Relating Boat speed to PY

[roblpm]

I've googled and googled and not found the answer (if there is one).

Is it possible to relate cruising speed to PY handicaps?

ie if you are comparing 2 boats one with a PY of 1000 and one of 1100 does that mean that the 1100 one will be 10% slower? ie if the faster boat is cruising at 5 knots the slower one will be going at 4.5knots?

Or something else..........................??

 

[Tomahawk]

One would think so.
However PY is a racing calculation wher upwind performance is the critical issue. By comparison cruising is mostly about comfort and ease of sailing. I certainly don't know many cruising sailors who short tack up a river bank to reduce tide and get that "little edge".. Indeed when cruising we will tend to sail off the wind where waterline length becomes the dominant factor in speed.

So yes a lower PY will indicate a faster boat, but I suspect it will not be a straight correlation..

 

[pteron]

I believe the PYs are modified by race results fed back from clubs so effectively it becomes a normalising handicap over loads of different conditions rather than a direct measurement of speed.

 

[bluerm166]

The difference has been well explained.It might help you to look and compare a few vessels on http://www.byronsoftware.org.uk/bycn/byboat.htm which shows both the yardstick no. and the theoretical hull speed based on waterline length.

 

[rwoofer]

I've googled and googled and not found the answer (if there is one).

Is it possible to relate cruising speed to PY handicaps?

ie if you are comparing 2 boats one with a PY of 1000 and one of 1100 does that mean that the 1100 one will be 10% slower? ie if the faster boat is cruising at 5 knots the slower one will be going at 4.5knots?

Or something else..........................??

PY is a measure of how quickly a boat gets round the "average" race course as it is based on actual results submitted to the RYA.

On the whole I would say it is a reasonable measure of boat speed as it is an average of all wind directions and one that I certainly use. However some boats do have spikes in their polars that mean they can massively outperform their PY on a specific wind angle. The classic example would be fast assymmetric dinghies (49er etc) in a 10-20 degree wide band at broad reaching angles.

Both my dinghies (Phantom and Albacore) have very even polars so can be viewed as having a PY faster than their very top speed might indicate. I view that as a good thing, because it means they are versatile.

 

[VicS]

You will find an explanation of the PY scheme on the RYA website http://www.rya.org.uk/racing/Pages/portsmouthyardstick.aspx with links to the current list

 

[roblpm]

You will find an explanation of the PY scheme on the RYA website http://www.rya.org.uk/racing/Pages/portsmouthyardstick.aspx with links to the current list

OK so thanks for that.

I have done some rudimentary maths and come up with:

Time Boat a = Time boat b
------------ -------------
PY (a) PY (b)

So if I buy a Fin Moody 31 PY 996 (from byron site) and sail 5 hours, my other self in the alternative Hunter Ranger 265 at 1042 (from byron site) will get in roughly 5 hours 14 minutes.

Doesnt seem like enough of a difference to me!!

PS spacing in post doesnt come out right!!

 

[doug748]

Looks ok to me.

1042 and 996 is about 5% difference - ie 5 mins in every 100 - so in 300mins = c 15mins lead.

There is a lot of huffing and puffing about fast boats on these pages but in reality similar types of boat tend to sail pretty close. In racing terms 15 mins is the far side of the moon, but if you are picking a cruising boat, it is very much the same speed.

 

[Javelin]

In theory the boat with a PY of 1100 would be 6 minutes behind of the PY1000 after 60 minutes of racing.

In a drag race between displacement boats then usually the longest waterline length will have the edge in pure speed terms.
For example,
Sadler 23 = 5.9 knots
Sadler 25 = 5.87 (slower in theory than the 23 as the lwl is shorter)
Sadler 26 = 6.07
Sadler 29 = 6.4
Sadler 32 = 6.56
Sadler 34 = 7.07

Many of the new French designs, and others, have very little bow or stern overhang these days so a modern 32 footer like the Oceanis 32 has a theoretical displacement speed of 7.05, almost as much as the older design 34' Sadler.

In light displacement boats that surf/plane all bets are off as it becomes a power to weight issue (along with balls of fire) for those who can carry most canvas and play the waves will win in a straight line downwind drag race.

 

[roblpm]

Looks ok to me.

1042 and 996 is about 5% difference - ie 5 mins in every 100 - so in 300mins = c 15mins lead.

There is a lot of huffing and puffing about fast boats on these pages but in reality similar types of boat tend to sail pretty close. In racing terms 15 mins is the far side of the moon, but if you are picking a cruising boat, it is very much the same speed.

