I've been looking into getting an SCHRS rating for the Isotope for a while, and have some questions/concerns. Using a tape measure, some published data, and some guesstimates, I've come up with a variety of potential ratings using the SCHRS calculator. Unfortunately, by using different assumptions/configurations, I get a very wide range of numbers. Clearly, SCHRS is not as straightforward as it's claimed to be.

For example, should the mast area be included in the mainsail area? The measurement instructions say that it should, but several popular boats listed in the official ratings table seemingly do not.

If I calculate mainsail area including the mast, and my current square-top mainsail, sailing single-handed, I wind up with a rating of 1.075. That's significantly faster than a Hobie 18. I'd owe a Hobie 16 nearly 6.5 minutes in an hour race. Under the Portsmouth Yardstick base DPN, A Hobie 18 owes me time, and I owe a Hobie 16 less than 1.5 minutes in an hour race. That's a huge discrepancy.

If I don't include the mast area, then my rating comes out around 1.098 - more realistic against a Hobie 18, but still way behind a Hobie 16 2-up. If I recalculate a Hobie 16 as 1-up, then it's handicap changes to 1.117, which translates to my owing it about 1 minute in an hour race. That seems more reasonable to me. SCHRS seems to place a large penalty on sailing single-handed.

If I were to do a lot of SCHRS racing, I think I'd make myself a high-aspect pin-top mainsail and race doublehanded. Then my rating would be 1.205 (omitting the mast area). That number would make me tough to beat.

Is there someone familiar with SCHRS measurement who can help walk me through the process, explain how other boats' numbers were generated, and get some Isotope ratings in place?

Regards,
Eric

Mast area is included in sail area (CM), if there are boats that don't included the mast area then I'd contact SCHRS and ask why.

http://www.schrs.com/contactus.php

Carla did the measurement for the FL300: carla (at) coconutgrovesails (dot) com

To be honest, I think only Mark has ever claimed that it was straight forward.

Read the Feb 16 report and scroll down to: 3. How to reduce the gap between the Dart 18 and Dart 18 cat boat? to understand the thinking on singlehanded sailing.
http://schrs.com/news.php

Man, there are some active super geeks over there working on that stuff. That is an outstanding set of reports and some high quality decision making.

Correct me if I'm wrong, but:

1. The Hobie 16 has (according to multiple sources some of which predate the push to SCHRS) 218 sqft (20.26 m2) of sail area NOT including the mast. According to the SCHRS table, it has 15.14 + 4.8 = 19.94 m2 total INCLUDING mast. That can't be right.
2. The Hobie 18 has 240 sqft (22.30 m2) of sail area NOT including mast. SCHRS has it listed as 16+6.32 = 22.32 m2 INCLUDING mast. That can't be right.
3. The Prindle 18.2 has 233 sqft (21.65 m2) of sail area NOT including mast. SCHRS lists it as 16.92 + 4.61 = 21.53 m2 INCLUDING mast. That can't be right.

Either all these old sources were including the mast - something I can't conceive of them doing, or SCHRS is not including the mast - contrary to it's instructions. Which one is it?

Yours in confusion,
Eric

Thanks for the pointer. Unfortunately, it doesn't help me out. The discussion there is changing the ratings of underpowered main-only boats. The Isotope is a somewhat overpowered sloop-rigged (main and jib) boat and is not affected by the change. By the way, the Dart 18 solo was rated 2:13 SLOWER than a Dart 18 in an hour long race. The change makes it only 0:38 slower per hour. According to my calculations, the Isotope single-handed would be rated 6 minutes FASTER than an Isotope 2-up in a 60 minute race. That's a 10% difference. Portsmouth Yardstick has the Isotope 1-up a bit less than 5% faster than 2-up. 5% seems to be reasonably accurate given a long history of the same pool of sailors racing in both configurations (that is, there isn't a big difference in skill between the racers).

If I have to race SCHRS under those ratings, I'll race 2-up.

By the way, what happens if a Hobie 16 sailor races single-handed? Does he get to use the same SCHRS rating (1.91) or does he have to recalculate (1.117)? That's 4 minutes (over 6.5%) in an hour long race.

The F18 main is 17 square meters including the mast and this is what SCHRS has for the sail area.

What is the source of your sail area number and what measurement formula was used to compute the sail area? Have you put a tape to a Hobie 16 sail and used the spreadsheet provided by SCHRS? If you have questions about SCHRS your best bet is to contact SCHRS, IMO.

