Single-person keelboat stability

[Hernandiz]

Hi,
I'm spending some time on a 18' single-person keelboat design.
considering that the skipper don't move transversally the righting moment shall be greater...
Based on Skene's Elements of yacht design I assume that the WPC might be around 1.5 or a Dallenbaugh angle of aprox. 10deg.

does it look right?
29210

[alan white]

No pivoting keel? A design like that almost demands some mechanism to keep the boat upright. If there's a wide stern to encourage planing, without crew weight to windward, she'll sail on her ear and develop a bad weather helm due to an assymetrical waterplane.
I think this kind of concept works well with a displacement speed-limited boat with canoe-like waterlines which remain balanced as the boat heels---- which it will without a pivoting keel, which is okay if it is designed to do so.
It will also work well as a planing boat using a hinged keel and a reasonably wide stern.

[PAR]

On boats that size and shape, you have to expect the crew to provide some "live" ballast, or make the initial stability very high to stand against her area aloft. Considering how light your design appears to be (18', very fine entry, firm yet modest width bilges, shallow hull, etc.), you'll have little choice but to move the crew or ballast the appendage(s). You could divide the rig up into smaller, lower aspect pieces, but then some elements of your performance envelope will suffer.

[Hernandiz]

I will reshape the hull to be wider ( about 6') but preliminary stability looking really bad! I think I will have to use a pivoting keel.
My first idea was a simple affordable ant exiting boat but do those 3 words can fit?

[alan white]

One further option, and one that isn't so expensive to do, is a water ballast that shifts between two tanks located at the greatest beam (and that area could be extended somewhat like a sponson)-----it's perfect for foot pump operation (bicycle crank chain-geared to diaqphragm pump, etc.)
100 kg wouldn't take too long to shift (and an electric pump isn't out of the question). That would be enough to tame the beast.

[Hernandiz]

That might be a good idea...
for the moment (if I'm right) the WPC=1.46 with a 6ft wide hull and pivoting keel.
Not a good as I expect but on the right way.
I don't think a water ballast could be as much efficient but look interesting.
29237

[alan white]

The movable water ballast is effective with a centerboard, which can be raised. This would substantially increase speed when running, where the deep bulb becomes a parasitic appendage. In such a case, the water can be discharged to lighten the boat allowing easy planing.
Trailering would become possible, something you might enjoy in a practical design.
I don't know if the engineering and construction, and day to day costs of a pivoting keel would be worth it. It depends on how much money you've got to play around with.
The concept of an airplane-like cockpit is interesting though, where one has all controls led to one place. Blondie Hasler's Jester, though larger, was set up that way. Lighter boats have to shift ballast somehow.

[Doug Lord]

Hernandiz, you might find this boat interesting-from a thread under "Sailboats":
http://www.boatdesign.net/forums/sailboats/18-canting-keel-single-doublehander-17349.html

[PAR]

Doug, that would be a fair representation of a performance dayboat of the general size desired, except for the hiking requirement.

A canting keel will likely also require twin daggers, or some other form of lateral area to offer some resistance to leeward skid.

[Doug Lord]

I came up with the idea to use a retactable foil within the bulb of a canting keel in order to get rid of the requirement of daggerboards or twin foils(CBTF).
Here are two renderings of the K FOIL:

[Paul B]

On boats that size and shape, you have to expect the crew to provide some "live" ballast, or make the initial stability very high to stand against her area aloft. Considering how light your design appears to be (18', very fine entry, firm yet modest width bilges, shallow hull, etc.), you'll have little choice but to move the crew or ballast the appendage(s). You could divide the rig up into smaller, lower aspect pieces, but then some elements of your performance envelope will suffer.


Don't listen to these "old style" thinkers who want every boat to be a wineglass hull with a yawl rig.

The SKUD 18 is similar to what you are proposing, only it is a 2 person boat. It is used for paralympic sailing (folks with paralysis, amputations, etc) and the sailors sit on centerline. It is a skiff shape, yet somehow does not exhibit the problems the "old school thinkers" always attribute to boats that are not of the 1950s style written about in books from the 1960s.

[Paul B]

I came up with the idea to use a retactable foil within the bulb of a canting keel in order to get rid of the requirement of daggerboards or twin foils(CBTF).
Here are two renderings of the K FOIL:

Of course this guy isn't telling you that for his foils to be big enough, the bulb that they would "retract into" would have to be so oversized and draggy that it would be a joke. Ask him to see a technical drawing and see where that gets you.

