Thread: Paradox Micro Cruisers and "Bilge Runners"

Michael, I've done quite of bit of "visualation" about flow, including bench, tank and model observations.

Chines have both good and bad tendencies, but all seem to be geared around the S/L ratio. At low speeds, say under 1.4 S/L, chines and runners (which in my opinion are little more then chine extensions) create a fair amount of drag, enough to warrant rounding them substantially or removal if possible. At higher speeds, the eddy making resistance is mitigated to some degree by the lift they can generate, more effective lateral area (compared to round bilge of similar volume) and their effects on laminar flow around the underwater areas and appendages. It's the effect on laminar flow that is most beneficial at higher S/L's.

This is the very reason you're seeing chines appear on the big open ocean racers in the last few generations of development. A knuckle or crease can be clearly seen in the last third of the hull. This "sheering" chine is intended to permit a clean release of the laminar flow once speeds get over, say 1.5 S/L. Yes, there is some drag associated with them, but not enough to offset the benefit of increasing speed potential by releasing the flow cleanly on a crisp, well positioned chine.

This of course flies in the face of previous, well written designers that argue drag of any sort, is to be "smoothed" in design development. This is one reason the bulb fin took so long to gain acceptance. Nat Herreshoff proved the value of the bulb keel in the late 1800's, but it wasn't until a few "hair brained" designers re-introduced it in the 1960's that new defendants could take up the discussion.

Yes, the bulb isn't as "clean" as a straight fin, but the advantage of carrying considerably more rig area, at similar angles of heel, offsets the drag loses created by the bulb. The purest "flow technicians" have real problems accepting this, but testing has bore out the facts, in spite of their best argued efforts.

I suspect these chine appendages are similar in function. At low S/L they're a hindrance, but if you have enough power to push through the resistance, then they come to shine. I also believe they have a limited point of usefulness. I don't think Paradox will achieve the S/L's necessary to cause these chine appendages to reverse their usefulness, but I could see them as a problem on faster craft.

In the end, we once again have the classic (excuse me) paradox of something working well within a specific range and vessel type, but not on other types or above or below the targeted effective ranges.

Keep on stroking it AJ, you're a man after my own heart. I do a fair amount of experimenting too. You're failure rate will be higher then your success rate, but this is the cost of finding something that really works well. Once you do find a success, the failures suddenly seem like stepping stones on the rock lined path toward success, rather then the boulders you encountered along the way.

Good observations here PAR,

Originally Posted by PAR

In the end, we once again have the classic (excuse me) paradox of something working well within a specific range and vessel type, but not on other types or above or below the targeted effective ranges.

Keep on stroking it AJ, you're a man after my own heart. I do a fair amount of experimenting too. You're failure rate will be higher then your success rate, but this is the cost of finding something that really works well. Once you do find a success, the failures suddenly seem like stepping stones on the rock lined path toward success, rather then the boulders you encountered along the way.

Hear, Hear!!!

MIK

I suppose the next test is to try deeper immersion.
4 or so heavy bodies should increase draft to about 6" or so, albeit ever so
slightly illegal, & leading to arguments about whose turn it is to drive.

So.... who is for a dunking at the next SA division meet ?
And when can we do it ?
I'm good for the weekend of 22-23 Nov or Sun 30th.

cheers
AJ

Cases of beer, preferably on ice, make wonderful ballast. From this I can personally attest, though my boat's ballast/displacement ratio seems to change substantially after a long day's sail. The trials, burden and difficulties of experimentation . . .

And Paul, Some of the methods of moving such ballast to the windward side have advantages and disadvantages.

MIK

Originally Posted by PAR

Cases of beer, preferably on ice, make wonderful ballast. From this I can personally attest, though my boat's ballast/displacement ratio seems to change substantially after a long day's sail. The trials, burden and difficulties of experimentation . . .

Not sure I'd be willing to risk something as valuable as beer as ballast during
testing. It might fall out & sink in event of capsize.
Or worse, fail to fall out & sink whilst still in the boat.
Same caveat applies to sandbags.

I figure live ballast would have the good sense to exit at an appropriate time,
& probably not require the services of a diver to recover.

This is why the conscientious experimenter keeps their ballast in a well insulated floating cooler. No need to jeopardize the lives of the ballast, in haphazard or ill planned endeavors, it's just not right. If the cooler has a lanyard, it could save an unexpecting crew from drowning, possible acting as additional floatation in the event of a swamping or capsize. In general the usually bright colors of these coolers, could be seen by the rescue ship sent to pull your soggy butt out of the drink, if all goes down hill.

