16 replies to this topic

[JeffM]

I'm not nearly ready even to buy plans yet, but I've been meditating on a spindrift 10 or 11, probably nesting. Which brings me to the following question: every db I've ever seen is either vertical or raked aft. This means that if you hit bottom, you stand a fair chance of damage and getting temporarily stuck. Why can't the db be raked forward, so that it will pop up more readily if it hits? It might also be easier to handle, since it would be readier to hand when not fully down. I know forward rake in airplane wings brings big stability problems, but I can't believe that's a critical in a small boat daggerboard. Anybody else ever thought about this?

[Ed Hawkins]

Well, I'm no expert but two problems I can see with reverse rake would be:
1 a shift forward of the center of lateral resistance which I think would increase weather helm significantly, even in a little boat like a spindrift.
2 when you happen to hit a submerged pot warp or anchor rode it would tend to travel up the leading edge and get stuck at the intersection of the db and the bottom. Probably easy enough to clear if you know what you hit but some reverse rake makes it easier to deal with.

just my $.02.

[Garry]

That is an interesting question.

You did say that you would probably build a nesting dinghy. A reverse or even straight daggerboard will not work on a nesting dinghy simply because the stern section must be kept clear for the bow section to fit in it. The daggerboard trunk must be located in the forward section.

You will notice that the non-nesting Spindrfits have a straight daggerboard. The nesting version has the trunk in the forward section so the daggerboard is swept aft to maintain the correct balance for the boat. At least, that is my guess.

[JeffM]

Excellent points! I had assumed relocating the trunk to maintain balance, but had forgotten it is right up against the bulkhead. (Could it, I wonder, go in the aft section?) I had not thought about the difficulty getting over anchored floats.

[Garry]

The only way to have the daggerboard in the stern section is to have a corresponding cutout in the bow section so it will nest in the stern.

Years ago, I adapted a standard pram design to be nesting. I also wanted a daggerboard so I came up with the design sketched below (you have to click on it to see it clearly). It worked great for nesting even thought it maed the bundle a little longer. It also worked great when assembling the two halves in the water since the tapered section guided themselves easily into place. I always assembled it in the water, even during a storm.

Unfortunately, it didn't work great for sailing because it was way out of balance. I only tried it once and gave up. I probably could have moved the mast location for better balance.

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[JeffM]

Thanks, Garry. Neat design you have there. I need to stare at pictures more so I don't get too far ahead of myself.

[Charlie Jones]

around our bay you'd have a miserable time with a forward raked board- you'd be stopping to clear seaweed from it constantly. On a cruise this weekend, another cruiser had to keep stopping his engine and clearing weed from the prop.

[Ken_Potts]

What about a daggerboard that is wide at the top and skinny at the bottom so the leading edge will deflect debris but the trailing edge will allow the board to be pushed up by immobile objects?
I think the thing would almost have to be triangular because it seems like the angle would have to be pretty drastic to overcome friction. In the end it would try to pivot in the trunk and would probably jam at exactly the wrong moment. Well, there's always a centerboard (or leeboards)...
Redesigning the shape of a daggerboard would probably have just as drastic an effect on balance as changing the angle though - Not something to be taken lightly...

[ChrisObee]

Its kind of reinventing the wheel isn't it? A center board is the best of both worlds. Its canted backwards and unlikely to collect vegitation and it will be knocked up by the hit on a rock.

[PAR]

Daggerboards are the lightest of all adjustable appendages available and have their compromises, concerning this weight economy. The case takes up much less room, invades the interior spaces with a smaller foot print, more so if you're not married to centerline configurations. All this savings costs some little amount, unless you need truly shoal craft. Popping about in gunk laden holes, may bring on wishes you could bounce a centerboard along, until you're in ankle deep seclusion, rather than hanging on each thick patch of grass, weed, broken anchor warp, gator trap tether, likely found in thin enough waters to catch a board boat. Lee and centerboard craft can bounce over most things that may snare a dagger, but many small sailors can ill afford the room for a properly sized centerboard. Manufactures have sold small centerboard boats with undersized boards for a long time, in an effort to make more useable interior area.

