flat vs Vee

[Kirbinator]

Grand day, I am in the process of starting an Aluminum dingy for My Cal26, about 8-9 feet trying to decide if flat would be more stable or about a 10 degree vee?

[tom28571]

With waterline beams equal, flat is more stable but that is not the only thing to look for. A V, even a slight one will make a more rigid and stronger bottom if scantlings are the same. Rowing a V is easier than a flat bottom. With aluminum, these factors are more pronounced. Look at the shape of the "flat" bottoms of aluminum jon boats. Lots of reinforcement in either ribs or corrugations are required. A slightly rounded bottom, like a Grumman canoe, may be the best for aluminum.

[Kirbinator]

Thanks Tom, all I need now is the courage to bite into my Plate without an oficial blueprint. haha

[thudpucker]

Take your digital camera to a boat store and Plagerize to your heart's content.

[Asleep Helmsman]

What's the beam?

[Kirbinator]

the beam has not been decided I have a 4x8 sheet I was going to use for the bottom and a5x10 for the sides one design I looked at uses one sheet 4x8 for the whole boat nice and light but not very large.open to opinions...

[Easy Rider]

Kirb,
The best paddling canoe I ever paddled was a V bottomed Mad River Explorer. It didn't seem to lack stability and tracked very well. V bottom canoes are rare and I think they are because flat bottoms are more stable. Directional stability is going to be low in a 8-9' boat as well so I think you need a compromise. That would be a shallow V or a flat bottom w a 2-3" keel. The V bottom and the flat w the keel would rest on the beach at about the same amount of heel but the V bottomed boat would float over very shallow angle beaches better. Under power the V would be better w over 3hp especially. Flat bottoms have greater load capacity and frequently that's a big issue w dinks. At slow speeds (for a 9' boat) the V bottom may make less waves as the chine would be higher. Just a few thoughts and of course all opinion.

Easy

[Ike]

You all say a flat bottom is more stable but you didn't define stability. There's initial stability when the boat is upright and then there is reserve stability when the boat is heeled over. It's the reserve stability that creates the righting moment to bring the boat back upright. Flat bottom hard chine boats tend to lack reserve stabiltiy compared to v bottom boats with some deadrise to the sides. That's why jon boats seem so stable initially but heel only so far and over they go. canoes tend to lack intial stability unless you keep the CG very low (sit in the bottom of the canoe).

But for a dinghy of that size I would tend to go flat bottom but give the sides some deadrise. This increases the stability and increases it's load carrying capability because as you load it down, (raise the waterline) the displacement per inch immersion increases and the righting moment increases. ( that is, it gets harder to tip it farther.)

[Kirbinator]

Well thank you gentlemen, this is all very good stuff. I think I'm leaning towards v-bottom I'ld like to equipe my little tender with a sail rig, as well be able to row, as far as motor maybe an electric but space is limited on a Cal 26 for dingy options. I am trying to find a design for a Sabot type, I remember learning to sail at 9 years old on one. Anybody know where to find the FREE design?

[Scott Carter]

Here's a link from CMD boats (Karl Stambaugh) that addresses this very topic. The title is "To Vee or Not To Vee". It's a quick read, but it concisely compares the benefits of each hull type. I'm tempted to re-state what it says here, but it's best read (it's a pdf viewable online, no download req'd).

http://www.cmdboats.com/pdfs/Vee_E-Book.pdf