Suggestions for my almost finished Mini

[JagerL]

Hey Folks,

Thank you to all of you that responded to my question about heeled waterlines. It helped a lot.

I have attached pictures of the nearly completed Mini. I would really like to hear coments and suggestions on the design. The Renderer made the hull look a little bit angular in iges format, almost chined at first, but the hull is very fair in DXF and Maxsurf format. Other than that, any criticisms are greatly welcomed.

[Phil Locker]

Are the rudders transom hung? If yes, then you'll have a mechanical strength issue as the transition to the head occurs quite a bit aft of the max thickness of the foil section. (They'd also appear to be over balanced). I understand wanting to bring them forward under the transom to reduce ventilation, but as drawn, you may have gone too far.

Cheers
Phil

[Doug Lord]

Nice Looking! Don't see any extra area to make up for that lost when the keel cants; are you going to use a daggerboard(s),wings? or?

[Paul B]

Nice Looking! Don't see any extra area to make up for that lost when the keel cants; are you going to use a daggerboard(s),wings? or?


Careful there JL.

Just like blood in the water, eh? Lord must again be thinking, "Here's a possible victim to pay for developing my pie-in-the-sky ***** (TM) keel."

So far no real details from this "designer" about his "breakthrough", other than the amateurish rendering shown on this site (probably done by someone else, right?).

[Doug Lord]

Paul B, you must glory in your limitations! You parade them so often you must be proud of them.
It's unfortunate that you don't seem to realize that a canting keel boat-generally- needs some form of extra lateral resistance-as I'm sure the designer of this mini recognizes-the question is what will it be? The choices available seem to be beyond your level of competence so it would be interesting to hear what a "real" designer has to say on the subject rather than an anonymous internet blowhard such as yourself...

[JagerL]

Phil,

The rudders are simply demonstrative as is the keel to some extent. I need to do some in depth CFD and some asking around in greater depth. The way I have developed the stern of the boat with an approximately 10cm scoop, I think I will need some sort of extension bracket to position the foil so it can be semi balanced and provide some resistance to ventilation. The appearance of the rudder head in this case is simply a product of the rudder being "absorbed" in to the hull when I positioned it. I will most probably outsorce the foil design as I know little in that subject. Have you ever built assymetric rudders for a case such as this?

Doug,

Thanks for the kind words. I will most probably use assymetric daggerboards. I am trying to incorporate the trunks into a delta bulkhead that links the hull and deck and provides much of the stiffness of the structure. I feel that this layout is most efficent and lightest. Again, don't know much about foil design, but I am reading up on everything NACA at this point.

Paul,

If I read your post correctly, I think you have attempted to insult my design and its designer. I have made no claim to being a breakthrough. Instead, I have looked at some of the conditions that Mini boats seem to do poorly in. I have addressed the symmetry of the waterlines under heel, as well as reduced the wetted surface area under heel in order to maximize the upwind potential of this type of design. Since the Mini Transat has recently included many more upwind light air miles, the designs are shifting to a boat that is more versitile.

As far as the amateur comment, you are spot on. I am 20 years old and am self taugh in the field of race boat design. I have taught myself Maxsurf, Rhino, and Auto CAD. I developed the design, as well as the rendering myself from the ground up. I am an undergraduate student at the University of California and an acitve dinghy and keelboat sailor as well as Captain of the best student run Sailing Team in the country. I have also started a custom High end Kiteboad fabrication company. I take what I do very seriously and try to do my best at it. Therefore I take pride in my design and offense in your comment, however amateur it appears. I spent a lot of time and effort into producing it and I am pround of it. While my design may not be the greatest development in modern sailing, I enjoyed making it and look forward to building.

Sorry for the rant.

Keep the suggestions coming!

[Paul B]

Paul,

If I read your post correctly, I think you have attempted to insult my design and its designer.

Sorry JL, you did not read my post correctly. I was not referring to you as a designer or your design. I apologize for the misunderstanding. I was trying to warn you that you were about to be targeted by Lord to use his unproven *****(TM) keel design (see it at http://www.boatdesign.net/forums/showthread.php?p=24420#post24420). He is the designer and his is the amateurish design I was referencing. Lord attempts to hijack every thread that he thinks might bring him a patron to fund and develop his imaginary "system".


