ski stable light vs. heavy ski tippy?

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9 years 4 months ago #18470 by Nelo Surfski Tahiti
Hi,

What would be the fastest, a steady light or tippy ski ski heavy?

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9 years 4 months ago #18471 by Stew
The one on which you can put more power down, and paddle technically correct.

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9 years 4 months ago #18478 by red_pepper
Boat weight questions seem to be somewhat polarizing. One well-known ski racer says a lighter ski is definitely faster for him; another well-known ski racer says the difference (in flat water speed) is generally insignificant (but there may be some small differences in how well you can accelerate on to a wave, etc.) My personal experience follows the second opinion: I don't see any difference in flat-water speed (between 21' skis weighing within 10 lbs of each other). I do, however, find that with identical hulls a heavier ski, with a correspondingly larger mass moment of intertia, seems much less reactive to disturbance in the water (and thus feels more stable). The lighter ski will be a little easier to accelerate and to "pop" in the shallows (if you're racing in shallower flat water).

So, a heavier ski with a lower-resistance hull will normally be faster than a lighter ski with a higher-resistance hull - IF (as Stew noted) you have the stability & paddling skills to apply the power in the conditions in which you're paddling (and the weights aren't too radically different). I currently have a light 19" wide ski, a light 17" ski, and a heavier 17" wide ski; on flat water I'm definitely fastest with my heaviest ski (lowest resistance hull of the 3); when conditions get to the point where my balance skills are being challenged, I'm faster in the lighter 19" ski because of the more stable hull design that allows me to continue applying full power. I have also found in the past that running boats with identical hulls but 10 lbs or so weight difference, I was having a blast with the heavier boat in waves that would have been challenging for me in the lighter boat.
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9 years 4 months ago #18489 by owenw

red_pepper wrote: Boat weight questions seem to be somewhat polarizing. One well-known ski racer says a lighter ski is definitely faster for him; another well-known ski racer says the difference (in flat water speed) is generally insignificant


I regularly (flat water) race my ski over distances ranging from 10 to 20 Km. It is a Stellar in Advantage layup and weighs 14.5 Kg. A few weeks ago I borrowed an identical Stellar, but in the Excel layup weighing 11.5 Kg. This 3 Kg weight difference (21%) felt so much lighter as I lifted it on/of the racks and carried to the water for the race start. I thought I would be unbeatable and almost felt like I was cheating. At the start it seemed to accelerate so quickly away, I started to rehearse my winning speech. However after a few minutes I noticed I was still in about the same place mid pack and had been passed by all the regulars as per normal. I paddled my arse off for the full 15Km and at the end, finished about where I normally do, with the usual suspects still all around me. Later, when checking my Garmin download, I found that the numbers were about average and equivalent to my heavier (but identical) ski. Reality then struck; whilst there was a 21% difference in ski weight, the total weight difference (ski + me) was only 3% difference and over that time and distance, this was really insignificant. :sick:

Life truly lived is full of risk; to fence out risk is to fence out life itself
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9 years 4 months ago #18490 by wesley
surfskiracing.org/2011/12/does-ski-weigh...-3300-miles-6-years/

Above is an article i posted in 2011 on my experience. This still holds true for me 2.5 years later and many more miles paddled. 4 pounds is the threshold I use. So if a same model ski/rudder is four pounds heavier for example a 22lbs versus 26lbs then that equates to roughly 5-10 seconds per mile if stability in a non-issue. Flat water paddling magnifies the weight difference while downwind paddling marginalizes boat weight some what. I found that the boats that are in the 26-27lb weight range are the best overall weights for everything: training, racing, stability, durability, so that weight is the most versatile. However, if racing is your game, then paddle the lightest ski you can afford and while maintaining technique. Anything over 32lbs in my mind is too heavy unless speed is not your concern. Wesley(surfskiracing.com)

Wesley Echols
SurfskiRacing.com
#1 in Surfski Reviews.

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9 years 4 months ago #18493 by red_pepper
Hey Wesley,

I appreciate all that you write, and I highly regard your experience, but my experience hasn't been quite the same when it comes to boat weights. Erik Borgnes wrote an article for Epic stating that the difference between the Performance layup boats (typically 34 lb) and the Ultra layup boats (around 25 lbs) was negligible in a flat water race (www.zoominfo.com/CachedPage/?archive_id=...rik&lastName=Borgnes) , although you might gain a bit in accelerating onto waves and such in bigger water. I'm finding my speed (and granted I'm not an elite paddler) doesn't seem to be impacted noticeably by boat weight (within 10 lbs or so). I'm also close to 200 lbs, so I'm probably somewhat heavier than you are, which makes the impact on the overall weight of paddler + boat less for me than it probably is for you (and thus making a more minor impact to displacement changes).

