Fin Keel vs. Full Keel

[Dockhead]

Originally Posted by bob perry

Thanks Dick.

It's about 8pm, nice evening, mid summer, you have been on the hook for three or more hours. A fellow sails into the harbor in a converted lifeboat. You know it took him all day to get up the Sound. He anchors. He putters. He rows his dog ashore. Maybe he is the winner.

Certainly any way to get out on the water is a good way. And that way which is cheaper and less trouble leaves more time, energy and money for staying out on the water. So the constant striving for the perfect sailboat, the perfect rig, the perfect sail trim, can defeat the whole purpose, which I guess is a corollary to the moral of your story.

But I'm betting, Bob, that you wouldn't strive to be the designer of a boat which works like that converted lifeboat. You do have design values, of course. So what works best -- sails better upwind, more comfortable motion, faster, safer, etc. -- is not an entirely stupid question.

[Dick Pluta]

At the risk of re-igniting this whole thing, the point is that there is NO perfect sailboat. What is perfect for you may be an abomination to me. I had a discussion with a broker in St. Augustine a few years back. She told me about her husband racing with Ted Turner across the Bahamas Bank at night in a Maxi with 14 feet of draft. In my wildest mad nightmares I would never dream of doing that. For Ted Turner, it was the perfect boat. I think he was nuts. He would laugh at me in my barge.

I won't speak for Bob Perry, but someone designed a lot of those fat, slow Spray replicas and someone else built them and someone else sailed them. For them, the perfect boat. That's the point. True, there are no stupid questions but when we argue "What's better? Fin keel or full keel?" the right answer is "For what?".

Dick Pluta
AEGEA

[ctl411]

[quote=Dick Pluta;284560]"What's better? Fin keel or full keel?" the right answer is "For what?".

Well said.

[speedoo]

Congratulations, Ray. I'm sure you will be happy with your new boat.

[bob perry]

I am very comfortable with my definition of the "perfect boat" for my own cruising needs. I really like good performance as measured by current standards. I also think I can design a boat that would be an excellant cruising boat for you but your ideas and mine would be different. I'd carefully explain why I thought my ideas were better for you. But in the end the client usually wins the agrgument. Not all the time but most of the time. Then I do my very best to make sure the client's ideas work and result ina great boat. I try not to blur the distinction between objective and subjective elements of design. I try to optimize both elements.

[Hiracer]

Originally Posted by bob perry

After buying the boat, a Peter Norlin design, I say down one day and ran the numbers on the boat.

The "After buying the boat" is the most incredulous part of your story, Bob. Really. Of all people, I never would have guessed. That IS funny.

I once put an offer on a boat, after having run the numbers, only to pull the offer after I learned that SA/D ratios for cutters are computed without the staysail. Ketches have the mizzen included, but cutters don't have the staysail included. Well, what did I know? Gotta learn somehow.

With the numbers properly computed, this boat had a SA/D of about 13. Thus I pulled the offer. I'm sure all parties, seller and both brokers, thought I was a wack job. But I know what I wanted and SA/D 13 wasn't it.

The difference, of course, is that you had been sailing the boat and liked it, and your Norlin boat probably has a SA/D of 15 to make a WAG. I, OTOH, pulled my offer without ever sailing the boat. And 13 is not 15.

I have now a boat that does not have a SA/D of 13, nor is she stiff, and I'm learning reefing. Yes, it's a PITA, but then that's where my obsession with mythical seakindliness plugs in . . but that's another contentious thread. Plus, I'm learning to love granny bars.

Someday after I win the lottery I'm going to commission you to design my perfect boat and we'll have lots of wonderful gentlemen arguments about how to do it. But we'll also have many points in agreement.

[bob perry]

Hi:
actually it was around 15.5. if I remember correctly.

Keep buying those lottery tickets.

When computing SA/D it is best to use 100% of the foretriangle. You can do it any way you like but stay consistant. I have always used 100% fore triangle so I'll stick with that. I have used that formula for years and just doing my monthly SAILING reviews I have computed over 1,536 SA/D's. That does not include my own design work and research.
I am comfy with my way of doing it.

I just might be the SA/D computer world record holder.

[Hiracer]

Originally Posted by bob perry

When computing SA/D it is best to use 100% of the foretriangle.

Yep, that's the only way that's ever made any sense to me, and it's easy to measure. I just didn't know about the mizzen/staysail difference.

BTY, when I was shopping for boats, EVERY single boat I looked at had major dimensional differences with the broker provided info. Either the boat was longer or shorter than advertised, beam different, or draft different, or some combination thereof.

I was looking at steel boats, many one-offs. Learned real quick not to believe anything and to verify everything.

I suppose with productions boats it's not so bad, except perhaps with displacement, which I think is a universal issue. Even just how to define displacement is an issue, much less getting an accurate measurement.

Which in turn makes lots of SA/D numbers very suspect. I think there's a bit of a black art to all this.

[bob perry]

Hi:
Yes, displ is always questionable but I just use what they publish and assume they are all heavier than what they print. There is just no way to consistantly compensate for overly optimistic displ numbers.

Sometimes I get builder feedback from my reviews. Often I get "Where did you get that number?" I tell them "I got it from your brochure or printed material."

[keelbolts]

I believe I owe many of you an apology. After batting around the question of a form's creating lift v. being lifted with my son, I have been persuaded that the process is the same. While I maintain that there is a difference ,one produces the differing pressures and the other doesn't, in the end, both are "lifted" by an imbalance in pressures on the surfaces. With that in mind, I was right in at least one of my statements. My front door would produce lift if I screwed it to the bottom of my boat.


Didn't Peter Norlin design the Scampi?

[bob perry]

Keel:
Please screw your front door to your keel and report back to us.
I love experiments and,,,,it's your front door.
I do think you are playing a little loose and free with the concepts here in order to cover your own ass. For many of us keels and foils and how they work are not new knowledge. But it's your life and you can be silly if that suits your overall purpose.

You were kind of right and it may come down to semantics or terminology. Maybe.
But today I go to town. That means a shower, a shave, clean shirt and a fresh attitude. I will leave you to your internal debate.

Yes, my boat was designed by Peter Norlin the designer of the breakthrough half tonner called the Scampi. Norlin is a very good designer. I know.

[keelbolts]

I've known how a wing works for many, many years. The only thing that's new to me is the idea that something being blown up or over can be thought of as "creating lift". In that differences in pressure cause both to lift I have to agree with those who say a flat plate and a wing work similarly, but I maintain that creating lift and being lifted are different. As long as we are willing to say that a keel that is forced to windward creates lift as it falls off, absolutely anything that is blown up or over can be said to create lift, thus my joke about the door. Besides, a door on the bottom would just be a fin keel & everybody out there with a modified full keel would be able to beat me to windward.

[bob perry]

Boy: you have a lot to learn. But you seem to celebrate your own lack of understanding so go with that. See where it gets you.
"Luddite" ( your word) yes, you seem to fit the bill.
Have fun.

[daedaluscan]

Oh the internet. the great equalizer. I can spout off and have Bob Perry actually reply to my drivel. You are very gracious, sir, to give us the time. Thankyou.

[keelbolts]

Oh, now that was uncalled for. Creating lift or lifted, if you believe a fin keel will beat a modified full keel to windward, we both have a lot to learn.