Welding the skin to the frames demystified

For years I've been biting my tongue while Evan put ease of construction ahead of seaworthiness, by using pipe for leading edges of keels for lighter handling, while I was warning him that it would collapse any time it hit a rock. He insisted on using flatbar for supports for twin keels , years after I warned him that it wasn't strong enough to withstand a hard slam against the rocks.
Why ? Its easier to build and looks tidier. He insisted on using only top and bottom pintles on the trimtab, no middle support, a setup so weak that a ten year old could pull the trimtab out by hand . He insisted on putting a 600 lb fuel tank in the stern right against the transom, the worst possible place for that kind of weight. He refused to put a proper watertank on the centeline ,where it would be structural for a twin keeler, and instead left the owners to put them higher up, taking up valuable space that was needed for other stowage. I finally had to list these and many other screwups he had insisted on doing over the years.
Evan has almost zero cruising experience, yet considers himself qualified to redesign my boats. He is a very meticulous metal worker , but someone needing surgery wouldn' t be wise to hire a surgeon on the basis of his qualifications as a meat cutter. It takes cruising experience to understand cruising boats, not just metal working experience. When I trained Evan and offered him half my job, it was with the assumption that he would gain such experience quickly . That was nearly 26 years ago and he has gained almost none, yet considers himself qualified to redesign things, based on metal working experience only.
I also believe he was trying to maximise the hours he takes to do a job, to pad his income. I'll never impose someone's obsessive, money grubbing greed on any client. We dedicate a lot of time and debate over trying to get a boat to do an extra tenth of a knot, while ignoring what the real hurdle is, time and money. Greed on the part of people they depend on is a much greater hurdle to most would be cruisers, and a much greater threat to their ability to achieve their cruising dreams..
Brent

 

I don't know either of you from a bar of soap, however, what you have described is unfortunately too common in this industry.

I know many very good fabricators, yet for some reason they like to set up a company and call themselves "designers". All they do is 'design' a 3D shape made from bits of metal, that fits a hull shape they have used for years, or bought.
There is no underlying knowledge of what has been "designed", nor why, nor often, they do not care. Being able to fabricate a boat from raw materials is a great and for some a true gift and skill, but it ain't design as defined by naval architects!

I see many "designers" sitting down with clients talking about lets change this engine or move the tanks there or some other aspect of a GA. Which is either poorly drawn, not theirs or something cobbled together. The implications of changing "things" on a boat no matter how small, is totally lost on them. Why, because they think they are the designers, because they have drawn it or built it.
My niece can draw better than some I have seen..but is she a naval architect, no!

Unfortunately it is also such "cowboys" that give aluminium and small boat design a bad name. They just repeat what they have done in the past and do not know why either...ask to make a change it is either , nope this is what you get, or sure no problem, and not a single thought is given to the implications.

So much for naval architects having to be licenced or registered!

Two of the best fabricators i have ever seen and had the pleasure to work with are real masters of their craft, their work should be in a gallery. What they can do i have never seen anyone else do. Yet they would never call themselves designers, because they know what is really required to design a boat -having worked on so many good and bad designs. Could they do it, yes, but would they, no.

 

O.K., didn't know more than what an "origamiboats" member told me, which was " They're even slagging Evan Shaler, these days". I've never met the man, but have seen his work & he is a high quality fabricator. Then again, I certainly agree that builders aren't necessarily the best ones to modify designs, unless the designer is involved. Some of the differences that Brent has pointed out, such as the fuel tanks positioning, are IMHO, better left to those who design. Too bad.
Mike

 

There is no requirement for yacht designers to be registered or licenced. In USA a Naval Architect has to be a qualified Professional Engineer. My qualification is as a Yacht Architect from Westlawn but I have 30 years of practical experience with designing and building boats as well. I cannot call myself a Naval Architect in USA, although I can if I live in most other countries. I can call myself a Yacht Architect but most people would know me as a Yacht Designer, so I stick with that.

 

DD

Very interesting.
You are correct, in the UK for example, anyone and I do mean anyone can call themselves a naval architect. However, only those with the correct level of academic education and/or practical experience can become a full member, by that i mean designated "M" not "AM" or "corp", member of RINA.

I have several friends whom are "yacht designers", but only one of them is a fully trained naval architect.

This is all where it becomes blurred, not just in the UK, as you have described. If one drops the prefix, of "naval architect" or even "yacht", one can then call themselves a "designer". As soon as one uses the term 'designer' it then becomes assumed by the other party that one is fully qualified!

Having said all that, if you needed some major work done on your house, you would probably go to a builder; but how would in uninitiated select the best builder? What procedures are there in place for one to call themselves a "builder" and a qualified one at that?? If builder A charges twice that of builder B, 99% of the time joe blogs would go with builder B. But would we actually check to see what experience or qualifications B has compared to A?

