economical coastal cruiser

[Guest625101138]

Originally Posted by Willallison

....
With this in mind, could you please explain how one might go about designing and building a prop that imposes no compromise? And how is it that you came to decide upon the diameter for the prop on your pedal boat?

First step is to define the design objectives in which to optimise.

Rick W

[Willallison]

There were 4 questions there Rick.
You've answered none of them

[Pierre R]

Originally Posted by Rick Willoughby

First step is to define the design objectives in which to optimise.

Rick W

Okay, I want to know how you optimize a design when the customer is never quite sure what they really want? In my opinion customers do not understand how comfort relates to what is possible on paper. The customer has an inate sense of the comfort level that they want but cannot put it into a quantitative value from which an optimum design can be drawn. In the absence of perfect data the NA must err on the conservative side lest he find himself in a lawsuit.

Most customers come with a dream boat in mind. The very idea of the word "dream" indicates a disconnect between reality and optimum design no?

With you little pedal design you are the customer and comfort is clearly not on your high priority list.

[Guest625101138]

To establish the design space I have found it instructive to start with looking at what the conditions are for the completely unconstrained case.

This helps in understanding what each constraint is going to cost.

In this case we do not know a lot about what the optimum solution is going to look like so I have set a relatively wide space for speed and displacement. The end result may be outside the range provided. It could be extended but most of what has been discussed so far is close to this. So displacement ranges from 0.5t to 2t and speed from 3m/s to 6m/s.

The attached shows the power level required to drive the respective displacements at the various speeds.

The design optimistation needs to start somewhere and establishing objectives for speed and target weight are good starting points.

If someone cares to nominate values, the optimisation process can continue.

I have found hull length to be the most demanding constraint so I can look at how that impacts on power next.

Rick W

[Guest625101138]

Originally Posted by Pierre R

Okay, I want to know how you optimize a design when the customer is never quite sure what they really want? In my opinion customers do not understand how comfort relates to what is possible on paper. The customer has an inate sense of the comfort level that they want but cannot put it into a quantitative value from which an optimum design can be drawn. In the absence of perfect data the NA must err on the conservative side lest he find himself in a lawsuit.

Most customers come with a dream boat in mind. The very idea of the word "dream" indicates a disconnect between reality and optimum design no?

With you little pedal design you are the customer and comfort is clearly not on your high priority list.

Pierre
Clearly the "customer" who started this thread and a few others who have asked questions on it are reasonably well informed.

My aim is to improve their understanding of how certain constraints or objectives impact on others not just offer accepted wisdom that others are apt to do. This is the process of optimisation - understanding the interplay of variables. This is the uncompromising approach to arrive at the best solution for the customer.

I am very comfortable on my little pedal boat. There are not many other ways to get fit while laying on your back completely destressed.

Rick W

[Pierre R]

Originally Posted by Rick Willoughby

I have found hull length to be the most demanding constraint so I can look at how that impacts on power next.

Rick W

You might find length and I love longer boats but I have found comfort to be the most demanding constraint in the real world of boats built and not on paper. I can easily design a boat to meet the 12/12 requirement and the size of 28' to 34'. I very much doubt that the original poster would be satisfied with the comfort level while taking the boat south along the ICW, north in the summer and south in the winter. To much time spent on the boat to have comfort as secondary. I think in sight of the port of departure that the original poster would be displaying the middle index finger at every go fast boat that passed him either direction. I also think the original poster would be disatisifed with the level of convienences and interior provided.

My guess is that if the boat where built, the orginal poster would be more than willing to give up some mileage for some creature comforts. Not to mention the difference in resale values. That would be little consolation once he spent dearly on a boat that could not be resold easily. It's fun to sit here and waste bandwidth on your dream charades but the original poster, I think ,was actually serious.

Myself I don't mind spartan accomodations and lack of real goodies but I don't want my drink to depart the table every time a boat passes me in the ICW. In my own designs, comfort and expectation trumps high tech and ultra green PC crapola nonsense and I sensed the same in the original poster.

[Pierre R]

Originally Posted by Rick Willoughby

Pierre
Clearly the "customer" who started this thread and a few others who have asked questions on it are reasonably well informed.

