Where’s the lift?

[delevi]

I have heard and read opposing views on which side of the keel generates the lift, windward or leeward. I suppose both sides have water pressure but one should get more than the other. Is this correct? I read here that the keel/cb/db though absolutely necessary to sail, actually induces heel. This would mean that the greater pressure is on the leeward side. Jeff at Arena Yachts, however, told me that using less daggerboard would increase heel i.e. more board=less heel. This would mean the greater pressure being on the windward side. So would someone please enlighten me. Calling all engineers. Chip, this one might be right up your alley. I guess all in all, the answer to the question may have little relevance, but being a sailing junkie, this sort of stuff keeps me up at night.

Leon

[beene]

Hi Leon

I use this site for all my Sailing lingo etc

See if this helps

http://www.catamaranvega.com/vega/saili ... son11.html


G

[beene]

Go here for the home page with all chapters

http://www.catamaranvega.com/vega/sailing/contents.html

G

[Trav White]

regardless of lift, you still have a 4 foot plank with a lot of surface area pushing up on the water as the boat heels. I think this moment arm counters any lifting forces. If not, wouldn't the keel keep lifting the boat over on its side?

[Alex]

Right position of keels with angle 12 -15 degrees. In this case no any extra lift with cross wind sailing

[delevi]

Great article. Thanks Beene. According to this, the lift is certainly generated from the windward side, which makes sense, since the lift of the keel is what moves the boat to windward or counteracts the leeward motion. A lot of good info on weatherhelm/leehelm as well.

Leon

[Theo]

Fantastic site. I bookmarked it!

Theo

[beene]

Thanks

Very glad you found it useful.




G

[impinnacr]

The only way I can imagine it (not being any type of engineer) is that the keel is like an airplane wing only vertical instead of horizontal. As it goes through the water it "lifts" toward the windward side like an airplane wing lifts upward.
Pls correct me if I am wrong in this type of thinking.
Chris

[Highlander]

Hi Beene

Thx for that site old novice like me needs all the help I can get if I'm going to whip your b_tt or I'll refrase that your would'nt want people to get the wrong idea that could hurt . I have read some of that moving c/e on another site thats where I got my info on setting up my bowsprit & moving me genny fore by the way my new top section 20ft mast is now ready for p/u $125. good deal could 'nt pass that price up maybe I'll go for it this wk end I'll be changing my mast from a 2 section to a three section adding a second splice at the top "second set " of spreaders as this is where most mast failures ocur & adding another 4ft to the overall height of the mast where did you say you stored that main sail I'll be replacing my original 93 upper & lower shrouds this yr so I'll get the top uppers made 4ft longer now & get a new back stay it will be shorter as I add a used traveller on an aft arch you just can't wait to see my boat can you I'm hoping it warms up soon so I can finnish off the wiring I started late in the fall first

soon to be sailing John

[KayakDan]

Also not an engineer,but it would seem that the daggerboard,being symetrical,would not generate any lift to either side. Purpose of the daggerboard is to act as a brake against the sideways slip to the leeward side,caused by the "lift" of the sail to leeward.

[Highlander]

Hi Alex

nice pic of the rudders . By the way have you finnished & installed the new rudders you were making for your & are you going to post them on the mod's section ? Although you have already sent me some pic's their might be some more people interested to see them . I bought an asome cleaning & shine product at the boat show as when you sent me your pics of your boat "sqeaky clean" I said I've got to get my mods done then clean up mine . When Beene lets me know when he's coming done to look at my boat maybe you can come down the same time & take a look at them mods you wanted to see of my wheel steering ok & as you & Beene will be on the same lake this summer maybe all three of us can get a sail in mini regeta

John

[delevi]

Also not an engineer,but it would seem that the daggerboard,being symetrical,would not generate any lift to either side. Purpose of the daggerboard is to act as a brake against the sideways slip to the leeward side,caused by the "lift" of the sail to leeward.

As I understand it, every keel generates lift. That is its purpose, and of course ballast (a real keel)

[waternwaves]

keels, centerboard, any board can generate lift if the path of the water vector (diretion of waterflow against the hull) is not exactly aligned to the centerline of the board axis.

Same as sticking your hand out the car window.....

So both of you are correct, The board is designed to generate no lift (minimum drag) when going forward or backward,

But as soon as we use the sails, we penalize our track with the board no longer being parallel to the water flow.

[DLT]

Yeah, what he said!

The board is symmetric about the center line. But, that line is not aligned with the water flowing past it when the wind is causing the boat to slip, make leeway...

So, when the sails are up and the wind is pushing the boat leeward, the board does not appear symmetrical to the water flow, and thus creates lift toward windward, thereby counteracting some of the leeward tendancy of the wind.

Note that you must have some leeway for the board to make any lift...