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Author Topic:   Length/Beam Ratio

jimh posted 05-25-2005 09:27 AM ET (US)
The ratio of a hull's length to its beam is generally considered to be a good index into its ride characteristics. The higher the ratio, the smoother the ride. With this in mind, I computed a table of length/beam ratios for classic Boston Whaler boat hulls:
Outrage 17 = 2.59
Outrage 18 = 2.58
Outrage 19 = 2.64
Outrage 20 = 2.73
Outrage 21 = 2.91
Outrage 22 = 3.0
Outrage 25 = 3.07
Outrage 20 WD = 2.99
Outrage 22 WD = 3.26
Outrage 25 WD = 3.31
The ratio of length to beam at 3:1 is considered a "classic" proportion, so it comes as no surprise that the Outrage 22 is precisely at this mark. The addition of a Whaler Drive appendage really boosts the length/beam ratio for a particular hull. This could explain the smooth ride characteristics that are associated with the addition of a Whaler Drive.
prj posted 05-25-2005 10:02 AM ET (US)
Fine stats Jim.
I'll add the 15 Classic to this, often considered an excellent ride
for a boat it's size.
If I recall correctly, it measures 15'-4" x 5'-4" yielding a
2.88 L/B Ratio, better than several of the larger models.
I often think of the conventional wisdom of 3/1 ratios
when perusing or riding in the aluminum fishing boats
so prevalent here in Wisconsin.
The "designers" (used lightly) maximize the beam in order
to maximize the visual and actual space/deck aboard the craft,
while maintaining typical lengths of 16', 17' and 18', for garage fit.
These tubs achieve 8' and 8'-6" beams in a 17'-0" boat for a
ratio approaching 2.00.
While the space, stability and fishability are fine traits,
I often look to port while running alongside my buddies
and gawk in amazement at the walls of white water they're blast ahead of themselves.

Peter posted 05-25-2005 03:02 PM ET (US)
Let me add two not previously covered
Whaler 27 = 2.66
Whaler 27 WD = 2.97
phatwhaler posted 05-25-2005 03:08 PM ET (US)
Interesting thread. I have calculated the ratio of my 1996 19 Outrage to be 2.36.
Trim tabs are my next major purchase.
phatwhaler out.
Moe posted 05-26-2005 09:12 AM ET (US)
The statement that greater Length/Beam ratio generally results in a smoother ride should be made with the caveat, "all other things being equal." Smoother ride was one of the touted advantages of the Accu-Track hull design. For example, the 170 Montauk at 2.49:1 is widely reported to ride much better than the classic 17 Montauk at 2.69:1.
The similarly designed 150 Sport, at 2.37:1, should ride at least as well as the classic 15 at 2.69:1 (15'3" x 5'8") due to the reduced sponson size and heavier weight.
As ride quality has become more important over the years, Whaler hull designs have evolved away from the original cathedral hull's huge sponsons. The change in hull designs has probably more than offset the wider beams of the newer models.
--
Moe
DaveH posted 05-26-2005 11:50 AM ET (US)
To expamd on Moe's statements, The term "ride" is very ambiguous and perhaps "stability" should be used instead. Length-to-Beam ratio of 3 is an ideal point from which to base your stability calulations and also produces a "fair" design, or one that is pleasing to the eye.
Ancient mariners building boats didn't have the mathematics that we have today and used the "thumb in the air" and an eye behind it. Boat design that functioned well just "looked right" over time through a series of success and failures and were termed "fair designs".
The term "ride" connotes a feeling of comfort underway. Anyone who has ever run a flat bottomed boat can attest that the ride in a chop is not comfortable-even witha 3.0 length-to-beam ratio. The ride is more affected by bottom plane shape rather than the length-to-beam as exhibited when running offshore in a deep V design.
Length-to-Beam can also be affected by height to overide the stability of the classic 3.0 ratio. A great example is the tale of the 17th Century Swedish warship, the Vasa. It was too heavy up top and rolled over in the harbor on its maiden voyage. Another lesson learned through life's hard knocks.
http://www.port21.pl/article_1062.html
Neat stuff.
jimh posted 05-26-2005 01:05 PM ET (US)
The nice thing with the classic Boston Whaler hulls is that, for the most part, all other things are equal, and when you compare the length-beam ratio of the various hulls, you do get some meaningful numbers.