Thanks for that, i am actually just surprised that the differences between boats discussed as fast and slow are not that great

 

[rwoofer]

Thanks for that, i am actually just surprised that the differences between boats discussed as fast and slow are not that great

As an average that is the case, but it can be deceptive for a specific angle. For the perfect angle one boat may be considerably faster, so for example if the angle was just right for a small lightweight boat to cross the channel it could it 50% quicker than a larger heavier boat even though they have the same PY.

 

[jwilson]

Not really just a straight speed issue. A Fisher 34 or Colvic Watson would have an appallingly high (ie slow) PY because that calculation would be based on them sailing on all points, including to windward. A small 18-20 foot sailing cruiser could have a lower (faster) PY yet on a straight reach or run the Fisher/Colvic type might well be faster, because of the longer waterline.

 

[LittleSister]

I guess that the differences in speed between sporty and not-so-sporty boats would be less in cruising practice than the race results & PY numbers would suggest.

Sportier boats will have a more tunable rig, high aspect ratio rig and keel, etc. Generally speaking anything highly tuned will produce more power/speed when tuned well, while falling off very markedly if not, while something less highly tuned will be less sensitive to tweaking and maintain close to its full (albeit lower peak) effectiveness in less than optimal set up.

The average cruising sailor isn't going to be either sufficiently skilled and crewed, or constantly tweaking and tuning on a long-ish passage, to maximise the benefit of a highly tuned/tunable boat, I would have thought.

I'm sometimes surprised by our boat (low aspect rig, long keel) keeping up with or overtaking boats that 'should' be faster. Much as I like to think this is skill on my part, I suspect its probably our boat plodding on regardless of my poor trimming, while the 'faster' boat is seriously disadvantaged if it ain't set up exactly right. (Even so, I expect the sporty boats' big advantage would be in pointing ability, which is useful but generally less critical in cruising rather than racing.)

 

[Tomahawk]

If you were a nail......

That would hurt...

 

[Otter]

Not really just a straight speed issue. A Fisher 34 or Colvic Watson would have an appallingly high (ie slow) PY because that calculation would be based on them sailing on all points, including to windward. A small 18-20 foot sailing cruiser could have a lower (faster) PY yet on a straight reach or run the Fisher/Colvic type might well be faster, because of the longer waterline.

Colvic Watson 34 has a PY of 1051 and that little rocket ship (Andersen 22) has a PY of 1063.

 

[onesea]

There is also another point, allot comes down to course, boat design and weather. I knew in my Trident if I was 60 deg + to around 130 off the wind, she would keep up with any boat of her size and annoy some allot bigger... Out side these points it would come down to allot of other factors.

Present boat if she is going up wind she can take most boats of her size and bigger, light airs no problems, reaching and running we are not bad either.... Heavy weather we are not comfy and on a long passage in bad weather, it would be tiring. All boats are a compromise.

Some boats do not handle certain sea conditions well, or gusty weather. I can remember as a kid "the log" Actually a beautiful long keel boat, but if she could escape the river without to many tracks. She set her course they drank gin and win races all down to handy cap, she never bothered with round the cans races...

 

[PaulR]

I have tried before to get a better idea of real world performance of different designs by looking at - for example- the round the island race results which show time taken (before handicap applied) for different boats - of course in practise the skills of the crew make a huge difference - I race a Laser during the winter and the difference between the fastest and slowest sailors in virtually identical boats is massive

 

[jwilson]

Colvic Watson 34 has a PY of 1051 and that little rocket ship (Andersen 22) has a PY of 1063.

I know you have a CW, and can appreciate their many good qualities, but I am amazed that it can compete on a PY of 1051. Could you really go round a triangular course including a couple of dead to windward legs faster than an Anderson 22?

 

[sailorman]

He has a Thorneycroft below decks

I know you have a CW, and can appreciate their many good qualities, but I am amazed that it can compete on a PY of 1051. Could you really go round a triangular course including a couple of dead to windward legs faster than an Anderson 22?

 

[Otter]

I know you have a CW, and can appreciate their many good qualities, but I am amazed that it can compete on a PY of 1051. Could you really go round a triangular course including a couple of dead to windward legs faster than an Anderson 22?

The very thought of it makes me shudder. The crew are 2, 6 and 13 years old, a coastal passage and they all get involved, a North Sea passage and they all go to sleep. An Olympic racecourse and they'd mutiny.