The daggerboard decision

This year I am going to experiment with substituting a high aspect ratio (long and skinny) daggerboard for the Mirage drive which is essentially a low aspect ratio (short and squat) daggerboard. A high aspect ratio daggerboard is more efficient than a low aspect ratio one in that it has less associated drag for the same amount of lift. Reducing drag increases the efficiency at which wind is converted into forward motion rather than heeling.

I will, of course, stand on the shoulders of those who have gone before me in this forum, mainly Stringy and Skua who did great work way back in 2008. Stringy showed how the cassette that fits the Mirage drivewell could be modified to take the daggerboard (DB) from the Hobie Adventure -- a very elegant solution. He reported: ‘A bonus with the DB, apart from stopping sideways drift when going upwind, is that it adds stability when sailing. With the DB in the down position, heeling is slowed noticeably, and you have more time to adjust the sheet in strong gusts.’

I will start with the Stringy approach. I have a daggerboard from a windsurfer that I think will do the job. It is much longer and narrower that the combined fins of the Hobie Mirage drive but about the same total surface area. It is also a bit thicker than the Hobie fins. However, this approach it is not perfect for my purposes because it means taking the Mirage drive out of its slot and a Sport doesn’t have much storage space to spare, particularly if it is also carrying a trolley.

I think the Skua approach of a sleeve or ‘sock’ over the mirage fins has promise because it leaves the Mirage drive in place. But Skua’s sock (made of aluminium) covered both fins and its low aspect ratio meant there was a lot of drag. While pointing was good, said Skua, ‘The performance was gone. Hardly any picking up of speed in a gust. It just heeeeled’. What I will do differently from Skua is fit a high aspect ratio fibreglass sleeve over the front fin only that will clip to the mast of the rear fin for a bit more rigidity. Maybe the drag problem will still exist because of the trailing Mirage fin but it is worth a try.

A discussion of potential daggerboards is not complete without mentioning hydrofoils. Most of us familiar with the foils on high performance yacht classes such as AC72 catamarans and International Class Moths that lift the hulls of these boats clear of the water. Now I don’t reckon this sort of foiling is practical for recreational or expedition kayaks. But I think foiling leeboards (Bruce foils?) of the sort seen on both sides of state-of-the-art monohulls like the Edmond De Rothschild in the Vendée Globe Yacht Race may work with kayaks. When a boat is moving and heeled, a foiling leeboard that is in contact with the water generates both lateral (resistance to sideways movement) and vertical (righting moment) forces.

Implementable in a kayak? I don’t see why not (though I could be mistaken). There could be appropriately shaped foils on either end of a (detachable) bar that is mounted on gear tracks on the rails of the kayak at the point that balances the forces generated by the sail and the below water foils. There is already something like this with the inflatable ama system that Hobie sells as an option. Essentially the amas would be replaced with more sophisticated and efficient foils. Some reinforcement of the mast receiver may also be required to cope with the increased power.

Maybe I’m dreaming but what I like about the idea of kayaks with foiling leeboards is it could blur the lines between monohulls and multihulls by giving monohulls some of the righting moment advantages that multihulls have. Monohull kayaks with foiling leeboards should be much lighter than catamarans and trimarans and would probably also tack faster. In my opinion, foiling leeboards could enable development of highly seaworthy sailing kayaks suited to events like the wonderful Everglades Challenge.

I don’t think I have the time, knowledge or construction skills to build efficient foiling leeboards but it is fun to think about the possibilities…

Too reduce heeling, you'd pull the daggerboard up a bit (or use a smaller one). This will result in more slip but will reduce heeling. It's a trick many sailors use in very heavy wind situations to help prevent capsize.

Interesting, which suggests that part of the response to an overpowering wind gust is to push a pedal forward to lay the Mirage fins flat against the hull.

There is an exhilarating video here that shows the Edmond de Rothschild foiling. Of course, I only have to narrow my eyes at little when looking at the video to imagine my Sport equipped with foiling leeboards storming down the same seaway.

Me and a mate are going to be playing arou d with foils on amas in the next few months.

Have fun playing with the boat.