You shouldn't discount the true value of well chilled beer in a brightly painted cooler. I'd rather float to shore, clinging to one of these then any PFD I've ever seen. Besides, if you have to drown, proving a new, hair brained boat idea, wouldn't you rather be good and drunk when the end actually comes?

I finally found a decent drawing of another boat that uses its rudder for basically all lateral resistance. As I mentioned before I am pretty sure that Paradox goes quite a long way down this road.

I actually got a go in one of these a couple of years ago and they go quite well to windward - tricky to tack though, you usually have to push the boom out and back the main to bring the head round. Felt really quick on a reach, considering it is basically a marine pick-up truck (or 'Ute' here I suppose!).

Chris

Originally Posted by PAR

Besides, if you have to drown, proving a new, hair brained boat idea, wouldn't you rather be good and drunk when the end actually comes?

I intend to be conspicuous by my absence from my demise.
Or at least, that's Plan A.
Still working on Plan B.

As for the coolers, I estimate that I only have stowage room for about 120KG of home-brew bottles.
And only about 40kg of cooler stowage.
I am reluctant to place the other 80kg at such dire risk.
In any event, 120kg is far short of the 300-400kg I calculate needed to drop Teal to a reasonable depth to test the winglets properly.
I also doubt I could trust the other 200kg or so with the 120kg.



AJ

Hey Clarkey,

I know what you mean of finding pics that reflect this feature.

Whenever the sail area is well back in the boat you can have some inkling that the rudder is carrying a lot of the lateral load. (In a land with WAAAAY too many palm trees)



Or a more modern variation - they found it was faster to lean the rig back ... the boom was designed to be horizontal ...


Interesting what you say about the boat in your image that you found hard to tack. It is exactly my experience of the Bolger Cartopper.

I can sail anything, backwards, forwards, sideways ... but I found it tricky to tack because is uses the same trick to make the centreboard small and move it well forward carrying most of the load on the big rudder.



It is an interesting idea, but seems to work better with heavier boats. That cockpit of the Cartopper is real nice though.

Michael

Actually, looking at where the CLP would be, including the rudder, it shows there's not much lead or possibly reversed lead (that Gozzo or whatever it is in the sail plan above), so I'd imagine it would be a bear in stays without something to pivot on.

I had the fortune to sail a tandem board cruiser some years ago. The boat above looks as if it could benefit from some sort of small "trimming" board, so it could tack. By adjusting the tandem boards, you could remove the rudder and sail along merrily without it. I remember playing with the boards, literally reducing the pressure on the helm to nothing and steering with the sails and board trim. This was a 40' cruiser so crew placement to steer wasn't an option.

I've sailed the Cartopper too and had to fall off a fair way to gain momentum to tack, then be confident about helm position so as to not kill drive through the eye. I found it an easy boat to "over sail" and never liked it much. I've repeatedly discovered that a boat that tacks, well is one that carries a healthy lead. I think you have to encourage a boat's natural tendency to round in plans development, if you want crisp maneuvering ability.

Centreboards or leeboards are almost completely unused in the upper adriatic except in very small boats. Everything from 6m to 25m in length sails just on the rudder.

Most of the boats use a what is effectively a 'forwards mizzen' (see pic) or a low aspect ratio jib to throw the head round (other pic). I should credit the pics to the Circolo Velico Casanova who have an epic flickr photostream here:

http://www.flickr.com/photos/17001721@N08/page8/

(organised into easier sections here - http://www.flickr.com/photos/17001721@N08/sets/)

Sailing the boats is strange, I expect the Cartopper is similar. The weather helm is quite meaty but never becomes really excessive, even on a reach. When you go to tack the boat flies up into the wind so fast you just can't believe that it won't go all the way round - then it stops dead in irons until you back the main (mainsail only) or the jib/mizzenesque thing. Absolutely impeccable manners when you are gybing though.

You can see that they set their lugsails very nicely and their hull forms are pretty sweet too.

Chris

This picture of Matt's Enigma shows just how far back the rig is carried, the very big rudder obviously providing a lot of the resistance to leeway.


Brian

Another, larger Enigma hits the water. http://e460.blogspot.com/


Interesting quote from Matt Laydon building the original Enigma
http://physics.bgsu.edu/~layden/FunS...2005-05-22.htm

2005 May 22
"Here are a few photos of some of the less exciting details that always need to be taken care of along the way. A note to the uninitiated: The chine runners, or winglets, are small horizontally protruding fins at the chines amidship, that help the hull function as a 'lifting body' to resist leeway. A centerboard or other retractible vertical fin would do the job better, but I have a mental allergy to moving parts and complication. The runners are easy to build and they protect the hull rather than weakening it as a board does. They take up no space in the interior, always an issue in a small cruiser."

cheers
AJ