Design Questions: SLSC spec skis v ocean surfskis

Looking for some smart design info from the surfski experts on this forum....

I'm currently writing a piece which compares the design differences between an ocean surfski (in this case, a Stellar SR) and an SLSC spec ski. There are three really discernible differences I've seen and would love some insight as to why these differences exist:

1. The ocean ski bow is wider but lower - the spec ski has a very high, but very narrow bow profile.

2. The cockpit in the spec ski is far closer to the nose of the boat than the ocean ski. In the boats I'm comparing (which are quite similar in length), the back of the cockpit is 19cm closer to the nose for the spec ski than the ocean surfski. Why would the spec ski have a cockpit closer to the nose and would this work against it in terms of hull speed?

3. The stern profile on the spec ski appears to have chines in the tail, as opposed to the ocean ski which has a smooth rounded profile. Why?

Any insight into these design differences would be greatly appreciated.

Cheers, FP

Most spec skis also have a flared bow do they not?

Yep, that too. A very definite flare on the bow of the SLSC surfski

Take it you have looked here where some of these diffs are evident

www.google.co.uk/url?sa=t&rct=j&q=&esrc=...537100,d.d2k&cad=rja

FatPaddler wrote: Looking for some smart design info from the surfski experts on this forum....

I'm currently writing a piece which compares the design differences between an ocean surfski (in this case, a Stellar SR) and an SLSC spec ski. There are three really discernible differences I've seen and would love some insight as to why these differences exist:

1. The ocean ski bow is wider but lower - the spec ski has a very high, but very narrow bow profile.

2. The cockpit in the spec ski is far closer to the nose of the boat than the ocean ski. In the boats I'm comparing (which are quite similar in length), the back of the cockpit is 19cm closer to the nose for the spec ski than the ocean surfski. Why would the spec ski have a cockpit closer to the nose and would this work against it in terms of hull speed?

3. The stern profile on the spec ski appears to have chines in the tail, as opposed to the ocean ski which has a smooth rounded profile. Why?

Any insight into these design differences would be greatly appreciated.

Cheers, FP

It's like writing an article comparing a mountain bike to a BMX, apples and oranges etc etc. They are different craft designed for different things.

In reply to your questions:

1. I've never paddled a spec ski with a narrower bow profile than an ocean ski, and I've had a Gibbins, which is one of the narrowest profiles around. So I'm not sure what type of spec ski you are on that has a profile you describe.

2. Think about the conditions the ski will be raced in, and then think why the set up is as it is.

3. You're talking about a design feature of one brand, it doesn't carry over to others.

For your benefit, I'm comparing the Stellar SR to the Hayden PR Fat Boy.

What I'm interested in is, if you were a designer, why would you have the cockpit further forward (eg easier to catch waves with weight forward? to keep the front half of the boat narrower and leave the width behind the paddler?), why would you use chines in the stern (eg for strength? better purchase on a wave face with a harder rail? ease of construction?), and why the higher bow profile (eg to allow greater rocker for surfing? to add volume to the bow?).

I don't think these are unreasonable questions, I'm just curious about the design thinking as I write up my views on both surfskis.

What Stew said.

Both types of skis are evolving all the time, as are the designs from different companies for each. If you were to compare your spec ski with another spec ski, you`ll probably find differences between them in the parts you`ve outlined.

Spec skis from around 1980 were much wider in the front end and the deck was a lot flatter and lower (Check out the skis they`re racing in the movie `Coolangatta Gold`.
Since then spec skis have all had to develop the built in wave-deflector (as opposed to a removable one); rudders have moved under hull with upper part hidden and wires inside boat; the front deck has been raised for strength, buoyancy and to shed water, with a spot to stick your paddle for jump starting. The list goes on, but you get the gist...
The design ideas get tried on both types of skis, so some speccies have chines and some don`t - just like with ocean skis.

Yes FP, they are very reasonable questions and great for comparing these two particular designs for your readers, just so long as they realise that not all speccies or ocean skis are the same either.
Good luck with your article.

Stew is correct in all that he says.

This is also not the ideal place to get any relevant info, not saying that it cant be but, WHO is answering your question? Joe soap who just takes a stab at what he thinks or a top end designer. These forums are at best to be taken very lightly in terms of accurateness. I definitely would not publish info from a forum like this. They are maybe helpful for some paddlers.

Back to your question first of all, you are comparing a tricycle to a racing bike, pick two top end skis if you trying to compare, even this is still not really relevant being two different applications of similar floating objects. Also you need to know what the relevant designers were thinking when they designed their craft, only they can tell you that, everything else is speculation!