Not to be too discouraging, but the "original" Triak (sailing kayak like an AI but made of fiberglass and with stiff carbon mast) floats had foils on them for stability from hydrodynamic force in lieu of buoyancy. Didn't work worth a darn. With a low displacement hull like a kayak or most multihulls, the foils weren't consistently at the correct depth except in mirror water conditions...and in those conditions there wasn't enough wind anyway to keep the boat moving forward fast enough for the foils to be useful. Foils need to be moving through the water at "take off" speed before they do anything except drag...

You might have more success, though if you tried placing the foils on the rudder and daggerboard ala Moth... https://www.youtube.com/watch?v=YZU_SqMW_5Y

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

My opinion is the size of the daggerboard is not very important, in other words a really big daggerboard does nothing to help you. The whole key to kayak sailing is 'forward motion', basically the boat needs to be moving forward for the rudder/daggerboard to function (ie...water flowing over them). Basically if the boat is going 1 mph thru the water, neither do much of anything. Because kayaks are tippy and difficult to counterbalance (with your weight), they must always have smaller sails than what a regular sailboat like a sunfish or laser would have. In other words if your out there trying to pretend your a sunfish, your defeated and not using the kayak sail for it's intended purpose, your much better off just going out and buy a sunfish or Laser ( I used to have a sunfish).
All Hobie mirage kayaks are designed from the ground up to utilize the mirage drive system and the Hobie kayak sail kit, (basically designed from scratch as a pretty good little sail boat, (think about it all Hobie's employees are sailers first.....). If you take the mirage drive out of the equation you are left with a pretty crappy paddle kayak (all Hobie kayaks except the TI track terribly when compared to even low end paddle yaks), whats the point in doing that (lol).
Same applies with the Hobie sail kit, if you omit the mirage drive out of the equation, the Hobie kayak with the sail kit (less the mirage drive) is even less capable than a standard paddle kayak with an aftermarket sail kit, (which is pretty much the most useless thing you can possibly do on any paddle kayak, (a gigantic waste of time and money)). If you wanta sail get a dang sail boat.

We have had many different Hobie Mirage kayaks and are out on them most weekends since moving to Florida ten yrs ago. We have never taken a Hobie kayak out onto any water without a sail kit strapped to the side of the boat (not even once). I had a sunfish sailboat and never took it more than 1/2 mile from shore and all we ever did with it was zig zag back and forth in the wind, and try to sail around bouys (pretty darn boring). Kayaks are a totally different world, you actually go out and do things with them, go to fun destinations, and really see and enjoy the natural beauty up close and personal, and can explore to your hearts content (not just a postage stamp sized 1/2 mile area). We have well over 200,000 road miles with our camper in tow and kayaks on the roof, and have dropped into every body of water that we could find, all over the country (even mild rapids). One of our favorite things is to kayak up rivers with our favorite place being the Sante Fe river (just north or us) and visit all the natural springs (13 springs in an 8-10 mile stretch). We still have our sail kits strapped to the side of the boats, but get little wind in all those trees, listening to all the crazy monkeys left over from the old Tarzan TV series from the 50's.

When we first started kayaking we were renting paddle kayaks and never wandered more than a few hundred feet from shore, and seldom went more than a mile or two (gets boring fast). Once we started using Hobie Mirage kayaks with the sail kits we were able to easily quadruple our range, and felt safe going much further out (even into open ocean). Our main pastime is snorkeling and diving, we get to do that all the time with our Hobies. If you ever snorkel around here you will quickly discover every body of land is surrounded by totally bare lifeless shallow sand with water only a foot or two deep, pretty hard to dive in knee deep water. We don't fish at all, but do a lot of spear fishing where we can select from the menu (lol). Just FYI I have never seen anyone fishing from a sunfish or laser, or seen one more than a mile or two from launch.
Both my wife and I can peddle our Hobies for up to 10 hrs if needed, adding the sail kit lessens the physical requirements tremendously, when usable wind is available. We still pedal 100% of the time even with the sail kit deployed, but can peddle at a much lower pace (walking pace) and still get where we want to go in decent time.
The whole key to kayak sailing (especially upwind) is to try to keep your forward motion up via peddling using the sail as a power assist,(not your primary propulsion), the sail is too small to do anything else, and there is no practical way to install a larger sail because of balance issues.
Don't try to pretend your a sail boat, what you have is way better.....
All just my opinions
FE

Just a few of our crazy kayak sailing setups...
Our old Oasis


One of our two matching (his and hers) Revos


one of our TI kayaks rigged for kayak sailing with a wing sail.


One of our TI's all rigged for far offshore.