I am not as sure of that as you seem to be.

I am very comfortable on my little pedal boat. There are not many other ways to get fit while laying on your back completely destressed.

Rick W

Oh really, where is the beer cooler? Where is the food? Where is the shade? Done don't seem to comfortable to me!

[Guest625101138]

Originally Posted by Pierre R

Y...
My guess is that if the boat where built, the orginal poster would be more than willing to give up some mileage for some creature comforts. Not to mention the difference in resale values. That would be little consolation once he spent dearly on a boat that could not be resold easily. It's fun to sit here and waste bandwidth on your dream charades but the original poster, I think ,was actually serious.

Myself I don't mind spartan accomodations and lack of real goodies but I don't want my drink to depart the table every time a boat passes me in the ICW. In my own designs, comfort and expectation trumps high tech and ultra green PC crapola nonsense and I sensed the same in the original poster.

You are guessing about the customers requirements. That is gambling not designing. You need to ask the customer and then give engineering definition to those requirements. You may find the customer is more aligned with your personal requirements or preferences.

Rick W

[Guest625101138]

Originally Posted by Pierre R

I am not as sure of that as you seem to be.

Oh really, where is the beer cooler? Where is the food? Where is the shade? Done don't seem to comfortable to me!

Esky under the seat. Bottle holders in front of the seat. Hat and tights provide shade as well as evaporative cooling once wet. All ready for 8 hours of fun and healthy exercise on the water. More fun and satisfaction than most will ever have the opportunity to experience.

Rick

[Pierre R]

Originally Posted by Rick Willoughby

You are guessing about the customers requirements. That is gambling not designing. You need to ask the customer and then give engineering definition to those requirements. You may find the customer is more aligned with your personal requirements or preferences.

Rick W

No I am not guessing. Read the entire thread from beginning to end and you will see what the original poster has indicated. The original poster has indicated that the comfort level he has in mind is above what he is likely to get with the 12/12 requirement and if necessary he is willing to give a bit on those numbers to achieve the comfort level he has in mind.

[Brian@BNE]

Ah yes! In Pierre's world where comfort is everything you end up with a few thousand lbs down below .... and optimise wake production.

but in the process make comfort sub-optimal due to noise, vibration and angry co-users of the ICW.

Pierre, just add a couple of out-riggers. You can optimize stability! That'll keep your beer and apple pie from sliding off the table - don't accept compromise, you dont have to hold onto everything!

Guys, I'm glad no-one has blown a cerebral fuse yet - seemed close at one point. Could we leave the semantics now? Yes, I'll try and leave my sins off the keyboard too.

[Pierre R]

Originally Posted by Rick Willoughby

As noted earlier on the design space I most often work with is return on investment. That means bang for buck. The way to achieve this is through optimisation of the design.

Rick

Duh! that is not what come out of your wordprocessor to the rest of us.

[Pierre R]

Boy Brian do you read me wrong.

[Willallison]

Post #124

The end result may be outside the range provided

How is it that when I use the word 'may' it's because I'm espousing laziness, yet when you do, you are promoting thorough design?

And I see you've still not chosen to answer any of my last 4 questions. The only conclusion one could draw from that is that either you don't know the answer or realise that it will obviate the absurdity of your position.

Even this statement "I have found hull length to be the most demanding constraint so I can look at how that impacts on power next", confirms that you must often compromise the ideal length in order to fulfill other conflicting requirements.

I've never chosen to belittle the value of your opinion on the basis of your lack of appropriate qualification. But what I do take exception to is the notion that you know better than every single professional designer who accepts that compromise is an inescapable component of naval architecture (with the rather notable exception of your one anonymous NA, for whom compromise is unneccesary).
That you are unable to distinguish between the terms opimisation and compromise suggests that your grasp of the variables at play is not just tenuous... it's completely non-existent.

[Willallison]

Brian,
I think you are missing the point of Pierre's posts. It would be a rare vessel indeed where there were not a set of design objectives, of which at least two were not in conflict with each other. The competent designer is one can find the best solution to satisfy the conflicting requirements. Invariably, that involves compromise.
Comfort is a fine example - and I can assure you that the motion provided by many a multihull would score pretty poorly on that front.