Why do surfskis with no rocker do so well in heavy water when Oc-1 seem to need rocker to perform?

Sorry, might be a dumb question but it is interesting that the fusion and zephyr for example which often piloted to victory in big seas suck on the flats...the standard answer is that the rocker is great for catching swells but not for the flats. So why do surfskis with very little rocker seem to do such a good job at both flat and swells??

THanks

Submitted by Shawn Michael on Thu, 11/13/2008 - 11:23am



Surfski's with a wing blade in the Flat can keep a higher tempo and thereby keep the Hull out of the water for a longer period reducing drag.
With a single blade you tend not to be able to keep the momentum going for as long as compared to a Surfski in the flat.
Having paddled both i don't think there is any difference with the average paddler (either Surfski or OC1) in speed in bigger seas or windy conditions.It comes down to the person who link the runs the best.


#1 Thu, 11/13/2008 - 11:48am


Shawn, the reason the skis have an advantage is not because of hull shape. Ski's are single hull, no ama, they can tack easily left or right, plus less drag. Im no expert, but that's my impression.


#2 Thu, 11/13/2008 - 11:50am


Skiis are also wider than OC1s, Most top skiis are in the 17 inch to 18 inch width/beam. While most new OC1s are now somewhere in the 14-15 inch range.

So skiis should be able to surf well given they have a good amount of surface area. Plus what the others said about the Wing blade and higher stroke rates and single hull.


#3 Thu, 11/13/2008 - 12:05pm


This is a good question and I often wonder the same thing too. All the answers people are putting up are very good and definitely helpful, but I think ShawnMichael is looking for more rocker based answers still ie: if surfskis can have very little rocker/long waterlines and fit into swells, then why can't OC-1's? I don't think he means to compare the two against each other, like surfski vs. OC1, but rather if there were an OC1 with a rocker like a V10 for example vs a conventional 'Hawaiian-style' rockered OC1, like a Fusion. For instance, a Haydn Molokai ski could be considered like a Fusion (not picking on any boat, in fact it a compliment that i'm using a Fusion as the quintessential downwind OC1), but if an Epic V10, with it's plumb bob nose and long waterline can surf as well as the Haydn and is better all around, then why not make an OC1 that emulates this comparison as well?

I don't know, but I think the V10, which i'm using in this example, has some good tail rocker, it just all occurs below the waterline so you don't see it. Because it maintains its long waterline it has great flatwater speed, but it's rocker under the water still helps it pick up in surf.

Also, allot of boat designers are playing with their hull shapes and finding new ways to for boats to surf well without just utilizing rocker anymore. Maybe with the popularity worldwide in Surf Skis, they're just making the advancements just a little ahead of us. This is good because we know OC1 design still has room to grow and hasn't been maximized just yet!


#4 Thu, 11/13/2008 - 4:48pm


Hey Shawn
Try posting your question here: http://www.surfski.info/component/option,com_fireboard/Itemid,254/


#5 Thu, 11/13/2008 - 5:21pm


double blade is moor efficient than a single . But I'm guessing that the ama tracking off the main hull and vise verse. which would drag a bit on the flat would make a difference in time. when your in the bumps the ama gives you great stability on one side witch in a over all race time could be a faster time than it not being there at all. but a ski definitely less stable in bumps.well for me.


#6 Thu, 11/13/2008 - 9:58pm


I was thinking along the lines of FF Kino
"but rather if there were an OC1 with a rocker like a V10 for example vs a conventional ‘Hawaiian-style’ rockered OC1, like a Fusion."

All these OC-1 are heavily rockered (like my fusion) so they can surf, but the SS's seem to surf great with much rocker and perform well in the flat too.

Got some good pieces of info, many thanks


#7 Thu, 11/13/2008 - 10:57pm


hurricanes have relatively flat rockers don't they ?


#8 Fri, 11/14/2008 - 4:25am


I tend to think that the one advantage that an OC1 has over a ski being its Ama is also its weaknest.

The strenght the ski has is to surf at an angle/sideways to the swell and be able to hold it in that position for a longer period. On an OC1 this can be done but the Ama can crab the canoe and be least effective, so to me it's not so much the rocker that counts but the positioning of the craft to maximise the most amount of power from the ocean.

The V10 has been mentioned, the one distinct feature the V10 has is its volume and width in its tail aft of the rudder, which allows you to feel the bump earlier, the closest OC1 i've used that has a similar tail is the fusion, and yes the fusion has way more rocker than the V10 and fits into the trough better than the V10.

