Importance of D/L ratio

[Polux]

Originally Posted by Snowpetrel

I think you only need to look at the sydney hobart 2006 results to see how well the heavy displacement/length boats did on a very hard windward race. look at "Bacardi" A 79 Peterson 43 and "Love and war"a 1974? S&S 47. They came 1st and 2nd on handicap, but the real surprise is just how many modern boats of similar length or much longer that they beat on line. Not bad for a couple of overweight boats built in the seventies!

As you know handicap results means nothing regarding the boat performance only says that the Peterson 43 and the S&S 47 were extremely well sailed, close to its potential.

Regarding the Peterson 43 to be a heavy boat you can only be kidding me A 43ft Peterson displaces about 8 500kg and that is the weight that today most cruisers racers of that size have. There was even a racing version, probably the one that made that race, that weighted less than 7500kg.

Anyway, just to put things in perspective regarding that upwind race (Hobart 2006) and upwind potential regarding boat power, being them light or heavy, the fastest boat to cut the line with the length of that S&S 47 was a Reichel & Pugh 46fter, Hardy's SM Business, a much poorly sailed boat since it only got 18th in compensated time.

Even so on that upwind race it won 11hours and 22minutes to that heavy S&S 47 and that in a short race with just a bit more than 3 days. Can you imagine how much it would have gained if it was sailed as close to its potential as the S&S 47 was sailed (2th and 18th on compensated)?

[Lennie]

Any thoughts about STIX numbers? I think anything equal to or over 32 is rated for offshore use. I know it's another very subjective number but is probably a better than looking at D/L ratio's.
Just adding fuel to the fire,

Len

[Cadence]

The whole discussion of D/L is a no brainer. Just give it a thought. Given a fixed length where is the weight. Displacement is just the water displaced. Do you want the lead ballast at the bottom of the keel or on the mast? The displacement would be the same.

Very simplistic but give it a thought.

[Snowpetrel]

Originally Posted by Polux

As you know handicap results means nothing regarding the boat performance only says that the Peterson 43 and the S&S 47 were extremely well sailed, close to its potential.

Regarding the Peterson 43 to be a heavy boat you can only be kidding me A 43ft Peterson displaces about 8 500kg and that is the weight that today most cruisers racers of that size have. There was even a racing version, probably the one that made that race, that weighted less than 7500kg.

Anyway, just to put things in perspective regarding that upwind race (Hobart 2006) and upwind potential regarding boat power, being them light or heavy, the fastest boat to cut the line with the length of that S&S 47 was a Reichel & Pugh 46fter, Hardy's SM Business, a much poorly sailed boat since it only got 18th in compensated time.

Even so on that upwind race it won 11hours and 22minutes to that heavy S&S 47 and that in a short race with just a bit more than 3 days. Can you imagine how much it would have gained if it was sailed as close to its potential as the S&S 47 was sailed (2th and 18th on compensated)?

Ha pollux, yes that brand new carbon fibre Racheal Pugh was very quick, but then the two old warhorses were hot on the tails of an open 60, being only a few hours behind her. And ahead of boats like arctos, and tevake2, and all of the Sydney 38 fleet. I was very impressed by how well these old girls did in that very tough race.

The handicap reflects how well the boats were sailed to some extent, but it also reflects how well the boats were optimised for the conditions encountered, in this case these older designs did better with the strong headwinds than many of the newer designs.

Bacardi, though light for a cruiser has a very short waterline, that gives her a d/l around 200. Whereas most of the more modern boats racing with her would be in the 80-120 range at a guess. She is slow downwind in comparison, not planing. Slower in the light, with a sa/d of around 20, compared to 30+ for the newer racing yachts. But she sure go's to windward well. Of course I am biased here, owning a near sistership

Saying all this I think the trend for shorter overhangs is good for motion comfort, even if it can make a boat wetter. It generally results in a lower d/l for a given overall length, so skews the figures if we use Loa as our starting point.

