Alternative hull design

[jacquesmm]

That chine is useful on planing hulls, it increases stability and cleanly separate the water from the hull. It also eliminate some sprays.
On most boats, we add a spray rail type chine there simply because it is easier.
On some boats like the OB15/18 and CS23/25, that chine is built-in, it is part of the hull.
On slower boats, it doesn't do much. It must be very wide to reduce roll.

[laporter]

laporter,

That's called a reverse chine. Typically found on planing hulls. Very deep vee boats (think bertram, blackfin, etc) tend to use them. It tends to reduce the degree of snaproll common to deep vee boats while at rest. On plane the reverse chine adds lift and helps deflect spray outwards.

Thanks guys. Somehow I knew that but forgot. Getting old ya know!

That's a feature that probably causes the "slap slap slap" of water against the hull when resting at anchor or dock eh? It gets somewhat annoying after awhile when you're in the v-berth trying to sleep. I guess some romantics enjoy it but personally I don't.

Rick

[flattie]

laporter,
As jacques noted on slow boats there'd really be no use for a reverse chine. Displacement hulls are all about smooth curves as the hull moves through the water - its okay for the water to actually rise up the hull sides. Planing hulls are all sharp edges to let the water separate from the hull and allow the hull to rise up out of the water and overtake its bow wake - something a displacement hull could never do regardless of how much horsepower you put in it. Overpower a displacement hull and it will just make a bigger hole in the water (larger wake) and burn more gas with no appreciable increase in speed....

And yes, the chines will cause that slapping sound.

Something else to consider is that displacement hulls have poor initial stability but excellent ultimate stability whereas planing hulls have high initial stability but poor ultimate stability. In short, a displacement hull will start to roll sooner than a planing hull but can roll much further and still recover without rolling than a planing hull can. The motion is also "slower". A planing hull will initially resist rolling much more but when in starts to roll it will be a more sudden movement and planing hulls generally cannot roll as far and still recover as a displacement hull can.

My vote would be for a semi displacement hull form (like many downeast boats) with a single diesel inboard, full keel and skeg protecting the running gear that can cruise at 20kts all day in almost anytype of sea...

flattie

[laporter]

Going back to what Bear was originally talking about before I so rudely hijacked his thread, he was talking about there being limitations in using flat panels, such as plywood, to create a more shippy looking hull by using radius shapes. Did I summarized that correctly? I think the answer was yes you can, but you don't have to. So my understanding is to have a radius'd chine vs a sharp chine will make very little difference in the ride of this boat, or at least what us meer mortals could detect. If, as Bear mentioned estetics are important and as was indicated the chine, for the most part, will be submerged it's a moot point. Now from an engineering & fabrication point it's easier to form the hard chine for the amateur builder using plywood panels, correct? Would not ease of assembly & economics be the determining factors for the design of such a boat?

Anywho, I just got wondering, it was bugging me for some reason. I'd like to see a hull form something like this!

[flattie]

laporter,

That looks like a "built down" downeast boat hull. Downeast hulls can also be skeg built. The built down boat has the hull smoothly transition into the keel. The skeg boat has a relatively flatter bottom aft with a skeg bolted on. Skeg boats usually carry more speed as there's less boat under water.

[boguesound kid]

hey, not to beat a dead horse but asthetics are important. if you go to my gallery you can see some very beautiful examples of the kind of shape you get out of plwood core panels. It's really a question of economics, these compound courves reqire(generally) at least twice the materials and twice the labor. Not to mention skill, and experience. if you would really like to give it a shot I strongly suggest you get a copy of"'the gougeon brothers on boat construction" and check out chapter 21. That book is often called the bible of boatbuilding. Any thing is possible but that is an ambitous undertaking. research it all you can before you commit.