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9 years 4 months ago #18494 by Fath2o
The fastest ski? The one your most comfortable in and is easiest to keep the foot petals pointed up in.

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9 years 4 months ago #18496 by wesley
Steve, (red pepper),

You don't actually believe that there is no significant difference in speed in a 22lb ski like your SE Ultra and a SE that weighs 32lbs or a 25lb Mohican and a 35lbs Mohican.

Wesley Echols
SurfskiRacing.com
#1 in Surfski Reviews.

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9 years 4 months ago #18497 by kayakchampeen
Well Wesley is that a question? or an editorial comment or what...
Why would Redpepper (or anyone else here) bother posting something he didn't believe? You seem aghast that someone could make an observation that contradicts your expert opinion. Or are you just trying to sell more boats? You always come across as condescending and sanctimonious and "more knowledgeable than thou" despite not really having any idea what you are talking about. People have figured out what a bloviating prick and martinet you are and it will come back to bite you on the ass one day. Go back to your rowing erg dude, you are nothing but a salesman

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9 years 4 months ago #18498 by Kennneee
I don't post much here but I do read a lot. Just want to say that Wesley has been one of the most helpful posters for me. I don't think he is selling boats these days, but that is beside the point. Not wanting to get into a screaming match with anyone but would love to see a little more mutual respect here. Thanks for listening!

Ken

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9 years 4 months ago #18499 by wesley
Facts:
I actually have known Steve for about 4 years now and discussed Stellar boats and other boats years ago.he bought 2 Stellar boats that I am aware of.I was helpful to Steve on several occasions since then when he called me or emailed me. I don't think Steve would describe me as a prick or condescending.

I have not been with Stellar for months now.

I am an award winning professional sales rep for over 22 years.

I do know alot about surfskis, paddles, and less about erging though I have been doing it for over 11 years.

I did come in fourth today in a 15 mile race in my new Evo2 that I am writing a review for, so stayed tuned for that.

I do know a surfski Poser when i see one.

I do know a guy who insults many people online including Scott L(his real name,not his online name) a few months ago so it is not just me though this is the 2nd time he has used this kind of language and later apologized for it.



Rob, as the moderator, you should censor kayakchampeen or atleast let him know about fair play.

Wesley(surfskiracing.com)

Wesley Echols
SurfskiRacing.com
#1 in Surfski Reviews.

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9 years 4 months ago - 9 years 4 months ago #18500 by PaddleFaster
Edited as not to take away from the original thread topic which is extremely exciting and entertaining...

So much so, it has to be stated that if this thread was adorned in a bikini and dancing around a brass pole, I would be inclined to willingly stuff dollar bills in said bikini...
Last edit: 9 years 4 months ago by PaddleFaster.
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9 years 4 months ago #18501 by red_pepper
Hey Wesley,

First off - I consider you a friend and someone who genuinely knows his way around surf skis, so this is just a friendly "in-house" discussion. :)

When it comes to surf ski weights, looking at it from an engineering standpoint, we know there's going to be some resistance increase due to an increase in weight, because any weight increase increases the displacement of the hull; it will also impact acceleration. The question is: is it really discernible (within the weight limits discussed)? Light skis definitely feel responsive and fast, but if you're paddling a marathon race is there really much difference? So, in search of objective data, I made some calculations.

The weight density of water is 62.4 lb/ft^3. If we assume a pair of identical 21' surf skis, one 22 lbs and one 32 lbs, and a 200 lb paddler (neglecting other gear such as water bottles, etc.), we find that the heavier surf ski requires 3.71 ft^3 of water to support the boat and paddler, while the lighter ski requires 3.56 ft^3 of water to support the boat & paddler: a delta of 0.15 ft^3. If you assume that the extra displaced volume is applied to a boat 21' long with an average width of 0.8' (making a guestimate on average width), or 16.8 sq. ft., the extra depth displaced by the heavier boat/paddler is .009 ft, or 0.1".

With all the other variables in a race (shallows, waves, etc.) my guess is it would be hard to discern a variation that small, particularly in a very streamlined boat like most elite surf skis.

