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Old 06-30-2008, 03:20 PM   #1
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I am looking for a bluewater boat, with good speed, but a size that I can manage as a solo sailor (so about 31 to 36 feet). As I understand it, the longer the LWL on the boat, the faster it goes. Some 36’ boats only have a 26 or 27 LWL, while some 33” boats have at 28 or 29 LWL. So, in this simplistic way, is it a better buy to get a 33’ rather than 36’ boat, if you pay by the foot and the LWL is the same or even longer? What are the advantages/disadvantages, and what might I be missing in this formulation?

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Old 07-01-2008, 12:55 AM   #2
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Your question/s , have the potential to open a can of formulae.

To answer without delving into complex measurements - the length of the water line is used to compute the theoretical speed of a displacement hull using Froude's law. So taking your average of 34.5' LWL, we take square root of 34.5' = 5.87 x 1.34 = 7.87 kts max. theoretical speed.

However, the other measurement that has the major effect on the above result is the beam of the boat.

Simply put, a thin 34.5' boat will go faster than a fat 34.5' boat because it has less whetted surface. In addition a boat with a full keel may have more surface than a fin keel - this will to a lessor degree effect the final speed.

So generally the factors that come into the equation are LWL : Beam : Draft : Windage : Speed : Space : Comfort : Tankage : Propulsion: Cost : Maintenance.

Richard
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Old 07-29-2008, 05:32 PM   #3
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Some earlier designs (60s) were shaped to take advantage of the racing rating rules of their time, which favored long overhangs. These boats tend to be initially tender, which allows them to heel and put those overhangs in the water and thus sail "faster than their waterline".

In drifting conditions where no boat will attain its hull speed, the boat with the least wetted surface will be quickest. Typically, this is the boat with the shorter waterline (though a lot of other factors come in to play, like the HP rating of the engine!).

If you're looking at a 38' boat with a 30' waterline, and a 34' boat with a 31' waterline, go with the 38' boat. You'll notice the extra 4' of interior accommodations far more than the extra 1' of waterline. Plus, long overhangs are downright sexy!

This is coming from a guy who thinks the center-cockpit Freedom 40 is the ideal cruising boat...
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Old 07-29-2008, 06:32 PM   #4
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Quote:
Originally Posted by Seafarer View Post
Some earlier designs (60s) were shaped to take advantage of the racing rating rules of their time, which favored long overhangs. These boats tend to be initially tender, which allows them to heel and put those overhangs in the water and thus sail "faster than their waterline".

In drifting conditions where no boat will attain its hull speed, the boat with the least wetted surface will be quickest. Typically, this is the boat with the shorter waterline (though a lot of other factors come in to play, like the HP rating of the engine!).

If you're looking at a 38' boat with a 30' waterline, and a 34' boat with a 31' waterline, go with the 38' boat. You'll notice the extra 4' of interior accommodations far more than the extra 1' of waterline. Plus, long overhangs are downright sexy!

This is coming from a guy who thinks the center-cockpit Freedom 40 is the ideal cruising boat...
Thanks all for your comments,

I suppose I will have some wiggle room and will allow the actual boat i purchase to charm me one way or another. I am in favor of a wide beam, simply for stability, and will likely sacrifice the advantage of a reduced whetted surface of the slimmer boat.

An interesting ponder...

SailorSaipan
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Old 07-29-2008, 08:28 PM   #5
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You might take a look at a few books....

Nigel Calder's book on cruising (don't recall the name, something like Cruisers Handbook?) that has lots of good info INCLUDING a discussion of hull and speed with a couple pics showing bow and stern waves. There's also a good book out there that was written by the Cruising Club of America (CCA) in the late 1980's that is still a great reference for someone looking into cruising boats.

Link HERE.

Those truly "yachty" looking boats with the long sexy overhang on the bow and counter timber tend to have a wineglass shape, full keel, pretty deep drafts and tend to "dig a hole" in the water as they go faster--the bow and stern wave engulfing the boat! Their design roots are based on the racing boats of late-Victorian through early 20th century naval architects; (Watson, Fife, Herreshoff, Alden) then notable mid-20th century NA's changed things a bit (Stephens, Rhodes) by getting rid of the extended rigs (bowsprits and long boom mainsails).

Designs of cruising boats often just copy the racing boats of the times--look at reverse transoms (originated with German Frers design around 1950 but became really popular seems like in the 1970's and later); these days look at the big "sled" ocean racers (with pointy low buoyancy bows and big wide sterns) and then look at the shapes of contemporary cruising boats....hummm... get the picture? Wherever the racers go with designs that skirt the racing rules...soon too the cruising boats will follow (sadly).

When you're considering speed, the newer boats having a flatter, fatter, shallower hull shape vs the traditional "wine glass" hull shapes are another consideration for speed and ocean cruising (beyond waterline).

Then there's the whole underlying issue of keel and rudder design which really impacts wetted surface, maneuverability, survivability (of the boat, not you!) ...

A good cruising boat will often compromise on ultimate speed to get a sea-kindly motion and superior heavy weather sailing capabilities.

There are many choices out there as others have mentioned. Numerous of the best cruising boats have designs much like the "working boats" (fishing and pilot boats) of years gone by.

When going through the thought process that you are now...we knew we wanted to live aboard for a number of years and wanted to incorporate our love of "old things" into our cruising boat. When getting down to the specs that worked for us, we wanted a "traditional" and wooden boat with a split rig and wanted a draft under 7', waterline over 40' with a hull between 50' and 60'; we wanted to stay under 40 tons gross, we didn't want anything with an American-looking clipper type bow; we liked the "style" of European boats with plumb bows and thought that a rising counter timber was both elegant and fast. We didn't want a super full bow because one can pound thru waves with that, but instead sought a bow with fine entry with increasing fullness as one goes "up" from the waterline and back. We began to look at boats built in the UK but found a Crocker-designed boat built here in the US that was perfect for us. It has a 46' waterline, 54' length on deck, 67' sparred length (long bowsprit and boom), 6' design draft.

Our own boat was designed to be an updated Brixham Trawler with schooner rig ("updated" all being relative as the boat was designed in 1930); she has a plumb bow with a fine entry and a fairly short counter timber at the stern. In fact, its a bit squat and I call it her "duck butt" her split rig normally carries between 1600 and 1800 sf of sails. For its time of design (1930) it has an unusual underwater shape going from wide shallow draft midships much like a modern boat then into a very "sexy" (rising floors) with wineglass shape into the counter timber. 29 Ton gross.

We were lucky to have racing yacht designer Doug Peterson walk into the boatyard one day, wandering around under our boat, he said "this is a fast hull." Of course, we didn't know who he was at the time. After he left someone told us that was Doug Peterson

I hope the info provided is helpful to you (or at least entertaining!) I wish you luck in finding just the right boat for YOUR planned voyaging!
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Old 07-29-2008, 10:50 PM   #6
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You asked what points you might be missing in your formula: I am no great expert, but I would certainly consider how well a hull would right herself if rolled (Righting Moment, Stability Ratio, Etceteras). You mentioned beam which can also work against you in a roll. Motion Comfort is another number that I pay attention too. Our particular sloop is not fast (6.5 knots), but she'll take care of us in rough seas!

Good luck in finding the boat that is best for you! The search can be stressful, but it is worth it! Asking the folks here many questions sure has helped us make more informed decisions. I am confident that they can help you also.

Fair winds,

David

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Old 07-30-2008, 02:09 PM   #7
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Not that Joshua Slocum is the last word on everything, but he did say,"For your life, build no fantail overhang on a craft going offshore."

Bill
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