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Numbers & Ratings

3K views 24 replies 13 participants last post by  cb32863 
#1 ·
Every once in a while when someone does the "What boat is best for xxxxxxx" thread, someone else posts PHRF numbers for various boats they think perform better. So seeing as these values vary by region, don't take conditions or crew in to account and are just a base number, what do they really mean? What is good and what is bad. Obviously yes, lower is better but, is say 170 good for a 30 foot boat? If your "blue water performance cruiser" has a rating of 195, is that a bad thing if it is 35 feet long? Then there is the whole capsize thing. Does that even really mean anything? What "numbers" really matter? Or should they just be ignored and you wing it and get what looks and feels good to you? Take the racing factor out of it.
 
#3 ·
It's true that handicap numbers don't really mean anything if racing or "performance cruising" isn't called into the equation.

It's like complaining that a 4X4 truck won't do 180 mph, when the reason for the purchase is to go off-roading.

The other problem with handicap numbers (PHRF), is that in some regions, there are politics invovled, and some boats get a "gift" handicap that isn't really reflective of their sailing ability. (PHRF politics is a whole other topic)

I've posted PHRF numbers in the past, but it's just meant as a very rough indicator or point of reference to start from, I don't swear by them.
 
#4 ·
Usually, its a subtle way of pointing out someone is looking at boats that are worlds apart. Its pretty rare that 2 boats in the same price range, size range and offering truly similar accomodations will have huge differences in PHRF numbers. So when I see a posting where someone is considering boats with base PFRF differences of 30+ seconds a mile, you pretty much know they are looking at two pretty different boats. From that you can surmise, that if one of those boats truly fit their sailing desire, they'd be miserable with the other choice. For example you if you try to compare a Sabre 36 or 362 to my Catalina 36, you'll find the S36 is about 20-30 seconds a mile faster and the 362 is <30+ seconds a mile faster. However, the S36 accomodations don't come close to my C36 if you intend to have guests aboard regularly. The 362is closer, but its in a whole different price class. So for someone staying in a similar price class that wanted speed and didn't plan to have a lot of guests the S36 would probably be a better choice than a C36, while for someone like that doesn't mind the speed penalty and really enjoys taking guests for weekend long cruises, the extra space is more important.

So to me the PHRF discussion reveals a good deal about how focused a person is on what they desire out of their boat. If they've really worked through it, there probably won't be a huge gap in the PHRF numbers between boats they are looking at. If there is, they are probably still conflicted about whats most important to them.
 
#10 ·
Usually, its a subtle way of pointing out someone is looking at boats that are worlds apart. Its pretty rare that 2 boats in the same price range, size range and offering truly similar accomodations will have huge differences in PHRF numbers. So when I see a posting where someone is considering boats with base PFRF differences of 30+ seconds a mile, you pretty much know they are looking at two pretty different boats. From that you can surmise, that if one of those boats truly fit their sailing desire, they'd be miserable with the other choice. For example you if you try to compare a Sabre 36 or 362 to my Catalina 36, you'll find the S36 is about 20-30 seconds a mile faster and the 362 is <30+ seconds a mile faster. However, the S36 accomodations don't come close to my C36 if you intend to have guests aboard regularly. The 362is closer, but its in a whole different price class. So for someone staying in a similar price class that wanted speed and didn't plan to have a lot of guests the S36 would probably be a better choice than a C36, while for someone like that doesn't mind the speed penalty and really enjoys taking guests for weekend long cruises, the extra space is more important.

So to me the PHRF discussion reveals a good deal about how focused a person is on what they desire out of their boat. If they've really worked through it, there probably won't be a huge gap in the PHRF numbers between boats they are looking at. If there is, they are probably still conflicted about whats most important to them.
I recently used comparative ratings in a thread by a fellow who was considering a Sabre 42 and an Island Packet 36. The reason why I did so was not to show that one was better than another but just to show that one was much faster than the other. It's just a healthy baseline to know that a boat is rated at 30 seconds a mile faster, or whatever it is. These ratings aren't perfect but they are useful baselines to use for comparison purposes.
 
