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 Boat Design Forums Is this too much flam??

#1
04-18-2017, 02:56 PM
 mcm Senior Member Join Date: Sep 2006 Rep: 26 Posts: 158 Location: Port Townsend, Wa., USA
Is this too much flam??

I am looking at a design that has a 0.72/1 ratio between the BWL and BOA.
This gives a 25deg. angle of outboard convex flam from the water line to the shear line on each side.

Is that too much flam?
Is the BWL/BOA ratio too low?
Will this high angle of flam between the waterline and the shear line continuously kill the boats momentum as it heaves in a seaway??

The waterline beam is 6.5'(1.98m) and the beam at the shear is 9'(2.74m).
The shear at midships is 2.75'(0.84m) above the waterline.
#2
04-18-2017, 07:09 PM
 messabout Senior Member Join Date: Jan 2006 Rep: 1279 Posts: 2,656 Location: Lakeland Fl USA
Semantics involved..... Flam is in some areas is thought of as the curvy outward trending forward section that makes the boat jazzy looking. It may also be a functional design element. Flare is the outward taper from chine to sheer. Let us not get too hung up on language.

If the sheer is 108 inches wide and the chine is 77 inches wide, then the taper per side is (108 - 77)/2 = 15.5. When the height of the triangle is 33 inches then the tangent is 0.469 and the angle is about 25 degrees. That is more than is necessary in most cases. It does give the boat a look of superior ultimate stability which is not necessarily a reality . If the boat is a Banks dory, that angle is actually modest. If it is a cabin cruiser then the flam/flare makes a place for counters and shelves that intrudes less into the living space. You have more deck area too.

In a small boat, excessive flare allows the occupants to get outside the vertical projection of the chine which is likely to make the boat a bit tippy...or worse. In a larger boat as in this likely case, that won't make a lot of difference...unless a numerous crew decides to perch on the gunnel.
#3
04-18-2017, 08:01 PM
 Mr Efficiency Senior Member Join Date: Oct 2010 Rep: 702 Posts: 5,443 Location: Australia
No mention is made of the boat length, or even if power or sail. Might be best to fill that info in.
#4
04-18-2017, 08:23 PM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,897 Location: Milwaukee, WI
Depends on the design
Attached Thumbnails

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#5
04-18-2017, 09:33 PM
 Mr Efficiency Senior Member Join Date: Oct 2010 Rep: 702 Posts: 5,443 Location: Australia
I now see it is posted under "sailboats" so apologies for that. Sounds like a sailing dory or sharpie.
#6
04-18-2017, 09:53 PM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,897 Location: Milwaukee, WI
Oops .
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#7
04-19-2017, 12:02 AM
 mcm Senior Member Join Date: Sep 2006 Rep: 26 Posts: 158 Location: Port Townsend, Wa., USA
I use this definition: Flare= concave, Flam= convex.
As relating to the outboard surface curvature of the hull from the waterline to the shear line at mid-ship.

However, whether flare or flam, is 25deg outboard angle at mid-ship from the beam at the waterline to the beam at the shear line to much?
Will a 0.71/1 ratio between BWL and Beam at the shear line stall a boats momentum as it heaves in a seaway?

Yes, it's a narrow beam, light displacement sailboat under 16m.
#8
04-19-2017, 12:40 AM
 Mr Efficiency Senior Member Join Date: Oct 2010 Rep: 702 Posts: 5,443 Location: Australia
Is it flat bottomed with a hard chine ? That more or less dictates a fair bit of overhang at the sides to avoid a slam-a-thon.
#9
04-19-2017, 01:15 AM
 CT249 Senior Member Join Date: May 2003 Rep: 215 Posts: 841 Location: Sydney Australia
There are too many factors for anyone to give a good answer without more information. Is the flam there to support 16 crew as live ballast? Is it a lake boat or a round the worlder? What is "light"? Is it an irc or orci racer? What wind and waves will it sail in?
#10
04-19-2017, 01:24 AM
 Mr Efficiency Senior Member Join Date: Oct 2010 Rep: 702 Posts: 5,443 Location: Australia
Good point CT249, unless the identity of the design is a state secret.
#11
04-19-2017, 08:59 AM
 Doug Lord Flight Ready Join Date: May 2009 Rep: 1362 Posts: 13,712 Location: Cocoa Beach, Florida
flam

I've been on and around the water all my life. I've designed and built boats since I was 12. I've tried to read every book I could find on yacht design.
But in all that time I've never heard or read the word "flam" used in the context of boat design. So, it's cool to learn something new-thanks!
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#12
04-19-2017, 11:39 AM
 mcm Senior Member Join Date: Sep 2006 Rep: 26 Posts: 158 Location: Port Townsend, Wa., USA
The hull is round bottom and no chine.
Like with most sailboats the flam is there simply to create a beam that is wider at the shear line than it is at the waterline. The purpose is to create a more livable interior for cruising not racing.
Light displacement meaning 9t on an almost 16m waterline.
The boat is intended to sail along most latitudes and in all wind conditions.
#13
04-19-2017, 06:40 PM
 bhnautika Senior Member Join Date: Feb 2006 Rep: 571 Posts: 751 Location: australia
Mcm the use of the words flam and flare is generally used (I have found) for around the bow area and flam is seen to be more advantages as it gives a gradual increase in volume, as apposed to flare which is some what more abrupt when the bow enters a wave. In the mid sections, flare seems to be used for the relationship between the waterline beam and the sheer and their angle, 25 degrees is at the upper end which is ok for initial stability but would roll more heavily.
#14
04-19-2017, 11:36 PM
 mcm Senior Member Join Date: Sep 2006 Rep: 26 Posts: 158 Location: Port Townsend, Wa., USA
Quote:
 Originally Posted by bhnautika 25 degrees is at the upper end which is ok for initial stability but would roll more heavily.
Is your answer based on reading of the pertinent literature on the subject, actual design experience, or simply anecdotal in nature?
Also, could you explain why the 'upper end' of mid-section (flare) such as 25deg. would roll more heavily?
#15
04-20-2017, 01:06 AM
 Mr Efficiency Senior Member Join Date: Oct 2010 Rep: 702 Posts: 5,443 Location: Australia
Do yourself a favour and name the boat that interests you, better still supply some pix/lines, and you are likely to get some decent opinions, at the moment it is guesswork for everyone.