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The daggerboard decision
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Author:  Roadrunner [ Sat Mar 18, 2017 3:07 pm ]
Post subject:  Re: The daggerboard decision

T-roc wrote:
I am experimenting with adapting part of a daggerboard to the torqeedo.
I don't understand the purpose of combining the Torquedo and daggerboard. Due to the huge drag of the unpowered prop, I would think you would be ahead by simply using the Mirage Drive as your daggerboard, or mounting the board on a drivewell plug. If you're looking at "motor sailing", that's another matter. 8)

Author:  T-roc [ Tue Mar 21, 2017 11:50 am ]
Post subject:  Re: The daggerboard decision

Have not tested it yet. I think it would need considerable strength reinforcing at that length. Already trying to think of a nice method of mounting a leeboard instead. As for motor sailing, It is very effective for fishing.. The two sources of power combine beautifully for all day trolling at a consistent speed in variable or light wind without draining the battery. Drag would probably be a factor at higher speeds.On my rig it isn't a problem. My boat will never go fast.I do however need some type of board. The torqeedo is better than the mirage fins for this purpose, but its lower skeg is not large enough or strong enough to extend very far.Any suggestions for a lee board would be great.

Author:  stobbo [ Thu Apr 13, 2017 12:55 am ]
Post subject:  Re: The daggerboard decision


Dunno what kayak you use but mine is an adventure (Revolution 16 by its current name I believe). It has a separate daggerboard slot and I would imagine that you could have the daggerboard down AND use the torqueedo (unless someone who has the same boat and motor says that the arc of the torqueedo prop hits the dagger - which seems doubtful to me but could be the case).

Anyway that would be my suggestion for you rather than messing about with trying to fabricate a leeboard.

Author:  fusioneng [ Fri Apr 14, 2017 5:38 am ]
Post subject:  Re: The daggerboard decision

We have hydrofoils for our TI that we use once in a great while, but you have to add massive sail sets to the boat before even trying them, the stock sail simply isn't big enough, (just sayin it's a lot of work and a waste of time). If I had to do it again I would start with an F17 class cat (widened).
Actually there is some merit to daggerboards and some worthwhile things we have done with daggerboards for kayak sailing that actually work.
If you want to mess with that stuff there are several things you can do.
First thing we tried was a weighted daggerboard. It worked really well. A 25 lb daggerboard with the weight at the bottom (2ft below the water) makes a revo or Oasis completely un tippable, you can sit on the gunwale of the kayak.
You can also convert it into a swinging keel pretty easily just by adding a hinge near the top, or in my case I used 1/8 x2" x 2ft long spring steel for the shaft (it bends very easily 15 inches to one side or the other to counterbalance the boat. Down near the bottom the weighted part (about 6" tall and maybe 8"-10" long) is shaped like a fin with the spring steel mounted near the leading edge. You mount your spectra control lines near the middle or near the rear of the fin (depending on how much steering twist on the fin you want).
Since the weight is on a long skinny bar, it's super easy to make the daggerboard retractable. I just cut open the top of a mirage plug, surrounded the 1/8"x2" bar (all greased up) withe automotive body putty, then filled the rest of the mirage plug with urethane foam, (4# foam is very strong). The plug is strong, but not too strong, if you accidentally hit somethin, it will break (you want that).
The setup works best on a tandem kayak, I use my turbo, or eclipse flow 90 fins on the mirage drive in the front mirage slot, (I alway pedal), and the retractible swinging daggerboard in the rear mirage slot. The steerable daggerboard actually works if you can keep your forward motion up, however if you stall out on a tack, or aren't quick enough adjusting the daggerboard steering you can imagine what happens, (found that one out the hard way).
With this setup I can run a much larger kayak sail (33 sq ft wing sail) without fear of tipping over. Actually this setup is almost as fast as my full blown TI with it's 90sq ft and AMA's.
Personally I prefer wing sails over regular sails because the heeling moment on wing sails is 1/2 of a regular sail, ( the heeling moment of a sail is the force trying to tip you over). Also a wing has more power than a regular sail, I'm guessin my 33 sq ft wing is equivilent to around a 50-60 sq ft regular sail.
When not using the dagger board we just retract it, (in the up position the DB is above the scupper cart wheels), or we just remove the mirage drive plug and lay it down in the boat. When not using the wing we just furl it up and strap it to the side of the kayak (just like we do with regular hobie kayak sails). We use PVC furlers (simple and cheap) on all of our kayak sails.
I'm just guesin here, but I'm pretty sure I could get by with a 25sq ft wing on a revo 13, (the mast would need to be fiberglass pultrusion vs aluminum (the 7/8's dia aluminum masts bend too easily). You may need to also re-enforce the mast holder inside the hull on regular hobies when you start putting bigger sails on hobie kayaks (I just mounted a 6x6 1/4" thick PE cutting board with a hole in it to the base of the hull, gobbed it all down with silicone). When you sell the boat you just remove it (peels out easily) and put it on the next boat. We mount those plates in all our hobies when we buy them, (lol because we are stupid and always put way too many sails on all our kayaks)
Just fun stuff to play with.

