PHRF rating adjustments

[Ted]

Assume for a moment that a sailboat was designed for a specific geographical area taking into consideration the following sailing conditions:

Predominately light winds under 10 knots true.
Short steep chop.

The boat's sail area/displacement ratio is 24
Total sail area is 702 sq. ft.
Deep draft keel 6'-10"
PHRF rating = 72

Now assume that the identical boat was going to be sailed in an area where the winds were typically 15 knots and above and would be modified as follows:

The new boat has a sail area/displacement of 19
Sail area reduced to 580 sq. ft.
The draft is reduced to 4'11" (beaver tail or bulb keel with about 500 lbs. of additional weight)

Questions:

1. What would you expect the PHRF rating to be based on this information?

2. Being that the modified boat would typically be sailing in stronger wind, do you think that the SA/D ratio reduction would have an impact on the modified boat's performance.

I was talking with a local handicapper about this and our views seem to differ. Just wondering what your thoughts were and how you might justify them to a handicapper.

 

[Apex]

I may be completely off track: but would expect the SA/D ratio to increase PHRF, while the keel configuration change would reduce PHRF....there are so many things going on for apples to oranges comparison. What were the prevailing opinions ....and WHY?

Sailing conditions should have much less influence on PHRFs? Since it is a boat to boat comparison. Take for example a race in the same area, on a light day versus a strong wind day the PHRF doesn't change for that day.

Deeper draft = stronger upwind performance
More weight lower = stands up to a blow better
Reduced sail area = more effect in a light wind area
WL length (same) = more influential in boat times in strong wind area.

 

[Jackdaw]

Lots of variables.

Sounds like we are talking about a J/35; true?

Anyway any time you modify a boat, raters normally assume it's to make the boat FASTER. So their inclination is give you a rating hit for your trouble. At the end of the day it's fairer, and it's easier to give time back than take it away. But this is complex.

Now the rig. Was it modified (shorter boom and/or mast, actual or banded) or are you just going to just declare a smaller headsail? I assume the original boat could fly overlapping genoas.

Most of a boats speed potential comes from its hull form. Once powered up, the boat (all else being equal) will be roughly the same performance-wise. But now the keel.

Doing that to the boat will likely hurt performance vis-a-vis the un-modified boat. The extra weight is never fast. And you loose lift. The real question is what the new keel looks like. The j35 has a typical for early Jboats trapezoidal fin, which sadly is heavier at the base, and not the foot.

For me, having 2 extra gorillas crewing on big days would be a better (if not always practical) option. The removable, movable ballast that also helps sail is a good thing. Maybe you want to sail shorter handed and this will help that, but it's not going to show up in your rating.

As for my position, it would depend on who's boats it was! If it was mine, I'd make a great case for a credit! If it was yours and you were coming to MY fleet, I'd argue convincingly for a hit.

Based on what I know now, I'm guessing they leave the rating alone. Unless the rater likes to ding new/unknown/modified boats and then give back time if warranted

 

[dlochner]

Assume for a moment that a sailboat was designed for a specific geographical area taking into consideration the following sailing conditions:

Predominately light winds under 10 knots true.
Short steep chop.

The boat's sail area/displacement ratio is 24
Total sail area is 705 sq. ft.
Deep draft keel 6'-10"
PHRF rating = 72

Now assume that the identical boat was going to be sailed in an area where the winds were typically 15 knots and above and would be modified as follows:

The new boat has a sail area/displacement of 19
Sail area reduced to 580 sq. ft.
The draft is reduced to 4'11" (beaver tail or bulb keel with about 500 lbs. of additional weight)

Questions:

1. What would you expect the PHRF rating to be based on this information?

2. Being that the modified boat would typically be sailing in stronger wind, do you think that the SA/D ratio reduction would have an impact on the modified boat's performance.

I was talking with a local handicapper about this and our views seem to differ. Just wondering what your thoughts were and how you might justify them to a handicapper.

PHRF is a performance handicap, i.e., the rating depends on how fast the owners sail a class of boats. There are measurements involved, but these are only for compliance with the rules, i.e., spin size, equipment, sail size, etc. Adjustments are made to a boat's rating based on these dimension.

The PHRF-LO (Lake Ontario Region) (http://www.phrf-lo.org) has an excellent site with a handicappers' manual that explains how the ratings are calculated. Conceptually the process is pretty simple, a boat's elapsed time in a race is compared to a yardstick boat and the rating is derived from that.

For a new design there is a formula that yields a "best guess" at the rating, but that is a provisional rating, actual results will change it.

So if you have a modified Whatever, the local handicapper will assign a rating based on the formula or a comparison to other similar boats. From then on the rating will depend on how well you sail the boat.

