Is rigidity a religion? Amas on the move....

[guzzis3]

Owly: I am both. I did my apprenticeship as a motor mechanic and studied engineering at night. I understand what you are saying but it's not 100% right. The problem is there are lots of people out there who think they know. Some have a piece of paper some don't. What they all lack is experience.

Land rovers have rigid chassis. They carry obscene loads and don't break. It isn't just a question of rigid vs flex it's about proper engineering having both the theory and the experience to make good calls. It's also about knowing your limitations and when to ask someone who knows what you don't.

Wharram and Piver promoted multihulls when no one knew much about them and how things would work. They played an important role getting us where we are today. The trouble with Wharram is he refused to move with the times. His boats have gradually improved but his stuff is a good 20 years behind what more open minded people are offering. The designers I mention above have both got formal marine design qualifications, but the also draw on practical experience. They both build boats, they both sail them. Wharram obviously built his boats and sailed them but he seems to be more of an "artist" than an engineer and "feeling" and "believing" is no substitute for knowing. The Wharrams I am familiar with are incredibly wasteful of materials and time to build and when your finished you have a boat that is an average performer at best and has no resale value. So you've wasted hundreds of hours of your life building something mediocre at best when you could have built something good for the same money and effort.

Anyway off topic...sorry.

 

[gonzo]

Wharram built flexible hull connections on his cats. They don't work either.

There are thousands of Wharram boats with flexible connections that have been cruising successfully for decades. Can you provide any links to flexible hull connections on his designs that failed when they were not modified?

 

[Michael Farmer]

You should also look at Professional Boatbuilder Magazine, Issue 182, Dec-Jan 2020, they address these issues.

What you term "traditional approach" is rather a rose tinted glasses view.
It was more of a case of what materials were at hand and what means of analysis were available... in both cases, going back to those "traditional days".. limited on both counts.

Im sure if you asked any one of the engineers of those bygone days, if they could use a stronger materials and hence utilise a lighter yet stiffer structure, would they.. and their answer most likley would be... yes.
But they, like every engineer of their day, they were limited to what was available and how to analysis its response with a higher degree of confidence.

Well put I agree about lighter and stiffer structure, weight is detrimental to multihulls. My point is that some flex between the main hull and amas would be beneficial in a sea way. This seems to be supported in the Gougeon brother Tri design posted by Garry Dierking (post 12), he might have describes it as suspension where I used the term flex of ama to the hull. Indeed Garry Dierking has used similar flex in Va''a Motu design.

 

[gonzo]

The Wharrams I am familiar with are incredibly wasteful of materials and time to build and when your finished you have a boat that is an average performer at best and has no resale value. So you've wasted hundreds of hours of your life building something mediocre at best when you could have built something good for the same money and effort.

Wharrams were originally designed to use small section lumber of medium quality. Also, the plywood on the hull is used in whole sheets with little cutting. Further, they have a cult following and the proof is that few are for sale, and those who are don't stay on the market for long. I understand you don't like Wharrams, but your statements have no basis on fact.

 

[Russell Brown]

I've never sailed on a Wharram, but I have to agree with Guzzis except for the money and effort part. They are pretty simple.

 

[Clarkey]

Land Rovers are prone to chassis failures, particularly the 127 and 130 variants.

 

[Skeezix]

Discussions like this are fun exercises. I do think this one is fundamentally flawed because it has ignored a factor that I don't see mentioned. A boat does not need to flex, because the water does ... unless you are designing an icebox or a high-speed planing hull.

The windward ama on a non-foil tri works because it is driven into the water. Interfering with that simple function seems bound to create more problems than it solves.

 

[Ad Hoc]

... A boat does not need to flex, because the water does ....

Water does not flex.

 

[Skeezix]

Water does not flex.

Well, I don't think we are talking about water in its solid state, when it does flex. If we need to be picky about semantics:
At displacement hull speeds, the water moves out of the way of all hulls (i.e. is displaced), in particular the leeward ama. My point being the boat structure does not need to move because it is riding on a medium that does.

 

[Flotation]

Can't say anything conclusive about the (dis)advantages but here's some footage of a traditionally build ama with lots of flexibility:

 

[Skeezix]

I wonder if the concept is quite different on a proa, helping the ama to work in both directions?

 

[guzzis3]

Sigh, really ? Now we are going to have an argument about flex vs flow ?

 

[Ad Hoc]

....If we need to be picky about semantics:....

It is not picky, nor playing with semantics, it is a fact, one that you wish to ignore.
And...one that you initiated too:

...I do think this one is fundamentally flawed because it has ignored a factor that I don't see mentioned.....

Thus, are you being picky, or selective in your reasoning?

.... My point being the boat structure does not need to move because it is riding on a medium that does.

So...shall we just forget buoyancy then, or how the transfer of energy occurs?

S...Now we are going to have an argument about flex vs flow ?

It all depends whether one wishes to use known definitions, terminology and theorems, or just make them up to suit a narrative?

 

[guzzis3]

You are being pedantic for the sake of being pedantic. His intended meaning was clear. Wouldn't it be more useful to discuss the issue rather than the language ?

 

[Ad Hoc]

...Wouldn't it be more useful to discuss the issue rather than the language ?

And there in lies the rub.
One must use words, words which have meaning and definitions. The definitions are based on the language being used. The language is the issue...

If one wishes to ignore the definitions and use a language based upon - well, whatever - then one will never be able to discuss - "issues" - rationally. Because the baseline definitions and understandings are incorrect....and so the debate becomes circular and goes nowhere. Because those that do not wish or cannot use known definitions become argumentative and/or just side track - because they like a bar room chat in the pub, and try not to let facts get in the way of a fun chat.

That's your prerogative.. but as an engineer, I prefer to use known and well established definitions, then there is a baseline for common understanding.