The public's perception of a "designer" is no different to that of "builder". Yet a fully qualified naval architect is somewhat different to a non trained and no experience "designer" or even a "builder" bidding for a job cheaply and saying they can do X,Y and Z!

 

Tardy reply sorry, work intervened .

It is interesting the comments on levels of qualification:

Following some of the design debacles (eg Maxfun 35 )it has been illuminating looking at the official responses to these sorts of issues, under the European RCD which requires manufacturers to ensure compliance for vessels under a certain size but requires external certification for vessels over a certain size (36 feet loa ?).

If you are a professional engineer ( graduate certified ) you are liable for any omissions in your design, if you are a ‘ boat designer or yacht architect ’ it appears you can claim confusion of engineering principals as a defense to poor design even when it costs a life. An engineer cannot argue that the scantling rules did not make clear enough the basic principals of engineering.

Yacht designers from schools like Westlawn have real trouble understanding the basics of stress, strain , bending moments, deflection fixity and combinations of tensile shear and torsional stress, they have no hope of understanding or assessing structural elastic instability and have a very poor knowledge of the very serious subject of fatigue. All this basic engineering should be taught IMO to every designer, the concepts are simple enough.

Scantling rules incorporate these sorts of factors hidden in those numbers that appear so meaningless in equations, note that modern rules have become lighter recently because of detailed structural computer analysis and detailed load measurements on vessels.

Non-engineers often seem to have this view of engineers but frankly most of the tales of ‘I used an engineer and it broke’ are worthy of further investigation, the courts will award full damages in very short order if the engineers work is really deficient. In reality our insurance would pay out long before it got to court following a peer review organized by the insurer.

With current engineering practices, computer tools and peer review there is no need for an engineered design to be anything other than robust whether its a novel rig, steering system, or hull supporting structure. Unless you have used and are familiar with current computer tools you cannot really appreciate just how much they have changed the design approach or how informative they now are.


Regarding running plans past an engineer….. I was suggesting it for those wanting to continue with ABS as their design guide and still being able to get their design checked which is the basis of any scantling society rule base. Think of it as a peer review.


On transverse frames standing off the plating.

Accept that the plating will buckle much more easily when panels are not restrained on 4 sides ( I think it will take around half the force for the panel to collapse )

If you standoff the transverses you should make two design changes that will add considerable weight. Firstly the new transverse should be close to the section modulus of the old frame with the plating attached, secondly the buckling resistance of that new transverse needs careful consideration.
Any scantling society (ABS in the past included) should (have) require(d) this. I’d be very interested to see any engineering analysis which suggests otherwise.

 

Thanks for the link.

 

and then again I had never seen a Dix with floating frames had plates bend or buckled....and most of them sail up and down the South African coast and Cape of storms and this is a shoreline notorious for most boat wrecks per mile anywhere in the world.

Dudley stayed in Capetown for most of his life and all his designs are designed to handled these waters on a bad day.

Then again Mike, getting to Eric Sponberg's quote; two things shout at one - aluminum and race. Then it became predictable that such a thing may just happens.
Racers are build as light as possible and failures are common all the time as can be seen in races. These guys build to win, regardless, if it breaks then just beef that up for the next boat...
I believe someone screwed up in his calculations doing that boat and having said that, it is unfair to to assume that this type of building is bad medicine and criticizing Dix for designing such designs. In fact, as said before, his designs and boats proved otherwise over time.

As a side note; Brent is sometime weird in his thinking and engineering views, but he is true with many of his statements that small boats are over designed and build to heavy with lots of frame and stringers that goes with it. His flimsy origami boat (although ugly from my point of view) proved just that and they sail all over the globe....

 

Wynand

It looks like Dudly's designs only have floating frames on the topsides ?
I also do not know whether he has beefed the frames up from the original attached scantling.

Strength for weight and military vessels are the most rigorously constructed, transverses are fully welded, next you would expect both racers and then light displacement cruisers. I guess whether you want a boat to be as stong as possible for the material used, or as easy to construct as possible is a personal choice. It's good if people understand the tradeoffs.

Whether a scantling rule is overbuilt or not is another issue really. Although as I said before most of them are now considerably lighter than they were in the past particularly since the engineering analysis has become so much more capable. Most of us would now consider the liesure boat rules to be the bare minimum not to be reduced under any circumstances.

We can easily model any section of hull structure and tell under what head of pressure it will buckle or whether sensible stress fatigue limits are exceeded. We do this analysis a lot for military and commercial craft and the loads are getting more accurately defined as more vessels of all types are fitted with data aquisition systems.

