SPEED

Many Hobie kayakers profess to have no interest in speed, yet it is important in many situations besides racing, such as getting out of the way of other boat traffic, finding safe harbor fast in sudden inclement weather, and getting to the fishing grounds sooner so there is more time for angling!

I like to go fast and my friend, Kilowatt Mike, likes beating me, so we teamed up to enter one of the few races where Hobies can officially compete. We raced with a "Tandem Adventure" (TI, hull only). There wasn't much of a Hobie class so we raced with the OC-1s, OC-2s and surfskis. Here's a video showing the highlights of our journey. https://youtu.be/JjrVEA1glmo . As you can see, a well prepared Hobie is a little faster than you might think!

There are 3 components of speed -- the person (strength, proper form and strategy), the efficiency of your Mirage Drive and the boat. Each plays a significant part. The remainder of this post highlights the preparation of the boat. One can't cheat the limitations of the hull, so the effort goes into getting the boat into the position to reach those limitations!

We started with an old early production TI hull that had seen better days. It was the perfect candidate for a face lift and a few mods.

The first task was to strip out some excess weight. We pulled out about 20 lb including the bilgeboard, rudder assembly, V-brace, cross braces, rear hatch and misc. hardware. More important than the weight though was the weight distribution. The bow tended to rise at higher speeds, shortening the LWL and limiting speed. So all that 20 lbs went right back in the bow to keep it in the water, and we obviously kept as much weight out of the stern as possible. To that extent, the heavier crew member sat forward.

The hull was somewhat scratched, dented and gouged so the hull was sanded and filled. Here's a before and after:




Our boat sat in cradles for years and the bottom looked like a roller coaster. Several methods of straightening the hull were tried including some serious pushing for extended periods in the sun:


In the end we employed a network of 11 foam pillars to straighten the hull bottom and eliminate hull flex:




The TA hull bottom has 11 openings. We eliminated 3 (bilgeboard and front cart scuppers), modified 4 (seat scuppers), made temporary plugs for 2 (rear cart scuppers) and kept the 2 drivewells open. Our competition had essentially no openings in their polished carbon fiber hulls.




We replaced the original 5 lb rudder with a 2 lb small rudder, enough to give us maneuvering room. Fortunately the boat tracked well and responded to very little input.


Finally we primed and coated the hull (after flame treatment) with a clear hydrophilic coating.

The competition made our 18.5' boat look like a small bathtub in comparison. Here you see our boat encased in the much longer, narrower OC-1 (inverted) and OC-2 (both of which we passed).




Although the boat played a big part of our success, there are a couple of forum members whose examples have been very helpful. Kal-P-Dal has been an inspiration in the art of pacing to the distance. Anyone who can race 24 hours in a Hobie is a great example of pacing to maximize speed over time! Rnykster was a sometimes controversial member who was a very successful racer and showed the advantage of combining the pedal and paddle. Unfortunately he passed away recently and will be missed.

The bottom line here is that Hobies can compete successfully with other "fast" kayaks and canoes, given the proper preparations. One can't ignore the fact that, in spite of its rather hefty weight, the "TA" makes for a very capable tandem kayak!

Interesting.

On the foam pillars, are they braced with anything, or does the compression create enough support?

How much longer are the pillars compared to the space they fill? In other words, how much are the pillars compressed?

Thanks for the detailed post and any additional information.

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2014 Outback
2016 Outfitter
2017 Sport

What great achievements Roadrunner, both in prepping and racing!
I’d wondered what your restoration project was for.
The ‘Hare and the Tortoise’ comes to mind, especially at the start with all that energy/speed from the other boats. You must have got some disappointed looks as you gradually overtook them!
What was your average speed?

Although the compression was handled entirely by the foam, we used shortened bamboo skewers to keep some of the noodles straight. The skewers were cut about 1" shorter than the final depth so as not to interfere with the foam's compressability.The pillars were mostly oversized, depending on the necessary expansion force. After placing a pair of pillars, I would check the result with a straight edge along the hull bottom and trim the pillars if necessary (or start over if I needed more length). After everything was in and stabilized for a day, I secured the pillars with silicone calking to keep them from popping lose.

