Importance of D/L ratio

[Island Time O25]

Originally Posted by Polux

GordMay, it is difficult to disagree with you with that avatar an all your nice manners.

I had one of those calculators many years ago and I through it out long ago. It really does not serve any purpose except maybe regarding comparing most common types of cruisers that existed when that calculator was created, or better, when the different ratings that served to access a boat and that are on its basis, were created.

We are far away from the 70's early 80's and most of the things the calculator indicates, regarding comfort, stability or even the definition of the type of boat make today no sense and does not provide valid information regarding the vast amount of different boats on the market that are all very different from the typical boat from the 70's.

So far every boat I've been on has more or less been in line what the motion comfort index predicted. Granted very few of those were personally tested in severe environments but still if when moored it starts bobbing every which way from a passing dinghy you know you've got a squirrel on your hand. Now it still may give a decent ride in a storm being faster and what not but at least the first impressions are usually in line with what's predicted by these indices. Thus IMO, while not being the final word, they are a good start to explore further the various models which will suit one's sailing style and needs.

[sailorboy1]

I don't feel using DLR to compare boats of different sizes really tells you much. In order for the ratio to have any meaning the boats need to be similar is size AND shape. Comparing say a 1985 35' with large overhangs and a high DLR to a 2005 45' with plum bow and length carried way aft will be meaningless.

I had a 1988 39' boat with DLR of 240 and now have a 2001 43' boat with a DLR of 165. The 2001 boat I feel is more comfortable because and it doesn't need to have the rail in the water to sail well (another part of "comfort")

But is similar and size and shape a higher DLR will be more comfortable (less uncomfortable really) in a very narrow set of conditions.

Just my opinion as I ain't no expert!

[Polux]

Originally Posted by thomm225

I still believe the video is inconclusive.

Plus by that camera angle after 5:50 the sea state seems to have fallen off a bit from say 3:25. Plus that boat after 5:50 appears larger than many of the others and appears to have come off the wind a bit more than some for more power.

Power is power, weight is weight, being it on a motorboat or sailing boat or even on a ship. Maybe the ship captains that are on this thread can tell us what boat would fare better upwind against bad weather and what would be the one that would have to run before, a navy overpowered destroyer or a fatter and heavier cargo ship with the same size, slightly underpowered?

[Island Time O25]

Originally Posted by sailorboy1

I don't feel using DLR to compare boats of different sizes really tells you much. In order for the ratio to have any meaning the boats need to be similar is size AND shape.

Agree! But that is also true for other indicators, not just DLR. Again, IMO, this should not be used instead of all other factors but as first step in the research process, albeit an imperfect one at that. After all we've got to start somewhere.

Personally I found the sail calculator very helpful as far as getting a broad overview of various boats while searching for the ones which will address my needs and budget. And in many years I have used it as a sieving out tool I have yet to find a glaring inconsistency or fatal flaw in it's general approach to give comparisons.

[Polux]

Originally Posted by Island Time O25

So far every boat I've been on has more or less been in line what the motion comfort index predicted. Granted very few of those were personally tested in severe environments but still if when moored it starts bobbing every which way from a passing dinghy you know you've got a squirrel on your hand. Now it still may give a decent ride in a storm being faster and what not but at least the first impressions are usually in line with what's predicted by these indices. Thus IMO, while not being the final word, they are a good start to explore further the various models which will suit one's sailing style and needs.

Not needed to discuss things many times. Here you have a thread about the subject:
http://www.cruisersforum.com/forums/...ios-71329.html

In fact the more useful ratios today are still the D/LWL and the SA/D, the ones that can provide some idea of the boat performance, however the classifications that come attached to those ratios is today ridiculous and many cruising boats will be considered racers.

Regarding motion comfort even Ted Brewer the creator says it is only intended to provide indications regarding yachts of the same type: "indeed, does provide a reasonable comparison between yachts of similar type...The intention is to provide a means to compare the motion comfort of vessels of similar type and size.....Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! It is all relative.""

You can see the confusion installed on a thread that had discussed it:
http://www.cruisersforum.com/forums/...ort-71347.html

[mitiempo]

D/L ratio has nothing to do with weight (displacement) by itself. It is the weight for a given waterline length.

For example:

Take an Alberg 37 with a displacement of 16,600 lbs and a waterline of 26.5 feet. It has a D/L of 398

Take the same boat and increase the waterline to 33'. This will make the boat heavier by say 1000 lbs of fiberglass and supporting structure. Displacement is now 17,600 lbs. The D/L is now 219 although the boat is heavier.

Not only will a longer waterline equal more speed - everything else being equal, but a boat with less overhang can be less likely to hobbyhorse as it has greater longitudinal stability.

[thomm225]

Originally Posted by Polux

Power is power, weight is weight, being it on a motorboat or sailing boat or even on a ship. Maybe the ship captains that are on this thread can tell us what boat would fare better upwind against bad weather and what would be the one that would have to run before, a navy overpowered destroyer or a fatter and heavier cargo ship with the same size, slightly underpowered?

Looks like you have decided to get away from your video argument where your larger boat sailing more off the wind (with lots of rail meat) in smoother seas appeared to be sailing better than the older, smaller boats that were pointing higher into larger waves.

Ok!

[thomm225]

Originally Posted by Polux

On this video on min 1.17 and over you have an old designed cruiser racer, heavier and less powerful than a racer that appears on the same video at the minute 5.50. Compare the movements ad the sail ability upwind and you will see that even if the conditions at min 5.50 seems to have gone worse, the lighter and more powerful boat does not only pitch and heel a lot less as it does more headway.

These are pretty nasty conditions to keep going upwind, not only in what regards the head wind but the nasty waves. Even the older boat that I mentioned is a powerful boat, a cruiser-racer. These condition would have stopped on his tracks considerably less powerful boats, being them heavy or light.