As for Eric's comments, yes aluminium lacks the stiffness of steel and that makes it more prone to buckling for an equivalent section modulus.
Elastic instability is an important concept. Engineers within the scantling societies take this into account when they publish those table graphs and equations that sometimes look so arbitrary.

Fatigue is just as important, the aircraft industry learned this the hard way, initially aircraft could operate for thousands of hours then suddenly break for no obvious reason, poorly designed or fabricated structures can be very reliable up to a point beyond which they can be very unreliable. This is the problem with anecdotal observations of reliability, particulalry of liesure boats that really have a gentle life and limited use.

Ultimately steel is a lot more forgiving than other materials.

Cheers

 

Thanks Mike.
The Dix boats I built only had floating frames to the topsides (deck edge). The decks are conventional frame to deck with stringers. But I cannot comment on Dudley's designs and best left for him to explain.

 

The Wife and I desided on building the Roberts 345 pilot for a retirement boat to live on. Found a lot of contruction photos on the net and here is a couple of the framing, not sure if this is from the builder or its on the plans that way, Cant see any frames welded to the hull skin and no limbers. Looks to me the chines are flush and they pushed out the stiffners a bit. In the one photo it does look fair.
Tom

 

There is nothing flimsey about boats that can survive 16 days pounding on a lee shore in 8 ft surf in Baja , boats that can pound across 300 yards of Fijian Coral reef, survive a collision with a freighter or do a single season passage thru the NW passage, all without serious dammage. They prove beyond all reasonable doubt that transverse frames in small boats add little or nothing to structural strength, and are a waste of time , money and potential distortion.
They are largely indistinguishable from round bilged boats when in the water, and sail every bit as well as most.
Columbus was wierd in his thinking that the world was round and not flat.
Small boatbuilding in metal is in pre columbian times, to some extent. It would stay there ,if we lowered our rate of progress to the limited ability of slower learners to comprehend the basic geometry.
Brent

 

Tazmann
check the welding schedule with Roberts. if the plating is this close it's daft not to weld it. I'd also ask Roberts what scantling rules their plans comply with.


Brent
Anecdotal tales are very subjective, small ships have been washed over reefs and inshore 300m without damage, light foam cored grp racing boats have been stranded on surf beaches for weeks and been recovered undamaged. Real strength is not related to subjective anecdote and is easily and accurately demonstrated theoretically but involves much more than simple geometry.

Longitudinally supported hulls are common, once the vessels get over a certain size bulkheads are introduced since the required strength goes up relative to the square of the span.

In metal construction better strength to weight is achieved by the use of transverses and this will never change. Your (Brent's) small boats 26 and even 36 footers are not frameless they have floors, longitudinals integral tanks and achieve additional longitudinal strength from chines and radiuses.
Try designing a 60 foot sailing vessel of say 40 tons displacement and you will quickly see that there’s no sensible way you can design without transverse support/framing without having a very odd looking hull or massive longitudinal girders.
Regular transverse supports however make a metal boat far more rigid since they resist the transverse shape change as the hull girder bends.

 

Tack up a model without transverse frames , then try to get it to bend , both without the decks on and with decks, and it will become very clear how irelevant the transverse frames are. Twist the model without the decks on , without transverse frames, then with transverse frames , and you will clearly see that the transverse frames have zero effect on twisting stiffness.
Build the square propane bottle that I suggested , fill it to 100 psi ,(water so it will be safe)and see how much difference shape makes in panel stiffness. Your theories are based on the assumption that shape has minimal influence on strength, and are based on flat surfaces. That is total ********. With a heavy material like steel we have to use every advantage we can find. The reason the myth that steel is only suitable for boats over 40 feet endures, is based on the assumption that we will naturaly use heavy, totally redundate bits and pieces like frames.
You say a boat that can survive 16 days pounding on a lee shore in 8 ft surf, t bone a steel barge at 8 knots ,and all the other examples I give, without serious damage, is flimsey. That is total ********. You a have a self delusion problem.
Brent

 

now ladies.......

I don't know much about designing boats, but sure have fun reading. I have looked at a LOT of aluminum boats, many of which have pounded a LOT of relatively large waves and even larger rocks.

It seems to me aluminum boats derive a LOT of their strength from Sheer, where a wood boat, especially made of boards, would not have nearly the strength.

If a fellow looks at the loads on a boat, they primarily come from up from the bottom and down from the weight of the cargo. If the load can be spread across the longtitudinal frames to let the bottom lift it up, then all is good.

It further seems to me transverse frames would help keep the boat sides and bottom from collapsing towards the center of the boat. This doesn't seem to me to be a very big issue, but if someone has pics of boats that have collapsed inwards along the sides, I bet we would all love to see them.