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Old 04-05-2011, 08:31   #31
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Re: PHRF as Estimate of Passage Making Speed

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formula, and came up with 5.5 knots, which is 72% of the theoretical Hull Speed.

Our actual average SOG on offshore passages (~9,000 nm) was 6.3 kts, which equates to 83% of Hull Speed.
That formula is suppose to produce the point to point great circle vmg (the actual GS miles divided by the actual time the passage took*), not the log SOG. I don't know if that would account for the 10% variation or not.

We did it that way because we could get very objective data on GS and passage time from a bunch of people, while we could not get equally accurate information on actual miles sailed or SOG. (Note: on passages were these is typically a big routing kink - say around a stationary high, we broke the passage into two GS legs).

Beth and I occasionally have debates - I will say we have done a 200 mile day based on the log and she will say no based on the noon to noon gs distance.

In any case . . . that quite excellent speed Hud - 150 miles/day average. On our similar sized boat (Silk) we averaged about 120 and on Hawk we do about 175 in the tropics but only about 150 in the mid/high latitudes (where the wind is less steady). Do you have a speed cut-off when you start motoring?
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Old 04-05-2011, 09:12   #32
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Re: PHRF as Estimate of Passage Making Speed

I think it could be used on a relative basis to give you some indication. I would not toss out the idea completely because it is not an exact science with respect to cruising.
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Old 04-05-2011, 09:37   #33
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Re: PHRF as Estimate of Passage Making Speed

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Originally Posted by estarzinger View Post
That formula is suppose to produce the point to point great circle vmg (the actual GS miles divided by the actual time the passage took*), not the log SOG. I don't know if that would account for the 10% variation or not.

We did it that way because we could get very objective data on GS and passage time from a bunch of people, while we could not get equally accurate information on actual miles sailed or SOG. (Note: on passages were these is typically a big routing kink - say around a stationary high, we broke the passage into two GS legs).

Beth and I occasionally have debates - I will say we have done a 200 mile day based on the log and she will say no based on the noon to noon gs distance.

In any case . . . that quite excellent speed Hud - 150 miles/day average. On our similar sized boat (Silk) we averaged about 120 and on Hawk we do about 175 in the tropics but only about 150 in the mid/high latitudes (where the wind is less steady). Do you have a speed cut-off when you start motoring?
I'd generally start the engine if our speed dropped below about 4 kts, and run it enough to bring us up to 5.5 or so. And my open-ocean sailing experience is small potatoes compared to yours. We have been lucky to have had pretty good winds on our six offshore passages. Had we done a lot more, I'm sure we'd be averaging in a lot more low-wind days.
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Old 04-05-2011, 10:29   #34
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Re: PHRF as Estimate of Passage Making Speed

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I'd generally start the engine if our speed dropped below about 4 kts, and run it enough to bring us up to 5.5 or so. And my open-ocean sailing experience is small potatoes compared to yours. We have been lucky to have had pretty good winds on our six offshore passages. Had we done a lot more, I'm sure we'd be averaging in a lot more low-wind days.
Its still very excellent mileage - good for you. That's terrific sailing and seamanship.

We have had about under 10kts of breeze about 30% of the time. Both our boats have been able to keep moving in that but certainly not 80% of hull speed.

Wind on different passages and motoring are big variables that I did not capture in the formula. Steve Dashew was able to rack up big passage speeds because be turned on the motor whenever the speed dropped much below 9 kts. Where as the people like the Pardey;s obviously just sit and wait. We once sat becalmed for 10 days just past the galapagos.

Does anyone know what the assumed/implied wind speed is for a phrf rating (secs/mile)?
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Old 04-05-2011, 11:35   #35
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Re: PHRF as Estimate of Passage Making Speed

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Does anyone know what the assumed/implied wind speed is for a phrf rating (secs/mile)?
As I recall it's about 12 knots TWS
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Old 04-05-2011, 11:45   #36
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Re: PHRF as Estimate of Passage-Making Speed

FWIW, keep in mind that a PHRF rating is not the number of seconds needed to cover a mile of distance, rather it is the number of seconds per mile of course that you are expected to finish behind the zero-rated base boat. As I understand it, the original zero-rating base boats were the America's Cup 12 meters.
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Old 04-05-2011, 12:05   #37
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Re: PHRF as Estimate of Passage-Making Speed

Just for grins I ran Evans formula and it indicated that my avg day should be about 143 miles, when planning I used 150 day which has proven true so far so it's pretty darn close...