I'm not trying to compare V10 (ski) v Fusion (OC1) just the experiences i've had surfing both canoes in open ocean.

I've often been asked would a ski make a good OC1 and my opinion is No, the Hull of a ski would have to made narrower the seat raised and an Ama attached. And basically that's where the current OC1 are at today.


#9 Fri, 11/14/2008 - 8:43am


Didn't TwoGood have basically a Mako ( surfski ) Hull set up as OC-1 for sale years back ?


#10 Fri, 11/14/2008 - 10:24am


Thanks Kaihoe, your feedback about V10's in the trough is really good and brings up this point: Maybe V10's can have a longer waterline because they spend alot of time crossing and diagnoal in the trough as opposed to just looking at hull performance fitting straight in and perpendicular to the swell (which is the moment you'd need the most amount of rocker). Maybe OC1's need more rocker because they, with the ama attached, don't surf as dynamically as Surk Skis?

Paddle Easy,

Hurricanes actually have decent amount of rocker, but instead of alot of curve, like a Vantage for example, which maintains through and behind the seat then curves hard to the tail, Hurricanes look like they have a straight diagonal line that shoots back to the tail from under the seat. It's a different rocker profile, but still has can be considered a good amount. I think it's waterline is 19'3", while overall length is 20'6" from the Maui Fiberglass website.

You can't make a surk ski into a OC1, obviously because of the width. You also don't need to be so strict on balance issues with OC1's because they have amas. Different canoes fit into different troughs better than others, depending on where you are doing you run. Are the intervals tight and close, choppy, big conditions? So with that, I think this question will be along the lines of what ShwanMichael is trying to ask:

If some V10 lover was to custom build a OC1 and basically emulate the V10 as far as design, rocker, etc. with some mods ie: bring the beam to 14", bring up the cockpit, and adjust the target displacement to match that of current OC1's (you'd lose alot of volume by removing those 3" on the beam), add the ama and now he basically has the V10 OC1, how would it perform against Fusion, Zephyr, Scorpius, etc.?

I think ShawnMichael is just basically asking why, with Surf Skis and OC1's comparable in length, are rocker lines so different?


#11 Fri, 11/14/2008 - 11:51am


Compare 2 boats with the same displacement and the same wet surface area:

The design with more rocker will have a shorter water line and be more maneuverable.
The design with little rocker will have the longer waterline and potentially run faster because it can afford a lower angle of entry = sharp bow.

Think of a wood log: leave it as it is or carve a rocker into it. It will behave differently.

My guess is that the wet surface area in OC 1 is smaller than in SS even with the ama taken into account.

Whenever you lift the ama or plunge it back into the water you have to overcome surface tension. That may matter, I don't know.

Probably the higher stroke rate in SS - at this point - leads to better results.

For someone that is able to paddle an OC 1 very 'light' with a high stroke rate it should be possible to beat SSs consistently.

http://www.oc1design.blogspot.com


#12 Fri, 11/14/2008 - 12:08pm


Oc-1 hull is way more efficient than any surfski can even dream of but it is equaly true that the oc-1 is mising propulsive power and paddling frequency of the SS,plus the ama provides not only drag but also a bit of turning moment which again has to be compensated for with some more drag.

The basic reason the surfskis are a bit flater is that they have enough power to push the boat to the upper end of its hull speed design envelope,(where wave drag becomes a bigger factor). the flat boat needs a bit more pushing but if that is available it can go a bit faster.

The oc-1 on the other hand stay well inside of that envelope due to the lack of power and the fact that hull could go much faster than that of the SS, but not the paddler so designers instead try reducing drag even further ,by having less weted surface mayor factor in the kind of speeds oc-1 move at.Rocker basicaly removes unwanted surface on the bow and stern

Rocker profile ,is mostly a the product of location of the center of gravity .Also a factori is the lenght of the hull ,shorter ones need more rocker and/or width than longer ones to float the same volume
Newer designs that push the cockpits further to the front in both surfskis and Oc-1 normaly have a relatively nice sloping rocker on the back and a bit sharper one the front. Older ones with seats more to the back have nicer looking continious rocker profile but are not as efficient.

directional stability of a rockered hull is a bit less than of a flat hull but due to Oc-1 having a big rudder it not that much of a factor compared to lets say V-1

9 out of 10 i would prefer to design to have more rocker as it guarantes less drag in the flat than less rockered hull ,and if done corectly provides dinamic lift on the bow while surfing so reducing pearling and again outpreforming a flat boat ,But as allways there are exceptions ,chined hulls have difrent hull crosection and volume&surface distribuitions so cant be directly compared to others with round crossections.