I think a near perfect modern design is oceanseasprays nordkyn.

[Polux]

Originally Posted by Snowpetrel

Ha pollux, yes that brand new carbon fibre Racheal Pugh was very quick, but then the two old warhorses were hot on the tails of an open 60, being only a few hours behind her. And ahead of boats like arctos, and tevake2, and all of the Sydney 38 fleet. I was very impressed by how well these old girls did in that very tough race.

The handicap reflects how well the boats were sailed to some extent, but it also reflects how well the boats were optimised for the conditions encountered, in this case these older designs did better with the strong headwinds than many of the newer designs.

Bacardi, though light for a cruiser has a very short waterline, that gives her a d/l around 200. Whereas most of the more modern boats racing with her would be in the 80-120 range at a guess. She is slow downwind in comparison, not planing. Slower in the light, with a sa/d of around 20, compared to 30+ for the newer racing yachts. But she sure go's to windward well. Of course I am biased here, owning a near sistership

Saying all this I think the trend for shorter overhangs is good for motion comfort, even if it can make a boat wetter. It generally results in a lower d/l for a given overall length, so skews the figures if we use Loa as our starting point.

I think a near perfect modern design is oceanseasprays nordkyn.

Nice to have some good sense here

Sailing in what regards racing has as much to do with the boat as with the crew and if a given boat hardly can go much faster than its rating, even with a top crew, the truth is that it can go a lot, lot slower, with a bad crew.

The S&S 47 even if not carrying much sail has a big draft and 50% of its weight is ballast, not being a narrow boat for that era and that means a considerable form stability. All that translates in a powerful boat at least if the wind is not weak, as I suppose it would have been the case, because with weak wind not even the best sailors would have managed to sail it fast upwind at least if compared with modern light powerfull cruiser racers.

The boat was a cruiser racer and a very fast boat on its own time.

Going fast upwind has nothing to do with weight or lack of it but with power. Put on that upwind race any boat, heavy or light with low power (stiffness) and you can be sure that it would have problems going upwind, much more going upwind fast

Regarding plum bows or even inverted bows not having a problem with spray happens because normally another feature on those boats are chines at the bow that have not only the function to create lift sailing upwind, making planing easier as also to prevent spray when going upwind.

Well, at least that works somehow the reality is that very fast boats are very wet boats no matter what you do. You can not have maximum speed against waves, specially if they are steep without having spray. Big overhangs only limit performance and increase pitching. In the end the increased pitch will contribute also to create spray.

[Don C L]

Originally Posted by Cadence

The whole discussion of D/L is a no brainer. Just give it a thought. Given a fixed length where is the weight. Displacement is just the water displaced. Do you want the lead ballast at the bottom of the keel or on the mast? The displacement would be the same.

Very simplistic but give it a thought.

Right, which is why it is useful to look at centers, like center of gravity. I think the Ballast/displacement is at least as important since a really heavy hull and lighter ballast may have an impressive D/L, but may not be too... comfortable...

[Polux]

Originally Posted by Don C L

Right, which is why it is useful to look at centers, like center of gravity. I think the Ballast/displacement is at least as important since a really heavy hull and lighter ballast may have an impressive D/L, but may not be too... comfortable...

I don't think it is a question of comfort but of safety (final stability) and sailing power.

You have said rightly, center of gravity, not to confound with ballast/displacement unless the boats have the same draft and keel type.

Older heavy boats and modern boats generally have very different keels and drafts.

A 50% ballast/displacement ratio on an old designed keel with 1.5m draft can provide the same effect regarding lowering the CG as a 2.25m draft torpedo keel (with all the ballast on the torpedo) with a 25% ballast/displacement ratio. Off course it is only a broad picture but for what I have seen, not very far from reality and it gives an idea of how B/D effect in lowering the CG and creating Righting moment can be affected by draft and type of keel.