As far as personal experience, I've looked at photos of me in my prototype Mohican (a heavier fiberglass layup - I'm guessing around 35 lbs) and a friend who weighs about the same in a production Mohican (26 lbs?) and I honestly can't see any difference in how the boats sit in the water. My experience racing skis of various weights (along with the Mohican) hasn't shown any real advantage to the lighter layups in my hands. Speaking of which, I had a good race today in my Performance layup V12. :)

Where I have seen a difference is in popping a boat in the shallows. Last year I brought along the S18S I had to the USCA Nationals to race in the Sea Kayak class to see how the boat ran. Even though it was the Advantage layup, I had to add six lbs or so to the weight to make the specs (USCA rules require Sea Kayak class boats to weigh a minimum of 40 lbs). I didn't see much difference in speed with the extra weight in good water, but I couldn't pop it at all in the shallows!

I suppose one mitigating factor in equalizing speed between the lighter and heavier layups is the increase in the mass moment of inertia of the heavier boat (with the increased mass distributed throughout the hull); this tends to make the boat less reactive, and thus effectively more "stable", meaning it's easier for a less skilled paddler to apply power more efficiently. I've definitely experienced that in waves; I found an Advantage SEL much easier to handle than my Ultra layup SE when the waves picked up.

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9 years 4 months ago #18502 by Sandy
Wow , way to go Champeen , you are well on your way to beating out "RAB" for the title of surf ski.info pariah....

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9 years 4 months ago #18505 by Metro
Far out. Champeen, almost always enjoy your posts and think that you add a lot to this forum. Everybody fires off a clinker every now and then, so perhaps that last post was yours?

In any event .... With no scientific backing, just lots of paddling behind me and some common sense (in my opinion), I think that Wesley on balance has to be right. Can we really think that a 22lb ski will NOT be faster than a 32lb ski? We are powering these things with our arms and core after all.

Obviously, a heavier ski will sit lower in the water and so will be less corky and more stable. But the question I think is an apples to apples question - assuming the same stability, what is faster, light or heavy. With anything human powered, I will never be convinced that heavier is faster. Nobody adds weight to their bicyle and no marathoner dons a weight belt at the line. I am surprised how relatviely frequently this question comes up on this forum. Like for some reason the law of physics that applies to bikes and runners does not apply to skis ... ?

My humble view is that you find a ski that fits you, then choose the lightest layup that you can afford. If you are 100kg +, then this opens up most of the skis on the market to you - so go nuts and have fun. If you are a lighter paddler, then it is a little more involved. I am 65kg and in an Epic V10 (which just isn't made for that weight), perhaps a heavier boat will be marginally faster because it won't be corking around as much as a lighter layup would and I can put the power down. But, find a ski designed for 65kg (Fenn Spark, Nelo Ocean M), and I'm taking the lightest layup all day, every day.

I will concede that another important consideration is what type of paddling or racing you intend to do. For me, lightness is really key when accelerating. So, in flatwater stuff where the go is to get the boat moving and keep it moving consistently under constant power, perhaps there is some tolerance for a little extra weight. I guess I don't really know because that style of paddling is not my thing. Ocean racing is all about acclerating onto a run, taking a breath, looking around for another run, accelerating, rest, accelerating, etc. In that environment weight is everything to me and I will always be looking for the next lightest ski. (For bike riders / racers out there the wheel weight analogy is perfect. For acceleration you always want the lightest wheels you can afford. Same goes for pedals although that is often overlooked.)

If somebody would like to call me a prick, please feel free, because if I am honest with myself it is probably true.

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9 years 4 months ago #18507 by Rod Thomas
Replied by Rod Thomas on topic ski stable light vs. heavy ski tippy?

Nelo Surfski Tahiti wrote: Hi,

What would be the fastest, a steady light or tippy ski ski heavy?


Hi, I'm no expert but I think you are asking a serious question which requires more than the standard 'don't sacrifice stability for speed' or "of course lighter is faster" reply.

You come from Tahiti right? Never been there but you get strong winds and huge swells don't you? So you are either a serious downwind paddler or want to become one. You aren't flatwater paddler anyway.

A 'steady light ski' may be very frustrating to use upwind. It probably has a wide flat bottom and you will slam as you go over each wave and shudder to a halt. Also if the wind is strong it may be blown sideways easily. A ' tippy heavy ski' will cut through the chop and smaller swells without slamming or losing momentum. Even a tippy ski when going fast is stable. And nothing is more unstable than a stationary surfski in rough water. So it may be less frustrating upwind.

On the downwind the "tippy heavy ski' will be a challenge to keep upright particularly as you turn but if you can do that it will cut a deep V in the ocean and hold it's line better on runners. If it is really heavy it maybe slower to accelerate but will keep its momentum and direction and be less likely to veer to the side or wallow on the back of waves which you might find a problem with a 'steady light ski' . Again as you maintain your speed you will maintain your stability.

