Fin Keel vs. Full Keel

[TAREUA]

Okay, I'll bite. Anything beats sitting here writing performance reviews. In my experience full keel boats track better (in the sense of locking onto a balanced point of sail) than do fin keels. The lack of squirrely helm makes it in that regard more stable. Probably not an engineers definition of stability, but not being an engineer, I've always been able to get dates, so it's a good trade off.

[speedoo]

Originally Posted by bob perry

How does a full keel equate with "stability"?
Just asking for a cogent explanation.
Waiting,,,,,,

Bob, isn't the answer that, all other things being equal, a fin keel actually offers more stability than a full keel? Because the ballast is deeper?

[sneuman]

I wouldn't necessarily make a race vs. cruise/fin vs. full argument. We've got an Alberg 30 and a Luders 33 in our PHRF fleet and in a blow they both do better than the C&C27 I race on. None of us can seem to cobble together more than about a 3-person crew, and naturally they can stand on their feet better than we can in heavy-air conditions. Aside from a little more acceleration at the line, the Alberg and Luders have a jump on us in those conditions -- especially the Luders, which much to our chagrin, enjoys a much higher PHPF rating despite having 3 more feet at the waterline!

Now, in light air, we have a distinct advantage. When we're having a good day, that is!

[bob perry]

If we are talking about athwartships stability, i.e. a boat's resistance to heeling then a full keel is no benefit. No, the ballast is not necessarily lower and the geometry and distribution of volume works against the full keel. I'm not going to try and write a chapter on stability here. All this information is available in any number of books on yacht design including my own. But to say a full is boat is more stable because of it's full keel is just wrong.

Think of all that volume in the full keel. When the boat heels over that volume is now on the wrong side if the boat's CG and actually works to heel the boat over even more. That volume is now moved to weather and we want volume to move to leeward in order for that volume to increase our righting moment. So to be accurate you could say, all else being equal, that a full keel makes a boat less stable. Of course "all else" is never equal.

If we are talking about directional stability you could have an argument but I have sailed many fin keeled boats that had great directional stability plus excellant slow speed manouverability. Once again I warn you against generalizing here. We can always come up with exceptions.

If we are going to discuss things alike stability is is good to stay accurate. The components of a boat's stability profile are not a matter of opinion.

[malbert73]

Funny I should find this post, because I think my Luders 33 is the target of that last post!!

The Luders, beyond most boats of its ilk, is fast in the right conditions, such as moderate to windy conditions that don't require much tacking.
Of course, it also helps to have year of college and beyond dinghy and big boat racing experience!!!

A boat like the Luders, when tuned properly (I have spent lots of time fairing the bottom and tuning the rig) and balanced correctly, in the right conditions, can outsail its rating quite a bit.

We'll have to see what happens in the next drifter...

To actually respond to this thread, one big advantage of the long deep keel and attached rudder of the Luders is it never loses steerage upwind. Just last night we heeled over 45 degress many times in gusts and the wheel was only 1/3 turn over to keep from heading up. (Last year we actually dunked the coaming and half filled the cockpit, and still kept steerage.) Boats all around us, with fin keels and wider transoms, were rounding up uncontrollably all the time. We chartered a Beneteau 46 this winter in the BVI and it also rounded up repeatedly in 15 knots when heeled less. Obviously the solution is to reef the main, but the point remains about design advantages of a rudder that cannot cavitate.

[keelbolts]

Stability? I'll readily admit that I don't know the definition of stability as it applies to sailboat design. Having said that, in static terms, I'd imagine a 6' fin keel with two tons of lead on the bottom looks, on paper, just as stable as a 6' full keel.

Two things i do know.
1. Whoever said that a fin keeler is better to windward than a full keeler is mistaken. Windward ability is about resistance to lateral motion and few fin keelers have as much lateral plane, and thus resistance to lateral motion, as a full keeler. When I hear that statement, my brain does the same thing it does when I hear somebody say that the sun comes up in the west each day. I didn't know there was even any question about it. There's room to discuss downwind merits, but no question about upwind. One of the reasons why the majority of racers have fin keels is because they often race downwind. I'll even recognize that it's possible that, figuring an equal amount of up & down wind sailing in matching amounts and conditions, a fin keel is faster, but upwind a fin-keeled boat doesn't stand a chance against a full-keeled boat.

2. This one is much more subjective, but a full-keeled, wine-glass shaped hull is more comfortable in a seaway. I won't even try to say why, I just know how it feels. Try one. You'll see.

The above, and all of my previous posts in this thread, assumes a cutaway forefoot and a wine-glass shape. Also, I'm thinking cruising, not racing.

