Volvo open 70

For my major project in my 2nd year of a 3yr degree course in boat design, I have decided to design an open 70 to compete in the 05/06 Volvo ocean race, this is a huge project seeing as i only have a year to produce a scale model and present my designs to a panal of boat builders, navel architects, material scientists, and other boat orientated people, The rules for an open 70 are very specific, all hulls must be 21.5m in length, a beam of no greater than 5.7m nor less than 4.7m, the draft must be no greater than 4.5m, there are measurements for distances between freeboards and deck edge, the bulb keel (which will be a canting keel) must not weigh less than 4500kgs, there are choices of 1 or 2 rudders, there must be only one fully self draining cockpit, the weight of the boat shall not be less than 12500kg nor greater than 14000kg. the rule book is 38 pages long and can be downloaded at www.volvooceanrace.org. I have attached some pictures of my initial hull designs drawn in maxsurf, any feedback or ideas would be much appreciated.

Cheers
Paul

 

It is difficult to tell from the foreshortening of the graphics, but it appears the BMAX is at the stern. That's rarely a good thing, the wedge-of-cheese. Makes for massive bow-down trim when heeled. That's not good for control.

Overall this looks more like an Open 60 style boat than the new Open 70 style. I belive there will be some short course legs in the Volvo, so that is somewhat driving the type. If you subscribe to Seahorse Magazine you'll also get the VOR Magazine which has had some good info.

Looking at the prelim graphics of the Farr (http://www.farrdesign.com/news/FarrHorizons_Spring-Summer04.pdf, http://www.farrdesign.com/news/FarrHorizons_Winter04.pdf) and Juan K (http://team.abnamro.com/) boats (shown below) they appear to be more slab sided and narrower. Probably going for less form drag and getting the desired stability from the canting bulb.

Good luck with the process. If you have to do all the construction calcs and drawings as well this will be a very large and difficult assignment.

 

Hi,

I did a similar project last year, this was my final year project. You can download my dissertation (http://vppguru.freeprohost.com/pdf/VO70-NR-PROJECT.pdf 8meg!)
Most of my time was spent on hull and appendages design (VPP+towing tank) but the whole design was done (structures, stab,..) everything is in my report + some 2d drawings too.
If you have some specific questions, feel free to ask.

 

they appear to be more slab sided and narrower. Probably going for less form drag and getting the desired stability from the canting bulb.

Why do you get less drag with slab sides?? compare to sides with flare

Hans Friedel

 

I think we're assuming that the waterline beam is the same in all cases, because all else being equal, is has to be. So the flared topsides are just more windage, more surface to be struck by waves, which of course slows you down. You can really feel the difference in smaller boats like skiffs. They also cause more assymetry when you are heeled, normally, and when they are immersed they just add to waterline beam which increases form drag. Or that's what I'm told.

I agree with Paul B (although I'm no designer), I can't quite work out why BMAX has to be so far aft in Woody's boat. With not much planing/dynamic lift surface up front, I wonder how it would handle driving down (or even into) a big swell.

I also wonder about the ultra-fine bow. A couple of the IRC 80s out here (the previous Wild Thing and Nicorette) had super-hollow bows and the front 10' didn't seem to create any bow-wave from what I could see. If it's not displacing much (because of the extremely fine sections) and not increasing the effective length (which means creating a wave in a displacement boat that's not super slim like a rowing shell) then what is it doing, beside adding wsa?

Of course, maybe it was doing something extremely effective. But Wild Thing was extended more than her designer had intended initially, and he shook his head when I asked him aboout it. I don't know exactly what that means. Nicorette was also created out of spare parts to some extent. And neither was as fast as the other 80 of the year. Shockwave, which had straight waterline, not hollow ones, and created the bow wave further forward.

 

I wasn't assuming that. Maybe I should have been. But it really doesn't have to be the same, unless restricted by the rule (I don't know if it is). A wider BWL will have a shallower, "skimming dish" shape for the same volume, with greater WSA.

Maybe I shouldn't have said "slab sided". I'm not describing my thought well. Really I was thinking about the underwater sectional shape. With the more upright hull side shape you will have a more semi-circular, less wetted area shape for the same displacement. Look where the latest AC boats have gone, and what their goal is. That is less drag, especially when heeled.

Hopefully this is more clear. However, I do agree with 249 re: windage, assymetry in the heeled waterlines, and wave drag.

I'm no yacht designer either, not in a strict sense. Have I? Yes. Can I? Yes. Do I? No.

I don't like bow hollows. My experience is that significant bow hollow can make a boat bow steer. That is, when surfing the bow itself can dig in on one side or the other, causing a low pressure side, and this seriously snaps the boat into a turn. Olson 30s are legendary for it. You do have to keep in mind we are talking about hollows in the waterlines, not vertical flare hollow.

Also keep in mind that we're looking at a model that might have issues with forming the bow without a hollow. I've fought that fight when doing lofts in certain programs. So I'll withhold comment on that until the linesplan is available.

249, the extra length probably is immersed when heeled in flat water, isn't it? It also allows for reserve bouyancy in the bow in swells, something fine bows probably need.

I've seen that same look on more than one designer after seeing their design "butchered".

 

Sorry Paul, the comment on all else being equal was meant to assume we were (for simplicity) assuming the same underwater shape for comparison.