I suppose you realized the one is longer than the other? maybe that is stating the obvious!

But the main difference is in the name "spec ski", they have specification they have to work to, one specification is a set rocker profile, if you were to put the seat farther back what do you thing will happen to the bow? I suspect it will lift up out of the water, reducing water length, slowing the hull speed down.

Here is a prime example of taking a stab in the dark, I could offer a lot more info, use it at your peril!

And yet Ranga when I read posts here, almost EVERYONE considers themselves an expert.

Like anything on this forum, I hoped to enjoy different points of view and ideas on the designs based on personal experiences with different skis and ski types. There are few places where so many experienced surfski paddlers gather in one spot, hence why I posted it here.

Unlike most paddlers on the forum, I don't care about racing, preferring rather to use my surfski in breaking surf, and often around rocks, where frankly a tougher, more maneuverable surfski would have an advantage. My SR is great for this (until I break it of course) but I suspect a spec ski will be better, which is why I'm comparing them. Besides that, I just find the comparison quite interesting, as I'm sure other paddlers might too.

Btw the spec ski is 5cm shorter than the SR but the cockpit is 19cm further forward (ie it has a much longer stern profile). Does that still correlate to your "nose lift" theory? Cheers, FP

Rocker and balance. The weight in a spec ski is probably further forward cos of the deflector. So the balance of the ski is different and the seat position would reflect this.

For the type of wave stuff you like, a spec ski is a good option. It's what they're built to do. That's why they're heavy. That's why they're shorter. That's why they have chines. That's why they have more rocker.
They're easier to remount when you come off and they have that funny big lump on the front and a big ugly rudder on the back.

Remember when you're comparing width that the SR has the widest nose of any ski I've ever sat in.

If you to look on surf life saving Aus site there is a section in it that states what specifications are required for a surfski to be able to be raced in sanctioned events. This includes rocker, boat width, length and among others weight of the ski. For a ski to get a SLSA compliance sticker it must weigh no less than 18kgs. This means the ski is to be built to 18kgs of strength not 13kgs and a weight placed inside the boat to bring it up to spec weight, something I am told that surf life saving officials a going to be checking this year. A bit off topic but I race a v12 in ocean races and a fenn LS spec ski in SLSC santioned races such as the George Bass Marathon. The v12 is like a formula one car compared to the spec being like one with flat tyres.
But in the right conditions both are a lot of fun.
Hope this helps.
Cheers

As a few people have mentioned SLS skis have to comply with the SLSA specification. The specification is available on the SLSA website and it details construction material, length, weight, rocker, width etc. Anyone who's been through SLSA scrutineering can attest to how seriously the specs are checked!

Some of the specs that define the way the skis look are:
- maximum length of 5.79m
- minimum width of 480mm at the widest point
- minimum width of 180mm at a point 400mm from the bow
- minimum width of 75mm at a point 200mm from the bow

All that and the fact that spec skis are much more likely (certain?) to see action in breaking surf means spec skis look and paddle differently to ocean racing skis.

Having said all that the scope for variation within the spec is still large and there are designs to cater for the same range of paddler as manufactures of ocean skis. Manufacturers are still actively improving designs. I've just replaced my 7 year old spec ski (Forcefield Millenium II) with one that's less than 12 months old (Slipstream SurfX). While the improvements aren't dramatic they are definitely there.

With regard to cockpit placement I have had that conversation with a ski designer but can't remember the answer - I think it came down to balance and the ability to catch waves. No doubt if you gave one of the ski manufacturers a call they'd be able to fill you in

Does the Fat Boy share the same front half as the PR2 with just a widened stern?
Thats important to consider when comparing two boats which may seem to have similar length and width, half the FB may be from an elite spec ski so out of proportion in comparison.

Doesnt the SR have a rather wide and low bow compared to a lot of ocean skis in general?

Great questions Jmuzz. Yes, the Fat Boy is exactly that - they've used the exact bow of the PR2, added a few cms of width behind the cockpit (roughly 5-10cm behind it), flattened the hull a touch under the cockpit and lowered the seat a bit. A slim-nosed PR2 with a fat arse effectively.

The Stellar SR does have a wide bow, in fact it carries a lot of volume across it's entire length, which is where its stability comes from.

Excellent points though... because so far (and this is without using a GPS, so it's gut feel only) the FB has actually felt faster than the SR.

I've taken lots of comparative pics for the write-up, it is really quite fascinating (for me anyway) comparing the differences.

For those interested, here's a couple of comparison shots of the hull.