#5 · (Edited)
So just to throw this out there, looking at base ratings for New England. Is a value of 174 good for a 37 foot boat? I guess my basis here is that I want to know if a certain make/model/length has decent speed for it's size. To make good time do you want one that has a PHRF under 200 or some other value? Just as something to consider. Looking for some guidance on all these values because if you don't know what "47 foobars" really means the number doesn't mean much to you. Obviously there are other factors in choosing a boat.
 
#8 ·
We both cruise and race, so I most certainly will consider PHRF numbers. For myself, I don't think I'd be happy with a 37' that rated higher than around 120-130 for cruising. Under 100 would be better. Then again, a Bermuda 40 is still a nice boat that I'd certainly be happy to have, but not race... Bottom line, it's just one measure among many to think about when buying a boat. The weight you place on it depends entirely on what you're planning to do. To answer your question, 200 for a 37' boat is very slow. Still might be a nice boat and serve your purposes just fine though.

132 for a 911s? Now that's a gift! They should be able to crush everything locally in light air.
 
#7 ·
To give you an example, my 25' sailboat is rated at 234 in the Chesapeake Bay PHRF system and that is s l o w w w w w. It's short, has an outdated form, a shallow keel with a long chord, and outboard sheeting (outside the lifelines).

Longer boats with bigger sails, a deeper keel with a better shape, and inboard sheeting (sometimes even multiple tracks) will sail faster. So 174 for a 37' sailboat really isn't that fast, relatively speaking.

I sail on a C&C 35 Mk III that rates 132, which is respectable. I have a friend that owns an Olson 911s (30 footer) that rates the same. Impromtu, a C&C 37 that I race against rates 126.

In the 37' range, you can find a faster boat.
 
#9 ·
For me a 37 should be at least 100 or faster. 120-130 as Puddinglegs points out, is probably on the ave end of things. My 29'ish foot boat rates 159 in your area. 188 here in puget sound. But we do not have too many reach races, so ratings out here sometimes as mentioned, get politicized per say! actually PHRF-NW has lowered IIRC ALL ratings 10% from the nat book for various and sundry reasons. Even still, 170 for a 37 is SLOOOOOOOOW, 200+ would be slower than a dead slug backwards! for a 37' mind you. A low 20' boat, probably more ave.

Use PHRF to get a base line for where the boat might be speed wise. In the end tho, you are the one that decides what you want. I wanted a fin keel boat that was no slower 3/4 of the way between a J30'ish at the faster end, and a Cat 30 on the slow end. I'm in the ball park!
 
#12 ·
And it can be a helpful baseline for new folks who don't really have the knowledge to understand the differences (hull form, rig, etc...) between the Sabre and the IP you mention. In the beginning, we're all in that "a boat's a boat, isn't it? I mean what's the difference? They're all slow" phase.
 
#13 · (Edited)
And that is what I am sort of trying to use the PHRF numbers for, a baseline. Just didn't really know what the numbers meant. Of course as everyone has said, boats are a trade off as to what you are going to use them for. Me? I want to have a cruiser that I can take anywhere if the mood strikes but not have the journey take longer than need be. Speed is not a bad thing, durability is not a bad thing, getting both is a compromise. As is most things in life. So much more to consider but, you need a starting point. All kinds of other numbers to interpret, including one of the big ones, $$. :cool:

EDIT: Let me add that the cruiser/sail away boat is a few years off. Going to hopefully have a trailer sailer by this time next year. But the goal is to get something about 37' and get the heck out of Dodge.....
 
#14 ·
Here's an attempt to clarify just what the numbers mean.. there's a reference earlier in the thread to "seconds per mile".. The PHRF number is in 'seconds' and translates to 'seconds per mile' against a competing boat.

For example, a boat rating 120, racing against a boat rating 100 on a 10 mile course can be up to 10x20= 200 seconds behind the faster boat and still 'win' the race. That same boat racing another rated 220 would have to finish more than 10x100=1000 seconds (nearly 17 minutes) ahead to 'win'.