As far as the amateur comment, you are spot on. I am 20 years old and am self taugh in the field of race boat design. I have taught myself Maxsurf, Rhino, and Auto CAD. I developed the design, as well as the rendering myself from the ground up. I am an undergraduate student at the University of California and an acitve dinghy and keelboat sailor as well as Captain of the best student run Sailing Team in the country. I have also started a custom High end Kiteboad fabrication company. I take what I do very seriously and try to do my best at it. Therefore I take pride in my design and offense in your comment, however amateur it appears. I spent a lot of time and effort into producing it and I am pround of it. While my design may not be the greatest development in modern sailing, I enjoyed making it and look forward to building.


Again, I was not making any statement about your design or your abilities. In fact I think it is commendable that you have produced something like this at your age. I was also an undergrad at a UC school, and a similar project done for an independent study credit got me in the door at a design office after graduation.

One thing I did notice in the rendering was the longitudinal crease. Did you loft one side only, then mirror? I know that can produce this kind of crease. It is better to loft the entire section to eliminate this.

[Doug Lord]

Jager L, yeah Paul was attempting to insult me not you but I must admit it's hard to tell with him. He is well known on this forum for a simplistic approach and a tendencey to level personal attacks when he is unable to understand something.
I think you've done a great job! Seems to me that on a Mini twin asy boards may be a bit much work plus there may be consideration of the room they take up?. I know some Mini guys are using gybing daggerboards and at least one design may use retactable wings-not proven yet but full of potential. Also, Andy Dovell in Sydney has used fixed foils on the bulb(like ACC wings) as a lateral resistance solution and PROVEN that they work upwind and down....
I noticed that Simon Rogers has done a canting keel installation that allows the keel to slide fore and aft as well as side to side.
I would suggest that you consider contacting Eric Sponberg on the matter of foils and dynamic pitch stability-he's a Naval Architect and Professional Engineer and would be able to consult with you I'm sure. ( www.sponbergyachtdesign.com)
At any rate good luck-you're on the right track! Merry Christmass and Happy Holidays!

[Phil Locker]

Have you ever built assymetric rudders for a case such as this?

I haven't had much experience with Mini's. One set of rudders for a project out in BC (French designer) were a pretty basic fixed transom-hung design. Another set of drawings I've looked at and quoted on recently (another French designer) were for a kickup design, but again quite basic. Both designs have the same spec for each rudder... perfectly symmetrical.

Have fun with the project, and don't take the bickering here to heart.

Phil

[JagerL]

I think you've done a great job! Seems to me that on a Mini twin asy boards may be a bit much work plus there may be consideration of the room they take up?. I know some Mini guys are using gybing daggerboards and at least one design may use retactable wings-not proven yet but full of potential. Also, Andy Dovell in Sydney has used fixed foils on the bulb(like ACC wings) as a lateral resistance solution and PROVEN that they work upwind and down....
I noticed that Simon Rogers has done a canting keel installation that allows the keel to slide fore and aft as well as side to side.
I would suggest that you consider contacting Eric Sponberg on the matter of foils and dynamic pitch stability-he's a Naval Architect and Professional Engineer and would be able to consult with you I'm sure. ( www.sponbergyachtdesign.com)
At any rate good luck-you're on the right track! Merry Christmass and Happy Holidays!


I believe wings on the bulb would not pass the draft requirement. When the boat is fully canted on a 2m keel with wings out, the wings would stick below the rule. Also, the center of effort is usually quite a bit farther forward than the LCB, so the wings wouldn't be far enough forward. The gybing foil can't be asymetric, so it requires a larger area than an asymetric foil. I still like the idea of using the daggerboard trunks as a link from hull to deck in terns of torsional and transverse rigidity.


I would like to try assy. rudders to generate more net lift/drag, but I need to do some more research.

I am also playing with the idea of making the keel able to rotate up to about 7 degrees. Also, thinking about making the trailing edge of the foil and ultra flexible material that deforms to pressure differences on the foil. My hypothesis is this: the goal is to eliminate all lift and basically behave more as a flat plate boundary layer case than an attacked foil case. Lift, especiall generated when the boat pitches for a keel canted at extreme angles on an extremely wide boat is inhibitive and thus quantitatively more a drag force than a lift force. I am trying to work with some professors in the hydraulics laboritory to test this theory. This would completely separate the tasks of keelstrut and daggerboard.

