Waterline length

[25931]

The thread LWR has caused me to wonder if the rudder is included.

 

[Tranona]

The thread LWR has caused me to wonder if the rudder is included.

LWL is exactly what it says - the distance between the two ends of the static waterline. The position of the rudder is irrelevant to the measure - it could be within it, outside or part in and part out. The rudder only beomes relevant in measurement if it is outside the hull as in the Mirage on the earlier thread.

 

[Salty John]

The thread LWR has caused me to wonder if the rudder is included.

According to designer Ted Brewer you don't include the rudder in LWL measurement:

"LENGTH WATERLINE (LWL): This is an important figure to know as it more closely represents the usable size of the yacht than LOD or LOA, and it is a necessary figure in some of the other calculations. LWL is the length of the vessel as measured from the bow ending of the waterline to the stern ending. It should not include any rudder tip that may stick out past the aft end of the hull proper. The LWL will increase as the yacht sinks into the water with the added weight of stores and equipment over the years".

 

[sailorman]

According to designer Ted Brewer you don't include the rudder in LWL measurement:

"LENGTH WATERLINE (LWL): This is an important figure to know as it more closely represents the usable size of the yacht than LOD or LOA, and it is a necessary figure in some of the other calculations. LWL is the length of the vessel as measured from the bow ending of the waterline to the stern ending. It should not include any rudder tip that may stick out past the aft end of the hull proper. The LWL will increase as the yacht sinks into the water with the added weight of stores and equipment over the years".

Also when heeled over hence some of the extremely distorted designs under the IOR

 

[ghostlymoron]

According to designer Ted Brewer you don't include the rudder in LWL measurement:

"LENGTH WATERLINE (LWL): This is an important figure to know as it more closely represents the usable size of the yacht than LOD or LOA, and it is a necessary figure in some of the other calculations. LWL is the length of the vessel as measured from the bow ending of the waterline to the stern ending. It should not include any rudder tip that may stick out past the aft end of the hull proper. The LWL will increase as the yacht sinks into the water with the added weight of stores and equipment over the years".

So, as the hull speed increases proportionally to the square root of the LWL, the more you load into the boat, the greater the hull speed.

 

[Tranona]

So, as the hull speed increases proportionally to the square root of the LWL, the more you load into the boat, the greater the hull speed.

Strictly speaking the increased waterline length increases the theoretical hull speed by approx 1.4* square root of the increase in feet. However, the increased displacement (ie weight) to increase the static LWL needs an increase in power - sail area or HP to achieve that speed. Increase of LWL from heel is a different animal as the increase in speed does not necessarily require an increase in power. Think J class and similar hulls with huge onerhangs at rest and sailing at large angles of heel.

 

[Lakesailor]

Even on Windermere 17ft class boats the counter stern extends the waterline length by 3 or 4ft when heeled. the boats are 25' LOA but 17ft LWL.
The white area is the waterline at rest.