The idea being that if the corrected times were equal, the boats would be even. It's meant to be an equalizer. Trouble is it's based on the assumption that the boat is perfectly prepped, clean, perfectly sailed including tactics.

One bad tack, or bad decision in a race can negate all that, as can boats that can plane, for example, which tends to blow away their rating based on the measurements used.
 
#15 ·
Well, I must say I still don't get the value of these ratings for a cruising boat. A difference of 30 seconds would translate to falling 5 minutes behind the other boat every hour given a generous 10 knot speed. If you consider that a more realistic cruising average speed is more like 5 knots, the slower boat would lose only an hour in an entire day's worth of sailing.

I am not disputing that a slow boat might feel like a ball and chain around ones ankle after a while. I am just trying to understand how to interpret the numbers. Clearly we have more at stake than a week long transit taking an extra 7 hours. Is it that the faster boat can still sail in conditions where the slower one has to resort to motoring? It is unlikely that the rating would apply linearly at all speeds. Maybe the performance difference gets dramatically worse at lighter winds? There has to be more to the numbers.
 
#16 ·
its not meant as a measure of preformance w/o competition, but rather more of a 'handicapping' system to allow unequal boats the ability to race on a more level playing field.
 
#18 ·
cb, the PHRF numbers represent a specific speed difference, over a specific course, in a specific locale which has specific wind conditions, with a specific crew and sails in use. Among other factors, which I'd bet your local PHRF committee members would enjoy spending an hour explaining to you, in person or on the phone. The USSA.ORG webs site probably also has a good explanation of what the phrf numbers are based on.

You can shortcut it somewhat to just mean "a lower number generally means a faster boat" and if you ignore anything within a 10-point spread as being "the same, really" they become more meaningful.

Among the finer points...Bubblehead mentioned an Ohlson 911s. What you won't see in the PHRF numbers is that in order to hit those numbers, that boat requires some fine sail handling and it is very easy to be unable to hit them. While other boats with a wider tolerance for sail trim, are easy to sail "to the numbers".

Like EPA numbers for MPG on cars, they're just one part of the whole story. And when you get into real purebred racing boats with low PHRF numbers? You may also find they have puny little engines, to keep the weight down. Or delicate rigs, that can break in rough weather. Even the America's Cup instructions may specify no racing in over 10 knots of wind--because they don't want to break boats.

Its just numbers, just one way to compare the speed of boats, in specific limited conditions. Not fair, not complete, just a place to start handicapping for racers.
 
#21 ·
I will keep the with/without spi in mind, thanks for pointing that out. As I have said before, PHRF is not the only factor in my decision making process. There is comfort level & durability as I plan on going where ever the mood strikes. Which, means a heavier boat. There is the interior as the first mate/admiral will be involved I am sure. Always nice to keep them happy. $$ of course and just what one likes in general. Not looking to race around the planet but I don't want to take forever getting where ever I am going either.
 
#23 ·
There is comfort level & durability as I plan on going where ever the mood strikes. Which, means a heavier boat..
Just to be clear, in and of itself weight does nothing good for a boat. It does not mean that the boat is stronger, more durable, more seaworthy, or more comfortable. Weight is often the result of poor workmanship, overly heavy interior appointments, and poor engineering. Making a boat heavier adds stress to the boat's structure, but without proper engineering, good build quality, and material selections, weight in and of itself, does not necessarily add the commensorate amount of strength. Seaworthiness and motion comfort, most directly come from weight distribution and buoyancy distribution, rather than from simply making the boat heavier.

Jeff
 
#22 ·
There are a lot of misunderstandings about the relationship of a boat's PHRF number and its real world speed. As has been mentioned, a boat's PHRF rating is intended a relative gage of its speed to other dissimilar boats. It assumes that the boat is properly prepared (good bottom, good hardware, and good sails). The regional rating represents the relative speed of the boat around an old-style Olympic Triangle course at the average windspeed for that venue. It is at best a very narrow snapshot of a boat's relative speed at particular windspeed. As noted it does not tell much about how the boat's relative speed will compare on any particular point of sail, or in any other windspeed.

