D/L Ratio Questions for Cruising Boat - SailNet Community

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  #1  
Old 01-30-2013
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D/L Ratio Questions for Cruising Boat

Hey All,

Still looking for the ideal cruising boat as we plan our escape from Southern California. The goal now is to sail across the Pacific to French Polynesia and eventually circumnavigate the Pacific a la Hal Roth and I'm sure many others.

I should note that I've always been a seat of the pants type and have little knowledge of non-dimensional figures like D/L ratio but I do know that, while a heavy boat my be a slug in light airs, it's not going to get tossed around the way a light boat would be in bigger seas.

We're looking for a CC in the 45-50 foot range (bumped up from a former max length of 46 feet) and have really taken to the idea of a deck salon. If we can find a used Oyster we can afford, that might be the ticket.

Anyway, the Oysters and other cruising boats we've looked at tend to have D/L ratios between say 240 and 280+, which - based on my reading - seems to be a solid compromise between stability and speed. I'm not really interested in a full keel, long overhang design. A close friend owns a Mason 44 and, while it's beautiful, it's really not very maneuverable and is something of a chore to day sail or enjoy in light airs.

While surfing the web the other day, we came upon the new Elan Impression 494, which is beautiful, a heck of a lot more affordable than an Oyster - we could buy it new - and includes the option of bunk/passage berths right by the companionway, which would work well for us on passage.

The boat was designed by Rob Humphreys, who does the new Oysters, and is recommended for bluewater cruising. It's got plenty of tankage, decent handholds and the option for a full, closed transom instead of a gate/swim platform. I was shocked, however, when I did the D/L calculation to see the boat comes in at an ultra-light 155!

Can anyone shed some light on this? Is Elan full of BS when they say the boat will be comfortable in a seaway? Is the "bluewater" moniker just marketing hype from a company that knows full well that 99% of their customers will only day sail the boat? I may be able to test sail the boat but there's really no way to know how it'll behave in heavy seas or a big swell.

I'd rather not fixate on the Elan 494 specifically, as I'm more interested in the value of D/L ratio for bluewater use in general.

Is there a legitimate "lighter is better" school of thought?

Thanks,
CCR

Last edited by ColdCutterRig; 01-30-2013 at 11:45 PM.
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Old 01-30-2013
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Re: D/L Ratio Questions for Cruising Boat

You will not win on this, as some like myself seem to like 170-220 or so, other 300, some as little as 100.

This number also means squat in some regards. as a 30'r with a 180 will handle different than a 50'r with a 180. Same can be said for some of the other numbers one can dig up too. ie comfort ratio to mention one.

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Old 01-31-2013
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Re: D/L Ratio Questions for Cruising Boat

If you're willing to spend $350-400K you'll have a wide open list of candidates in the 45-50 foot range, especially if you are looking at used as well.

Even something like this:

2000 J/Boats J/46 Sail Boat For Sale - www.yachtworld.com

Probably best of both worlds.

Or Tayanas, larger Passports (47) Hylas, etc etc.

Those are my dream parameters!! .. tho like Marty I'd probably drop into the high 100s/low 200s as an ideal D/L... but please don't get hung up on those numbers.
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Last edited by Faster; 01-31-2013 at 12:39 AM.
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Old 01-31-2013
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Re: D/L Ratio Questions for Cruising Boat

Cold,

I didn't re-run the numbers so I will assume you did the math right. Given this there are a few things to consider. D/L is not really so meaningful a number. Unless you are comparing two very very similar boats the numbers can be very misleading.

1) a boat that uses a lot of carbon fiber will have a much lower D/L than one that uses CSM. Simply because one is much heavier. But when you look at performance they will be almost exacally the same.

2) a boat with deeper draft can have a lower D/L than one with a shoal keel because less weight is needed to generate a given amount of righting moment.

3) a D/L of 150 is not really that low. Say in the light cruiser/racer catagory.

4) a boat with long overhangs will have a lower D/L even if everything else is the same. Since D/L uses LWL not sailing water line.

Finally while I know and respect the oyster, I don't have any familiarity with the …lan. But my thought is that Oyster must have been pretty impressed by the designer if they offered him a design job.
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Old 01-31-2013
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Re: D/L Ratio Questions for Cruising Boat

here is a good site to plug all the numbers in to compare. some boats are already listed for convenience.
Sail Calculator Pro v3.0
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Old 01-31-2013
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Re: D/L Ratio Questions for Cruising Boat

If you like Oysters, you might like the Najads, too. If you deal with the funkier side, Joubert designed some nifty deck salon boats.
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