PHRF versus approx. passage times on dif. boats?

[roland stockham]

As an example Jeanneau recently launched a new Sunfast 3300 aimed at the weekend racer. It is a super-light fast boat with, I am sure, a very high PHRF. However it would get this by virtue of a very broad beam aft, fine entry and flat run plus a displacement of 7716lbs and a keel weight of 3086lbs that will make it very stiff and easily driven.

Trouble is that a typical weight of cruising gear including crew and all the stuff like ground tackle and extra supplies typically weighs in at between 3,000 and 4,000lbs even if you a very weight conscious. Result, you loose all the stiffness because you have gone from a 50% ballast ratio to probably under 25%, the nose will bury as it does not have the volume to lift that weight. You also loose the form stability because the hull is too deeply buried for the weather side to lift. Result is that your initially high PHRF has, under cruising conditions, been drastically lowered.
This is an extreme case I will grant and in fact the 3300 would probably have a cruising PHRF of 0 since it would be unsafe to put to sea as its max load will be likely be under 1000lb including crew. Makes the point though

[Scaramanga F25]

Hellosailor,

You have your numbers right.

However, 600 miles upwind with a modern lighter boat design could be vastly different than an older heavy design with the same PHRH. Same with a downwind sled.

[wingssail]

Originally Posted by roland stockham

This is an extreme case I will grant and in fact the 3300 would probably have a cruising PHRF of 0 since it would be unsafe to put to sea as its max load will be likely be under 1000lb including crew. Makes the point though

People keen enough to purchase a Sunfast 3300 and go on a passage would probably not load it down with 3000 to 4000 lbs of cruising gear. And 1000-2000lbs in the stern on a downwind leg would probably not hurt the performance much. But anyway, that is not the purpose of those boats.

Back to the OP's question, could you use PHRF ratings to predict arrival times on a 600 mile cruise?

I'd say YES, sort of, to an order of magnitude, but luck weather, sailing skill, all play a very important part. Use the PHRF rating as a guideline, don't make your marina reservation based on the PHRF predicted speeds.

[hellosailor]

"It appears you are describing a buddy boat situation and a reasonable distance of cruising the sailed boats,"
Ayup. Nothing to do with buying boats. Nothing to do with placing bets. Just confirming that it is a ballpark of limited but some usefulness. Like "How many paces from the treasure chest?" Paces will vary, but they'll get you close.
I know very well that two different hull shapes will perform very differently in different sea states, which PHRF totally does't account for. Some will slam and jerk when hitting square waves head on, while others will ride up and over them and be affected way less. Some run downwind wing and wing, others bear off and gybe--and with a following sea and the wrong hull shape, some will try to gybe relentlessly on their own.
I'm not trying to do anything more than the original question, i.e. to know if the PHRF numbers will approximate what the time difference on a longer run will be. As I thought they would.
Ghosting in one and a half knots? The difference will be who's got the drifter or caves in and lights the engine first. Pushing into 20 knots and six foot waves gusting to 40 knots? The difference may come down to who can keep the boat upright without breaking ribs.
But that's all something else again. I'm not looking to see who can beat Ruth and Mantle, just looking to see where's there's a ballpark.

[Singularity]

Originally Posted by hellosailor

...I'm...just looking to see where's there's a ballpark.

From the thread I linked above a routine ballpark/estimate passage speed is +/-75% of the boat's theoretical hull speed (i.e. working LWL). FWIW my take is that there is so much overlap in all the other variables that it's practically impossible to make comparisons without dozens of qualifying stipulations for each comparison.

[Paul L]

Originally Posted by Adelie

Evans Starzinger and Beth Leonard published a formula for estimating daily passages based on SA/D & LWL. Using a database of boats including PHRF ratings I did a regression analysis and found their formula corresponds very well with PHRF ratings. The values their formula gave we’re about 2/3 to 3/4 of what the Rating gave.
I don’t have the formula handy but will look it up tomorrow.

The formula for PHRF is 360sec + rating in sec = sec/nm. Working that out for daily progress:
86,400sec/day / (360s/nm + rating) = progress in nm/d.

Interesting formula. I took some random boats and some that I know about in a cruising environment. I calculated the daily run based on 75% of the PHRF rating. The numbers were pretty rational.
Boat PHRF @75% day
Alberg 35: 201 115nm
Beneteau 42s7: 60 154.3nm
Cal 40: 120 135nm
Calilber 40: 120 135nm
Cape Dory 30: 207 114nm
Catalina 470: 102 140nm
Island Packet 38 168 123nm
J-37 wk: 84 146nm
Pacific Seacraft 37: 186 119nm
Outbound 44: 90 144nm

[Singularity]

Originally Posted by Paul L

Interesting formula. I took some random boats and some that I know about in a cruising environment. I calculated the daily run based on 75% of the PHRF rating. The numbers were pretty rational.
Boat PHRF @75% day
Alberg 35: 201 115nm
Beneteau 42s7: 60 154.3nm
Cal 40: 120 135nm
Calilber 40: 120 135nm
Cape Dory 30: 207 114nm
Catalina 470: 102 140nm
Island Packet 38 168 123nm
J-37 wk: 84 146nm
Pacific Seacraft 37: 186 119nm
Outbound 44: 90 144nm