#13 Fri, 11/14/2008 - 2:21pm


And here is a practical fact maybe not a god case but here it is anyway.
I designed and built 2 marathon kayaks of the same lenght and to the same volume.Both aimed at max efficiency but one desinged more towards reducing wave drag(less rockerd one) and one reducing the friction drag to the minimum(lots of rocker)bow and stern barely touching the water difference in weted surface cca 12 % resulted in the rockered one being up to 5 seconds faster per every minute a (dominant marathon racer) but other wise slower in a 100-200 yard sprints where the flat one could outpace it every time .

And as for waterline width i also designed & built an 1in wider version that is more stable for novice paddlers and both computer and the praxis shoved cca 1knot less speed with all other parameters the same.

I think that SS would be in similar disadvatage to an Oc-1 hull(if used as an SS) not counting the ama


#14 Fri, 11/14/2008 - 2:28pm


So it seems that a lot of people are saying that we lose out because of the single sided paddle versus the double. So what happens if you use a double sided blade in an OC. Is the position too high? And if so has anyone done an OC with a scooped out seat for a double sided paddle. And yes, I know its not traditional.


#15 Fri, 11/14/2008 - 3:42pm


Jibofo, you're looking for trouble....


#16 Fri, 11/14/2008 - 4:54pm


Yeah, some questions are dangerous to ask.


#17 Fri, 11/14/2008 - 5:35pm


Jibofo,

Good Q, i tried a wing blade on a OC1 and kept hitting the ama, so wasn't successful for me.


#18 Fri, 11/14/2008 - 5:42pm


More rocker does not guarantee less drag.
The reduced wetted surface area is responsible for the reduced drag.

If you run a theoretical hull with a given buoyancy for least drag, the computer will spit out a very slender vessel with a specific length for a given displacement, with no rocker at all.
Check the hull simulation programs Michlet and Godzilla from E. Lazauskas.

With more rocker you shorten the waterline. To compensate you either need to increase draft, increase beam or angle of entry - the volume has to go somewhere; the boat will be less slender.

The least wetted surface is obtained by a semi-circular cross section.

Cut away from the wooden log at the bow and at the stern and the log will sink deeper and present a different cross section to the water.


#19 Fri, 11/14/2008 - 8:27pm


During a race awhile ago in Maui I read that Mael Carey's outrigger blade snapped while paddling his one man. A passing safety boat had a surfski blade on it so they gave that to him and he still managed to win. Thats gotta say something...of course the guy also did Maui to Molokai and then the next day got 10th in the solo...


#20 Fri, 11/14/2008 - 9:32pm


Its true rocker alone doesnt decrease weted sruface.But the rocker is the main means with which we reduce the weted surface.We dont do it for the handiling.
But if you take a U shaped hull to Oc-1 lenght and have it straight it will have a draft of cca 2 1/2 in but also bow and ster that are 2 in deep..Then you start refining while keeping in mind that at these speeds frictional drag is the dominant factor. A you quickly get a 1/2 to 1in deeper hull with less bow and stern in the water which at the same time reduced both waterplane and weted surface.

Michlet and Godzila are Toy programs,+ the guy was designing a theoretical K1(never built one) with it and a K1 is a very diferent kind of beast ,it is the fastest kayak there is but runs on a bit different set of rules where wave drag is the main factor .that is why the sprint kayaks don't glide well they have to be pushed and pushed hard (real energy vampires)
They can be pushed to 20kmh but on long run you only get speeds around 12kmh. On the other hand a SS can't go nearly as fast on the short run but is barely slower on the long run.glides much nicer

One factor most disregard is that boats,more optimised they get the more they are weight sensitive.For every 20lbs you need a new design if the design is realy optimised.So designers some times put less rocker in the bow so that with differnt paddler weight the handling and speed wouldnt change to much.


#21 Fri, 11/14/2008 - 11:34pm


That's interesting - 2 1/2 inch daft only.

Rick Willoughby in AU (?) builds outriggers strictly based on Godzilla/Michlet. These two programs are calculating resistance of underwater hulls:

Example: You set the parameters that you want fixed, such as displacement = 200 lbs., target hull speed, etc etc.

Other parameters you leave for the program to optimize: length, beam, draft, rocker.