I know these things because I have sailed both and the full keeler wins on both counts.

[sneuman]

Originally Posted by malbert73

Funny I should find this post, because I think my Luders 33 is the target of that last post!!

The Luders, beyond most boats of its ilk, is fast in the right conditions, such as moderate to windy conditions that don't require much tacking.
Of course, it also helps to have year of college and beyond dinghy and big boat racing experience!!!

A boat like the Luders, when tuned properly (I have spent lots of time fairing the bottom and tuning the rig) and balanced correctly, in the right conditions, can outsail its rating quite a bit.

We'll have to see what happens in the next drifter...

To actually respond to this thread, one big advantage of the long deep keel and attached rudder of the Luders is it never loses steerage upwind. Just last night we heeled over 45 degress many times in gusts and the wheel was only 1/3 turn over to keep from heading up. (Last year we actually dunked the coaming and half filled the cockpit, and still kept steerage.) Boats all around us, with fin keels and wider transoms, were rounding up uncontrollably all the time. We chartered a Beneteau 46 this winter in the BVI and it also rounded up repeatedly in 15 knots when heeled less. Obviously the solution is to reef the main, but the point remains about design advantages of a rudder that cannot cavitate.

Good points all. And yes, sounds like you're guilty as charged!

[bob perry]

Boy oh boy this discussion has a lot of misinformation in it but I'll back off and leave you to your opinions.

Race boats have fin keels because they go down wind a lot? That is one of the silliest things I have heard in some time. Go ahead and believe it if you like but you could not be more wrong.

Ah the internet, the great equalizer.

[Dockhead]

Originally Posted by bob perry

Boy oh boy this discussion has a lot of misinformation in it but I'll back off and leave you to your opinions.

Race boats have fin keels because they go down wind a lot? That is one of the silliest things I have heard in some time. Go ahead and believe it if you like but you could not be more wrong.

Ah the internet, the great equalizer.

Well, we are all amateurs. You are a professional. Maybe you could explain it to us, and enlighten us? It would really help us all a lot to have it from the horses mouth.

[speedoo]

Originally Posted by keelbolts

Stability? I'll readily admit that I don't know the definition of stability as it applies to sailboat design. Having said that, in static terms, I'd imagine a 6' fin keel with two tons of lead on the bottom looks, on paper, just as stable as a 6' full keel.

Two things i do know.
1. Whoever said that a fin keeler is better to windward than a full keeler is mistaken. Windward ability is about resistance to lateral motion and few fin keelers have as much lateral plane, and thus resistance to lateral motion, as a full keeler. When I hear that statement, my brain does the same thing it does when I hear somebody say that the sun comes up in the west each day. I didn't know there was even any question about it. There's room to discuss downwind merits, but no question about upwind. One of the reasons why the majority of racers have fin keels is because they often race downwind. I'll even recognize that it's possible that, figuring an equal amount of up & down wind sailing in matching amounts and conditions, a fin keel is faster, but upwind a fin-keeled boat doesn't stand a chance against a full-keeled boat.

2. This one is much more subjective, but a full-keeled, wine-glass shaped hull is more comfortable in a seaway. I won't even try to say why, I just know how it feels. Try one. You'll see.

The above, and all of my previous posts in this thread, assumes a cutaway forefoot and a wine-glass shape. Also, I'm thinking cruising, not racing.

I know these things because I have sailed both and the full keeler wins on both counts.

You could not be more wrong about this. You've had a very accomplished yacht designer explain how it is that a deep fin keel allows a boat to perform better upwind, but evidently you still cling to the belief that full keels are superior upwind.

Your keep referring to your own sailing experience as your proof. I don't know whether you have actually done much racing, but I have and there is no doubt in my mind that in a properly prepared fin keel boat with a good crew, I can beat any similarly sized full keeler upwind.

[speedoo]

Originally Posted by Dockhead

Well, we are all amateurs. You are a professional. Maybe you could explain it to us, and enlighten us? It would really help us all a lot to have it from the horses mouth.

He already has, just read the thread.

[Dockhead]

By the way,

What kind of keel would you guys call the one depicted in the attachment?

[Amgine]

On the hard, I suspect.

[Dockhead]

Originally Posted by Amgine

On the hard, I suspect.

Duh. But how would you classify the keel?

[speedoo]

Originally Posted by Dockhead

By the way,

What kind of keel would you guys call the one depicted in the attachment?

I'd call it a "cruising fin". A "racing fin" would be deeper.

On edit. looks like there is either a bulb or wing at the bottom.