Mini6.5 design

Hello Kristian, I pay attention, an interesting datum, the mini rules says "the boat must not exceed a 10 degree heel angle in the most unfavourable ballast mobile keel and mast configuration", Well, the idea is clear, i've a great form stability, improve my weight distribution (hulls lighter, more ballast in the bulb in order to low the KG) and I cant my keel, or ballast the tanks, to carry more sail, more power, but careful, the upper limit of the added "dynamic" GZ (heeling moment due to the keel or ballast) is such that the equilibrium would be less than 10 degrees, so that Manuard is doing is adjust to the limit... We have a more stable boat, then more "static" GZ curve and my "dynamic" righting moment would be bigger (to heel up to 10 degrees) and much better, more sail up in all the conditions.
Anyway, i think that the combination of canting, sliding, ... keel and ballast tank seems to be complicated. It depends on how far do you want race... local, semi-ocean, transat...
Daniel.

 

I have never sailed a mini but I do sail an ultra light about the same size, a moore24. I have raced for years offshore: down California coast, to Hawaii etc... My best time to Hawaii with the moore was 10 days 11 hrs. which worked out to be an average speed of 7.25kts for the course sailed,and many hours of sailing between 11 and 17kts, and a top speed of 22kts. What I am wondering is; Has there been any narrow minimum wetted area type designs lately in the mini fleet? My boat incidently would be 21' loa if the bow and transom were plumb.
I have often wondered how the moore and a mini would stack up in a "windy" transpac. Attached is a pic of my boat shortly after the start of the 1998 pacific cup race to Hawaii from San Francisco (the fast year).

Just thinking about diminshing returns with all that weight,power,wetted area,and complexity.

Anyway, great thread and great looking boats. I would love to see them on the US west coast.

Doug

 

The Moore doing what it does best

 

Great thread guys!

As Kristian point out, the competitive boats are wide and flat, I think Daniel's boat is much prettier than the current winners, but I fear that it will not be nearly as powerful as the current fast boats when considering the 10deg rule.

I think it is Raison that has patented the 3d keel, with a gimbaling keel bulb and a ball joint attaching it to the hull.

McKee's (previously Thompson's) boat has a 2-1/2d keel, which cants P/S and slides F/A. Most competitive swing keelers also carry a centerline ballast tank to allow a little more punch for the upwind slog. I'm particularly impressed with Sayer's Bakewell/White design, which has a keel raked forward at 8-10 degrees, and swings P/S. This allows more useable real estate (which still ain't much) below deck, eliminates the need for a kelp cutter (stick your hand in the well and clear it by hand) and I theorize that is keel torques in an unusual way that creates a hydrodynamic righting moment when canted.

I've toyed with the idea of the raked keel myself, but I'm uncomfortable quantifying the loads without a whole slew of testing, and one must remember that in order to finish first, first one must finish.

 

There are lot of references for the structural response of forward swept wings, from the aircraft design world. Basically the big advantage is in reducing the tip vortex and associated drag. I dig up some specific references to post.

 

I've sailed here in Las Palmas, Canary Island, in a narrow minimum wetted surface boat, the Brenta 24', and in a Mini of a friend (1991 Finot design). There was a fleet of around 12 or 15 Brenta 24' but the local conditions, Wind of force 3 to 5 and a wave height around 1 to 2 meters most of the year (we normally sail with NE trade winds, called "alisios" increased by the venturi effect around the island) made in a few years almost disappear the fleet. The Brenta 24' is a nice boat but demands too much effort and a skilled heavy crew, (the craft don't have water ballast or canting keel) and a good, concentrated every moment, helmsman.
A mini, (i'm thinking in the actual designs) although logically goes upwind worse than a Brenta, downwind is by far more stable to steer, to the nke pilot or the suffered helmsman.
it would be a good idea to do a race with crew minis vs "minimal wetted surface boats" to see the results...
regards
Daniel

 

A few comments (strictly my oppinion, so don´t flame me too much
- 3D keel (as from Lucas/Raison) is a complet nuisance. It is just another buggery thing you have to worry about. The moto of a mini is KISS / Keep It Simple and STUPID/. If you don´t have it, you saved weight and it can´t break. The boats that win Transat are personified simplicity. Remember that!
And most important thing, you have to consider what will happend after a couple of sleeples days/nights in heavy weather. You will be a half conciusness (i know i did not spell this right zombie, dealing with water ballast, twist/rake/angle of keel, daggerboards, sailtrim, ... where does this leave you time for weather strategy?

2D by McKee is cool & a good idea, but still simple canting keelers are just as fast or faster.