Maybe you should get both and use the 'steady light ski' for when you are tired, when the conditions are scary, or when you just want to have fun and dont want to get wet. And use the 'tippy heavy ski' at other times. Above all make sure you can remount it in all conditions. It wont forgive bad technique but will be more rewarding in the long-term as you chase the holy grail of surfski which is to ride those ocean swells. If you cant afford both use the 'steady light ski' until you get fed up with it and then change to a tippier ski. And for both skis consider getting a large elliptical surf rudder.

And perhaps a 'downwind pro' like Rob can give you a better advice...

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9 years 4 months ago #18508 by Metro
Rod Thomas -

Just my two cents, but if your post was premised on Nelo Tahiti deserving a serious reply regarding ski weight, I'm not sure that laying out all of the very obvious pros and cons that have been long hashed on this forum and concluding with that old chestnut, "buy both", really hits the mark. Likewise, "Go with the one that you can remount", really seems to asnwer a question that was not asked! :)

Nelo Tahiti asked a straight forward question and Wesley and I feel strongly that lighter is better. Wesley has done some structured testing and I have what I think is a fair bit of empirical evidence as a smaller paddler long looking for a proper fitting ski.

So, let's assume that Nelo Tahiti (i) is not made of cash and/or (ii) has limited storage space. Which ski do you think he should pick? And, if the heavier ski, why? And yes, for this exercise we can assume that both skis can be easily remounted and, if necesary, that both are in a color that is pleasing to Nelo Tahiti.

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9 years 4 months ago - 9 years 4 months ago #18509 by nell
To simplify a bit, we should be phrasing this as how does boat weight affect boat speed relative to power output, i.e. steady power output vs. nonsteady power output (lots of accelerations), and not relative to water conditions.

At our racing speeds, about 80% of total drag is skin friction drag which increases with boat weight. I suppose form drag and wave drag would also increase, but that seems faaarrr more complicated to measure and the difference might be minimal, anyway.

Here's the math:
www.atm.ox.ac.uk/rowing/physics/weight.html
This guy's from Oxford and likely knows 100x the physics that I could ever hope to understand. Among his conclusions for rowing shells, which I assume to be applicable to racing skis, are these:

1. At steady, uniform power output and speed, "... the percentage loss of speed is one sixth the percentage increase in mass."

Therefore, my rudimentary math skills calculate an increase in speed of roughly 7.0 mph to 7.05 mph if you went from a 32 lb boat to a 22 lb boat, and from 7.0 mph to 7.11 mph if you went from a 40 lb boat to a 20 lb boat, assuming a 180 lb paddler. 10 lbs shouldn't be noticable at all. Lighter paddler/boat combinations would be more affected by boat weight because the difference in boat weight would be a greater % of total weight, but it's still likely not that much unless you're 120 lbs or so.

2. Also, "If boats ran smoothly, then a lighter boat hull would always be a faster boat since boat+rower would have less mass, therefore less wetted surface area, therefore less drag . However, the boat speed varies throughout the stroke, and the amplitude of oscillation is larger for lighter boats, requiring extra power to maintain a given average speed "

Rowing shells, I assume, have a greater variation in speed because of the sliding seat and the lower stroke rate, however, there is also some variation in speed, not to mention, yaw, roll, with the kayak stroke and therefore, I suspect there is a ski weight that is actually too light - though I have no idea if that weight is 20 lbs, 15 lbs, 10 lbs . . .

The bottom line then should be that with steady power output, on flatwater, or upwind, or downwind, or in cross-chop, boat weight does not significantly effect boat speed until you get to a fairly large difference in boat weight. But, when power output varies considerably, i.e. accelerating onto waves, or to stay with the group's repeated accelerations, whatever the water conditions, boat weight matters considerably due to the energy required to accelerate that mass over and over again. Erik
Last edit: 9 years 4 months ago by nell. Reason: typo
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9 years 4 months ago #18510 by Fath2o
What about safety? If we assume that "Nelo" will be paddling in strong winds with large swells in the south pacific, wouldn't a heavier boat be safer and less prone to catastrophic failure miles offshore? Will the absolute speed of the boat really matter?

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9 years 4 months ago #18518 by red_pepper
So following the "Oxford model", if a 10 lb drop in weight increases boat speed from 7.0 mph to 7.05 (with 180 lb paddler), that would equate to an improvement of approximately 26 seconds over the 7.2 mile course I raced Saturday, or 0.7%. It could make a difference in a tight race, but it would probably be hard to discern that level of improvement without running the course a great many times to factor out variations in current, depth, paddler fatigue, and other variables.

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