While it is true that there can be some politics in a given rating, that is far less common today than it once was since computers allow a more accurate crunching of data and understanding of the norms. That said, new boat designs and custom boats are often over-penalized due to the lack of experiencial data.

PHRF ratings tend to be a little more generous toward cruising boats than full blown race boats, but not for the reasons mentioned. A well equipped boat that has a design that sails well over a wide range of wind speed and direction is easier to keep at speed in almost all conditions. This allows this boat to sail extra distance in order to take strategic advantage of variations in wind speed and direction around the race course. Skilled racers tend to gravitate towards boats that afford and can take advantage of that kind of strategic advantage. There is no fair way to actually rate this tactical advantage, but because these boat have a strategic advantage and are oftyen sailed by more skilled sails, it does show up race result data and so can creep into the rating process making it harder for an unskilled sailor to sail to the resultant rating.

In terms of real life cruising, a 30 second a mile advantage for an equal length boat can be a huge advantage in terms of passage time. While it sounds like nothing, say 12 minutes on a 24 mile leg, in practice, a rating gap that large typically results in much greater gains. In coastal cruising, the faster boat will generally have fewer tacks upwind (each adding several minutes to the passage time) and will hold its speed more consistently through windspeed changes, to sail at reasonable speeds in ligher winds, and therefore be able to sail from gust to gust, and will have the a greater ability to optimize the postion of the boat to take advantage of where the fairer wind is located. While this is not always the case, it means less time spent motoring or the ability to comfortably cover a significanctly greater distance in a day.

One reason for this is that PHRF ratings only look at a boat's relative speed at an average windspeed for that venue, but in most venues boats rarely sail in winds that are that actually at the average speed (San diego being a well known exception). As compared to boats which are rated as being slow for their length, boats which are rated as being fast (low rating) for their length will generally have a much bigger speed advantage in both heavier and lighter wind speeds than they will in moderate conditions.

My sense is that 30 seconds a mile, more realistically takes an hour or more out of a coastal cruiser's typical daily passage or in other words therefore allows an additional 5 to 10 mile as a comfortable daily range. In off-shore passages the advantage can be more dramatic that is predicted by a boat's PHRF rating. A few years ago I crunched the numbers on the results from ARC, comparing boat lengths to PHRF ratings to elapsed times. As broad generality, those boats with a low PHRF number relative to thier lengths had much faster elapsed passages times than their PHRF numbers would have predicted.

There are some very long and detailed discussions about the relative merit of the capsize screen formula and motion comfort index. Most yacht designers that I have spoken to dismiss these formulas as being a useless relic of a bygone era. I have posted following here many times and I had written for an earlier discussion but it does discuss the basis for considering the capsize screen formula and motion comfort index worse than useless.

It seems that as soon as someone posts a question about the seaworthiness of some particular boat, that a well meaning responder sends them to Carl's Sail Calculator to look at the Capsize Screen Formula and the Motion Comfort Index. And no sooner than a poster questions the seaworthiness of some boat, that someone cites the Capsize Screen Formula and the Motion Comfort Index in that vessel's defense or prosecution. But as I have explained many times in the past, (and I am about to explain yet again) these surrogate formulas tell almost nothing about how the reality of a boat's likelihood of capsize or its motion comfort. In fact they provide so little indication of a boat's behavior that to rely on them in any way borders on the dangerous.
<O:p</O:p

Both of these formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats other than those which are very similar in weight and buoyancy distribution to each other. Neither formula contains almost any of the real factors that control motion comfort, the likelihood of capsize, or seaworthiness. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution (of the hull both below and above the waterline), the extent to which the beam of the boat is carried fore and aft, and neither contains any data on dampening, all of which really are the major factors that control motion comfort or the likelihood of capsize. <O:p</O:p
<O:p</O:p

