Boats with a Flair

[rhutchinson]

On more than on thread Keith has brought attention to the amount of flair in the side of his pirogues vs. other designs like Uncle Johns.
My question is how does the amount of flair affect the boat, in particular a pirogue. I'm guessing how much you put in would depend on intended use and both more and less would have it's drawbacks.

Thanks
Richard

 

[JEM]

With the Uncle Johns style of building, more flare creates more rocker. More rocker decreases straight-line tracking but increases maneuverability.

Also with more rocker, you're decreasing the capacity slightly (and also slightly increasing draft)... but unless you go extreme with the flare/rocker, I doubt you'd notice any change in capacity.

 

[jdupre']

In my experience, flair increases secondary stability, depending on the width of the boat. As you lean the pirogue, it becomes more stable up to any reasonable angle of lean. I've read a good kayak does the same.

In an Uncle John's style pirogue, more flair will give you more rocker. If designing from scratch for more flair, you would have to cut the sides with top and bottom edges forming long subtle arcs. I think Keith had pictures of that in some of his posts.

Joey

 

[seedtick]

The amount of flare is indeed dependent on personal preference and intended use.

More flare increases the footprint of the boat in the water as you load it thus giving more bouyancy (hence higher loading capacity).

Here's a 14' pirogue with a wide flare that's carrying maybe 600 pounds

I'll agree that it's loaded but they are going down the bayou

More flare also increases the stability of the boat as it leans because the flare adds to the footprint. Consider the stability of this \__/ tipping over vs. this |__| tipping.

For the same width bottom more flare also gives more total width at the top, so if you're weaving your way through trees and such in the water then having aboat that's 8 or 10 inches narrower is a benefit.

I agree with Matt that with UJ style of building, more flare is more rocker, but if you cut an arc in the bottom of the sides - instead of just leaving them straight- you can reduce the amount of rocker. Less arc is more rocker, more arc is less rocker. Here's how we cut the sides of a pirogue that's going to have a 35 degree flare to reduce the rocker. These sides will have an inside bottom chine

I don't know what the flare on a UJ is but I've seen pirogues with flares ranging from 20 to 45 degrees. Here again it's personal preference along with the capabilities of the boatbuilder. The easiest boat to build is a shoebox (vertical sides). As flare increases, the degree of difficulty of build also increases - compound angles become more compound, the stems are not as simple to cut out and the ribs are more unique

 

[rhutchinson]

Thanks guys, thats a lot of info. I was thinking in the right direction on some of it. I hadn't gone as far as thinking about the rocker. A lot of this makes sense to me but it's not realy going to hit home until I build my first one.
U.J.'s is about half of what yours are seedtick. I was thinking a little more flair would help lift the side of the boat in some mild chop or some boat wake and maybe make a little dryer ride, unless it lowered the overall gunnel to water height to much.(also making a little more violent ride).
Thanks again for the info.
Richard
P.S. HAPPY NEW YEAR :lol:

 

[jdupre']

Richard, test a 1/12 scale poster board model just taped together at the bow and stern. As you flare the sides, you'll see the rocker increase. That's how I set the rocker on my pirogue. If you flair as much as seedtick does, you'll have about a foot of rocker on an Uncle John's pirogue.

Joey

 

[JEM]

I need to qualify my capacity statement:

If you take 2 hulls of the same design like Uncle John's, add more rocker to one than the other and then sink them to the same draft, the one with less rocker will have more capacity.... more boat in the water.

Even with a wider flare on the hull with more rocker, the hull with less rocker will have more wetted surface area in the water and displace more.

Now the draft I'm speaking of is paddle craft draft... like 2-5" and changing flare amounts within 10-20 degrees. If you go to extremes with the flare, that would change things.

 

[rhutchinson]

I noticed on the picture example seedtick posted above that there is a lot of ark for 35 deg. flair. Is there a formula for this, as in (for example) an inch of ark nullifys (sp?) 5 deg of flair? Or is it not that simple. I noticed that the sides in seedticks example didn't seem to be the same width stem to stern.
I will get some poster board and play around.
Thanks
Richard

 

[rhutchinson]

Mat, looking at it from the other way, your saying that two hulls of the same design, one with more rocker and flare than the other, loaded with the same weight, the one with less rocker would pull less draft, right?

Thanks
Richard

 

[seedtick]

Rocker and flare are connected only if you change the flare without changing the sides. A large enough arc in the bottom of the sides can give you no rocker with a 45 degree flare.

A pirogue with a 2" rocker will have slightly less draft than one with no rocker. I don't believe that it would be noticeable as the small triangle of boat bottom that is out of the water (with the rocker) doesn't change the footprint that much. I believe that rocker (or lack thereof) has more to do with handling than capacity. More rocker is more maneuverable while less rocker tracks better.

More flare will deflect waves better but it also lowers vertical depth of the boat. You can overcome this by building with wider (deeper) sides or by adding a tumblehome (see first pic i posted).

I don't know if a mathematical formula exists that correlates amount of arc with flare and rocker. The old boatbuilders that taught friend Keith and I didn't have written plans they built by hand and by eye. I suspect their correlation of arc, rocker and flare was done experimentally by them over the years to achieve a design they liked.

No the sides in the picture are not the same width stem to stern - more of the by hand and eye architecture.

Joey's dead on with the suggestion of playing with the posterboard only i'd scale up to a 1/6 or 1/4 model as some of the small nuances won't show on a 1/12. For example a 1" arc on a 1/12 is 1/12" - pretty hard to cut. But a 1" arc on 1/4 is 1/4" - much easier

 

[seedtick]

oops, correct my second paragraph to read "...will have slightly more draft..."

 

[jdupre']

Tick, good call on experimenting with a bigger scale. I just didn't think posterboard had enough body to go that big. Heck, if he went 1/4 scale, with some scrap luan , he could build a nice holder for boiled crawfish, shrimp, crabs or ????.

 

[rhutchinson]

Thanks guys for all the info. Gives me a lot to study on and play with.

I'd have to come down your way to get any of those things. We have Catfish and Crappie. Lets see, 4' pirogue filled with catfish and crappie fillets, and hushpuppys. Not quite crawfish, but it would work! :lol:


Richard

 

[JEM]

The relation between flare and rocker is relevant/real in the regard to the Uncle John method of building... when the side panels' top and bottom edges are parallel and in a straight line with no curve.

If you deviate and using shallow arcs in the bottom of the side panels, then that relationship is broken.

I'm just pointing out what will happen if you follow Uncle John's instructions. I'm not saying either way is right or wrong.