is not correct as you are using your optimised n=1 example to generalise. If it was true, many more catamarans of your sort would be sailing in the conditions and directions that we commonly see them motoring.

Physics do not lie: the foil profile and geometry of a low aspect fixed keel have more drag and lower efficiency than a high aspect daggerboard of the same size.

Outremer AFAIK has not made any boats with fixed keels. But Larouge (sp?) has a mixture of fixed keels and daggerboards on his designs. His comment is that for a small performance and safety hit the fixed keel gains interior space, simplicity for those who consider lifting and dropping daggerboards to be a hassle, and slightly less structural weight (3 of your points above). Note that Larouge designs are relatively light, semi-custom, performance cruising catamarans.

Break and possible hull damage - same problem for fixed keels.

Deck space cluttered? It’s one extra control line and clutch per side, out of the 10 or so already there.

You didn’t mention safety in bigger seas - the ability of a daggerboard boat to raise its leeward daggerboard and reduce tripping hazard.

Nor the ability of daggerboard boats, especially if combined with lifting rudders, to go into shallower waters and to comfortably beach, without being up on stilts. Not a benefit of ours unfortunately, unless it’s a sloping beach, due to our fixed rudders and skegs sticking down about 30cm more than our hulls.

[44'cruisingcat]

Originally Posted by arsenelupiga

Speeds will be slightly to considerably less due to hull growth but dont see why tacking angles would be affected.

Then I'll try to explain it to you again.

The slower you sail, the smaller the difference between TWA and AWA. So if you sail the same apparent wind angle, but slower, your tacking angle will be reduced.

This is why it's easier to achieve the fabled 90' tacks on slow boats.

[Jim Cate]

Originally Posted by 44'cruisingcat

Then I'll try to explain it to you again.

The slower you sail, the smaller the difference between TWA and AWA. So if you sail the same apparent wind angle, but slower, your tacking angle will be reduced.

This is why it's easier to achieve the fabled 90' tacks on slow boats.

This. Plus, fouling on the mini keels will increase drag and reduce lift so leeway will increase.

Jim

[Factor]

Originally Posted by arsenelupiga

The fact that fixed keels produce excellent results regarding leeway one is forgiven to ask :

WHY BOTHER WITH DAGGERBOARDS?

they cost you 600kg in carrying capacity including properly reinforced hull

they cost extra space

extra gear required and deck space cluttered.

then can break, and cause hull damage if unlucky

You can push them all the way down when sea running and sailing upwind, this is when bad seas and uncomfortable drive. You get better angle. But if you do not like beating in such conditions then this argument not valid.

You can also pull them up and have less drag downwind.

Is it really worth it? How much would Outremer 55 be slower with fixed keels overall ?

Because they are better upwind, there is simply no way a Low Aspect Ratio Foil can perform as well as a HAR foil. Thats not me talking that is NACA, then again the study of foils has only been their focus for about 100 years.

Because they are better downwind, less drag,

Because they are better in severe conditions, less tripping danger.

I have sailed a SW1160 and Sw1190, pretty much the same boat, the 1190 (the one with daggerboards) is demonstrably quicker and sails higher, that doesn't make the 1160 a bad boat, just makes the 1190 a better performing boat. Notably boat boats are reasonably light and have slim hulls

But if you sail heavy and fat hulls, and you sail slow you can get tight angles, but in the real world when dealing with current tide wave action on hulls fat bows that move with the sea rather than through it you wont go anywhere.

And anyway, what would the people who designed your boat know, when tasked with designing a high performance gunboat they thought that daggerboards might work. (See attached reference from their website) When tasked with designing a 77foot Outremer they did the same. Still what would they know, or indeed what would Chris White, Jeff Schionning, Tony Grainger, Loch Crowther, Rachel Pugh Design, et al know. What would NACA know?

Mini keel boats are not by definition bad, indeed for most people they are probably the best choice, BUT performance to windward and downwind is not their forte.

[Factor]

Originally Posted by arsenelupiga

Done test in Lake Mcqaire. Patchy winds but managed to get drawn legit results. Wind 6 - 8 kn during test. Tack angles 2 x 91 degrees. Used apparent wind 32 on AP. Used speed from GPS as wheel stopped work. More precise as no current. This translates into 1.6 to 2 kn VMG.

It means boat sailed at 43 true angle, so with no leeway we should see 86 degrees tack. But we have seen 91. Therefore leeway in such conditions is 2.5 degrees. This is much less than what literature says - 10 degress +.

If we get chance will repeat my test with gennaker. Now I am pretty sure sub 90 tacks are real and that is where best VMG lies for our boat.

Have also checked under water shape and it does makes sense boat does so well upwind. Keels are quite large compared to body, especially as hulls are shallow. We draw only 1.25 m (measured with 2.5 t of stuff). red line is actual waterline.

Do you have to bear away to tack? It seems so from your track diagram?

[44'cruisingcat]

Originally Posted by arsenelupiga

The fact that fixed keels produce excellent results regarding leeway one is forgiven to ask :

WHY BOTHER WITH DAGGERBOARDS?

they cost you 600kg in carrying capacity including properly reinforced hull

they cost extra space

extra gear required and deck space cluttered.

then can break, and cause hull damage if unlucky

You can push them all the way down when sea running and sailing upwind, this is when bad seas and uncomfortable drive. You get better angle. But if you do not like beating in such conditions then this argument not valid.

You can also pull them up and have less drag downwind.

Is it really worth it? How much would Outremer 55 be slower with fixed keels overall ?

1: Not 600 kg, or anything like it.

2: Reduced draught.

3: Greatly reduced sailing around at anchor.

4: Significantly less wind against tide hassles at anchor. We once spent a week repairing a friends minikeel from damage sustained when it got chain wrapped around it.

5: Significant performance gains on virtually all points of sail. The windward gain is possibly the least of it. A minikeel boat is sort of like a daggerboard boat with boards stuck partway down. Not really what you want on most points of sail.

6: Greater safety in extreme conditions. As pointed out above, reduced grip in big waves can help prevent capsize.

7: Safer for bar crossings. A cat with boards up is like a surfboard. It'll tend to keep pointing down waves, rather than turning side on.

[Factor]

These blokes need minikeels if they really want to go well.