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Scaling up plans

Posted by J-Mo 
Scaling up plans
July 04, 2022 12:58AM
Sandy, I have a question for you. I’ve seen it on the forum but can’t remember the ratio. I built my first boat a couple years and it’s the 16’ double ended with transom as found in Fletchers book. What is the equation for scaling it up to a 17’ vessel?

We just returned from fishing the salmon around Clayton, ID and we went through Bozeman to fly out. I wanted to swing by your shop but I didn’t want to come by unannounced. I should’ve reached out beforehand but I thought you were still out of town. This TN boy is seriously considering moving out there.

I hope you’re well and on the mend.
Re: Scaling up plans
July 04, 2022 04:52PM
In 2D or 3D computer graphics if you want to shrink or blow up any onscreen image, where that image is defined by two or three number vectors:

123,13 .........might be a point on any 2D graph that exists as a long list of 2d points like this

14,117,345 ....or a 3d example of a "vector"

Anyway, to blow everything up proportionately you multiply EVERY vector number by a constant factor.

It is the same for 2d bloat blueprints.

If you have a boat that was originally made with 16' foot side panels and you want to make the same boat but bigger you just need the right multiplication factor.

Let's say you want to make that boat with 18' foot side panels instead of 16. 18 divided by 16 is 1.125

So make a copy of the original blueprints. Replace EVERY every every number on those blueprints with a new number, that is the original number times 1.125. Now you have it.

Sort of. The only complication is how to deal with dimensions given in feet and inches.

15' feet 3-3/16" inches?

15 x 12 is 180 inches
180 + 3" inches gets you closer

183 + ( three divided by 16 is 183.3875 )

Now you have a number you can use in a multiplication: 183.3875
Re: Scaling up plans
July 05, 2022 02:13AM
Convert decimal inches back to feet and inches?
This is the only tricky part.

198.3875 inches for instance? How many feet and inches is that, on a tape measure?

198/12=16.5 feet or 16' foot 6" inches ......which is close to the answer but we still need to add .3875 inches

Let's say we want to convert .3875 inches into 16ths of an inch?

.3875 times 16 = 6.2 sixteenths .......... round that off to 6/16ths or 3/8" inch

so the final answer is 16' feet 6 and 3/8" inch
Re: Scaling up plans
July 05, 2022 02:15AM
Thanks Sandy

I have a construction calculator that makes fraction multiplication super easy. The math won’t be difficult, I just wasn’t sure about the number to multiply by.

Is it worth scaling the boat up to 17’? I would like to be able to row with that third person, but does that extra size help that much?

Re: Scaling up plans
July 05, 2022 05:54PM
Ah. Ok.

RE> "I would like to be able to row with that third person"

Three passengers and one person rowing, four in all?
You need a big boat for that. 18' foot side panels makes a boat almost but not quite 17' feet long end to end.
With that boat you can put three passengers side by side on a maybe 62" or 64" inch wide bench slightly forward of the middle.

Rower's seat slightly adjustable forward and back six to eight inches .........with the front edge of the rower's seat about 40" back from the rear edge of the passenger compartment.

You could do the sane payload with a 16' boat (17' foot side panels) where two passengers sit side by side in front of the rower and one passenger sits behind the rower. That would work but it does spread the weight out closer to the ends of the boat, so it would not row as well as the bigger boat with all three passengers side by side just a little forward of middle.

The closer to the center of the boat the payload is the better it rows, the faster it will turn and the more side to side stable it will be. Weight out at the ends of the boat makes a very tippy boat.

For fly fishing purposes you have to bite the bullet and put the weight out at the ends. You do pay a performance price for rowing that way. For white water purposes it's far far far better to concentrate the weight as close to the middle as possible.
Re: Scaling up plans
July 05, 2022 08:09PM
Sorry I should’ve specified but you have given me some great info. I’ve only really rowed with one person in the front seat, and with a smaller person behind me, rowing definitely isn’t as easy. Is this to be expected or would scaling up a foot make enough of a difference to justify the extra costs?

I would like to have the capability to row with another grown person in the rear, and I am intrigued by the challenge of scaling up
Re: Scaling up plans
July 06, 2022 02:54AM
Which boat? Honky Dory or Beavertail?
Re: Scaling up plans
July 06, 2022 02:41PM
My first boat was the 16’ double with transom from Fletchers book.
Re: Scaling up plans
July 06, 2022 02:47PM
Ah. I like Bigger boats. You can walk around inside without tipping the boat. They are more stable in white water. They are more work to build and harder to deal with on and off the trailer. It all boils down to ................... what you use the boat for.

White water? Fly Fishing or pulling plugs?

It you are fly fishing you need (need need need) a symmetrical bottom, so there is as much buoyancy in the back as the front.

If you are pulling plugs or mostly into white water you can put all the passengers on the front seat, and also move that front seat closer to the middle. And you do not need the symmetrical bottom. You can make the bottom profile a bit like a Chinese soup spoon, so it is wider were the payload is and narrower where only the rower is.

The Chinese soup spoon shape (not symmetrical) more narrowly focuses the turning axis to the boat's natural center of gravity, ever so slightly behind the passenger seat, where all the weight is.
Re: Scaling up plans
July 06, 2022 05:13PM
We have some pretty good rapids around here, and I mostly use deep water lures but I also fly fish. I am intrigued by the honky dory being 56” at the middle. Is there an discussion/example of it being built on here?

I’m out of town currently and it’s hard to use this site on my phone, so I will be able to view pics better on my home computer
Re: Scaling up plans
July 07, 2022 02:37PM
What's online is what I have.
To make a 56" inch bottom it is possible to scarf plywood. Honeycomb core is easier and better, far better, at the same time. It became impossible for DIY boat builders to buy Plascore for a while. Is it still that way? I'm retired and I still have a few sheets left. I don't know. There are other brands.

RE> discussion
My online plans include a lot. Diagrams plus an online book, with a few pages about honeycomb core. I don't make much money selling passwords to the plans. It basically pays for the website, which is more of a hobby than a business. Marketing is all switching to social media now. I haven't made that jump. I might start a youtube channel at some point.

I bought a fancy camera, in order to make video. I'll start that project after I get my current boat finished. I'm slow. I'm 73 and have Long Covid. So I move in slow motion. But not dead yet.

Re: Scaling up plans
July 07, 2022 11:00PM
I’m going to buy your password for sure, at the very least as thanks for the help this site has provided. I would like to find the material for the honeycomb and give it a shot, I’ll just have to locate some locally. If not, it’ll be plywood.

You should definitely start a YouTube channel.
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