flat bottom hulls

I would very much like to continue this discussion but "par" said in another thread that, "I will haunt your every move on this forum-" I offered a sincere apology for somehow hurting his feelings and I extend a hand in friendship but i guess it was to no avail. So i've decided not to avail myself to his pointless ridicule.

Ladies and gentlemen:.


Presenting --------------> PAR!

 

PAR,
In a discussion, to call another "arrogant, simplistic and narrow minded" indicates you may have an "inherent design flaw" in your brain.

Easy Rider

 

Exactly. So when sideways on the face of a wave, a round bottom (or v) has the ability to easier roll/rock and will remain more upright.

A flat bottom has more initial stability, but a round or v bottom has more dynamic stability in waves at sea.

 

Loveofsea has accused me and most every other designer of criminal misconduct and depraved indifference. He has refused to quantify his repeated accusations, so, yes, I've taken it personally. Simply asking for a clarification of his views hasn't been forthcoming, he merely attempts to change the subject or blatantly ignores these reasonable questions. It's not a matter of opinion, when being accused of a crime.

 

I would think there would be a lot of turbulence around the chines on a flat bottomed boat when rolling that would dampen the roll but as SamSam says the high volume chines on the flat bottomed boat make them too snappy and dominates their roll characteristics. In a kayak abeam to a wave a V bottomed or round bottomed hull will allow the paddler to remain much more vertical. With a flatter bottom the boat itself is forced to assume a position more parallel with the water. This presents paddling problems especially on confused seas. I think the best flat bottom boat may be the double chine sampan type. These boats are much less likely to trip on their chines sliding sideways on the face of a wave. That way a broach stays a broach instead of becoming a capsize.

Eric Henning

 

It is not the flat bottom itself that make for snappy action in waves. For instance, a banks style dory has a flat bottom but does not react snappily in waves. A shallow V bottom hull that takes its bottom out near the max sheer beam will be more snappy than a dory in waves. A flat bottom hull with vertical sides will be most snappy of monohulls.

The question is whether the transverse volume distribution causes the boat to want to follow the shape of a passing wave from abeam. The boat least likely to do this would be the old "plank on edge" types. Boats like the Boston Whaler also like to follow the wave shape. For a really snappy and very uncomfortable ride try a lightweight catamaran in bad slop with no wind.

 

In my mind I was commenting on the two extremes, flat bottom with vertical sides and round bottom. The two would have the opposites in stability, flat having the most initial/static and round theoretically having the most dynamic. And as a general black and white picture picture of stability, everything in between the two extremes would have different shades of gray. The stiffness or snappyness of a flat bottom would be related to leveraged buoyancy, the more buoyancy on the beams of a boat, the more leverage and the less ability to act independently of the shape of the water. It's more prone to lie flat on the surface of the water and if the water is tilted as in a wave, the flat bottom will still tend to lie flat on the water, albeit tilted.

As said, a flat bottom itself is not unseaworthy. Boats are combinations of many shapes and weights and dimensions. Some are good for one water condition and not another, some will work well in both. A wrong combination in the wrong water conditions are what make a boat unseaworthy.

It's time for Neal283 to check back in as to whether his questions have been answered enough or if he has more.

 

I've decided that since i've logged over 90,000nm of open seas in a flatbottom, i would continue to try to contribute to this thread despite the lunatic that is "haunting" me. I will deal with him as required...

Because a flatbottom hull has a different relationship with the surface than a V bottom, the means of controlling the hull must be enhansed. Helm controls common to most small boats consist of a steering wheel (3 and a half turns lock to lock) and a lever for the throttle. Both of those are very cumbersom in seas and do not afford the quick response that makes a flatbottom work so well over the swells. I use a tiller because it allows for articulate throttle controll and instant lock to lock steering. A flatbottom in seas is much more like a dirtbike or a powered surfboard than a jeep.

 

There's a thought a tiller control on a 40' flat bottom, yep, that'll fix it . . .

So how many think their steering wheel is cumbersome? How about those pesky throttle controls?

Yep, you still think you're the only one that has anything "figured out".

How about thrusters on all corners to really "enhance" the helm.

Maybe a joy stick, fly by wire control for the ultimate "gaming" feel.

 

Sam Sam; I take issue with your statement that a round bottomed boat will have the better ultimate stability. The top sides have a very signifigant bearing on ultimate stability so I do not think you can assign merit on the basis of bottom shape alone.

 

ladies and gentlemen welcome to boat design dot net late night professional mud wrestling

I think what we need is a few snazzy outfits and set you guys up for a cage match
you can fight over who gets the cape and who gets the mask

I want a clean fight
no biting no designing and no kicking or scratching

and
break

( waves hand in a vertical chopping motion and backs away )

 

Boston

I have only fought twice in my life, both times defending a woman from assult. PAR doesn't qualify~ Besides what is one to do when a nutcase thinks he is "haunting" you by throwing popcorn your way PAR, mebby you should be looking into an anger management class, or semester.

just say'n~

I have to agree with messabout, a hard chine will always resist rolling better than a round bottom. The more it rolls, the more hull in the water and the more resistance to roll.

(PS, if you want your skiff to be dryer ride, sharpen the edge of the chine)

 

I think we are all guilty of having a bad day from time to time
I'm sure as hell guilty at least


my thing is I'd like to learn something about chines and flat bottom hulls, how they effect roll characteristics and how they effect forward resistance of the hull. My bet is hard chines are slower as none of the ocean sailing racers use a hard chine form hull although Dashew looks like they took a blue water racing sail hull stabilized it and stuck a huge engine in it, ended up getting pretty good millage with almost no roll and flat bottom power boat with vertical sides.
ok they have a million dollar stabilization system but that flat bottom with soft chines does seem to be working for them in a power displacement yacht

 

picture throwing a sheet of plywood on the surface in the wind and seas

then a canoe

 

Before anyone makes a broad statement like that, you should look for exceptions. You might google Ragtime or Infidel, designed by NZ native John Spencer, a 65' hard chine ocean racer that set records in Pacific ocean races. Built of that awful plywood too. The long racing career of this boat is amazing.

This is not a claim that hard chine is better than a round or soft chine hull, "just the facts ma'm."

One reason that soft chines dominate in big boats is that a boat can be made lighter and structurally stiffer in round chine than in hard chine.