Canting forward does offer a slight performance increase, test have born out, but the disadvantages have so far discouraged the fad catching on. Of course you'd like the root of the board to start in an acceptable location, placing it's center in proper lead. On a small boat this could be just a few inches.

Curved daggerboards have had some successes in the "retraceable on strike" column (also clearing the boom). Several designers have tried this arrangement, most with variations in curve and angle. Which ones work best is subjective.

A razor let into the leading edge can solve many of these issues, but like all things in yacht design, brings up its own set to contend with.

In small craft, particularly sail, it is a delicate balancing act, you have little margin for error. Every piece, its size, location, weight, relationship and effect with, or on others, make the tasks required interesting.

[JeffM]

Ken, I'd guess a triangular db would have to be so wide that it might as well be a cb, with its big footprint. Also, it would be so low-aspect it would need a larger area to be effective.

[Ken_Potts]

I agree, Jeff.
I was sort of thinking out loud on that one. I've had daggerboards before and I've never grounded hard enough to hurt the boat but it certainly is a warm fuzzy feeling knowing that I can use my (future) centerboard as a depth sounder...
I think that if I required that warm fuzzy feeling in a boat I'd either convert to a centerboard with the same underwater profile as the original daggerboard (and lose the interior space) or switch to a boat design that started out with a centerboard. It's all about the tradeoffs isn't it?

[mustangermatt]

My current rudder has a slight forward cant as I used a high aspect foil rather than the swinging one in the coresound design. The problem I found is that at speed the rudder starts to oscillate, vibrating the entire boat. If I return it to verticle this is eliminated. Probably a combination of angle and foil shape, in any case I am building a new one :-)

As far as "bouncing" the board as a depth sounder...
I don't know what its like where you are but where I sail just a slight touch on those barnicle infested rocks and I am spending two days building my three layers of 8 oz cloth back up :-)

[Ken_Potts]

I meant the depth sounding comment as a comparison to using a daggerboard as a depth sounder. That can get even uglier.

[David Heady]

I've built three small boats in the past five years, all with daggerboard variations from the norm. The first was my pram "Matins". I was given plans from my son in law and was a total neophyte to the craft. The plans called for the daggerboard to be right in the middle of the midship thwart. Since that was about the only place for a passenger to sit I did some research on the balance of Center of Effort and Center of Lateral Resistance and decided that I could move the daggerboard forward, but have it slant back to move the CLR toward the planned position (pic attached). It has worked out pretty well thus far.

I also built an OSB with my Grandson and incorporated the design of a PDR center daggerboard into it. Not unusual other than the OSB plans were for a row boat and not a sailboat. It sailed well, but performed more like a sailing canoe than a sailboat.

Finally, I made a PDRacer for my wife. One of her specifications was that she have ample room to carry Grandkids. After more research online I discovered an Oz PDR that had the daggerboard in the side air box. I engineered her PDR to that end. I used plans I bought online, but modified them considerably as the plans called for a traditional center located daggerboard box. As it is the box is encased in the starboard air box and is both easy to use and leaves the cabin of the PDR completely open. After tuning the rigging she sails like she has an outboard motor attached.

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•  Screen Shot 2012-02-25 at 9.49.33 AM.jpg   24.01K   8 downloads

[Dale Niemann]

I just happened to check out the design forum and saw your question. I have attached a production dingy of the 1950s which I aquired some time ago and subsequently have given to a friend to restore. I have no idea how well it sailed. But it definitely has the forward dagger board.

Dale

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[Tom Lathrop]

The many reason for having an aft angled CB or DB have been stated. I raced a Windmill for many years that has a DB that can be angled in either direction. Some would angle the DB forward in light air to get more weather helm and feel to the helm. In most cases, collecting weed and grass on the foil is an overriding factor and can ruin your speed if you are not alert. Even with an aft rake, you have to be alert to weed in many areas. A forward rake will theoretically reduce tip vortices and increase lift to drag ratio.