Reverse bows

Had a paddle of the OSS2 and OSS3 today to compare them with my current boats, Stellar SES, SEL and FENN Swordfish. I have also paddles mates boats, V10L, V10S, EVO 11 and FENN SL which will also be useful in the comparison.
Firstly the Layout:- (NOTE these were preproduction boats)
Both Boats had similar Cockpits WRT size. Small footwell, deep seat (similar to Fenn SL) well rounded with moderate hump. Seat reminded me of the EVO 11. Seat was comfortable but for me tight. With width between SES and Swordfish. But did allow rotation.
Foot rest was rigid, between 3 point Stellar and Swordfish. Very nice. Adjustment very easy. Venturi wasn't set up yet but located in front of footplate needed a cable activation system to be fitted.
Quality was very good behind the Stellar and Epic but basically the same as the EVO 11, very good for PP.

Hull interesting. both boats followed same philosophy, flat botom from nose to tail,large radius rounded chine. Very stable. OSS2 was more stable that the SEL, but didn't fell as fast. Very reminicent of the V10L in stability and speed. OSS3 very stable same class as V10S but felt a little faster.
Speed and stability was assesed using a GPS but both boats (being PP) were over weight (OSS2 13.4Kg, OSS3 18Kg) and fitted with long rudders (about 220mm), SEL (11.5Kg) had 100mm rudder.

The Bow can be classed as a reverse bow as it has it max fullness down low near the keel and tapering to the top. We paddled in Harbour conditions with weed not to be seen any where, but we managed to pick it up on both boats bows. The first unprompted words of my paddle partner when I joined him on the water was "these are weed magnets", however they soon cleared and didn't hamper our speed, though I would like to see how they performed in a lake or river with frequent weed.

Overall a pair of pleasing boats certainly to be looked at if you were in the market for a stable performance boat.

red_pepper wrote: but I still fail to see a hydrodynamic advantage provided the waterline is the same length and all else is equal.

It aint necessarily so. As Merijn alludes to - prismatic coefficient (i.e. fullness of the underwater sections towards the ends) has a significant effect on the effective waterline of the boat. I wonder if this is part of the reason the Stellar boats are perceived to be fast for their stability, as they look like they have bigger sections carried toward the bow and stern.

As for that old trope, the Bourbon Orca video... Having spent several months of my life up in the Arctic on one of her big sisters in truly horrendous conditions, I'd agree that the 'X-bow' as Ulstein calls it seems to smooth out the motion. Especially compared to the more conventional bowed Skandi boats. However, given the enormous differences in displacement/length & beam/length ratios, weight, operating speed vs hull speed and intended use between a support vessel and a surfski, the comparisons are little more than flights of fancy.

Reverse bows on some racing yachts do in some cases seem to act as intended, smoothing out the motion of the boat (mostly upwind/upwave) and thus the mast, therefore reducing the disturbance of airflow on the sail and providing more consistent power. So the question for this feature on skis is whether pitching really affects paddling technique (if anything the pitching perhaps keeps the paddler's height relative to the water more consistent, avoiding burying the paddle excessively in the wave)? Considering that the major purpose for skis is to go downwind, where moving in the same direction of waves means meeting changes in the water surface more slowly, is it really relevant?

The jury is still out for the bows in sailing - some designers have admitted as much as it is purely a styling thing. If anything if you want an example of a boat (and bow design) that has dominated a major downwind / downwave race for the past 3 editions ( The Mini-Transat )then maybe the bulbous bows of spec skis aren't so far out...

I think there are two diametrically opposite ways to look at optimizing downwind paddling.

1) Keeping the nose out of the water at all cost. This will involve having either a very large rocker, a bulbous nose with a lot of flotation, and or a whole lot of skill at steering, stalling and keeping the boat in the desired position.

2) Allowing the nose to bury. Well I can do that with pretty much any boat easily, but the result with most skis I've tried is a loss of speed to the point that you lose or nearly lose the wave you're on. Having a nose with a sharp top profile will allow the wave to actually push you forward while slicing through the water, thereby not slowing down to the point of losing the wave.

Hi PhilSE2,

Thanks for the detailed feedback.
The OSS2 is in deed our "low" volume ski designed for the lighter paddler (similar to the V10L by Epic), the OSS3 the intermediate, more stable ski. As you mentioned the skis are both pre-production and quality will be no less than any Stellar or Epic, rather the opposite way. We, by purpose, have 12 pre-production skis circulating around Australia to get as much feedback as possible to optimise the products before fixing all parameters for production (which is happening at the moment).
A weed rudder is also in development and will be offered soon, production weights of skis will be +- 10.5KG, +-12.5KG and +-15.5KG.