For whatever little it's worth, I took the same list of boats, looked up their LWL, plugged the LWL into a simple hull-speed calculator, then multiplied that value times 75% times 24 hours to come up with the nm/day numbers listed (I'm unable to improve the text formatting):

Boat PHRF @75% day LWL simple hull speed calc x 0.75(%) x 24 (hours)
Alberg 35: 201 115nm LWL = 21.66 112nm/day
Beneteau 42s7: 60 154.3nm LWL = 35.75 144nm/day
Cal 40: 120 135nm LWL = 30.33 133nm/day
Calilber 40: 120 135nm LWL = 32.5 138nm/day
Cape Dory 30: 207 114nm LWL = 22.83 115nm/day
Catalina 470: 102 140nm LWL = 42 156nm/day
Island Packet 38 168 123nm LWL = 33 139nm/day
J-37 wk: 84 146nm LWL = 32.42 137nm/day
Pacific Seacraft 37: 186 119nm LWL = 27.75 127nm/day
Outbound 44: 90 144nm LWL = 40.25 153nm/day

[dfelsent]

As a past phrf handicapper in a racing situation the best you can hope for is that over a few seasons the handicaps are equally unfair to everyone.
As a sailor and an occasional boat buyer I’ve used phrf numbers to inform my initial thoughts about potential cruising speed performance. That is speed only. Not comfort or seaworthiness
or anything else.
On a short passage it’s a possible indicator of arrival time potential. Ignoring the upwind/downwind etc.

As a really rough ballpark it’s not bad.

[lifeofreilly57]

Gee, after having several racer/cruisers and having raced and cruised them I can tell you that cruising and racing has very little in common. I don't really sit next to.my headsail winch with the mainsheet in my other hand on long passages.
My cruising boat can do 9 to ten knots in 15 to 17 knots on the beam, in perfect weather and seas. But throw in a bowl current, big seas, wind that never seems to be quite the right direction when you need it. This makes PHRF ratings just comparative. Real world distance calcs can vary dramatically. What part of the world are you sailing. How much crew? Comfort or speed?
So far our performance cruiser averaged about 5 knots over 2500 miles, upwind, downwind, offwind, no wind, motorsailing, and drifting. RI to Southern Bahamas, but we'll get better averages in the Caribbean, but for now 5 knot averages have worked well for passage planning.
PHRF is ok for comparative knowlegde but is not an end all do all comparison. Sea kindly? Upwind, broad reach, or downwind boat? Heavyweight or lightweight?
There so much more to it when doing actual comparisons. What compromises are you willing to live with?

[Don C L]

Originally Posted by Singularity

For whatever little it's worth, I took the same list of boats, looked up their LWL, plugged the LWL into a simple hull-speed calculator, then multiplied that value times 75% times 24 hours to come up with the nm/day numbers listed (I'm unable to improve the text formatting):

Boat PHRF @75% day LWL simple hull speed calc x 0.75(%) x 24 (hours)
Alberg 35: 201 115nm LWL = 21.66 112nm/day
Beneteau 42s7: 60 154.3nm LWL = 35.75 144nm/day
Cal 40: 120 135nm LWL = 30.33 133nm/day
Calilber 40: 120 135nm LWL = 32.5 138nm/day
Cape Dory 30: 207 114nm LWL = 22.83 115nm/day
Catalina 470: 102 140nm LWL = 42 156nm/day
Island Packet 38 168 123nm LWL = 33 139nm/day
J-37 wk: 84 146nm LWL = 32.42 137nm/day
Pacific Seacraft 37: 186 119nm LWL = 27.75 127nm/day
Outbound 44: 90 144nm LWL = 40.25 153nm/day

I was hoping someone would do that! Thanks! Pretty interesting stuff... I'd go with the LWL myself... just as a general workable rule. Surfing downwind in a ULDB will mess with the numbers a bit
There is one little thing though, a boat like the Alberg will probably be heeling and lengthening her waterline so probably will do better than the numbers suggest.

[JPA Cate]

@hellosailor,

If you're contemplating a trip in company with a boat with a slower PHRF rating than yours, be prepared to slow down to stay in company. If it's the other way around, leave a half day ahead!

Explanation for others: It is a pita to slow down to stay with slower boats, the more hours, the more difficult. This is basically a caution, to leave when your boat can make the destination in daylight hours, and to not tie yourself to a slower boat, it can be quite frustrating, for little gain, except when buddy boating someone with a problem that might need you to be there.

Ann

[hellosailor]

Ann-
"@hellosailor"
You've been spending too much time on The Social Media App. (G)
Using an ampersand has zero effect on plain web forums and web pages, fwiw. A site, or an application, has to be programmed to "push" that flag to folks. Of course, if Jim's just chosen a very young partner...I had someone young try to tell me how I could program a contact list in a plain "Princess" phone last week, too.(G) (No, the T9 text entry doesn't work on those.)
FWIW.

[Pete17C]

& is an ampersand

@ is just the 'at' sign/symbol

fwiw

[Paul L]

Originally Posted by Don C L

I.......
There is one little thing though, a boat like the Alberg will probably be heeling and lengthening her waterline so probably will do better than the numbers suggest.

Not much. The PHRF number already takes that into account. I owned an Alberg 35 for a long time. 125 miles a day is a reasonable number.

[hellosailor]

Thanks, Pete. Nothing wrong with my memory, it was North Korean Hackers that put the wrong word in the message. That's my story and I'm sticking to it.