Beam to Waterline Ratio

AusCan said:

My ratio is somewhere around 0.30, depending on how I measure my Water Line Length.


What is the proper way to measure WLL on a boat with a canoe stern?

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If not heeled....perpendicular to the points where the hull meets the water.

If heeled ....the same...but that would probably be a challenge...

Xlantic, great info. That looks like a least squares fit line of that data?

I am continually impressed at the depth of knowledge and data that some of you guys have readily at hand.

FF said:

Years ago the AYRS came up with a simple method of figuring "hull" speed for a variety of boats.

The old formula was created by looking at fat boats of the time , and doesn't work well for skinny fast boats.

S = L/3b X SQRT of (LWL)

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What is "L" and "b" in that formula?

dhays said:

That looks like a least squares fit line of that data.

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Yes, R2 of 76% which suggests a pretty good fit.

I suspect the larger boats in the sample are non-planing and hence relatively narrower for greater efficiency. For planing boats there may be a smaller or no efficiency penalty for being relatively wide?

Spent a couple days aboard Iowa running from Norfolk to Ft. Lauderdale. Pic below shows firing the 16" guns. Most terrifyingly awe-inspiring thing I've ever seen.

BTW, Great Harbour GH37 and N37 have a 36' 2" LWL and 16' 0" beam.. Works out to .44

KK42: 15' / 39.167' = 0.383


Jim
Sent from my iPad using Trawler Forum

An interesting comparison of the same perspective shot taken many years apart.

psneeld said:

Be careful comparing apples to oranges.....if using beam to lwl...make sure you use beam at the waterline to get a usable figure...


I have no idea what my waterline beam even is.

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Gosh darn it, Scott! You're right, I've never thought (or cared until this thread) about "waterline beam". I'm probably closer to 0.29 than my previous 0.33.

Art, I'll try your plumb bob thingy....man, you must have been bored!

Regardless, the Iowa-class battle ships are skinny compared to our boats.

Man she sure went on a diet.

Some day maybe Ill get to feel a big ole gun fire a round or two.

Giggitoni said:

Gosh darn it, Scott! You're right, I've never thought (or cared until this thread) about "waterline beam". I'm probably closer to 0.29 than my previous 0.33.

Art, I'll try your plumb bob thingy....man, you must have been bored!

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Try to let a feather weight plumb the bob as if you lean over the side and cause a list...the bob measurements might be "blob" measurements....

Not that I am suggesting anything.....

what_barnacles said:

Man she sure went on a diet.

Some day maybe Ill get to feel a big ole gun fire a round or two.

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All the weight she lost was all the attractive accessories above her waist. She retained her big butt.

Early in my flight inspection career, we were conducting an orbit around a Navy TACAN transmitter on the south end of San Clemente Island. There's a firing range on that end that often had Navy ships lobbing shells toward the shoreline. We were at about 2000 ft above an Iowa Class battleship (perhaps the New Jersey or the Missouri) when they started firing the big guns at the island. We could hear and feel the concussions of the guns firing inside a Rockwell Saberliner 80, a pressurized business jet not known for being quiet. Obviously there was a breakdown in coordination with them firing while we were still operating in the area. Not the last time something like that happened to me on the job.

what_barnacles said:

Man she sure went on a diet.

Some day maybe Ill get to feel a big ole gun fire a round or two.

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We're talking pre- and post-retirement!

Giggitoni said:

Gosh darn it, Scott! You're right, I've never thought (or cared until this thread) about "waterline beam". I'm probably closer to 0.29 than my previous 0.33.

Art, I'll try your plumb bob thingy....man, you must have been bored!

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Man - I was! And, anyway, isn't it always good to know your gal's waist size too!

In all due respect, to everyone here... just being on most threads = a form of boredom!

Of course, on this very important thread... no chance of being bored here

Happy Baby-Boat WLBeam Daze! - Art

psneeld said:

Be careful comparing apples to oranges.....if using beam to lwl...make sure you use beam at the waterline to get a usable figure...
I have no idea what my waterline beam even is.

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Neither do I, but it makes me ponder the difference between a vessel with a relatively flat stern vs. something purposely rounded or double-ended. Is the WL of a fat round boat actually the radius of it's footprint on the water, and because of that, could the WL of something like a fat double ender actually be greater than it's overall length.

healhustler said:

Neither do I, but it makes me ponder the difference between a vessel with a relatively flat stern vs. something purposely rounded or double-ended. Is the WL of a fat round boat actually the radius of it's footprint on the water, and because of that, could the WL of something like a fat double ender actually be greater than it's overall length.

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was pondering that myself...but for definitions...lol doesn't follow the boot stripe...

I think there is a term immersed waterline that varies with hull shape and heel , then there is just variables to the into account stern shape.

I thought I read awhile back that the 1.4 time the square root of the waterline was just an average. The shape of the transom changed that number by a few tenths up or down.

psneeld said:

Try to let a feather weight plumb the bob as if you lean over the side and cause a list...the bob measurements might be "blob" measurements....

Not that I am suggesting anything.....

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Just fer S&G... not that I'm suggesting any suggestion is ever made ~

While trying to have boat sit vertically plumb with no one aboard (pets over 16 oz. included): At dock... on one side of boat, place the bob (almost to touch water) on string hanging off edge at widest beam area of boat... Then measure at waterline to point on the bob. Take bob to other side and hang similarly. Then again get off boat so it vertically equalizes same as a few minutes ago. Measure same as you did on first side. Take combined measurement and subtract from deck line's broadest beam. Note: no breeze and no wakes/waves allowed.

Voila - you will know your baby-boat's true waste size!! Yeah Baby! I learn all my larger boats' waste size during first couple months ownership... Call me weird if you like. I call it loving care; i.e., getting to know you!

PS: I also always make sure my boat-babies have rubber reverse flow aprons on each exhaust pipe out of hull. So her power plants don't ever need to be (burped) drained before starting.

Happy Boat-Baby Daze! - Art

"Some day maybe Ill get to feel a big ole gun fire a round or two."

Probably not , the gun barrels are recycled as bombs to penetrate very hardened underground bunkers.

FF said:

"Some day maybe Ill get to feel a big ole gun fire a round or two."

Probably not , the gun barrels are recycled as bombs to penetrate very hardened underground bunkers.

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As in the term Alan Greenspan coined... "Creative Destruction"... this time in more ways than one!