[Doug Lord]

You can view the patent here: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=2&f=G&l=50&d=PTXT&S1=(foil+AND+lord.INNM.)&OS=foil+and+in/lord&RS=(foil+AND+IN/lord)
----------------
And if there is any serious interest ,Eric Sponberg has done some technical drawings for the application of the K Foil to a "mini".

[Hernandiz]

Hi Paul,
The skud is a quite good example of what I'm looking for. did you tried one? Or have some extended spec. I would like to compare with my design.

[Paul B]

Hi Paul,
The skud is a quite good example of what I'm looking for. did you tried one? Or have some extended spec. I would like to compare with my design.


You can see the class website:

http://www.skud.org/?Page=18384


No, I have not sailed one. I have seen them up close. The design was by Julian Bethwaite, same person who penned the Olympic Class 49er.

Safe and easy enough for handicapped (handicapable?) people to compete in.

Therefore claims by people who only know what they read in 40 year old books about 60 year old designs should be ignored. I don't drive a 60 year-old car and claim it is better performing and safer than current design, why would I believe it when someone makes the same claim about sail boat design?

[PAR]

It’s quite amazing how a person with as many previous posts as yourself, can only muster innuendo, assumption and insult, particularly in regard to people you don’t know and who’s skill sets you are clearly in poor regard of. Arbitrary speculation, laced with barbs are the products of a small, narrow focus mind and it would seem your “reputation points” reflect what most have already derived from your previous input here on this board. Why should anyone consider your opinions, especially in respect to the lack of it you’ve shown others, which is likely just a latent expression of yourself?

In this particular instance you’ve offered a good prospect for the original poster’s question. Of course you couldn’t resist an obviously feeble attempt to “up” yourself by belittling others and off you went on several occasions. Possibly another tactic could be suggested more effective Paul, such as a defined discussion and debate. Then naturally you’d have to accept the realities of your personality traits and make adjustments, or face the prospect of having even less reputation then those that have just joined the forum, of which you are quite close to now, congratulations.

[Paul B]

Arbitrary speculation, laced with barbs are the products of a small, narrow focus mind

Cite, please.


and it would seem your “reputation points” reflect .

Reputation point? Seriously? I had no idea such a thing existed, and the instrument to measure how little I care has yet to be invented.


Of course you couldn’t resist an obviously feeble attempt to “up” yourself by belittling others .. personality traits and make adjustments, or face the prospect of having even less reputation then those that have just joined the forum, of which you are quite close to now, congratulations.

Your reply makes it seem maybe something wasn't so feeble? I have no need to "up" myself, but simply illuminate this instance of the dullard roar against reality.

Maybe you feel you need some points here to feel good about yourself. Yes, show everyone your expertise. Maybe you should spend some time with some other rum sodden crunchies and collectively spew bile at the "terrible modern boats" and the "blue blazers crowd at those damn yacht clubs". You can appease yourselves by saying all manner of salty things like "jib and jigger". After that I'm sure you will feel righty-right.

[alan white]

"You could divide the rig up into smaller, lower aspect pieces, but then some elements of your performance envelope will suffer."

Seems PAR did correctly analyze the limitations placed on your handicap exanple. Its mast is 23.5 ft with a boat length of 19 ft, overwide beam of 7.5 ft. Sounds like a classic low aspect rig to me. And PAR pointed out that performance would suffer due to the necessity of spreading sail area out down low.
No matter what you do, if the crew is to remain in the middle, either some aspect of performance must suffer, or some sort of movable ballast will be required.
Not old fashioned thinking, just physics at work.

[PAR]

Bait is an easy thing to lay, but only fools and rats stick their head under the bar for a nibble. You've admirably proven my assessments of you. Again, congratulations are in order, you passed with flying colors.

Since you were so willing, lets see what you really are, as I know my abilities and reputation. I know how many of my designs are being built world wide and how many have been crafted under my hand. There are even forum members here, building my designs. So, how many designs have you penned for a client? How about the number of boats that bear your builder's plate or better yet your USCG prefix?

I don't usually get into pissing contests, but sometimes assholes should be wiped after a big stink comes through.

[Hernandiz]

Well...

My first worries was the applicability of the Wind pressure coefficient and the Dellenbaugh angle.
I'm sure that the canting keel is needed to reach the 1.5 WPC and I get close to it but the skud 18 doesn't have such complex keel.
I will try to use some sketch from the skud class site to approximate the righting moment.

