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Any way to make the Firefly 20" wide


mdavis121212

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Who knows what it would do? If you do that it is a new  design and I wouldn't dare to guess what would happen.

 

On a side note, my clientele is 95% or more causal paddlers who want stable boats. It is in my plans to start to offer some more serious, as in smaller, less stable boats. I realize that many of my designs feel like barges to those that that can paddle narrow boats. Firefly and Long Shot are likely candidates for miniaturization. There is no time line set. So don't expect anything soon.

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Yea seems like the Firefly would work well that way.  I shaved 2 inches off going form a 24 inch beam Carolina to a 22 inch beam Tempest but I still want something faster.  Stability is getting to be less and less an issue for me.   I guess stability on an Aleut Birdarka wasn't much.  I hear they would roll over unless a paddler was inside.

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Width is just a number and doesn't meant anything as to the performance of a boat. Don't get caught up in that number game. What matters is what is under the water and what is above it doesn't have any bearing on the speed (for the most part anyway).  

 

Once I took Long Shot and just let the computer software scale the width down an inch at a time and compared the numbers, the decrease in resistance (directly related to the speed) was minimal while the decrease in stability was rather quick for each inch. By making it a couple of inches narrower all I really gained was a SLIGHTLY faster boat that was much less stable. 

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Jeff,

 

When you scale the numbers in your program which I assume is something like FreeShip do you scale the width, length, depth uniformly or have you come across a more consistent approach whereby the hydrostatics remain similar?

 

To be more specific do you shrink width, length and depth all by 1 inch at a time or if you shrink width by 1 inch length  does length go up say 2 inches.

 

I guess what I am wondering is if one day someone could tell you -> I like the "Iggy" shape and I am 5-11, 225 lbs and then your program scales for more individual fits. Almost like ordering a pair of shoes.

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Chris, all I ever did was just to change one factor, such as width, to see what effect that had on the boat. I didn't do it very scientific and document it or try to correlate one to another. Mainly I wanted to see what effect length had on resistance and just a general idea of what to expect. 

 

It might be possible to do what your saying but there is just so much involved I would ever attempt it. And I am skeptical that you could get good results. There is just so much personal preference in what makes a boat 'good'.

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I guess what I have always wondered is take any of your kayaks for example the Long Shot.

 

Currently it is designed for max paddler I think at 250 lbs and for that design you have a set of hydrostatics

 

Suppose a 200 lb and 300 lb person said make me Long Shot with the same hydrostatics as for the 250 lb design

 

I have always wondered if this would be possible and how you would tweak the length, width and depth to maintain nearly the hydrostatic numbers.

 

I am a math guy by trade and yes I ponder these weird ideas but in the past have been too lazy to really put it to a test.

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I guess what I have always wondered is take any of your kayaks for example the Long Shot.

 

Currently it is designed for max paddler I think at 250 lbs and for that design you have a set of hydrostatics

 

Suppose a 200 lb and 300 lb person said make me Long Shot with the same hydrostatics as for the 250 lb design

 

I have always wondered if this would be possible and how you would tweak the length, width and depth to maintain nearly the hydrostatic numbers.

 

I am a math guy by trade and yes I ponder these weird ideas but in the past have been too lazy to really put it to a test.

 

I have a spreadsheet set up that allows quick calculation of the effect of changing the shape of the waterline on sinkage.  I integrate a fourth order polynomial equation to get the waterline area, then calculate the volume required for a particular displacement.  I'll post a typical example if I can figure out what I need to do to host the picture(s).

 

I'll put the example I intended to post into words.  Waterline length: 15 feet, beam: 20 inches, location of maximum beam:  0.55(15) feet from the bow, entry angle:  7 degrees, required displacement:  50 pounds, water density: 62.4 pcf.  The slope of the water line plane is zero at the maximum beam.  The resulting equation for the waterline shape (half shape along the centerline) is buttline, y = 0.000 000 029 71x^4 + 0.000 014x^3 + 0.000 884x^2 + 0.1222X.  Multiply the integral by 2 to get the waterplane area.

 

The waterplane area is 15.81 square feet, so the sinkage to support 50 pounds is 0.61 inches.  Not much.  But, the perimeter length is 30.23 feet, so the added wetted area is approximately 1.5 square feet (using a constant area cross section).

 

This squares with a bunch of layout work I made last summer; these little boats have wetted areas that are very sensitive to minor changes.  (I was working on minimum wetted area shapes for the E340 race which requires solar power and battery storage with no other motivation for propulsion, so the power required to move the boat has to be extremely small in order to complete the long race.  Or even get to the end of the first day of the race!)

 

Fooling with length in addition to the beam can screw up the stability simply due to the loss of volume along the length of the boat even though that volume might be relatively close to the centerline of the boat, it's still contributing small righting moment.  This is the reason long boats with beams and reasonably similar cross section shapes equal to a shorter boat can yield more rolling stability.  It's also the reason very short kayaks get fat, the volume and stability has to come from some place and there ain't much place to get it from lengthwise.

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I had to think on you question Chris and "I think" the answer is no. But that answer depends.  

 

There are a lot of measure of Hydrodynamics so to get two boats exactly right would be take a computer that could process all the combinations. But I question if, because of all the difference in weight, it is possible to get an exact match? The fact the displacement is different makes me think that the hydos would be different and never get an exact match. Maybe close but I don't know enough to say for sure. 

 

Now, if you just picked a few measurements then it is probably possible. My software has the capability to enter a two or three measurements and tell it what you want them to be and it will adjust the boat to those. I have only used it a couple of times playing with it and didn't like the changes it made to the boat and it didn't seem to have any practical use for kayaks. I can see it being useful for a bigger boat. 

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