My best,
OSS

Firstly a comment on the reverse bow. Ski designers go to lengths to design bows that will generate a dynamic lift force on the bow when buried to prevent pickling. The reason the reverse bow is popular on catamarans is that on a reach they have a tendency to bury the leeward bow. The reverse bow counteracts this and minimises drag whilst under. Ideal behavior also for a ski. The Ocean skis bows are shaped to achieve this.

Further to my comments on our trial paddle I need to mention that of the three of us that tried them we all found the width of the seats too tight. Whilst similar to a number if Ski's on the market it was much tighter than the Epic 10 and 10L . All of us came to the conclusion that the bucket width would preclude us selecting the boat. Pity because so much else was good.

Ohana Mana cup had some this year, too. With the Windseeker a predecessor design of the OSS (all 3 Felci). Their facebook (FG Canoe Kayaks) page has actual pics, the vid below is 3 years old vimeo.com/43104521
www.facebook.com/FG-Canoe-Kayaks-Made-in...nia-355547484469816/

Hi PhilSE2,
we took the feedback on and will have the seats of the OSS3 and OSS4 slightly wider in future.

Cheers
OSS

OSS, I appreciate the response. Our comments on seat width also applied to the OSS2. I realise that at 43 wide there is not a lot to play with but an extra 4 or 5 mm would make the ski useful to us. A good number of medium weight .ma le paddlers have wide hips and these would be precluded fro the 2. Similarly many female paddlers are of wider hip and currently the only ski on the market to accommodate the lighter wider hipped paddler (both men and woman) is the V10L it would be great if there was on other option available on the market.

Hi PhilSE2,
Unfortunately, we can't change all top hull molds, that would simply be to costly for us, just starting the new brand.
But this is just the first range. If all works out well and as planned, a larger variety of OCEAN skis will be on offer soon.

Phil, Interesting to read your feedback on the OSS boats. Certainly sounds good for smaller paddlers as even the V10L cockpit has me sliding around without padding.

I'm a bit more skeptical over the other points.

PhilSE2 wrote: Ski designers go to lengths to design bows that will generate a dynamic lift force on the bow when buried to prevent pickling.

If ski designers as a whole were going to great lengths in this regard then I'd expect to see a much greater correlation in bow styles between the different makes. If anything they are all over the place which suggests everyone is following their own beliefs and no little amount of artistic licence. Also for dynamic lift you'd expect to actually see more bulbous sections near the water line or a flattish forefoot (maybe the OSS does have a bit more than most other designs?) It's also questionable how much dynamic lift helps you if you stick it it in the wave in front, especially when you consider the circular motion of water within a wave which is moving downwards on the rear face of the wave, pressing down on the deck.

PhilSE2 wrote: The reason the reverse bow is popular on catamarans is that on a reach they have a tendency to bury the leeward bow. The reverse bow counteracts this and minimises drag whilst under.

There is some truth to this, but still the main reason is pitch-reduction. With some very slight weight and aero drag reduction.

Pete Melvin (America's Cup and designer of many racing multihulls): “To make it short and simple, wave piercing reduces pitching motions and hull resistance though waves. Pitching results in motion discomfort for passengers, increases hull resistance and reduces sail efficiency.

Steve Clark (multiple Little Americas Cup/C Class world champion) and Gelnn Ashby (9? times A class world champ) largely say the same thing (I would post the links but it won't let me publish the post with them).

The fact that the development wave piercing bows have gone hand in hand with curved centreboards or even full hydrofoils designed to keep a bows up (as in almost all the big ocean racing multis and the new Olympic Nacra 17 class), suggests that wave piercers aren't much good at keeping the bows up on their own.

PhilSE2 wrote: Ideal behavior also for a ski.

Much like the Bourbon Orca video, it's good to look around and be inspired to ask 'what if' but dangerous to assume you can simply extrapolate from very different vessels and uses. Small racing cats and surfskis are closer cousins than support vessels, but the differences are still great.

A cat plus crew probably weighs 3-4 times more than a ski and paddler and in wavy conditions will be going around twice as fast minimum (thus overtaking the waves where the ski is fairly limited by the prevailing wave speed) and operating in planing mode. That's a huge increase of momentum before you even consider the sailpower driving the boat on. You'd probably need to clone Sean Rice quite a few times before you got to level of power a cat can lay down to carve through the waves.

