Join Date: Feb 2012
Location: New Orleans Louisiana
Thanked 82 Times in 78 Posts
Rep Power: 4
Re: PHRF Rating Vs Miles/Day
If you run the numbers...
Taking two similar boats a J-35 and a J-30. Both are former race boats, and have a phrf split around here of 63sec/mile (75 and 138). Assuming the J-30 in a day will do 100 miles, then the numbers indicate that the J-35 will have sailed that 100miles in 22:45:00. Now the J-30 would have sailed at an average of 4.1666knots. The J-35 would have sailed at 4.3956 knots. So over the course of the day the J-35 would have sailed ~105.5nm.
Others have pointed out that there are a lot of other things that come into play, and I will point out a few more... Planning hull boats will absolutely destroy their phrf numbers in a downwind course, but will sail much slower than it going upwind. Something like an Open 60 is absolutely capable of 500nm days downwind, but will be no faster beating than any other 60' boat. So it is important to understand the specific boats in question.
There is also load carrying. If you assume that you will need to bring 10lbs of food/water/stuff per person per day, a large boat has a few advantages... One they can absorb the weight much easier. Just because their lb/in immersion is going to be so much higher. So on a large boat a few thousand pounds may not matter much, while on a small boat it may be an appreciable amount of total displacement. The extra speed from waterline also means you don't need to carry as much, which makes you faster still.
There is also a crew issue. Long distance sailing on small boats is uncomfortable. The boat is constantly moving up and down waves, speeding up and slowing down, heeling over as a gust hits, ect. The larger the boat the less these small variations effect the boat, which makes it more comfortable. This means the crew is fresher, more likely to keep their head in the game, better rested, ect...
All in all for distance sailing a bigger boat (to a point) is more comfortable, and much faster. PHRF may indicate this, but does a poor job making allowances for it.