A couple of additional notes:
1. Most of the pillars were placed along the ribs or seams (to avoid high spots) as shown here:

There were a couple of exceptions, one where a scupper cart dent had to be pushed out and another where the hull was on-dimension, but there was some flexing causing hull resonance when going through boat wakes. That one was simply inserted for rigidity. It worked like a champ.

2. All the work was done with the boat upside down resting on its rails so there was no pressure at all on the bottom. When our boat went in the water there had been some additional local hull compression due to the weight of the boat and load. This factor alone caused a measured distortion on part of the hull bottom. The pillars corrected that problem as well.
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Thanks stringy -- it was a fun project and it turned out better than we imagined! The preparation definitely paid off! We got off to a slow start -- had just barely gotten set up when the flag went down for our start. The river was quite low and we unknowingly picked up some river grass on our fins. It took us a couple of miles to finally figure it out. Once we got squared away we started to rock and roll.We averaged 6.27 MPH. In practice we had been running 6.16 MPH over 90 minutes with no current, light winds and no fin fouling. In the race, we had a small favorable current, light headwinds second half and we had to clear the fins a few times.

On weight distribution, I've noticed that the bow is out of the water on the Outfitter with two equally weighted occupants. The Outfitter seems to have a similar shape as the TI, so I'll consider adding weight on longer trips. Is there a target depth for the bow when the kayak is loaded in calm water?

The Outback's exaggerated bow flaring doesn't leave much bow depth to play with. I'll probably just leave that one as is.

Thanks again for the info.

_________________
2014 Outback
2016 Outfitter
2017 Sport

My gouge is that the bow should at least touch the water at your cruise speed. You don't want the first foot of bow clear of the water like this:


With the bow in, notice there is less bow wake, therefore less drag:

Additionally, the greater the distance between the bow and stern wave, the greater the hull speed!

Hydrodynamic lift raises the bow as speed increases. For instance, with the Revo-11, I can cruise at 4.5 MPH with 8# in the bow, but at 5.0 MPH I need 18# (without it, there is no way I can cruise at that speed). At 4.25 MPH, though, there is not enough hull lift to merit any weight addition.


The Adventure (Revo 16), with a longer bow, can cruise at 5.5+ MPH with only about 7 or 8 #.

Obviously, the further forward, the better the leverage. In all cases it makes more sense to store supplies and equipment forward to the extent that they are on board. On our TA, we used the scupper cart as part of the forward ballast. No sense carrying more weight than you have to! Each situation is different so you have to experiment to see what is best for you.

Wow Roadrunner, that is very impressive!
In terms I understand that’s 10.09 km/h, which is an incredible average. Great effort!

Very cool Roadrunner! Amazing how you guys passed those other boats - not by a little but by a ton - you were were flying! You had to love seeing the competition peeking at you (in amazement!) as you passed them....WOW!

Roadrunner:
Most of the hull mods you did, I also performed on my TI. But me being simple minded, I didn't flame treat my hull before applying the hydrophillic coating. Instead I cleaned up the entire hull bottom, (like you did), contoured/removed all the scupper hole openings, and modified my rear mirage plug so it matches the hull shape (when I'm out solo, I put that plug in).

Instead of flame treating, I soaked down and cleaned the hull with Bestest rubber cement thinner, from Home Depot, (Heptane, (which melts PE)), strictly optional, alcohol will also work. Then sprayed the entire hull bottom with Krylon for plastics clear coat, (active ingredient is Heptane), Then finished off with the Rustolium hydrophillic coating. I did that work a couple three yrs ago, and it has held up surprisingly well over time. Who knew LOL

I also put in a bunch of hull re-enforcement (similar to what you did with the pool noodles), but I ended up using urethane baggie bombs, which are much faster and way easier to install inside the hull, and provide more rigid support, and weigh next to nothing. And they are easily removed if you ever sell the boat. Basically you take polypropylene bags shaped similar to the final desired shape, (tall and skinny, like shake and bake bags, or some type of zip lock bags, whatever you can find). What I did was poured in a measured amount of four pound 2 part expanding urethane, (use trial and error to determine the right amount). Place into the hull and let it expand to fill the desired space, once dry it is very rigid and follows whatever contour it encounters, (obviously stay away from all the control cables). I really like this method because the foam is completely contained and sealed inside the baggie so it can't soak up any water over time. To remove you just tear it out (nothing sticks to the hull itself). I ended up with about a half dozen baggie bombs ( a lb or two of foam) inside the hull to re-enforce the hull in strategic areas for high speed and offshore operation in really rough conditions. Just thought I would share the technique....