That would be interesting to compare the 2 similar design
disp= 838 vs 890
sail area= 163 vs 166
beam= 7.5 vs 6
draft= 5.6 vs 6.6

[Hernandiz]

Results are surprising...
with some sketch from the skud 18 class rule and some pics I made a model of the hull. The weights are from the designer site, class rule and wiki. I think it's accurate enough to make a comparison...

here are the surprise...

assuming a 210 pound skipper sit at the centreline.
The Wind pressure coefficient is between 0.65 and 0.7. That's far away from my theory of 1.5 and realy close to the Kinney's diagram.

I also note that my hull is inappropriate, I will reshape again.

here is my approximated skud hull
29289

If someone know about the skud. Did the hull look accurate? is that boat tender or stiff?

[Paul B]

Bait is an easy thing to lay, but only fools and rats stick their head under the bar for a nibble.

You said it, I didn't.


Since you were so willing, lets see what you really are, as I know my abilities and reputation. I know how many of my designs are being built world wide and how many have been crafted under my hand. There are even forum members here, building my designs. So, how many designs have you penned for a client? How about the number of boats that bear your builder's plate or better yet your USCG prefix?

Sorry not to recognize your stature in the industry. My faux pas I suppose.

If it makes you feel better thinking you have had more success than someone else on a bulletin board, well you go girl.


The one thing I do know is more Macgregor 26s have been built than boats my pencil has been involved with. Does that make me envious of that design?

[Paul B]

"You could divide the rig up into smaller, lower aspect pieces, but then some elements of your performance envelope will suffer."

Seems PAR did correctly analyze the limitations placed on your handicap exanple. Its mast is 23.5 ft with a boat length of 19 ft,

Seeing as how you know what you pal said, you are bing disingenuous with your comment. No surprise you are of the same mindest as PAR. I will admit you do post far more disinformation on this board than he does. Congratulations.

As to your idea to compare the length of the boat with the rig height, maybe you should check out a high performance dinghy like the 505, and then comment again.

[alan white]

It's true I post a lot of disinformation. I never claimed to be telling the whole truth. It's not my desire to be empirically accurate because I know that there is no one true explanation.
What do you think, Paul?

[PAR]

So Paul, how many clients have had you draw up yachts for them? What's your experience or I guess what I'm asking is there a rationale behind your attitude, besides reading way too many magazines.

[Paul B]

So Paul, how many clients have had you draw up yachts for them? What's your experience or I guess what I'm asking is there a rationale behind your attitude, besides reading way too many magazines.


After hearing of your fantastic relevance to the art, how could someone such as I ever compete?

Now does that make you feel better?


Hopefully you'll happily go back to drawing the cartoons of your gingerbread boats. No doubt you'll find a few customers who find them attractive. As I mentioned in another thread, there are plenty of wingnut "designers" out there who match perfectly with the wingnut dreamers.

Capt. Nat and L. Francis are looking down at you and having a good laugh.

[PAR]

In other words, you are an arm chair boater, never built anything, never designed anything, education included most of high school and most likely never proud of you work, at least not enough to warrant patting yourself on the back.

You'll sole joy in life is degradation and belittling those that have attempted to attain their goals. 600 plus contributions to this forum and the best you can muster is the rank of a antagonist. Good luck in your future endeavors, attempting to tear successful people down to your level. I can think of little more fruitless an enterprise

[Paul B]

In other words, you are an arm chair boater, never built anything, never designed anything, education included most of high school and most likely never proud of you work, at least not enough to warrant patting yourself on the back.

You'll sole joy in life is degradation and belittling those that have attempted to attain their goals. 600 plus contributions to this forum and the best you can muster is the rank of a antagonist. Good luck in your future endeavors, attempting to tear successful people down to your level. I can think of little more fruitless an enterprise

Ho ho, looks like someone has a little captain in 'em tonight.

Funny, this armchair boater might have been dominating on the racecourse this weekend, while someone else was sitting at a keyboard. Projecting much there, rummy?

I have no doubt you've already wasted time looking into "me". So your schoolboy name calling looks even more pathetic.

Aside from the fact that we both know which of us has had more success in sailing design, I have to tell you it is more lucrative to design items in other fields.

Just FYI, successful people don't need to pat themselves on the back. Speaking for myself, I have no need to try and impress someone like you. I will say for you to get to my level it wouldn't be tearing down, you'd need a couple of crates to stand on.

It must be horrible to go through life knowing you don't have the chops. Hey, maybe if you can get a high enough rating on a bulletin board you'll look in the mirror and not see a failure.