Angle on sides of jon boat

Let's have an argument about what the "right" depth of the sides might be ! :D
 
Mr Efficiency said:
Simple example, if I place my weight on the gunwale of a 6' wide flat-bottom boat that is 4' wide at the waterline, I will notice more heel than if the waterline is 5', all else being similar. Which is what gonzo is talking about.
Click to expand...
What really Gonzo is talking about only he can know. So I started by assuming what I think he means when speaking of "initial stability".
Forget sides angle: If you change the position of the center of gravity, away from the center line, the heeling arm will be higher, the boat the willheel much more the farther the weight (that's what you're saying), but the initial stability does not change. Are two totally different things. The initial stability depends, among other things, on waterplane breadth. While floatation, and other things, does not change, the initial stability will be the same.
However, if you raise the center of gravity, though not absolutely change anything else on the ship, the initial stability decreases, whatever the inclination of hull sides. If you change waterplane breadth, without changing anything else, the initial stability may change. This is not my invention but the way things are.
If you define the initial stability otherwise, we should think how the angle of the side influences at that initial stability .
We must seek effectiveness, not efficiency. Happy to help.
Cheers.
 
TANSL said:
What really Gonzo is talking about only he can know. So I started by assuming what I think he means when speaking of "initial stability".
Forget sides angle: If you change the position of the center of gravity, away from the center line, the heeling arm will be higher, the boat the willheel much more the farther the weight (that's what you're saying), but the initial stability does not change. Are two totally different things. The initial stability depends, among other things, on waterplane breadth. While floatation, and other things, does not change, the initial stability will be the same.
However, if you raise the center of gravity, though not absolutely change anything else on the ship, the initial stability decreases, whatever the inclination of hull sides. If you change waterplane breadth, without changing anything else, the initial stability may change. This is not my invention but the way things are.
If you define the initial stability otherwise, we should think how the angle of the side influences at that initial stability .
We must seek effectiveness, not efficiency. Happy to help.
Cheers.
Click to expand...

I was assuming the same overall beam, with varying angles of the sides, clearly the one with best initial stability has vertical sides.
 
One of the reasons I figure it's good to have flare on a jon bot is to help keep the outside chine from catching on a turn. When that happens it is comparable to being in a nice, smooth 4 wheel drift into a curb.

The biggest help to stop that though is some strakes on the bottom.
 
The outside chine is mostly out of the water when you turn at high speed.
 
The outer chine is usually, but not always, clear of the water in a turn. A typical hydroplane, for example, runs very flat and they almost always have a small beveled chine, affectionately and hopefully known as "non trips". The normal flare of an ordinary boat does little to affect the outer chine lift. Jons usually have some runners (strakes) on the bottom to dampen the skid as Sam has said.

Meanwhile we might have scared the OP away. He still has not given us any details of what size or application his boat is to have.
 
If you are trying to minimize materials, and you consider 10 degrees of heel at max load is about where the rail goes under, then 14-17 degrees puts you in the sweet spot. This can be important if you are trying to build the biggest boat out of sheet stock. File bottom hulls end up a tad less with 5 to 7 degrees of deadrise on the bottom and 10 to 14 degrees of flare at midship. This says nothing about performance, its just a packaging, stability and load carrying compromise that works quite well over a wide range of loads. If you are bumping in to road width limits, or seriously concerned about high speed performance (or low power performance, for that matter), there will be different answers.
 
Without something to stop a flat bottom from skidding sideways, or more like spinning sideways, the chine will catch and trip even with flared sides. It just seems it might be mitigated somewhat with flared sides as opposed to vertical scow type sides. But a small dampening effect isn't really much help when too much skid happens, it's a pretty abrupt or even violent action no matter what when a chine trips.
 