Looks like that same racer at 5:50 is doing about the same as the old cruiser racer boats in similar conditions from about 4:30 - 5:55.

[fatherchronica]

That lower left number on my chartplotter is as fast as I have been able to sail my Cape George 36, and while we only covered 172 miles that 24 hours, we were astonished at how stable, smooth and safe the ride was. I have owned as many racers as cruisers, including a Bill Lee design, and would not consider cruising in an ultralight. But we are old, and I have fractured 16 vertabrae and had many surgeries, and need the comfort of a boat not pounding. When we bashed back from Mexico to California last year, a little late, and 3 hurricanes ( far south) into the season, we found that every light weight boat we met, waiting weather windows, here and there had delivery crews. Of course there are a lot of old people cruising who don't like being beat up. If I were young, or only going to, say, The Sea of Cortez, I would still have a light boat. But for being on oceans I prefer the stout ship now.

[Paul J. Nolan]

Originally Posted by Island Time O25

...with all my lunches passing through their proper hole...

I believe the phrase is, "With all my lunches following their proper course..."

Paul

[Snowpetrel]

Originally Posted by fatherchronica

That lower left number on my chartplotter is as fast as I have been able to sail my Cape George 36, and while we only covered 172 miles that 24 hours, we were astonished at how stable, smooth and safe the ride was. I have owned as many racers as cruisers, including a Bill Lee design, and would not consider cruising in an ultralight. But we are old, and I have fractured 16 vertabrae and had many surgeries, and need the comfort of a boat not pounding. When we bashed back from Mexico to California last year, a little late, and 3 hurricanes ( far south) into the season, we found that every light weight boat we met, waiting weather windows, here and there had delivery crews. Of course there are a lot of old people cruising who don't like being beat up. If I were young, or only going to, say, The Sea of Cortez, I would still have a light boat. But for being on oceans I prefer the stout ship now.

A good friend has a Tally Ho Major, I think the Cape Georges are modeled closely on Atkins lines for the Tally Ho. I cant think of a more seakindly boat over all. The motion is silky smooth, no pounding or jerkiness at all. She can roll. but that's about her only fault, and with a big rig and bowsprit she sails like a witch. lovely boat. Id rate her as having a far more comfortable motion than many light weight 50 footers. But of course she is not as fast or as roomy.

[Snowpetrel]

Originally Posted by Polux

Power is power, weight is weight, being it on a motorboat or sailing boat or even on a ship. Maybe the ship captains that are on this thread can tell us what boat would fare better upwind against bad weather and what would be the one that would have to run before, a navy overpowered destroyer or a fatter and heavier cargo ship with the same size, slightly underpowered?

Interesting, a fat chubby underpowered roro I worked on was far better punching into some nasty steep waves then the much finer, more powerful container ships (for her size). The chubby wee thing just bobbed up and down over the waves like a cork but still kept going forward while on the big box boats we had to slow down pretty early to stop the waves sweeping the foredeck or the ship pounding severely.

I wasn't aboard, but the crew told me how she once steamed right past a much bigger warship that was forced to slow right down to avoid damage as the waves swept her fine bows. One tough little ship that Straitsman.

[Snowpetrel]

Originally Posted by Polux

..Snip..

Due to that superior power (on the light boats that have it) they can be sailed much longer than less powerful sailboats that have to run sooner, unable to be sailed in any other course. Not all old heavy boats were low power boats dough.

On this video on min 1.17 and over you have an old designed cruiser racer, heavier and less powerful than a racer that appears on the same video at the minute 5.50. Compare the movements ad the sail ability upwind and you will see that even if the conditions at min 5.50 seems to have gone worse, the lighter and more powerful boat does not only pitch and heel a lot less as it does more headway.

These are pretty nasty conditions to keep going upwind, not only in what regards the head wind but the nasty waves. Even the older boat that I mentioned is a powerful boat, a cruiser-racer. These condition would have stopped on his tracks considerably less powerful boats, being them heavy or light.

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!

[thomm225]

Those blunt/plumb bows on the racing boats (and newer style cruising boats) did nothing to help smooth out the ride either.

I have seen this on smaller boats racing through passes etc where the waves can get steep.

The blunt/plumb bowed boats with little overhang tend to pound whereas the older style boats with rocker hulls/overhang tend to ride through and over the waves much smoother

This article explains it quite well along with points on heavier verses lighter, etc:

Shaping an offshore hull - Ocean Navigator - January/February 2003

From the article:

Ocean voyagers might sail for days on end without stopping. They might face bad weather and large seas, so the hull must be able to ride out a storm without causing too much crew fatigue. Comfort and ease of motion through the water mean that the boat needs to have a reasonable displacement. You only need to watch video of some of the boats in the Sydney-Hobart race to realize that light weight equates with increased motion. Because increased motion increases crew fatigue, it can induce a crew to make bad decisions.

Contrary to current trends, I believe that a voyaging boat should have moderate overhangs. The length of overhang that I like to see is between 18 and 24%. This will give the bow and stern some reserve buoyancy to help stop the bow submerging in heavy seas, and the boat from pitching in a seaway.2.

[fatherchronica]

About 40 years ago I read an article about some fellows on a Morgan Out Island 41 who were going to Columbia from Florida. They decided, on a lark and for possible weather/routing information, to enter a race from Florida to Cartegena. A hurricane interupted the race, but they reefed down and continued on. They said it was fairly rough. I don't recall how many finishers there were anymore, but it was a slight fraction of starters, and the Morgan was several days ahead of second place. It said they were the only boat that was not under bare poles in survival conditions for an extended length of time. I think the article was in Sail magazine.