Add to that that the cat needs to go both upwind and downwind fast, whereas most ski races are one way racetracks. Bow design may therefore be complicated by the need to provide some side loading to help the boat go upwind efficiently and to reduce aerodynamic drag with the big apparent windspeeds encountered upwind.

Then add in the rudders (10-20x bigger area than a ski rudder) and the centreboards, which provide a huge pivot point to turn the bows out of waves, even when partially immersed. Comparatively when you stick even a small amount of ski bow in the wave, the small rudder is overpowered and you mostly have to go straight ahead until it emerges (usually after the boat is almost at a standstill).

Ultimately I reckon that avoiding (with shorter length, more rocker, better steering) rather than mitigating any deep nosediving (through 'wave-piercing) might be a more successful avenue for big downwind race skis, even despite the trade off of poorer flatwater speed.

That said I'm certainly not knocking the OSS boats. Just trying to add a bit of context to the reasoning behind wave-piercing bows. I think it's great that people are experimenting and I hope they are a success.

Spacehopper,

we did some homework before we started with the project and Umberto Felci, our designer and naval architect, is a leading yacht and cat designer in Europe for many years.
Here a sample (I hope it works, gif files) of a the Windseeker, Umberto's previous design project (paddled by Daniele Scarpa).....okay, tried, looks like it doesn't work, will try other means to get the videos running...

Hi OSS,

I'm very aware of Umberto Felci - he (and his team) produces what are undoubtedly some of the most stylish racing yachts going. However, I would note that I don't know of any successful cats or wavepiercing designs (the skis/proas excepted) and his projects page doesn't indicate he has designed any (successful or otherwise).

It doesn't necessarily mean anything - if anything having no preconceptions may be an advantage. I'm not knocking Felci or OSS, just attempting to suggest some counterpoints about whether wave piercing will work on skis.

With Farr Yacht Design having just got into the SUP design game. as well, it will be interesting to see if perhaps better resourced yacht designers can come up with faster solutions than what often appears to be largely trial and error in the kayak design game.

There have been some interesting posts on the possible postive and negative sides of such bows, all a good read. The discussion is valuable and I learn from the posts here. Thanks.

And the obligatory dogma-argumentation popped up too ... reminds me of:
"Mountain bikes for mountains, trekking bikes for trekking, racing bikes for street racing, touring bikes for touring, ..."

Do the folks at the bicycle forums still have similar discussions as to what vehicle is allowed to exist, to be modified and to be used on whatever ground? One does see mountain bikes on hills, in forrests and on streets though ...

Just glad that nature is not a kayaker, there would be less species around and trillions of niches would have remained unfilled. The world would be less diverse if there were only seagulls and no ducks an no hawks lol. If a design does not succeed in real life conditions, it disappears sooner or later.

So IMO, if someone takes the risk to play with bow and hull design, and yes - to just add another set of boats to a crowded market - the diverser it gets and the better for the users. Reviews and races will show, no need to be a first adopter if too critical about it and nobody is forced to buy without test paddling or thereafter.

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With reverse bows (hybride or not, true or "somehow") I'd hope for a less bumpier ride in nervous or medium upwind chop and higher ripple, less cross-wind affection coming together with longer waterline for speed. "Wave piercing" in above mentioned small "waves" would do it. No big surfs planned. No weed&leaves where I paddle; my only concern would be floating tree branches, etc.

So even if Felci would have tailored and optmized the OSS design merely for the Largo di Gardia, I could live with that lol.

Some racing SUPs have "reverse bows", too, anyone has/heard experiences there?

I'll surely be testing a Nelo Cinco next spring and hopefully a Code Zero in Sardinia in Summer.


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Copy&paste the urls, add www, remove the § and replace it by a dot

OSS (design by Felc & OCEAN team), OCEAN Surf Sports, Manly , NSW, AUS
vimeo§com/142200491

Code Zero (design by Felci), FG Canoe & Kayaks, Cagliari, Sadinia, IT
vimeo§com/43104521
facebook$com/355547484469816/videos/vb.355547484469816/785216708169556/?type=2&theater
Wave piercing? Rather bouncy. Seems to be their widest boat.