Yet another one of our TI's at Lake Hartwell GA last summer, (thats our new camper in the background), lake hartwell is 45 miles long, we covered quite a bit of the lake. In both sailing mode and kayak mode....


We love our Hobies (lol)

Nah, a Sunfish or Laser is double the hull weight of a Hobie Sport and is unwieldy in length (13'9") and beam (over 4'). My Sport is easy to car top and it can be launched/retrieved in many more places than a barge-ass Laser or Sunfish. Good luck with your surf landing in a Laser or Sunfish.

I have a Laser sailboat mouldering in the backyard (and a couple of windsurfers under the house). My Hobie Sport with its boomed sail is a sweet little sailer and I would go so far as to say it is a better sea boat than the Laser when winds are fresh. [Cue gratuitous Hobie Sport sailing video]

Agreed, I have way more fun kayak sailing and can do much more than I ever imagined with my sunfish, thats why I got rid of the sunfish. However there are a gazzilian sunfish and laser sailers out there doing their regatta thing (chasing little bouys (lol)) that look down on us and are downright mean to us, (try joining a sailing club, they are downright hostile toward us kayak sailers (lol)).
That's their thing and I respect that, it's just not for me.
FE

FE, point taken. Our kayaks are hybrids and any daggerboard decision should take into account how it affects use of the Mirage drive.

But I love the idea of having a specialist daggerboard in my bag of tricks that can be easily inserted when conditions are favourable. Why pass up the opportunity of an effort-free extra knot or so* of Velocity Made Good (VMG) to windward through lowering leeway and increasing inline speed?



*Edit: I have done my sums and now think ‘an extra knot or so of velocity made good (VMG)’ is a tad optimistic. The minimum performance improvements I am hoping for in fresh winds are: (1) a leeway reduction of 2.5 degrees and (2) an inline speed increase of 0.5 knots. Together, these imply an increase of roughly one third of a knot VMG. But it is the ability to better handle fresh winds that I am mostly after, not extra speed.

For me anyway, It's the messing about with the stuff that makes the hobby fun for me.
3/4 of the times I out I'm trying out new stuff and inventions and testing, 25% of my trips are practical destination minded.
FE

when I pull the MD on my Adventure and replace it with the drivewell plug I reckon to get approximately half a knot to a knot more speed depending on how strong/ideal the wind is for sailing. The boat definitely performs better under sail like that

Stowing the MD is not an issue for me: I have replaced the hook on the end of the cockpit bungee (the hook that is meant to go over the pedal shaft) with a large s/s spring clip; this clips into one of the pedal shaft adjustment holes on the drive and it doesn't interfere at all with pedaling so I often just leave it like that. If I want to pull the MD I just pull it, insert the drivewell plug and then turn the drive over in the footwell so that it lies forward-end-down with the pedals under my knees.

As to the idea of crafting hydrofoils for these kayaks: I also own a windrider rave foiling trimaran. Knowing the engineering that has gone into the foils for that boat I think to create the same for the MD kayaks would be a significant undertaking and I doubt attempts on the back of a cigarette packet would be likely to be successful. PLUS (and I think this is a potential knockout blow) the Rave has a massive rig; the little kayak sails just wouldn't come close to giving enough power/speed to create the required lift and it is doubtful whether the AI or TI sails would be big enough too IMO.

Adding the foils to the rave hulls adds a huge amount of weight and when they are in the down position a huge amount of drag. The Rave's oversized rig is needed to provide the power to overcome the additional weight and drag to get the boat moving forwards fast enough to create the required lift to get it foiling... and that is when the engineering calculations start proving their worth.

My recommendation is: retain the resale value of your MD kayaks & trimarans by leaving them as much as possible 'as sold' and/but if you can't resist the temptation to get into sail-powered hydrofoiling buy a Hobie Trifoiler, Windrider Rave or Foiling Moth and knock yourself out!

As my gramma used to say, "You can't make a silk purse out of a sow's ear."

But, there is no doubt in my mind that any production boat can be improved incrementally to better suit the conditions you typically see on the water and what you want to accomplish with the boat.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Test image , desperately trying to figure out posting images.

I am experimenting with adapting part of a daggerboard to the torqeedo.

T-roc any news to report on this idea? I have been thinking of the same kind of mod for my migrate drive installed trolling motor (not the torquedoo


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