Bruce Roberts admits design flaws

[JimCooper]

The post re-produced below is from Bruce Roberts, on the SSCA discussion forum

http://www.ssca.org/sscabb/index.php?action=vthread&forum=2&topic=151

Interested to note that after considerable concern about Roberts designed skegs failing that the company now freely admits that their boats were not well designed. BUT we now have the new "Full keel design" that has no skeg problem!

AND a statement condemming all skeg designs from all other designers presuming thay have just iscovered the marketing pull of the NEW FULL KEEL

Come on Bruce.....................

I'll leave this with you

Jim




Bruce Roberts Yacht Design
Offices: USA - The Netherlands - Ireland - Australia
Telephone Bruce Mobile / Cell Phone + 353 872 483 085
www.bruceroberts.com design@bruceroberts.com


Regarding Skegs ... We have long since discouraged the use of skegs and prefer to design and recommend our 'Modern long keel' designs ... these sailboats are proving that they handle and generally sail as well as any boat with a skeg and are a lot safer.

IF you are building or own a Bruce Roberts designed boat with a skeg then please get in touch with me for an update on the plans etc.

I would point out that there have been MANY skeg problems in boats I did NOT design ... skegs are bad news in all boats so contact me for some advice.

Regards, BRUCE
R Bruce Roberts-Goodson Chief Designer
Bruce Roberts International Yacht Design

[MarkC]

After reading all the comments I am left with a bitter taste not only for BRI yacht design but also for Brent Swain.

I have found that Brent never misses a chance to slam other metal boat-building methods and flog his book with 'his' (flawless) origami method. I

BRI Yacht Design may have 35,000 boats or so in the water - good on them, they persue their business well. I am not sure BRI Yacht Design can say 'we have changed our proceedures (skegs) due to problems - but many other yacht designer's designs have problems too'. Why say that - and, why rise to the bait?

[Wynand N]

Just because Bruce Roberts screwed-up designing a proper skeg, he has the audacity to say that all skegs are bad news......... :?:
I always said that BR is a better marketing person than a boat designer. Now I am positive this is the case.

BTW as for Brent Swain and his origami (steel) boats; I won't touch it. Im of the opinion that a proper built steel multi chine is better looking than his creations. The origami method limit the design within the ability to cut pull and bend the plate in position, hence the name origami. There is no "purity" of line and sorry to say so, all them hulls look the same and in my humble opinion again, aesthetically, the hulls not very pleasing to my eye.
In life there are no profitable short cuts, rather take time and build a proper, well designed hull - round bilge, raduis chine, multi chine - they are all well worth the effort if well built.

Disclaimer: No attack intended on any of the above mentioned, just personal views.

[PAR]

In pure cruising designs, skegs generally aren't necessary and have reputably caused trouble in all hull configurations, models and makes when compared to full keel sisters. A number of noted cruiser designers don't do or will talk you out of a skeg in a custom design, favoring a well designed full length keel. Even the best designed and over built skegs can be damaged or tweaked enough to cause damage, much sooner then a full keel design. This is inherently the nature of an exposed skeg and rudder assembly, not as protected by the keel before it. This isn't to say you can't damage a full keel, of course you can, but a skeg is easier to do so with and the whole point.

Though in honesty, BRI is likely trying to cover it's bases and redeem liability and reputation with this "change of heart" about skegs. Now performance oriented cruisers (which BRI cut it's teeth on) can benefit from the increased maneuvering and sailing ability a skeg can bring. Does this mean BRI will do only pure cruising work from here on out? Not terribly probable, considering the market focus on racer/cruisers, they're just blowing out candles, so when you stuff your skeg into a coral head and break the boat. They've got a fall back "I told you so . . ." line to toss in your path of pissed offness.

[Milan]

Origami boats

Wynard, beauty is in the eye of beholder, and everybody has his own taste, so can say that he likes or doesn't like particular boat looks. But what do you mean when you say that origami method limits the possibilities for different shapes? Any (single or multi) chine boat can be built in origami with a lot less work then conventionally. Brent's boats looks similar to each other because that's his taste, he likes that classical boat shape, and being single chine welding is minimized, But there is no reason not to use any other shape you like. For example Van de Stadt multi chine boats which you built before would be very easy to build origami way.

Don't you think that Gerd's nice gaff yawl looks very different than Brent's boats?

www.justmueller.com/boats/

Or Greg's boats?
www.origamimagic.com


Milan

[yago]

We had a very long and heated discussion about that some months ago in the origami group. The issue was about skegs added to the hull versus skegs slotted through into the structure, and, in that context, traverse framing in general.