 

[tommays]

Not to insult the hard working members of WLIS PHRF BUT we do have the worlds SLOWEST J80s and who you know and how much you whine can have as much to due with it as anything

The most complex thing going on NOW is asymmetrical Vs symmetrical within the same division due to ease of jibing and different downwind angles

On the other hand the J24 has carried pretty much the same number for 30 years

 

[Bill Roosa]

I was of the impression that the location of the boat was not one of the factors in determining a PHRF. All the boats in the "race" would see the same conditions and so you don't need to account for "average winds, temp, water salinity....." in the PHRF. PHRF is about the boat not the place the race takes place. all boats (with the same PHRF) will sail faster or slower so it cancels out.
I know that when I had to submit my "boat parameters" for our club they only looked at model, type of prop, and if I had something other than the "standard rig/sails.

 

[Ted]

Lots of variables. Sounds like we are talking about a J/35; true?

Jackdaw, nice guess! Actually I was referencing a Thomas 35. Very similar to the J35 as they both rate about 72. The modified boat in my original post example was a Thomas 35c.

Just to clarify my thoughts here, if a boat is rated partially due to the amount of sail area carrying ability, and has a high SA/D ratio, it would (should) sail faster in light winds. But if the sailing venue is typically heavier winds, that boat would need to be de-powered. (more than likely by reducing sail area) If the identical boat was modified so that the rig and sail area were optimized for a high wind venue, wouldn't there be a benefit in those conditions because the advantage of more sail area of the original boat is now a detriment? The modified boat with a shorter rig and less sail area would most likely get some additional time by a handicapper. In this case, the modification was not made to maximize performance but to de-power the boat and turn it into a performance cruising boat.

 

[Ted]

I may be completely off track: but would expect the SA/D ratio to increase PHRF, while the keel configuration change would reduce PHRF....there are so many things going on for apples to oranges comparison. What were the prevailing opinions ....and WHY?

Sailing conditions should have much less influence on PHRFs? Since it is a boat to boat comparison.

Apex, I'm not sure what you mean by "but would expect the SA/D ratio to increase PHRF" If you mean that a higher SA/D ratio will increase the PHRF rating, I would have to disagree and suggest that the opposite is probably true.

 

[Sandy Stone]

I was of the impression that the location of the boat was not one of the factors in determining a PHRF.

Actually PHRF ratings can vary a fair amount from place to place. (Some would say due to politics, but surely that can't be true). US Sailing has a list of high, low, and average ratings for a long list of boats and there is a surprising amount of variation. Boats that tend to sail better in heavy air rate lower (faster) in, say, San Francisco, and boats that sail better in light air rate lower in Long Island Sound. Local ratings are supposed to be based on experience with a particular boat, or one very similar, in that locale.

 

[Jackdaw]

Jackdaw, nice guess! Actually I was referencing a Thomas 35. Very similar to the J35 as they both rate about 72. The modified boat in my original post example was a Thomas 35c.

Just to clarify my thoughts here, if a boat is rated partially due to the amount of sail area carrying ability, and has a high SA/D ratio, it would (should) sail faster in light winds. But if the sailing venue is typically heavier winds, that boat would need to be de-powered. (more than likely by reducing sail area) If the identical boat was modified so that the rig and sail area were optimized for a high wind venue, wouldn't there be a benefit in those conditions because the advantage of more sail area of the original boat is now a detriment? The modified boat with a shorter rig and less sail area would most likely get some additional time by a handicapper. In this case, the modification was not made to maximize performance but to de-power the boat and turn it into a performance cruising boat.

A boat with a better SA/D ratio simply powers up faster than a boat with a lower value. Overall this is a GOOD thing, as power=speed. Once a boat is fully powered up, you have to have a strategy for dealing with the excess pressure. But all else being equal, more power is good.

Our First 36.7 powers up very quickly. We go to jib in 15 knots, and reef in 20 with a full crew. We are fast as snot. Now if COULD mod the rig so it flew that much sail area as default, but we would be underpowered in lighter airs.

Permanently depowering a sail plan is normally done as a matter of convenience. Its rarely faster overall. Any pro will say 'give me the full area, and I'll find a way to deal with the excess power when I need to.'

 

[Apex]

Ted, we are on the same page:
Higher SA/D is "faster" or as Jackdaw put it, powers up faster, and would have a faster PHRF rating (lower number)...

 

[Kings Gambit]

Questions:

1. What would you expect the PHRF rating to be based on this information?

2. Being that the modified boat would typically be sailing in stronger wind, do you think that the SA/D ratio reduction would have an impact on the modified boat's performance.

The modified boat probably should rate about 9 [+/-?]sec/mile slower [approx. PHRF = 81] based on boat metrics. However, it [the lower SA/DISP modified boat] might still be adjusted down some from that to nearer the reference boat in the higher-wind racing venue.