And
Quote:
FWIW, keep in mind that a PHRF rating is not the number of seconds needed to cover a mile of distance, rather it is the number of seconds per mile of course that you are expected to finish behind the zero-rated base boat.
is absolutely correct, they only value is relative speed.
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Old 04-05-2011, 12:26   #38
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Re: PHRF as Estimate of Passage-Making Speed

These days I think the J/35 is used most often as the control boat and assigned a value of 72. The PHRF rating of other boats is then determined empirically by race performance. For example, a boat with a rating of 92 would be expected to fall behind a J/35 by 20 seconds per mile. At the end of a five mile race, the J would have to "give" the slower boat 100 secs.

The point of my original post is that these determinations are based on race performance in unloaded boats. I imagine if we put as much gear on a J/35 as some of you have on your cruisers, it won't go quite as fast. But then I wonder if we put as much gear on an Alden 46 as you might on a Mason 44, would the Alden still be a faster boat.

And by comfort, I certainly intended Zeehag's interpretation--motion of the boat. Not to dipute how good a hot shower feels, but I am very comfortable with camping-level accomodations and my hot showers can be few and far between. I hope to find good sailing performance with good comfort/motion and am wondering if money can buy that or are the two mutually exclusive.
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Old 04-05-2011, 13:21   #39
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Re: PHRF as Estimate of Passage-Making Speed

I think the bit about cruising load vs. racing load can sometimes be a bit overblown.

Take a 35-foot cruiser/racer for example -- it would typically be cruised by just a couple, using a relatively limited sail inventory. Yes it would have more groundtackle, dinghy and other weighty accoutrements. But the same boat racing in a distance race would have a crew of 6 to 8 plus all their gear, provisions and water to support a large crew for the duration, plus a large sail inventory. Just the extra crew bodies on a racing boat could accounts for about 1,000 pounds right there. The distance racing boat will generally have all the same electronics, navigation, communications and safety gear -- if not more -- than the cruising boat.

Certainly any cruiser interested in sailing performance would do well to pay attention to how much weight they put on their boat, and where they put it, but I really don't think this "cruising load" concern disqualifies PHRF or other ratings numbers as a basis for comparing relative speeds of boats that might be used for cruising.
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Old 04-05-2011, 13:50   #40
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Re: PHRF as Estimate of Passage-Making Speed

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I wonder if we put as much gear on an Alden 46 as you might on a Mason 44, would the Alden still be a faster boat.

Yes, it has a longer waterline and bigger sails, so, with equal payload, in all likelihood will be faster.

I hope to find good sailing performance with good comfort/motion and am wondering if money can buy that or are the two mutually exclusive.

Size can both make the boat less slow and less motion uncomfortable. Size does create other headaches, but you I guess are not asking about that trade-off.
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Old 04-05-2011, 16:25   #41
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Re: PHRF as Estimate of Passage Making Speed

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Beth and I occasionally have debates - I will say we have done a 200 mile day based on the log and she will say no based on the noon to noon gs distance.

I
G'Day All,

I think about this issue as well. To me, if you are trying to compare boat performance, the miles on the log matter more than the miles over the ground. Currents, from whatever direction, can make huge differences in DOG. For instance, coming south along the east coast of Oz we can get boosts of 2-3 knots for a couple of hundred miles or more. This makes the elusive 200 mile day a piece of cake, even in a pretty mediocre boat.

Further, if the course does not lie in a straight line, the noon-to-noon (or other interval) run will be shorter than the logged miles. In the extreme case of sailing 100 miles in 12 hours and then doing a 180 and sailing 100 miles back, your log would read a 200 mile day and your GPS would show zero miles per day. Silly example, I know!

For passage planning purposes, though, one should include expected sets from any known currents in your predictions.

It's all good fun, and when we do manage a 200 miler, it feels good (and that's silly, too!).

Cheers,

Jim
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