I think we had consensus that skegs simply welded onto the skin represent a risk. Different methods of interior re-inforcements were discussed, also in view of adding them to existing boats. Brent also has modified his designs and makes his skegs now much wider at the top to increase strength.

What worries me most with added skegs is fatigue, I have seen a skeg on a 11 meter hull that was just welded to the plating, and when sailing you could feel the plating move and bend and feel pronounced vibrations in the skin next to the skeg. I can imagine that the skin will be weakened over time near the weld.

Personally I would always go for a slotted skeg, solidly embedded into traverse frames and central stringer.

Gerd

[MikeJohns]

Skegs can be designed very strongly , the big problem with some designs has been thin hull plating in the skeg attachment area and narrow deep skegs with a relatively small attachment area.

If you intend building an older skeg design of Roberts the skeg could be re-designed to make it bullet proof. Steel will be more forgiving but skin attached skegs in Aluminium construction will be troublesome unless designed very strongly..

I have surveyed many Bruce Roberts steel vessels and found the odd bent skeg and signs of supporting plate buckling but whether from normal loads or from grounding I do not know. So far I have not encountered any fatigue fractures.

Skegs protect the rudder, allow a smaller rudder area, and in combination with a shorter keel certainly improve the tracking.

Yago.....With steel construction Slotted or not makes little difference to strength if the assembly is properly welded to a good strong base plate.

[MarkC]

Milan wrote:

'But what do you mean when you say that origami method limits the possibilities for different shapes? '

Here is an interesting discussion from Kasten Marine regarding 'Pre-cut plate' and 'Folded Plate/Origami':

Quote:

With the Folded Plate / Origami method however, one must realize that the designer is unfortunately extremely limited in terms of the possible hull shapes that will actually do this trick. Try it with paper cutouts and you will be immediately convinced. You can achieve a few minor variations and still get shapes that will fold together, but regional subtleties of hull form are just not possible. If a different type of hull form is desired, then quite a lot of trial and error time must be spent - usually by making actual trial cutouts and seeing if they will fit together in an attempt to discover a totally flat plate layout that will provide the intended shape when folded together.

This is not only a severe limitation on the designer - it also restricts the builder who may as a result have only one basic model to offer. In other words, variations to the hull shape are difficult and time consuming to create, so the vessels are limited to being either larger or smaller, fatter or more slender, taller or shorter, having more or less sheer, yet essentially the same in their general shape and appearance.

Further, it must be kept in mind that just as with the "pre-cut-plate" method, the "Folded-Plate" or Origami method is generally only applicable to the hull plating itself, and not to the keel, rudder, deck, or superstructure.

We observe then the following disadvantages of the "Origami" method:

Only a limited portion of the total plate surface will be addressed by the Origami method;
The variety of hull shapes that are possible both aesthetically and functionally are quite limited;
There will be quite a lot of fussing around with trial shapes prior to achieving the desired result.

End Quote

http://www.kastenmarine.com/frames_first.htm#THE_QUESTION_OF_PEDIGREE..._

A good series of articles.

[yago]

Yes, that is right, origami limits the shapes you can archieve... but so does hard chine construction.

Origami produces a hardchine hull with ends where due to the tension during folding you will get a compound curve. Keeping the remaining chine(s) just below the waterline, the appearance at rest is very close to a round-shape.

You also do not need trial and error, I designed all in CAD and the finished hull is at least as close to plan as my earlier hard chine hulls and perfectly symmetric. Symetry is literally archieved automatically, the halves will come together in one way only. The only thing you have to check for is twist, which is very easily controlled after the halves are tacked together.

If you look very closely you might find that an origami hull with long darts has the advantage of the chines in the midship area where they are good for you (anti-rolling and form-stability) and has very sweet sweeping entry and exit like a round-bilge hull. Can't be all that bad, can it? ;)

You can check out my site, there is a section on the design process that worked for me, as well as the first part of the workbook to download, showing the hull construction in detail with lots of pictures.

If you want to see how round such a hull can be, have a look at Gregs desings at origamimagic.com there is teh buildign sequence of a large alloy hull that is very very nice indeed.

I am really not an origami missionary, and do certainly not pretend that origami hulls are in any way better boats or even significantly different from other hulls with similar scantling, but from my own practical experience after having built several steel boats, I know now that compared to classic hard chine construction, origami is a lot faster and easier, no expenses or work for jigs, less welding, less deformation and so on. and it is simply FUN to bring the hull together like that in a couple of hours without ever lifting a single plate off the ground!

Yes, it gives a typical shape, but so do chines, and that's what I compare it to. With a lot more work, cost and effort you could go for radius chine, you can get very nice hulls, and if ever I start over I might give that a try as well ;)

Gerd