I have said it's straight forward, it's not difficult to understand and the calculations are done for you by the provided spreadsheet. The system doesn't take any special skills it just requires the ability to follow directions and an attention to detail. Once the number is created for a stock boat it's as easy to use as DPN. Let's not forget... DPN is supposed to use a measurement formula for new boats too.

Given a choice I would NEVER sail under DPN <insert all DPN flaws here>. The OA just needs to have the backbone to commit to the system and be ready to push back on its detractors.

My sources are:
http://www.hobiecat.com/sail/hobie-16/
http://www.hobiecat.com/sail/hobie-16/specs/
http://hobieclass.com/hobie-16/
https://en.wikipedia.org/wiki/Hobie_16
http://sailboatdata.com/viewrecord.asp?class_id=3852

Now, there are some websites that list a smaller area for the mainsail than SCHRS does, but they also spec a larger jib than SCHRS does. So, does the 20.25 m2 value given by these sources include the mast in that number, or not? I know that sailboatdata.com does not include mast area for other classes. I don't have a H16 myself - otherwise I would have measured the main myself to find out. That's why I asked.


Yes, there's a spreadsheet, and if you already have all the numbers that are needed to plug into the spreadsheet, then it's straightforward.

However, if you don't already have those measurements, and if the class allows different configurations, then it is not at all apparent how to generate the numbers that go into the spreadsheet. Using different inputs that I have tried for an Isotope, I get a rating number anywhere from 1.053 to 1.205. That's a huge range and the outlying values are obviously incorrect. There's no way that an Isotope is faster than a Taipan 4.9, nor slower than a Hobie 16. Reality has to lie somewhere in between, but how to get there is definitely NOT simply a matter of following directions.


Unfortunately, I don't have a number for a stock Isotope yet - that's what I'm trying to create. And, what happens if you have a stock boat that has a different configuration than the one that the SCHRS rating used? What do you do?


I know that under Portsmouth, if someone sails under-crewed, then there's a modifier to apply. Under SCHRS I have to call and ask? What about pin-top vs. square top? Should I call SCHRS and ask? Where I race, SCHRS is not as easy to use as DPN.

But, I'm not trying to detract from SCHRS, I'm just trying to follow the process to get an appropriate SCHRS rating for my class - and understand how to handle all the different configurations that are class legal. Oh, and apparently I need to get the measurements done by an ISAF certified measurer. Does anybody know where I can find one of those?

Sincerely,
Eric

Well, I've "just followed directions with attention to detail" (honestly taking all the hits the way I read the instructions), and plugged the measurements into the SCHRS spreadsheet. The end result is that I get an SCHRS rating for a 1-up Isotope of 1.050. That is essentially the same as (marginally faster than) a Viper 1-up with spinnaker.

How in the world a 52 year old design without a spinnaker is supposed to beat a 6 year old design with a spinnaker is totally beyond my comprehension. There's no way I can sail the boat to that rating, so I guess I'll stick to one-design and Portsmouth Yardstick racing.

Manufacturers website says it's an F16!

http://www.intl-fiberglass.com/isotope.php

"The strong points of the Isotope are that its balanced helm allows it to out point any other catamaran to windward". LOL. A real F16 class winner they have their. FYI, the Viper is more than 6 years old, probably a 8 or 9 year old design, there are boats from 2009.

Anyway, on SCHRS, it does punish single handing in many cases fairly 'harshly', on paper. For example, we have a Viper F16 that races solo but in the doublehanded configuration (with jib). His rating is 0.964 when you plug in the Viper F16 data into the formula (the data on the SCHRS website), then plug in 1 and 1 for # of crew and # of crew trapezing. That is very very slightly slower than a Nacra 20. You can see the results here: www.wrcra.org

On the water results tend to suggest this configuration is fairly similar in speed to the N20 across a wide range of wind conditions (neglecting sea state, it is fairly flat where these races occur).

Yes, and the Hobie 16 also meets the F16 box rule. So what? Marketing hype that predates the first production F16 boats aside, I don't see anybody entering a Hobie 16 nor an Isotope in an F16 regatta with hope of success.

Again, that's a bit of dated marketing hyperbole. I did outpoint a Nacra I20 on an Isotope in a race several years ago, but I doubt I'd be able to outpoint a modern A-class cat.


Sorry, I was going by sailboatdata.com, which says the Viper F16 was first built in 2010. Wikipedia says the Viper was first made in 2007, so go ahead and change that to 52 years old vs. 9 years old.