I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. <O:p</O:p
<O:p</O:p

And while this example would clearly appear to be so extreme as to be worthy of dismissal, in reality, if you had two boats, one with a very heavy interior, shoal draft, its beam carried towards the ends of the boat near the deck line, a heavy deck and cabin, perhaps with traditional teak decks and bulwarks, a very heavy rig, heavy deck hardware, a hard bottomed dingy stored on its cabin top, and the resultant comparatively small ballast ratio made up of low density ballast. And if we compare that to a boat that is lighter overall, but it has a deep draft keel, with a higher ballast ratio, the bulk of the ballast carried in a bulb, its maximum beam carried to a single point in the deck so that there was less deck area near the maximum beam, a lighter weight hull, deck and interior as well as a lighter, but taller rig, it would be easy to see that the second boat would potentially have less of a likelihood of being capsized, and it is likely that the second boat would roll and pitch through a smaller angle, and would probably have better dampening and so roll and pitch at a similar rate to the heavier boat, in other words offer a better motion comfort....And yet, under the Capsize Screen Formula and the Motion Comfort Index it would appear that the first boat would be less prone to capsize and have a better motion when obviously this would not be the case.<O:p</O:p
<O:p</O:p

There are some better indicators of a vessel's likelihood of capsize. The EU developed their own stability index called STIX, a series of formulas which considered a wide range of factors and provides a reasonable sense of how a boat might perform in extreme conditions. Unfortunately meaningful results require a lot more information than most folks have access to for any specific design. The Offshore Committee of US Sailing developed the following simplified formula for estimating the Angle of Vanishing Stability (Sometimes referred to as the 'AVS', 'limit of positive stability', 'LPS', or 'Latent Stability Angle' ):<O:p</O:p
Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD * DV 1/3 )<O:p</O:p
Where; <O:p</O:p
BR: Ballast Ratio ( Keel Weight / Total Weight )<O:p</O:p
HD: ffice:smarttags" /><?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com
<ST1:place w:st="on">Hull</ST1:place></st1:City> Draft
<O:p</O:p

DV: The Displacement Volume in cubic meters. DV is entered as pounds of displacement on the webpage and converted to cubic meters by the formula: <O:p</O:p
Displacement Volume in Cubic Meters = ( Weight in Pounds / 64 )*0.0283168<O:p</O:p
The Beam and <st1:City w:st="on"><ST1:place w:st="on">Hull</ST1:place></st1:City> Draft in this formula are in meters. These values are entered in feet on the webpage and are converted to meters before SSV calculation.<O:p</O:p
Angle of Vanishing Stability approximately equals 110 + ( 400 / (SSV-10) )<O:p</O:p
<O:p</O:p

There is a convenient calculator at http://www.sailingusa.info/cal__avs.htm<O:p</O:p
<O:p</O:p

It should be noted that the AVS is only one indicator in evaluating the likelihood of capsize, meaning it only predicts the point at which the vessel wants to turn turtle. It does not predict the amount of force that would be required to heel the vessel to that limit, nor the force to re-right the vessel, nor does it predict how the shape of the boat might encourage wave action to roll the boat closer to an angle at which it no longer wants to return. <O:p</O:p
 
#24 ·
Jeff, as always, very well put. I had read your post some time ago about Capsize Factor being not all that worthwhile. Mainly I guess I am looking for a way to pare down the potential list to something manageable and not to eventually waste my time looking in the wrong place or wasting money. I know, due to responses on this thread, that the PHRF is not real-world and that was something else I was looking to gain from this thread. What "numbers" are valuable, what ones are useful but not really carved in stone, and those that are not all that meaningful. Cutting through the BS so to speak and this thread has helped with that.

I am going to continue to research and read and learn as much as I can before making the "That's the one" decision. I have a few years, maybe more, to do that. I appreciate everyone's input and I hope other people are finding this discussion educational as well.

CB :cool:
 
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