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Old 07-06-2011, 06:22 AM   #1
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Anyone know the formula for calculating the rise of the water-line in shear to the stern of the boat. (using a laser or the old fashioned water filled clear plastic tube)
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Old 07-06-2011, 08:56 AM   #2
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Anyone know the formula for calculating the rise of the water-line in shear to the stern of the boat. (using a laser or the old fashioned water filled clear plastic tube)
Richard, Please explain if what you are asking is in a 'static' or 'active' - - sailing mode . The question is - - - of course- - as always - - valid - - but is very open-ended. Please define & we might be able to 'assist you' (ha ha). What with your knowledge of boats & sailing, I do think - you might be - - playing with us - & I'm personally - not going there. Stopped loosing to my Lady, 55 years ago - - in our house it's called - - 'zip' (as in I 'zip' my mouth shut & leave/flea the scene. Ciao, james
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Old 07-06-2011, 09:48 AM   #3
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Richard, Please explain if what you are asking is in a 'static' or 'active' - - sailing mode . The question is - - - of course- - as always - - valid - - but is very open-ended. Please define & we might be able to 'assist you' (ha ha). What with your knowledge of boats & sailing, I do think - you might be - - playing with us - & I'm personally - not going there. Stopped loosing to my Lady, 55 years ago - - in our house it's called - - 'zip' (as in I 'zip' my mouth shut & leave/flea the scene. Ciao, james
Hi James,

No games , the formula/e required for a displacement Monohull, with all it needs to go cruising. Sails, ground tackle, fuel and water tanks full. No provisions, spares etc.

Assume that this is new boat just sold by the dealer to a customer.
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Old 07-06-2011, 12:07 PM   #4
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Anyone know the formula for calculating the rise of the water-line in shear to the stern of the boat. (using a laser or the old fashioned water filled clear plastic tube)
I'm afraid that I do not understand the question. Could you explain shear and what the rise of shear means to using the boat?
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Old 07-06-2011, 11:50 PM   #5
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Hi James,

No games , the formula/e required for a displacement Monohull, with all it needs to go cruising. Sails, ground tackle, fuel and water tanks full. No provisions, spares etc.

Assume that this is new boat just sold by the dealer to a customer.
Gooday Richard. WOW - some subject, this one. I went into 'google' - Water line shear effect on a sailing yacht - & I'm sure if I was smart enough to understand any of it - then it would take me years to get a starting point to understand it. Lots of great feeds in there, I thought. Good subject though. I'd like to know what Bob Pattison thinks about this subject from his professional point of view. Think I'll just stick to - getting back on the water ina cruising multihull asap. I'll keep watching this space with great interest. Thanks & ciao, james
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Old 07-07-2011, 02:48 AM   #6
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I'm afraid that I do not understand the question. Could you explain shear and what the rise of shear means to using the boat?
My error in spelling of 'Sheer' (Being a Scot, shear being a Scots word derived from shearing sheep)

The nautical term "sheer" is "a measure of longitudinal deck curvature in naval architecture"

So that the question is rephrased, I have extracted the picture of a friend's Whitby 42 Ketch and added some lines to illustrate.

Whitby Water Line.jpg

But first another nautical term:-

Gunnel (from Gunwale)

the upper edge of the side or bulwark of a vessel.

2.

the sheer strake of a wooden vessel; the uppermost strake beneath the plank-sheer.

----------

The Red line is parallel with the water. Above the Red line is a barge board, the top edge of which is the line of gunwale.

The Red arrow is the point at which the gunwale line rises to the stern and to the bow.

--

The Green line represents the horizontal level of the sea. Above the Green line is the existing painted Black water line.

The forward Green arrow marks the position (on this boat) where the Black line starts to curve following the sheer. The aft Green arrow marks the position where the Black line starts to rise following the sheer of the gunwale.

-- The reason for not painting a dead straight line, is to correct the illusion that the line droops towards both ends of the boat.The sweep or sheering of the boot and the painted water line solves this problem. In addition, a dead straight boot will show the slightest trim imbalance, but a swept boot and bottom line cures that.

So to return to the question first posed :-There is a formula/e for determining the correct positions of the Red and Green ARROWS. Where can I find it?

_____________________________________

To the second part of your Question -

"what the rise of shear means to using the boat?"

In simple terms:- the higher the bow, the dryer the boat.
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