Windseeker protopye, Felci, Italy
youtube§com/watch?v=0fzZaDn3O5c

X-Bow, Opium, Brasil
from 1:18 onwards
vimeo§com/88621303

Sea Vortex, Sipre, Portugal
youtube§com/watch?v=FFFwke3gdaY

Bourbon Orca, Point 65, Sweden
youtube§com/watch?v=YFZKwiWiRHM
See nose diving issue.

at spacehopper:
surfski-mv605 > simulation

Uffilation wrote: Just glad that nature is not a kayaker, there would be less species around and trillions of niches would have remained unfilled.

I know what you mean, though to be fair I think for most people who race skis or flatwater the fitness aspect is their main interest.

By the sound of it a wave-piercing bow could work for you and even if it doesn't, you'll look cool anyway...

Hi Uffilation,

Thanks for the comparison with bikes, I had similar thoughts...

Umberto may have designed the Windseeker and Code Zero for Lake Garda and the Mediterranean sea but they also perform very well in larger surf. The OCEAN skis are a joint development with heaps of experience in big oceans (Pacific, Indian).

If you plan to test the Code Zero, why don't you contact Umberto to paddle the Windseeker?

at spacehopper, yes that is exactly what I meant reg. racing/flat water fitness ... skis can be tuned for only that, too ... the downwind surfer sure has no need for a "flatwater ski", but why question the possible demand for such skis? Many inland paddlers around that don't allways want to be limited by conditions with a K1 only.

If it pierces smaller waves, enough for me.

This is getting an interesting and well-informed discussion. Thanks for that.

I think a reverse bow (or even the hybrid bow on the OSS skis) is not necessarily similar to a wave piercing bow. If you build a reverse bow with sufficient volume it will generate the same amount of floatation as a normal bow. So the true functionality depends on more than the form alone.
From the images I have seen, the bow of the OSS skis is certainly not very low in volume, but due to the "reverse" design more volume is carried low, just above the waterline. This might even mean that the bow has less tendency to bury in the wave, a V-bow has to go deeper to reach the same amount of floatation. So is a wave-piercing bow with sufficient volume still a wave piercing bow?

In cats the whole wave-piercing started out with very slender reverse bows, with some disastrous results regarding capsizing over the leeward bow. Nowadays designs seem to have drifted to a slightly reversed or almost vertical profile, with quite some of volume. These sites have some nice information :
www.catsailingnews.com/2011/04/wave-pier...me-distribution.html
www.sailmagazine.com/multihulls/a-look-a...-bows-on-multihulls/

The whole "reverse" design (if combined with sufficient volume) might also be a way to get the bow to rise quickly, with the added benefit of an increased Cp and less lateral resistance. I would love to see some more details of these boats. A line plan may be to much to ask, but some proper 3-view images would be nice.
Or some words of the designer himself, he must know best why he did design the bow as he did.

One last question: what became of the Point 65 Orca, the first reverse bow ski? That ski went out of production, but why?

at OSS,
'cause I'll be on vacation there next summer, but you are absolutely right, I could combine it by "spreading the route a bit" on the way there. Thanks for that suggestion, I would never have considered that at all > the ski being a prototype and him having more important stuff to do. But yeah, I should at least try to ask.

See, I am the average paddler guy compared to those many pros here, no need for me to paddle "high tech" or "fast stuff" at all, esp. as I mostly paddle against myself, see eg the time/speed comparison list of all EPIC surfskis for a 10k course by Greg Barton = I can afford 2 extra minutes between fastest and slowest model
, but I want to feel a difference e.g. in upwind bounce and crosswind, if ... and if it suits me, I'd go for it.

at merijnwijnen
bourbon orca > hear say: nose diving (see video link I posted above), too high/big volume bow <> crosswind, weight ... but I don't know.

What I liked are the features for cold water paddlers:
The slit in the seat to drain the water to the foot well so one does not sit in cold water.

EDIT: I googled a bit, spacehopper seems to be right ... quality issues, pedal/steering/rudder system an issue too, leaking etc.

merijnwijnen wrote: One last question: what became of the Point 65 Orca, the first reverse bow ski? That ski went out of production, but why?

Actually one of the surviving examples has turned up at our club, though I haven't had an opportunity to paddle it. I believe there were production issues with some Point65 boats and this one also seems rather on the heavy side. Also, it's an example where the designer maybe extrapolated from something he liked (the Bourbon Orca) without giving that much thought to the execution and relevance.

This in another good article on the development of different bow shapes. Case 5 is instructive!: www.boatdesign.net/forums/attachments/mu...horese_vplp_bows.jpg