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Author	Topic: Length/Beam Ratio
jimh	posted 05-25-2005 09:27 AM ET (US) The ratio of a hull's length to its beam is generally considered to be a good index into its ride characteristics. The higher the ratio, the smoother the ride. With this in mind, I computed a table of length/beam ratios for classic Boston Whaler boat hulls: Outrage 17 = 2.59 Outrage 18 = 2.58 Outrage 19 = 2.64 Outrage 20 = 2.73 Outrage 21 = 2.91 Outrage 22 = 3.0 Outrage 25 = 3.07 Outrage 20 WD = 2.99 Outrage 22 WD = 3.26 Outrage 25 WD = 3.31 The ratio of length to beam at 3:1 is considered a "classic" proportion, so it comes as no surprise that the Outrage 22 is precisely at this mark. The addition of a Whaler Drive appendage really boosts the length/beam ratio for a particular hull. This could explain the smooth ride characteristics that are associated with the addition of a Whaler Drive.
prj	posted 05-25-2005 10:02 AM ET (US) Fine stats Jim. I'll add the 15 Classic to this, often considered an excellent ride for a boat it's size. If I recall correctly, it measures 15'-4" x 5'-4" yielding a 2.88 L/B Ratio, better than several of the larger models. I often think of the conventional wisdom of 3/1 ratios when perusing or riding in the aluminum fishing boats so prevalent here in Wisconsin. The "designers" (used lightly) maximize the beam in order to maximize the visual and actual space/deck aboard the craft, while maintaining typical lengths of 16', 17' and 18', for garage fit. These tubs achieve 8' and 8'-6" beams in a 17'-0" boat for a ratio approaching 2.00. While the space, stability and fishability are fine traits, I often look to port while running alongside my buddies and gawk in amazement at the walls of white water they're blast ahead of themselves.
Peter	posted 05-25-2005 03:02 PM ET (US) Let me add two not previously covered Whaler 27 = 2.66 Whaler 27 WD = 2.97
phatwhaler	posted 05-25-2005 03:08 PM ET (US) Interesting thread. I have calculated the ratio of my 1996 19 Outrage to be 2.36. Trim tabs are my next major purchase. phatwhaler out.
Moe	posted 05-26-2005 09:12 AM ET (US) The statement that greater Length/Beam ratio generally results in a smoother ride should be made with the caveat, "all other things being equal." Smoother ride was one of the touted advantages of the Accu-Track hull design. For example, the 170 Montauk at 2.49:1 is widely reported to ride much better than the classic 17 Montauk at 2.69:1. The similarly designed 150 Sport, at 2.37:1, should ride at least as well as the classic 15 at 2.69:1 (15'3" x 5'8") due to the reduced sponson size and heavier weight. As ride quality has become more important over the years, Whaler hull designs have evolved away from the original cathedral hull's huge sponsons. The change in hull designs has probably more than offset the wider beams of the newer models. -- Moe
DaveH	posted 05-26-2005 11:50 AM ET (US) To expamd on Moe's statements, The term "ride" is very ambiguous and perhaps "stability" should be used instead. Length-to-Beam ratio of 3 is an ideal point from which to base your stability calulations and also produces a "fair" design, or one that is pleasing to the eye. Ancient mariners building boats didn't have the mathematics that we have today and used the "thumb in the air" and an eye behind it. Boat design that functioned well just "looked right" over time through a series of success and failures and were termed "fair designs". The term "ride" connotes a feeling of comfort underway. Anyone who has ever run a flat bottomed boat can attest that the ride in a chop is not comfortable-even witha 3.0 length-to-beam ratio. The ride is more affected by bottom plane shape rather than the length-to-beam as exhibited when running offshore in a deep V design. Length-to-Beam can also be affected by height to overide the stability of the classic 3.0 ratio. A great example is the tale of the 17th Century Swedish warship, the Vasa. It was too heavy up top and rolled over in the harbor on its maiden voyage. Another lesson learned through life's hard knocks. http://www.port21.pl/article_1062.html Neat stuff.
jimh	posted 05-26-2005 01:05 PM ET (US) The nice thing with the classic Boston Whaler hulls is that, for the most part, all other things are equal, and when you compare the length-beam ratio of the various hulls, you do get some meaningful numbers.