Another key thing I did that I feel really helped me was to modify the hull design slightly in order to convert the hull to a planing hull design (vs displacement), similar to the shape to the WETA sailboat hull design. I found thru much research and testing that the hull on the TI even though it has a length to width ratio of 8 to 1, (which is kind of important), the boat in the current design at around 7-8 mph runs into a kind of brick wall, anything above 7-8 mph the horsepower requirements to propel the boat above those speeds go up exponentially, rather than going down as on a planing hull design, (once on plane of course). I just made up a foam epoxy removable slipper to the hull at the rear, that changes the stern shape from a point to a bulbous rounded shape to prevent the stern from squating down when approaching displacement speed, (basically burying the stern in the displacement wave). This simple removable mod only weighs about ten lbs, but adds about 100 lbs of additional flotation capacity to the hull.

Another thing I found (from much testing) is the regular mirage turbo drives kind of give up the ghost at around 8 mph, basically you have to peddle so fast and expend so much energy you can't provide any useful additional propulsion above those speeds. What I did to remedy that was to switch to the Eclipse flow 90 fins on my mirage drives. This moves the effective power range of the drives from zero to about 8 mph (with turbo fins), up to 6 to 12 mph effective power range with flow 90 fins. Basically similar to a car running in low gear or high gear. I extensively tested my mirage drives and found the flow 90 drives still provide useful propulsion up to 12 mph (where I found my turbo fins kind of gave up the ghost at around 8 mph). Obviously at speeds below 6 mph the peddling effort is too great with the flow 90 fins, (too hard on my legs and muscles, and probably the cables). Basically what occurs is the leg energy and cadence to propel a TI at 6-7 mph with turbo fins, is equal with the energy consumption using flow 90 fins at 9-10 mph, ( ie... low gear vs high gear). This assumption assumes you have already increased the displacement speed limit with minor hull mods as outlined above. If you didn't then the power requirement of course goes up exponentially once you hit displacement speed (, ie... 7-8 mph with current hull design). Once the boat gets up on plane, the energy requirements to maintain those speeds actually go down. In other words it would be like starting your car from a stop sign in second or third gear, yes it can be done, but it takes a while to get up to speed, (you have to work up to it carefully), but after a few hundred yards once you are up to speed, you can maintain that higher speed expending much less energy for the long haul (the rest of the race).

If you follow some of my ideas I see no reason you can't go back next year averaging 9-10 mph, expending the same amount of energy you expended this year......(please blow everyones doors off, no matter what boat they have).

Just ideas, that's all, just tryin to help.

FE

EDIT:
Actually the concept of low gear/high gear would be valid for the next generation of Mirage drives, ( I would much rather have that feature than reverse). Basically a simple lever system that on the fly during operation converts the fins from low to high gear, (like a shifter on a car), lol a two speed transmission, (similar types of levers and concept to what they are currently using). Basically in low gear the fins would be very sloppy (allowing for much more slip), then once up to speed switch the the lever to high gear (pulling the fins tighter, less slip). Actually you could even expand to 3-4 gear ranges (like a car) eventually if desired (tons of R&D and testing required of course, (which I'm not about to do for them)). Result would be you could make much larger, and much more powerful fins tune-able to the actual varying speeds vs one size fits all.

This event included a famously delicious meal after the event. It was first come, first served, so we were motivated to get an early spot in the lunch line. It was definitely worth it!

You bet we did! There were even a few friendly comments made. Some tried picking up speed to hold us off, but they couldn't maintain it. Interestingly, the more we passed, the less tired we became. By the end we were really closing fast on the last OC-6, trying to catch them before the finish. Almost made it.

Actually a lot of our ideas came from your previous mods, for which we're very grateful! One of our favorites we stole from you was the hidden straw in the sealed seat scupper to maintain drainage. Here's a pic showing the straw in place before sealing (the long end pulls out after the closed cell foam sets):


I also studied your hydrophobic coating methodology also before applying the hydrophilic coat. Next year, if we go again, we plan to adopt your hydrophobic idea. It sounds promising! Mike has also done some previous work with rudder foils and, reminded of your earlier foil experiments, we may explore that idea as well.

