Performance Study: Daggerboards & Fixed Keels

[catsketcher]

I remember reading the article on testing the first Spectrum 42, Shuttleworth was testing it against the 42 ft tri - Damiana. He did some tank testing as well and found that the cat was faster with one board rather than two smaller ones. I guess he designed them with one board from then on.

Spectrum 42 Article

I have designed and built two little cats with single boards and can't tell the difference between tacks. On my larger cat I have two boards but they are about as large as is comfortable for me to handle so that could be an issue to consider - size and weight for easy removal.

[Russ333]

Dan GB what performance differences do you note on port v stb tack?

[Dan GB]

Originally Posted by Russ333

Dan GB what performance differences do you note on port v stb tack?

To be honest, can't say I notice any difference. In terms of performance. John Shuttleworth cited a difference of 1.5% - was that pointing ability or speed - of one board Vs two. Too small to notice.

One windy night off Freeport it seemed to tack easier to port, and went into irons when I was trying to tack to starboard. But that could have been situational with seas. However, it did occur to me that maybe it was easier for the boat to pivot round the dagger board rather than bring it all around, of you know what I mean.

[Russ333]

Particularly in windier conditions, I would have thought the leeway hull would always bury deeper than the windward hull. So depending on whether that was port or stb, there would be a different in leeway amongst other things on one tack verse another. But it seems not from the article referred to, and your comment.

[tp12]

Originally Posted by Russ333

Dare I say, I think it's a very balanced article. The author is comparing an efficiently keeled cat, verse the same dagger-boarded (always down) cat. Results predictable and significant, not only for racing, but if you've ever tried to sail off a lee shore, or make an approaching headland hard on the wind. As stated, the comparison would be even starker if comparing a typical keeled charter cat verse a more performance driven dagger-boarded cat.
Two additional comments from experience, low profile fixed keels really suffer much greater performance degradation going to windward in short steep waves, as their hydro-dynamic performance gets totally disrupted. On the flip-side, more than once, I've been extremely glad of robust fixed keels and sked protecting the rudder, where only superficial damage was sustained. Not that I'm accident prone, but s... does happen when living aboard out in the wild.
Which do I prefer, well it depends ......

It seems to me to disadvantage the board cat off the wind by leaving the boards down. Sailing both cats how they were designed to be sailed, boards up off the wind, would provide a balanced article.

[Dan GB]

Originally Posted by tp12

It seems to me to disadvantage the board cat off the wind by leaving the boards down. Sailing both cats how they were designed to be sailed, boards up off the wind, would provide a balanced article.

I agree. I certainly get a tangible performance improvement when I raise the board going down wind.

[44'cruisingcat]

Another advantage (apart from shoal draught) is that you can, to some extent, adjust the amount of leeway the boat has.

I've been doing this a bit lately, especially reaching with the assymetric. Sometimes when deep reaching, letting the boat slide a bit to improve apparent wind angles, but then when closer reaching using a bit of board to reduce leeway and ease the apparent angle a bit.

[admiralslater]

Originally Posted by 44'cruisingcat

Another advantage (apart from shoal draught) is that you can, to some extent, adjust the amount of leeway the boat has.

I've been doing this a bit lately, especially reaching with the assymetric. Sometimes when deep reaching, letting the boat slide a bit to improve apparent wind angles, but then when closer reaching using a bit of board to reduce leeway and ease the apparent angle a bit.

I do the same when racing . I do put a bit of board down if there is surfing to be done , I find it helps me pop onto a wave more easily.
Regarding 1or 2 boards our PDQ has two but is designed to ail with one . We Swap them each time . Lee board is the working one.

[arsenelupiga]

daggerboards are one of most expensive performance additions, looking at cost vs benefit. Cost a lot, increase chance of structural issues, cost at least 500 kg in carry weight, take space and deliver overall 0.5% increase in performance if one is to believe rating numbers derived from racing results over many years.

Much better $ spent for performance enhancement is probably replacing sails more often or cleaning hulls or folding props, etc.

But they look good, so this is probably why they are around in such numbers.

[44'cruisingcat]

Might be an idea to read the article rather that just inventing numbers off the top of your head....

[Teleman]

Another point is that fixed keels add buoyancy in the middle of the boat, making it more prone to pitching in a short chop. I read something by designer Richard Woods that reckoned daggerboard boats were a bit more seakindly.

I would prefer a fixed keel cat. Anything to avoid extra cost and maintenance. Common sense, planning and a decent engine should keep you from situations where that extra windward ability becomes crucial. Well, most of the time...…

(I should add I'm not a sailing purist, not in a hurry, not rich, and a bit lazy.)