The new keel for the old boat

[Perm Stress]

Originally Posted by Alexander UA

The project bulb keel?

http://ncnp.net/Cascade/C29%20Plans/KeelPlan.JPG

This keels look like Star class keel; ~1911 design... .

[sean9c]

I think you're looking at keels from your aesthetic viewpoint rather than functionality. So, have fun.

[Alexander UA]

Beautiful airplane flies well, beautiful yacht goes well!
I'm sure they used the magnificent yacht without patronage NACA-NASA. Now I want to find these projects.

[PAR]

You are absolutely right Alexander, we haven't learned a thing about foil shapes in the last century, so go ahead and employ your relic and screw NACA shapes - what do they know anyway . . .

[Alexander UA]

The problem is that modern yachts do not go to the wind cool as classic. We lavirovochny angle of 80 degrees - perfect! And all but the profile NACA 0008-0012. Riddle?

[PAR]

I'm not sure what you're trying to ask or say, but the numeric codes for NACA foil sections is about as simple as it gets.

The 4 and 5 digit series were developed using analytical equations, that describe the camber of the mean-line, of the foil section, as well as section thickness distribution along it's length. Later testing and refinements include the 6 series section, which are typically more complex and achieved through theoretical, rather than geometric techniques.

There's a huge wealth of information about these foil sections available on line.

[Alexander UA]

Bulb to make a round or ellipse? Ellipse lower center of gravity.

[souljour2000]

I own one of the old DC-3's of thick-cross-section laminar flow full keels...and she's still flyin'...1966 Columbia 40....has sort of a cutaway forefoot keel....okay maybe the Lockheed Constellation of full-keelers...oh wait..not many of those still flyin'...anyways...she's not quick but I'd say she's fairly agile due to her narrow beam ....She was made in Costa Mesa,CA where a mile or two away there were multiple factories making supersonic fighterjets with the same aluminum alloys and sub-sonic NACA-airfoil for commercial jetliners like Mac Douglas and Lockheed...I like my child of the 60's...from the SoCal region of aircraft manufacturers which produced the DC-8 and the L10-11 and numerous military super-sonic interceptors while a mile or two away they were making Columbias and Coronados... I like to think she still holds her own with the new sailboat designs....if not as speedy...If I wanted to cross the pond in a week I'd go for the new hotrod class 40 stuff...but for my wallet and likely destinations...the old DC-3 keel works for me and I ain't worried about it breakin' off anytime soon after hitting somethin' hard on the channel shoulder...just some thoughts...

[Alexander UA]

souljour2000
Senior Member
Photo of your keel is? I want to see.

[MikeJohns]

Originally Posted by michael pierzga

The classic shoal draft keel is called the "Scheel keel."

There are also many variations of the bulb keel.

The Scheel keel was not successful. Tank testing showed it had a significantly higher drag than simply using a more traditional shoal draft keel section. It's prone to developing some very draggy vortices from inevitable cross flow from a long low aspect keel. It's also hard to construct.

A simple wide base box keel tapering in toward the root with the corners rounded ( not sharp as Scheel drew) has much better characteristics.

The Scheel keel pops up occasionally when designers think it sounds high tech.

[Alexander UA]

The bottom plane of the keel is not parallel to the waterline of my sailboat.
There are some questions.
What is it better - tilt it forward or backward?
In which case it will be better flowing - when the nose of the keel is deeper than its back or vice versa?

[sharpii2]

Originally Posted by Alexander UA

The bottom plane of the keel is not parallel to the waterline of my sailboat.
There are some questions.
What is it better - tilt it forward or backward?
In which case it will be better flowing - when the nose of the keel is deeper than its back or vice versa?

The forward end of the bottom edge should be higher than the aft end. This is what the old timers used to call 'drag'.

There are two reasons why this is thought to be a good idea:

1.) rudders used to be mounted on the trailing edge of keels. With a longer trailing edge, a deeper and usually bigger rudder could be mounted, and

2.) The bottom edge would be going through the water at an angle, which would cause a slight upward flow past it. This upward flow counteracted, at least to some extent, water on the high pressure side, the leeward side, from flowing under the bottom edge to the low pressure windward side.

This applies mostly to long, shallow keels. The shorter and deeper a keel is, the less difference 'drag' makes.

[PAR]

Drag on most old school relatively shoal keels was to facilitate haul out on a marine railway. Ideally, you'll want the bottom of the keel, especially if it has any type of bulb to parallel the LWL. The reasons should be obvious.

[Alexander UA]

As a side surface of the fin keel should go to the bottom plane? What is the range? Or right angle? Which is better? Or bottom of the keel may be a semi-circle?

[PAR]

The edges of the keel at the bottom should be crisp, but eased enough to permit paint to adhere. Rounding them off, decreases efficiency.