[JagerL]

One thing I did notice in the rendering was the longitudinal crease. Did you loft one side only, then mirror? I know that can produce this kind of crease. It is better to loft the entire section to eliminate this.

The deck was lofted as a single section, but was changed at the last minute to accomodate the deck canber rule for the Mini class. I would most probably fix the crease (probably just a small radiusing) in the mole stage or quickly right now. Part of the problem with being new to the Tools of the trade so to speak, is that making apparently small changes like that seem to take forever since i know of no way of importing just the deck and not messing up all the trimming that was done later in the rendering program and not in the hull design program.

[Doug Lord]

JL, I'm not sure this is applicable to the wide mini hull form but I thought I'd mention it anyway. Many canting keel boats are designed with the extra lateral resistance forward of the canting keel-I'd say most are. But if you look at what happens as the wind picks up and the keel cants(assuming a non rotating keel) the CLR shifts forward but the CE in those same conditions may tend to shift aft.The fwd CLR shift is also augmented by the hull shape as the boat heels.
There are two boats that I know of that buck the trend by placing the daggerboard AFT of the canting keel so that the forward shift of the CLR is reduced as the keel cants. One boat is pictured in the new(Jan.) Sail mag on page 100 (a 60' cruising boat)and the other is Full Pelt ,a boat that is ,in essence, a 38' 49'er. ------------------------------------
Have you given any thought to the notorius pitch instability of the mini's? Any idea's for solutions?

[yago]

The appearance of the rudder head in this case is simply a product of the rudder being "absorbed" in to the hull when I positioned it.

If you really think about racing it, I would most certainly see that your rudders are transom hung/kickup etc.
Being able to carry a spare and change at sea has already made the difference betweeen abandon and carry-on for several participants in the current vendee globe (http://www.vendeeglobe.org/). Looks like every race there is more floating junk out there knocking off rudders keels and dagerboards.

Minis are a lovely subject, because even an excercise like this can be built and raced, budgets are relatively low and starting from scratch you have a fighting chance to find a local sponsor in your hometown... when I was building boats in La Rochelle / France, some 20 years ago, there were lots of mini-projects under way all the time, lots of fun and talent and great dream and many of them came true. Minis are a fantastic breeding ground for the open racing scene.

Good Luck with your boat, and keep us posted ;-)

[JagerL]

yago,

The hope is that I can either use a cassette style rudder that also has a breakaway kickup system, or a manually hinged rudder (up and down control lines) with a simple schockcord kickup system. This would make it possible to take the windward rudder out of the water to minimize drag. In anycase, they would definately be transom hung with overbuilt pintles and gudgeons!

[gonzo]

Hobie Cats have used hinged rudders for decades. In their application the rudders usually hit the ground and kick up. Rental units last several years of abuse. That is something to consider about a simple design.

[Phil Locker]

If you really think about racing it, I would most certainly see that your rudders are transom hung/kickup etc.
Being able to carry a spare and change at sea has already made the difference betweeen abandon and carry-on for several participants in the current vendee globe (http://www.vendeeglobe.org/). Looks like every race there is more floating junk out there knocking off rudders keels and dagerboards.

Might be the subject of a new thread, but can anyone describe the design/engineering of fuses/shear-pins for rudders? Don't want them shearing under sailing loads (even when dragging weeds) but of course you want them to let go as soon as you contact something substantial. Does anyone use anything more sophisticated, such as a ski-binding type device?

Cheers
Phil

[Richard Petersen]

My only real concern is if it releases in heavy seas. You have little control when you need it most. It must be resettable from a safe position.-------- I am available for consulting. Room board and boat.

[Paul B]

I would like to try assy. rudders to generate more net lift/drag, but I need to do some more research.


When you consider what a rudder does in all modes you will probably re-think this idea. Rudders need to develop lift in both positive and negative angles of attack. Having the amount of lift vastly different would not be good, especially for self-steering systems.