Then you run the program; it calculates hull resistance by changing the variables at 1000? different hulls/second. The hulls with higher resistance are thrown out.

You want another target weight, such as 210 lbs, a different target speed ? Change the numbers and run the software again.

The programs create an offset file that you can import into design software such as FreeShip. FreeShip will compose a complete underwater hull from the numbers.
You can fare the hull, add the deck etc.
Your final result can be returned to Michlet, and Michlet will give you a detailed resistance report on that hull.

It doesn't get much better than that, and the program is in high regard, see forums www.boatdesign.net.
The problem is rather that you need the tooling to build a hull that is a precise reflection of those calculations. You would need a CNC router/mill to do that.

That limits its practical use.

You can preset the rocker front and aft in Godzilla also, but I have unfortunately not fully understood this feature, it is based on an index for a parabol in the side view, I think.

The other limitation is that OC 1 are paddled in the ocean. I do not know about any programs that can predict all the different wave actions. So it's back to experience.
But both together, experience and theory, should lead to the best results. Theory is after all developed from experience, too.

Another interesting fact about weight: it appears that there is an optimal weight for a boat related to the paddlers weight; a boat to light for a heavy paddler may suffer from sorts of resonance. I have no experience with this, just read it. But it suggests that lighter is not always better.


#22 Sat, 11/15/2008 - 8:16am


My mistake depth it not 3 in but 100mm and changes to 115-120mm with more optimised shape.And due to more foward cockit it is actualy the deepest at the footwell.

We prefer other other programs(maxsurf,hydromax,+range of custom software made for multihulls )and in the end the best one Mk-1 eyeball and gut feeling. As the programs can calculate the hulls but to generate a right one you have to make it so that the computer can measure it, and redo it again and again ,and again.And it still might not be god enough. Remember that most Oc-1 and SS vere made without help of a computer ,on trial and error basis.

About the handling on the ocean ,you cant simulate that but so can't anone else .Still trial and error.

About the wight i am not aware of any weight being to light but ,the boats are not that light anyway due to size and stiffnes.
Maybe a 3 kg boat would be a problem ,but i doubt it


#23 Sat, 11/15/2008 - 9:28am


A custom OC-1 that would be amazing. It would be interesting to see what it would look like for different bodyweights. I have two friends who are NFL line size guys who have wrecked knees and want to get into OC for fitness etc but that is a tough fit.

Since I cant get that I had a shaper design me a stand up paddleboard. For my height weight and the local water condition he came up with 18'6X28...I compromised and got 18ft so I could hang it on the surf rack inside the garage. The boards he makes are all shaped different based on where they are being delived, Hawaii, Austraila, etc I can paddle that board almost as fast as I can move the Fusion...whereas I beyond suck at OC-1 I am sort of "on the radar screen" for a race pace on the stand up board so I can imagine having something that is right for your bodyweight and waters is a huge factor. It would be great if OCs could be ordered in "sizes" with some customizable options


#24 Sat, 11/15/2008 - 12:54pm


Shawn.... Shawn.... Shawn..... man your a tool. Do you read what other people right on here. Better yet did you read what you just posted you are changing your own post.

First step... Learn to paddle
Second step... Learn to paddle well
Third step... Don't be a TOOL.


#25 Sat, 11/15/2008 - 11:27pm


"Rick Willoughby in AU (?) builds outriggers strictly based on Godzilla/Michlet. These two programs are calculating resistance of underwater hulls:"

sounds cool got off on a tangent. Learned a lot from another great thread. It would be great to have custom built boats.

This is the answer that clicked in and the rest is education

"The strenght the ski has is to surf at an angle/sideways to the swell and be able to hold it in that position for a longer period. On an OC1 this can be done but the Ama can crab the canoe and be least effective, so to me it’s not so much the rocker that counts but the positioning of the craft to maximise the most amount of power from the ocean.

The V10 has been mentioned, the one distinct feature the V10 has is its volume and width in its tail aft of the rudder, which allows you to feel the bump earlier, the closest OC1 i’ve used that has a similar tail is the fusion, and yes the fusion has way more rocker than the V10 and fits into the trough better than the V10."

have a nice day


#26 Sat, 11/15/2008 - 11:54pm


Rick builds those OC 1 for flat water conditions not for the ocean.


#27 Sun, 11/16/2008 - 2:47pm


our so cal ocean is pretty flat! Looks like a lake today, covered with ash from all the fires


#28 Sun, 11/16/2008 - 3:38pm


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