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Scaling Ravenswood


mfrankel

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Dear Jeff:

 

I recently built and posted pictures of my Ravenswood.  It is exactly what I wanted and I am pleased with its performance.

 

Now my wife wants one.  She is ready to move on from our tandem.

 

She is 5'1", 115lbs.

 

Although she can paddle the Ravenswood without any apparent problem, I thought it would be an improvement for her to paddle a smaller kayak.

 

I was thinking 92% of the Ravenswood.

 

If this is a good idea, for the appropriate fee, would it be possible for you to program your computer to print me out full size plans for such a scaled down version? 

 

Mark Frankel

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NO!   

 

Don't buy into the scaling BS. Scaling a boat is just asking for trouble and I would NEVER scale a good boat.  Yes people in the forums do it all the time but have you ever seen a designer that offers a 95% scaled down version of his/her boats? There is a reason for that. Height, width and length are not directly related and just scaling it can produce some weird results.

 

If the Ravenswood works for her build it as is.  If she wants something snugger fitting then look at Shad. It's a lower volume and even if I do say so, a beautiful boat!

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Okay,  I understand that you can't shrink a particular boat to get the same result for a smaller person.  (And for the record, I would have no objection to adding a Shad to the fleet.)

 

My next question is:  For flatwater paddling, can a short lightweight person get the same performance out of, say a 14ft kayak, that a larger person would experience out of, say a similarly proportioned 15ft kayak?

 

 

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  :blink:   I know  you didn't mean it that way but that is such a loaded question. There are just so many variables that there is no way to answer that with any reasonable accuracy. You would need to define what performance means  Speed, tracking, maneuverability, rough water ability......? Then what weight differences are we talking, Strength differences between the two paddlers. Boat shape. Dozens more variable come into play and even then I couldn't do more than guess what would happen.

 

Overall length means nothing. It is all about the part of the boat that is underwater. My personal Curlew is a great example.  I like paddling it, but you put a 100 lb person in there and they do not sink it enough to make it track. The waterline length shortens up considerably and it becomes a miserable boat for them and probably a slow boat too. The characteristics change so dramatically that wants to constantly turn on the paddler. That is because the underwater shape changes so much with the light paddler in it. 

 

So the best answer I can give is maybe, but it depends.

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And the moral is, just because you can build a paddle a boat doesn't mean you can design a boat.

Lots of truth to that statement.  It never seems to amaze me how many people who don't understand design at all think experimenting is amusing.  I understand the desire, but their expectations are totally unreasonable.  They actually think they will trip over something.  Unless you are willing to really study how the design process works you are better off finding a good design and putting your creative efforts into the paint job, rigging and hatch access and other personalizations  that don't effect handling.

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It is hard to get a boat downsized to custom fit a person's weight etc.... Christopher Cunningham's book is unique in its way to figure the length-width of a kayak to a person's size..... Take that and learn the kayakfoundry design program ..... But it takes a lot--lot of time and from experience, my 3rd design build.... I finally got one I like to paddle.....The lighter and shorter a person is the narrower the beam they can handle...

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I hate to admit this, but while I was wasting time trying to figure out how to shrink an existing SOF design, my wife strayed from the SOF fold and was lusting after the Pygmy Arctic Tern 14 stitch and glue kayak one of our kayak club members built.  To make a short story shorter, tonight I ordered a Pygmy Osprey 13 kit.  It is a 22" beam, 13ft kayak.  It is designed for paddlers 5'3" and shorter and has been in the Pygmy lineup for some time.  I am told that it is popular with petite women.  This will be my first stitch and glue experience, and I am looking forward to a nice late fall early winter project, (except for the sanding figerglass part).

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Stitch and glue make for some beautiful kayaks, but I hate sanding fiberglass and epoxy so much I opted for the SOF.  I have a little sail boat I started over 8 years ago and have it 2/3's done but I gave out on the sanding.  What a mess.  Maybe some day I will get back to it.

 

Get your wife to help on the sanding, she will appreciate the kayak more.

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  • 1 month later...

I used to build hang gliders professionally in the mid- eighties and we ran into similar problems trying to scale down a successful model.  Had to experiment with completely different airframe geometry and completely different planforms and aspect ratios for larger or smaller models of the ....same....glider.  which meant it wasnt really the ...same...glider except by name (not design)

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