Performance Study: Daggerboards & Fixed Keels

[Shammi]

Multihull Company recently commissioned an 'apples-to-apples' study on comparing the performance of Balance 526 catamarans. The intent was to demonstrate a clear performance difference in favor of daggerboards. The article does provide a caveat that, "The disparity between keels and boards on a mass-production cat compared to a Balance or any other performance cat would be exaggerated considerably compared to the study that follows."
The article makes a few bold statements like, "...it can be seen that the daggerboard design will typically not only outperform the keel design but also out point it, make less leeway close to the wind, therefore giving the daggerboard design a substantial advantage when racing, or for performance focused sailors."
However, just before the above statement, the article presents tables 1, 2 and 3 for speed comparisons at different wind angles and the differences are modest, leading the author Phil Berman to write:
"While close reaching the daggerboard design is expected to sail 0.5 knots faster and 0.75 degrees higher." (This is hardly a significant advantage)
"...As the true wind angle approaches 90° for a beam reach, the keel and daggerboards become more closely matched...In the beam reaching comparison the daggerboard design will sail slightly higher with a leeway advantage of about 0.25 degrees but it’s speed advantage in 5 knots TWS of 0.3 knots will fade to a 0.5 knot deficit in 16 knots TWS. At this point of sail the two designs are considered to have equal performance as the differences in leeway and boat speed are negligible. Finally, while broad reaching the following speeds and leeway’s are expected."

In other words, the data presented in the tables and the author's own comments seem to belie the bold assertion (in bold, of course) above.
The rest of the article provides weak evidence in support of the overwhelming advantage of boards over keels.

Am I missing something that the numbers do not do justice for? Is the evidence unequivocal?

[smj]

It appears that when close hauled in 10 kts of wind the daggerboard boat was making over 2 kts more speed and pointing higher, that’s a substantial difference. As the wind picked up and the boats fell of the wind the daggerboard boat didn’t seem to have as much advantage but in all conditions of the wind the daggerboards were left down which would induce more drag than if they were up. Even a .5 knot gain in racing is huge.

[billknny]

Originally Posted by Shammi

In the beam reaching comparison the daggerboard design will sail slightly higher

I am totally confused... how do you credit a design feature for sailing "higher" when on a beam reach? That makes no sense. The helmsman picks the course...

I mean a beam reach is 90 deg to the wind--by definition. You can't sail "higher" except by helmsman's choice!

[Thumbs Up]

There are advantages to having daggerboards other than increased windward ability and speed off the wind (with them raised). A lot of daggerboard cats draw lees than minikeel models (18" compared to 48") and it has been proven that with the boards up can slip sideways over big waves (storm survival tactic) whereas minikeels could cause "tripping" thereby contributing to risk of capsize. On the other hand, minikeel cats are more forgiving to operator error.

[thinwater]

At 10 knots TW, including leeway, there is about a 40% difference in VMG. That is not huge? Is that not unequivocal?


Obviously it is less at greater wind angles.


Not saying you need to have boards. Just sayin' the evidence is as expected.

[Kiwi Dave]

That article appeared in Boating New Zealand also. I agree fixed keels (my cat) are not flash upwind especially coming from a performance monohull. I think we could all agree that dagger boards have a significant performance benefit close hauled. Likely slight benefit at all other angles, but do come with their own downsides in other respects. As is usual everything is a compromise.

[Mike Banks]

The good thing about dagger-boards, regardless of sailing performance, is the ability to raise them and get into safe anchorages where a bar makes it impossible for fixed keel vessels. Boats with dagger boards can be pulled up a beach on inflatable rollers. Boats using dagger-boards can raise the down-wind dagger-board in a blow, making the vessel less likely to trip and more likely to slide laterally down a wave.

[thinwater]

I think it is worth adding that boats with boards are not just faster up wind, they are easier to sail up wind. Learning how to optimize VMG with mini keels requires advanced "feel" for cats.



I've had both. I like the ruggedness of keels and the clear cabin space. The handling is not much.

[Saleen411]

I spoke with Phil at the Annapolis Boat Show a couple years ago.

While discussing $$$ for his cat, he informed me that I could probably save about $45,000 if I ordered the Balance 451 WITHOUT daggerboards.

I was like REALLY?.....we could do that?....hmmmm. That's significant. If I were to order that yacht today, I still couldn't say if I would opt for the daggerboards considering the cost and modest performance gains.

[Thumbs Up]

There are a couple things about this study that fail to quantify the advantages of the daggerboard model. In the offwind part of the tests, they said that they left the daggerboards down so that part of the study is obviously flawed. But the the thing that stands out in these polar diagrams (I had to brush up on how to use a polar diagram to find the point of sail with the best VMG) is that to windward, with the daggerboard arrangement, the best VMG sailing angles in winds over 10 knots were not plotted. According to this diagram, the best VMG (over 10 knots windspeed, with boards) are at true wind angles of less than 45 degrees. Not only are they faster and easier to sail upwind, they are also capable of sailing much closer to the wind which gives you greater ability to actually sail away from leeward shores without power. I am pretty sure that would also make it quicker and easier to tack through the eye of the wind.

[catsketcher]

Thanks for the link - it is interesting.

I think the part about going about 2 knots faster (40%) and higher in 10 knots is pretty stunning and seems to correlate to what we find. The extra wetted surface of the keels and higher induced drag must be making a big difference in low power mode of sailing. Also it states in the article that these keels are deeper than most and the boat is a low drag design, so she won't be putting huge side loads on inefficient keels. Your typical minikeel boat will probably perform worse than this.

40% extra speed and a higher mode is a massive improvement in performance and in sailboats where people are glad for 1% going daggers is an easy sailing upgrade choice for anyone who likes sailing to windward.

As to the other areas - I am not so interested. Leeway when cracked off is not important and most daggerboard boats would approach keeled boats anyway as their boards get pulled up somewhat.

[barnakiel]

Daggerboards would not be there if builders had an open road. There are benefits hence they are forced into the boards to please niche clients.


b.

[belizesailor]

Originally Posted by billknny

I am totally confused... how do you credit a design feature for sailing "higher" when on a beam reach? That makes no sense. The helmsman picks the course...

I mean a beam reach is 90 deg to the wind--by definition. You can't sail "higher" except by helmsman's choice!

I suspect in this case "higher" was a bad choice of words, perhaps what they meant was with less leeway.

[thinwater]

What about protection for rudders and drives? Also, the great reduction in draft is probably exaggerated for some boats, since the drives and rudders do not always kick up. 30 inches is a practical minimum water depth even with a mud bottom, even for slow maneuvering.

[thinwater]

What about center boards vs dagger boards? We speak of damage in terms of groundings, but a few days ago I cut a trip short because there were just too many logs in the water, the result of heavy rains the past few weeks. I bent a rudder once and I broke a dagger board once, both by hitting submerged, invisable logs at speed. I currently have a centerboard, but I haven't hit anything hard yet.



But also any difference in convenience, performance, weight, etc. What say you?