I tried the Eclipse fins and couldn't get the performance out of them that the Turbos have. Perhaps the problem it getting enough speed to make them viable. If you're sailing, you can easily get into that speed zone, but under pedal/paddle power it's a different matter. Both of us have dolled up our Drives somewhat and we are able to pull up to over 9 MPH in boat wakes, so we're pretty happy with our Drive set-ups.

As we get a little older each year, we are trying to make the boat a little faster so we can keep competing well enough to get that early lunch line spot. Thanks again for all the suggestions!

Roadrunner:
Yes that makes perfect sense, my only reason for using the eclipse fins is because I'm using tri-power (sails/wings, etc) my desired cruise speed is beyond the range that the turbo fins can produce usable power. At 10-12mph the turbo fins flutter dangerously and you have to pedal at a madman pace to get any additional useful propulsion. Also at the same time I'm beyond the displacement speed of the standard TI hull, (which hits you like a brick wall), physics are hard to overcome.
Fitting mirage drives to a 24ft OC-2 would likely require custom mirage drives (possibly with the flow-90 fins) because of the achievable speeds, Since that hull design has no displacement speed limit, I have a feeling you would break all records. I've seen wood kayak builders add a little box that the mirage drive drops into, would be a real hoot, and something I think Hobie should sponsor, (racing team). I'm sure any of the big OC players would love to partner with Hobie. I'm just imagining in my head the speed and endurance possibilities. Would likely anger most people in the sport though, (tradition is an odd thing in that sport, they don't want to change a thing, but accept the 22lb exotic boat designs with open arms).
I think you and I already know what the result would be, to test my theory just take the TI you built with the mirage drives removed, and see what speeds and energy consumption you achieve with paddles.
Currently you are racing apples with oranges, (different hull classes), imagine if you could race apples to apples (similar hull design and weight, you already know the answer, (Greg Ketterman proved that one out in that pool video)
FE

I would be curious as to the maximum speed of the kayak with only one person on board. Two people add more power but also a great deal more weight and the boat will sit lower in the water. I would also expect that the output from the rear Mirage drive is compromised as it gets "dirty" or turbulent water from the wake of the forward Mirage drive.

Great discussion points! The general gouge on weight is, for every 6% of weight gain, there is a speed loss of 1%. So the addition of a second 200# person to a 100 # boat with a 200# person in it would increase the overall weight by about 67%. Sixty seven / 6 = about 11 or 11% drop in speed. But what if that second person doubles the power output? According to the following source, net speed should increase by about 8%:
http://www.surfski.info/images/stories/ ... t.%201.pdf .

That's not far off. In actual comparisons with a previous TA, the difference was about .4 MPH (5.2 MPH vs 5.6 MPH). Of course, this depends on who the second pedaler is!

IMO, you can lose a lot more speed if the weight change takes the boat off its optimal lines; conversely, a weight gain can add speed if it corrects the boat's posture in the water. For example, adding 18# to the nose of my Revo 11 adds about 8% to total weight. This keeps the bow in the water at faster speeds for a fast cruise speed increase of about .2 MPH or 4% instead of a 1+% theoretical decrease. Boat balance is a big deal, especially with Hobies with their hull design and propulsion dynamics, and weight location is the key ingredient!

There can be a "dirty water" effect with the second Mirage Drive, but not necessarily. As with synchronous paddling, pedaling in unison (or close) can avoid turbulence. You can feel it when you hit it if you're looking for it. On the other hand, the net gain is greater with each pedaler going at his/her own optimal cadence than any loss due to dirty water.

Gem-quality stuff! Thanks Roadrunner.

When I fish in my 13' Revolution, I have a lot of gear in my rear cargo area, and nothing in the bow. I'm going to have somebody take some pictures of me while I'm trolling, typically at around 1.5 mph, and when I'm steaming from place to place. If my bow is out of the water due to the weight of my fishing gear in the rear half of my kayak, I'll try putting some weight in the bow of my kayak and see if that increases my speed and reduces my effort.