Author:  daft [ Fri Apr 14, 2017 3:40 pm ]
Post subject:  Re: The daggerboard decision

fusioneng wrote:
it bends very easily 15 inches to one side or the other to counterbalance the boat.
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The steerable daggerboard actually works if you can keep your forward motion up, however if you stall out on a tack, or aren't quick enough adjusting the daggerboard steering you can imagine what happens, (found that one out the hard way).

I am puzzled by the bending being helpful to heeling balance. I could see bending helpful to lateral resistance or maybe to helm balance, but giving less heeling resistance than a stiff weight. I remember your dangling weight on wires, and thought it also would have a weaker influence on heeling vs stiff. Maybe the well slot would be over stressed by side leverage of a stiff weighted keel tho.

As for a daggerboard left steering the wrong way when drifting into irons, I guess it turns the hull broadside to the wind on the old tack? I recently read about someone installing a rudder just in the front, and something odd happens when tacking close to a shoreline. I guess the stern swings too close? Anyway he decided it would be better to have a big steering rudder both in front and back (and get rid of daggerboard trunk which was in his way).

Author:  fusioneng [ Fri Apr 14, 2017 4:57 pm ]
Post subject:  Re: The daggerboard decision

The bendy daggerboard is kind of like the cantelever keel boats. Think about the weight being an near bottom dead center of an arc. So the counterbalance effect doesn't change alot 15 degrees one side to the other from center. But if you swing the weight to one side or the other it counteracts the heeling moment more. I have mine restricted to only 12-15 inches side to side, (because it on a spring), If I were to add a hinge at the top I could probably lift the weight out of the water on a tack like you see on the swing keel boats. I didn't need to get that fancy. Plus the steering part of the keel doesn't do much, a kayak can't sail fast enough.
With the keel weight swung to one side two people can sit on the gunwale, but the downside is if nobody is in the boat, the keel weight tips the boat over if it is swung out at 90 degrees. Think of the keel weight as points along an arc 90 deg to the left, 180 degrees is straight down, 270 is pointed to the right.
My opinion is a really big daggerboard would hurt you much more on a kayak than it would ever help. The boat would flip way faster with a big daggerboard in a gust (like tripping over a curb (lol)).

Author:  daft [ Fri Apr 14, 2017 10:11 pm ]
Post subject:  Re: The daggerboard decision

- So if I reread with the above in mind, you first built a rigid weighted daggerboard that worked great.

- Then you built a retractable bendy weighted daggerboard with lifting lines to bend it up on the windward side. That should pull down the rising side of the boat at some sacrifice of the daggerboard's traditional role of lateral resistance. This gave you the righting moment you wanted, like in this animation: https://www.youtube.com/watch?v=YyMEO5TgpRg&t=22 . Another source said such "canted keels" sometimes need additional daggerboards to make up for the loss of lateral resistance, like in this model starting second 23: https://www.youtube.com/watch?v=_LqWHBy_g2E&t=22 . If not "decanted" during a tack, it may roll you over.

- Lastly you tried attaching the lines near the rear of your lower fin which brought you no joy. I think this is because while it gives you additional righting moment based on downward thrust, that same thrust in the horizontal component is sabotaging your lateral resistance. It is actually driving you downwind to a modest degree. Daggerboards are supposed to act like airfoils, with a positive angle of attack towards windward due to your leeway. It apparently makes quite a difference even to have a blunter end forward and thin taper to rear, to avoid stall as you say.

Author:  Lead Belly [ Mon Nov 27, 2017 6:13 pm ]
Post subject:  Re: The daggerboard decision

Underwater foils are revolutionising sailing. It is not preposterous to think of applying them to make more seaworthy (and faster) sailing kayaks without going to double or tri hulls:

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