Sailing Downwind . . . Centerboard Up or Down for Max VMG ?

[senormechanico]

It depends a bit on wind strength, but in 8 true, it's around 130-40?
It also depends on how much junk and food we have aboard.
If we're going on a 6 week vacation, the boat's about an inch and a half lower in the water !!

Ever driven a VW bug by yourself and then with 3 more people? Same thing.

[northwestsailor]

For me it depends on sea state too. We are a mono but retractable. The hard chines by themselves give some directional stability so we adjust the keel to match the wave action ie bigger the waves the less keel is exposed. On the other hand we rarely have the keel fully up and almost always leave the trailing edge exposed to the slipstream. Fully up means we want to beach or use a very shallow anchorage.

[Tri]

In 8 true I have 150 TWA (6kn) as target for VMG max downwind with bord down.


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[Tri]

We tried it now with board up or down in about about 13 knots tws and constant twa of 150. the difference in vmg (course to waypoint) according to the instruments was 0,3 knots.

Given the fact we had to go ddw to get the board up and later down again I felt it will only be worth the hassle on a longer passage (if at all).

[44'cruisingcat]

Originally Posted by estarzinger

I would have thought Up = less wetted surface = less drag = faster.

Exactly right.

[Tri]

Sure, sorry, I thought that was self explanatory. Board up = 0,3 knots faster but more hassle and a lot more active autopilot (we tried to keep conditions as equal as possible).

[44'cruisingcat]

More hassle to go faster? Well, trimming sails is more hassle than not trimming them. Hoisting sails is more hassle than not. But you do sail faster...


If you're just going to leave boards down all the time, might as well have mini-keels.

[thomm225]

Board should be about half way down on the downwind legs.

You don't need it all the way down for tracking...........It's downwind

[44'cruisingcat]

You don't need it down at all.

[Tri]

:-). Up is 50 cm, down is 2 meter draft, a mini keel will not do the trick (especially for beaching or in shallow areas).

If you figure the time lost to go ddw in order to take the board up and down again so you don't damage the boards swing mechanism vs just sailing a max VMG (course) downwind to follow your (not straight) course, you might end up faster one way or the other (depending on how long the leg is).

To be frank, I think there are other ways to increase speed significantly (especially for a tri) but in essence of course you are right.

[44'cruisingcat]

Really, you ought to be able to raise or lower the board on any point of sail. We can. Takes a little longer when it's loaded, but it's still easy enough.

[Tri]

No chance if there is pressure on the board. You would also ruin the stuff.

[thomm225]

Originally Posted by 44'cruisingcat

You don't need it down at all.

That's true since many catamarans don't have boards at all. I've had 2 with boards, and 2 without boards

(but) I certainly like a bit of board in the water going downwind at 20 knots with the spinnaker flying and being singlehanded on a 300 lb cat.