Yes, the extra length on the maxis was immersed; but it seemed to me to be doing something similar to what would happen if you just stuck a 15' long wooden plank 2" wide out in front of the bow; it extended the waterline but did nothing effective with the extra length.

I supppose there was extra buoyancy in the bow, but not much, and Nicorette (the only one I sail in swell) would really stick her snout into even quite small swells, perhaps because of the lack of volume up there. She could stick the bow right in even in moderate swells, which seemed to me to create a lot of wsa on the topsides.

There aren't many designers who do like bow hollows, are there? I tend to not like them, but apart from possible problems with the amount of volume for wetted surface, reduction in prismatic, and the handling issues, what problems to you see with them?

Actually, maybe those problems alone are more than enough; they probably stuff up light air, hull speed and high speed performance respectively.

 

The new generation of narrow maxis don't really need hollows, do they? I have to think the original intent of hollows was to sharpen up the entry. But with the half angle already so sharp on very long, narrow BWL boats the sharpness is the least of your worries.

Sticking a "narrow plank" out the front does add some volume, plus a good bit of WSA. Is the trade off worth it? I guess that's what designers get the big money for.

I know a certain maxi cat had some pretty fine bow extensions added and that helped relieve some scary moments. However, they weren't hollow so the area of the old bows was significantly more voluminous, with even more volume forward of that.

On the other hand I've seen some cats with pretty bluff bow waterlines and they seem to go OK. I don't follow cats much, or Round the World racers, so my view on these types is limited. Do many of the current Open boats have hollow waterlines?

If you have a certain BWL a certain distance from the bow the waterline has to get there. If you hollow the bow you just have to add more of a pronounced sweep out at some point. Does the water like that better than flowing along a somewhat straight line? Again, that's what real designers get the big, big money for.

I like to see nice, straight waterlines at least through Station 3. I like to look at a linesplan and lay a straightedge from the bow and see the waterlines follow along it. Not concave nor convex looks right. Probably has to do with the training I once received.

With the long skinny maxis of today you don't have much other choice. Your WLs are going to be pretty straight forward.

You're from Sydney? Funny, I thought you were from somewhere more down south. Don't know why. Great town that Sydney. I'm thinking about getting back there after one of my Hong Kong jaunts this coming year.

 

Canting Keel

Paul Woody-what type lateral resistance have you considered using with the canting keel?

 

Who can guess where this is going? Another thread about to be hijacked.

Woody, be careful. I forsee someone trying to get you to do design and evaluation for his hairbrained scheme for gratis.

I can see it now. "My Canting-Thingaroo (TM) is currently under development at a major university and the results appear to show it is the greatest idea ever!"

 

Cbtf

Paul B, it's amazing how you work so hard to illustrate your limitations!
Paul Woody, I think choice of lateral resistance is going to be critical in these canting keel boats. Seems to me that CBTF ,modified slightly to include a retractable (full or partial) forward foil, could be the best answer and I'm curious about your thinking on this critical detail....

 

I agree about the current boats being so narrow they may not need fine bows. There's an interesting analogy, possibly, with the old Div 2 round bottomed 13' windsurfers, where the "boat type" bow was found to be slower than the full, wider spoon bow. Same as it was in J Boats and metre boats, I suppose. There may be a certain minimum bow angle and under that there's no advantage, perhaps?

I assume the problem with bow hollows is as you say.

I'm becoming a bit of a fan of the U-shaped bow, with more volume underneath than Nicorette etc seem to have. It seem to work nicely on just about every boat, maybe with the exception of an 18' skiff which has wave-impact problems because of its pace and has a low DLR and a big rig so has fewer wsa problems. Rob Brown ("world" champ 18 designer/skipper) and others reckon the 18 bows are all about wave penetration but many people seem to be following the theme for very different boats.

I got to drive Nicorette one fun sail, which was fun. Nice boat, but crappy rudder; they'd put the old one back on after the Hobart and you could really feel the C of E or whatever shift back and forth as the boat gained speed down the swells.

I'm not up on Open Boats, they fine for some but don't do too much for me (although the ex Open 60 Xena was a hoot to sail).

 

The main limitation in Volvo 70 appendages developement is rule 2.16.1:

"Appendages shall be fixed, or free to move with one degree of freedom only (translation, retraction or rotation)"

 

Lateral Resistance

Nico, can't open your pdf file-what choice did you make for extra area- and why?

 

I can see the problems with having BMAX so far aft when i'm trying to keep the LCB as central as possible, the pics I posted were probably not the best to show the actual position of BMAX, however I have altered the design to move it further forward, I have attached a pic of Ecover (www.finot.com), a successful open 60 that has completed: Around Alone 98-99, Route du Café 99, Transat anglaise 2000, Vendée Globe 2001, and Transat Jacques Vabre 2001, you will notice that the BMAX is about a third forward from the transom and the beam only has a very slight decrease to minimise drag. You also have to consider weight distribution, there is a minimum and maximum weight specified in the rules, and obviously with the bow being so slender on my design there will not be much weight forward. This design has been influenced by open 60's, perhaps I need to take into consideration the Length to beam ratio of an open 60 compared to the style of the open 70 i am designing.
Designing the boat with steeper top sides is going to produce much higher curvature below the water line, surly this is not a good thing when the boat is heeled over, although i do feel that i need flatter sections aft, to help planning capability.
This design is very much my initial idea, and has a fair way to go before I want to think about producing a plug for the scale model. Your feedback is proving very helpful.
Cheers