Yes, SCHRS's penalty for sailing an Isotope singlehanded is over 10% (1.050/1.157, compared to a less than 5% (1.002/1.050 or 1.105/1.157)penalty if I added an F16-size spinnaker. 40 years of Isotopes racing 1-up vs. 2-up against each other indicates a less than 4% difference (although I could probably be talked into 5%).

Now I'm just a club-level racer competing in a small local fleet, so I don't hold any delusion that I'm sailing my boat to its full potential. There are many sailors out there who are much faster than I. Nevertheless, I still would like a rating that yields a fair test of skill. Does anybody really think that if you took two equally skilled sailors, put one on an Isotope with main and jib, and the other on a Viper F16 with main and spinnaker, that the two should finish a 60 min race within 4 seconds of each other? I'd like to think that boat design has advanced more than that in 40 years.

Doesn't the Isotope class allow 1 up or 2 up configurations without penalty? I thought it was designed to be a single hander, so why is it penalized under SCHRS? Don't they also permit sail plan changes as long as they conform to a specific sail area measurements?

I don't think two equally skilled sailors would even be close on an Isotope vs. an F16.... but those Isotopes do point incredibly high. They are pretty impressive on flat water, but still no match for an F16. We have both at my club and the F16 is always waiting for the rest of us to finish.

The Isotope has two different Portsmouth ratings - DPN 74.3 for 1-up and DPN 77 for 2-up. Wind-dependent factors range from 2-4.5% speed difference. Except at the Nationals (where everybody races boat for boat), the Isotope fleet scores its "one-design" races on handicap between the two configurations. Now, there are two skippers (both usually sail singlehanded) who regularly dominate the fleet -- it is rare that another boat wins when they are racing. Aside from them, two-up boats do frequently correct up over one-up boats in the standings.

The Isotope is a 16-foot version of the 14-foot Cheshire, from which it was derived. Rumor has it that the builder made the first Isotope by cutting the Cheshire molds in half and lengthening them by 2 feet. The Cheshire was designed to be sailed single-handed. The Isotope was designed to be sailed by one or two people. Originally, it was raced 2-up quite a bit, but now is mostly 1-up.

There is no official manufacturer's sail plan, nor approved sailmakers. The class rules limit the boat to 185 sqft of soft sail, but allow you to divide it up between main and jib any way you like. One of the fleet members has a sail loft, and since we began sewing our own sails (maybe 15 years or so), we've pretty much gravitated to 44 sqft in the jib and 141 sqft in the main. Some sailors like a square-top mainsail, and others (including the designer) prefer a pin-top. The class as a whole decided that the performance difference between the two was small enough that we wouldn't differentiate between them. Either is permitted for one-design racing.

Regards,
Eric

Thank you for this information. Mast area should be included and you appear to have identified three classes where it isn't. This feedback is useful; with 250 variants to watch we don't have the capacity to check everything. I've spoken to David Chivers, an experienced measurer, and he will try to check the measurements and class rules next week when we are all at Texel. If materially wrong we will correct the figures.
William Sunnucks, SCHRS Technical Committee

Thanks, but please don't take my statement as an accusation - just confusion. It is entirely possible that the sources I used include mast area and I didn't realize it.

On another note, I performed the following thought experiment: I removed the 3.72 m2 jib and added a 17.5 m2 spinnaker. The rating changed from 1.050 to 1.108. That's right, I added nearly 14 square meters of sail and the boat got 5.5% SLOWER! I could cut 1.72 m2 off my jib (leaving a 2 m2 blade), add a 15.5 m2 spinnaker, and wind up with the same rating. Apparently SCHRS calculates that jib area is 9 times as valuable as spinnaker area. If that's true, why are boats bothering with spinnakers?

I noticed another oddity - when jib size gets too small (under 1.4 m2 in my experiments), the rating shows the boat getting faster. That's probably just a pathological case, since nobody would design such a jib, but it is still confusing.

Also, why does a low-aspect (height-to-width ratio less than 1.5 : 1) boom count as mainsail area, but a high-aspect boom (greater then 1.5 : 1 ratio) doesn't?

Yours in puzzlement,
Eric

Eric,

I could see where reducing UPWIND sail area and replacing it with DOWNWIND sail area could indeed slow the overall rating down.

Think of it this way... you're spending a LOT more time upwind sailing than downwind sailing on a typical W/L course, even if the distance is identical.

So, slowing a boat down even further upwind (by removing jib) will drastically penalize your overall "Time to finish" even if you speed up your downwind leg.

I don't have any specific math to back this up, but anecdotal evidence supports my general hypothesis...