For the topsides to participate in an anti-trip role, they'd need to be near 45 degrees, which is a wee bit much for topside flare. At the speeds a trip is possible, bottom and chine strakes have little effect, preventing it, mostly because they're in very turbulent flow and not "biting" much. In fact, my observations have shown it's this turbulence, partly caused by the strakes that prevents a trip. In a high speed turn the bottom is skidding, literally dancing on this aerated turbulence, eventually this wash of turbulence causes the inner chine to drop down, the boat's lateral trim changes and she "digs in" (on the inboard chine), at which point the turn sharpens dramatically. This is the point a trip is likely and it's pretty random, depending on many factors, with sea state and luck playing major roles. The usual set of events is the lateral trim changes enough (for one or more of several possibilities) to lower the outer chine, where drag goes up astronomically and momentum takes over.

I've tripped quite a few boats over the years, though none in recently and each one was just a little different. Some were what you'd expect and sudden flop over the beam ends, but many others gave you a hint - a double tap sort of thing, then you tripped. I've also experienced near trips, where the boat was upset enough to toss an unbelted occupant over the side, but not enough to complete the rollover. I remember saving a near trip by having fast enough reactions, to enter enough steering input, as the boat started to roll, literally on its topside flanks, that she slammed back down. I've also been in turns where the bottom was skidding and you could feel the boat was trying to trip, but the set of circumstances and speeds were just slightly in your favor, so you feel the popping and vertical accelerations, but she just continues to dance and doesn't trip.

Jon boats in general and some hull forms in particular, need to be reasonably powered. You can have a plumb sided craft with reasonable power that'll never trip, but you can have a dory flare, with a wide bottom panel and trip in a heartbeat (literally) if overpowered. I have a number of designs that could be considered trip prone, but I keep the power recommendations on these lower than what the USCG says I can employ, knowing what can happen if you drive them too hard.

To qualify these comments, much of it was derived with flats boats and Hickman sea sled studies I did on a few prototypes. The anti trip attributes for the sea sled modifications were the most enlightening, as this hull form doesn't have a conventional bottom, to cause the skidding turbulence to sink the inboard chine. I also ran flat bottom drag racers and "up and backs" when I was younger. We all played hard with anti-trip contrivances on the up and backs, with everything from fins and forward rudders to blade strakes and about every shape and device you can think of.
 
troy2000 said:
And I could definitely have been more diplomatic in my response. My bad. :)

Don't mistake PAR's bluntness and lack of obfuscating pretty language for condescension... he's willing to go out of his way to explain and inform, and is one of the best resources for amateur builders I've run into online. I've learned a lot from him - and he also happens to design boats with a nice blend of looks and practicality.
Click to expand...

I also apologize for taking it that way, I was sick and ornery that night, and right before leaving on vacation. I never mean to take the helpfulness here for granted!
 
messabout said:
The outer chine is usually, but not always, clear of the water in a turn. A typical hydroplane, for example, runs very flat and they almost always have a small beveled chine, affectionately and hopefully known as "non trips". The normal flare of an ordinary boat does little to affect the outer chine lift. Jons usually have some runners (strakes) on the bottom to dampen the skid as Sam has said.

Meanwhile we might have scared the OP away. He still has not given us any details of what size or application his boat is to have.
Click to expand...

No, didnt scare me away, just been traveling, will post details in just a bit.
 
So, This is pretty close to exactly what I am shooting for, the folding jon boat in this video But made out of wood(ply) and fiberglass.
It meets all the requirements I am looking for as far as portability, want to be able to just slide it into back of pickup. It is only going to be used with me or one other person at the same time, in small calm lakes and mild rivers, with a 5-10 hp motor. Does not look like a whole lot of angle on the sides, maybe 10-14 degree, I kinda like around 10. I wont be out jumping wakes as seen in video.
I could go 14 foot I suppose, but think I will be happy with a 12 foot. I and my fishing buddy both weigh around 175# each.
42" at bottom, approx 48" at gunwales with a 10 degree angle. It will have oak chines/runners on the bottom.
 
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