Sayer´s forward raked keel is just another thing. We talked and he pointed out that the keel is raked forwar just because he doesn´t want to have a keelbox in the "salon". To me , this is not a prob, because you spend as much time as possible in the cockpit. But it has a big drawback, the fin should be longer to achieve 2 meters, so it si less rigid and induce momentum on the attachment points. Mybe that´s why it broke off when he hit the container? The boat is good, but has some problems with not enough forward wolume (nosediving), but was capable of sailing 1300 miles in 10 days. Impressive isn´t it?

That is to say about mini capabilities. They slog upwind at 6.5 kts with tacking angle at about 90°, but your upwind is miserable, wet, jerky and like living in a washing machine. It really wears you down. Downwind they shine. Max speed is over 20 kts, but the most impressive thing is its averages. It can very comfortably surf at 12 kts, while surfs at over 15 kts are pure fun. We did 60 miles in 4 hours 10. Two brits on "Reality" sailed 38 miles in two hours. Daily run is 254 miles, but this should be exceeded during the last two Mini Fastnet regatas, but the organizer did not provide ARGOS beacons so it can´t be verified. But, from the Fastnet Rock to France (350nm), lots of competitors had averages arround 10.5 kts

Compared to let´s say Melges or any boat of similar length/weight, Mini is much more stable and friendly to drive. It can hapily sit under autopilot at 16 kts while you take a nap (with sheet in yout hand, though). Above 15 kts, it starts to get a bit more tense but the real adrenaline starts flowing above 18 knots. Here you too must be very concentrated at the helm, but the boat just slides on its flat&fat butt.

About crewing minis (max crew is 2-3, the rest is just a crowd) vs. min.wet surf boats: hmmm... Upwind , the MWS boats will have better angle, hence better VMG, except in big, rough sea. Downwind: Melges might have occasional bursts of speed that will be on pair with a mini, but with power/weight ratio of 140m2/ton and stable behaviour (BTW, minis don´t tend to burry the nose, because asymetric kite on the 3m pole rise the bow) my bet goes on a mini. Especially if the sea is big...

Have fun,

Kristian (www.4ocean.si)

 

I'm agree with you, Kristian, the simplicity is essential in a mini to an effective usage... great post, well, i think that the only way to "improve", if it's possible, the sailing against the wind is (to a canting keel, beamy boat) to design a good pair of daggers correctly placed with the more efficient planform, dimensions and section but i'm worried about the choppy seas and the light displacement, do you know if the faster boats has ballast tanks in order to gain weight (not only for trim)?
Regards Daniel

 

To be competitive, you must have a canting keel. Armer is a terific sailor, but with his water ballasted Finot could not win this Transat if three top sailors would not be dismasted (they all broke D1 diagonal at the junction of rod and terminal ...)
All canting keelers have between 200 and 360 liters of central ballast to provide more umph! for beating upwind. Also, the weight distriution on board is essential, all gear forward, etc... The difference in speed can be easilly up to a 1-1,5 kts if you fill the ballast or not in short, choppy seas.

 

Kristian, do yo refers to the water that remains inside the keelbox when you talked of 200 or 360 litres of central ballast?
Has anyone taken into account the added weight, or loss of overall volume, of this water, inside the keelbox? (although depending on the breadth the free surface moment should be low, this plays against the mini)
Perhaps i shall be a bit.. mad...¡¡¡ )
Daniel.

 

There is only a small amount of water in the keelbox and above 6-7 knots the water is gone due to suction.

 

Kristian, thanks for you experienced answers, i'd not thought in the suction, Like the bailers on the bottom of the old plywood snipes!. it's difficult to design a 650 far from continent, many times the photos aren't so clear as i want.
Regards, Daniel.

 

Hi.
I'm a Marine Engineering Student at UFRJ (universidade Federal do Rio de
Janeiro) - Brazil and we were projecting a mini 6.5 until last november. The
boat was designed for the Mini Transat in 2005, but because the money
restrictions of the government, the project were stopped. So I'm interested
in the project that you are making. We can talk about it? As soon as
possible, I will send you some pictures and details about our project.

Your e-mail posted here didn't work.
Answer me at benyjr@peno.coppe.ufrj.br

Wainting answer.

Beny Pitrowsky Júnior
Departamento de Engenharia Naval e Oceanica - Poli - UFRJ
Programa de Engenharia Oceanica - COPPE - UFRJ
Cel.: 8101-9865

 

what foil section did you use in your mini's keels and appendages? do you think a symmetric Eppler could fit for the keel?

 

Hello Nemo, i suppose that it depends on the type of keel, fixed or canting, if it's fixed you shall look for a section thinking in the best ratio lift/drag (to a minimum mechanical characteristics) but if it is canting we should choose a foil with a low drag...
There are people that usually reply in the forum that know a lot of foils, (see the topics related)
Regards, Daniel.