6.5 Meter Racing Sailboat

I think that with such light materials these days, getting a boat that can plane is more easily achieved. It was rare to see a 30 foot timber planked hull get out of displacement mode. Now with foam core sandwich constructions, carbon fibers, and all sorts of other awesome things a 6.5m hull can be built at only 150 kg or even lighter if you dare. Even after you add everything else, a boat can top out at 350-400 kg, including 100 kg of lead on the bottom. The crew probably equal that if your sailing with 4 big guys, so its easier to sail these things flat than most boats. As messabout said, its unlikely to sail at 30 deg heel intentionally.

As you seem to be into analysis, do a short weighs and moments table to get the VCG and LCG and determine what your righting moment is. Then figure out your sail forces, and you can estimate what angle of heel you will sail at. Better yet, if you have access to a VPP, use this to help design your boat. (There is a free excel based one here, I havn't used it but apparently its not bad: http://www.cruisersforum.com/forums...eet-to-make-vpp-for-sailing-yachts-89998.html)

 

Mini 6.5

Here is another continuation of this thread. I wonder if anyone with experience in this field would comment. Thank you.

 

• Blunt Nose Mini 650 Analysis

I decided to experiment a little with "blunt nose" shape. It appears to be a very good concept disregarding everything except speed. I did move the mast aft a bit to place directly inline with the keel. I also didn't fiddle with displacement and the bulb shape too much. It should be in the ballpark.

In my mind, if built, this mini 650 racer could be pretty fast. Could anyone please be so kind as to give me an opinion and help me with some discussion about this model? Thank you very much.

 

It doesn't look like any successful boat of the type. This is a good indication that you do not know what you are doing. Honestly, it looks like something drawn by a kid.

 

Not everything is lost

Thanks for constructive judgment and critical remarks. I would like to ask you in if you could kindly point out the really bad features of the last post #18 of this thread. For me it is an exercise and any valuable input would be warmly welcomed.

I tried to balance and shape of the hull while watching out for coefficients and ratios. If I made a blunt mistake would you please point it out to me? The boat below won recent TransAm race with room to spare.

I do think that the mast is a little bit too aft and that I would adjust the bulb shape slightly to something more traditional. I didn't draw anything but the hull and appendages (no deck, cockpit, etc.) Also, I didn't use any dagger boards and used just simple fin keel. Even accounting for the heeling angle I think it is a bit too much in area though. It wouldn't hurt for incidental sailing but would be an extra drag for racing purpose.

The purpose of this particular exercise was to balance waterlines that they are parallel to the longitudinal axis. If you look closely, both "Magnum 747" dagger boards have yaw angle of about 15° It will create drag, which is corrected by the rudder and thus drag multiplied once more. I tried to eliminate this in the last model.

Here is the link of the similar (at least in appearance) boat which was an example to me: http://www.boatdesign.net/forums/sailboats/mini-ocean-racing-scow-39114-8.html Specifically post #112 down the page.

Thank you.

 

Have a look at this design:

http://www.jpdonovandesign.com/new_site/index.php/projects/current-projects/donovan-6m-racing-yacht

If you go with the scow approach, make sure the blunt bow is out of the water like the mini.

 

Blunt rounded bow should be in the air above the water

Thank you, Paul. It is a good pointer and I do understand that blunt rounded shape would create significant drag and resistance under pounding waves. I am trying to watch out for this in my studies as well. Ideally I hope to arrive at the compromise between heeled waterplane area, its shape and orientation; entrance angle, LWL and other parameters. That is why every opinion does help me to inch forward. Thanks again.

 

Is it a progress?

I took in account Paul's recommendation and refined slightly the model. Now it is not as blunt as before, I adjusted the appendages, this time only one rudder for the time being and more refined keel. I wonder what other experienced NA think about this shot? Any non-personal opinion is greatly appreciated -- thanks.

 

I am still trying to figure out what type of race this boat is being designed for.

Without a canting keel it is going to be heavily penalized compared to other modern boats. With the blunt bow it is going to have problems racing inshore buoy stuff.

Either way you will likely need a asymmetric pole. Downwind this will cause the bow to lift which drives a different bow shape than a symmetric chute.

With this radical a hull shape twin rudders are going to be pretty close to required, and likely twin daggerboards (particularly with a canting keel). Which raises issues of curved, lifting, or strait boards, and at what angle.

 

Hi KV,

I admit, I am a little confused. Reading relatively quickly through the thread it appears you got some very good answers earlier on, and made progress.

Then suddenly in came the blunt nose design and things fell apart a little.

However, I do know your enviable reputation as an innovative engineer, and knowing how you analyse problems and end up with unique and elegant solutions, i look forward to further developments.

Pete

 

Kvsg,

I went back and reread what I had wrote and think I may have been drunk at the time.

My point was that is seems the design of the boat is being optimized for different races. And as the thread progresses the intended use of the boat is being modified. The same 20' boat designed for day races is going to be radically different than a 20' ocean racer.

At this point I am not sure what your boat is supposed to be designed for, so I am not sure how to interpret what you have.

 

This racing sailboat is pretty nice... I saw some of them at Cannes for the Festival de la Plaisance! It makes me dreamy...

 

Thanks, asmith -- those boats do make a splash. I hope that my boat would glide over whose waves instead of throwing up lots of water. Every gallon thrown up above the waterline translates in loss of speed. I would like to have a boat which behaves like a skipping stone as much as possible instead of an iron plowing through waves.

 

I try to come up with something feasible for ocean racing and not for choppy waves of shallow bays.

 

For ocean racing..

1) to be competitive these days in the mini class it has to have a canting keel. And because of the complexities of installing this it has to be taken into account early on.

2) asymetrical foils start looking pretty good

3) water ballast systems

4) remember to design around huge rigs. Minis are carrying 40' masts, and 12' bow sprits.

5) because of the powerful rigs, and massive righting moment these boats carry, it can almost be assumed that they are in planning mode most of the time. This requires a hull that can easily get on top of the waves and stay there.

I think you are headed in the right direction, but I would consider a harder chine, flatter bottom, and bigger planing surfaces.