v hull dory
 

Okay, I know that this is a stupid newbie question, but I'm planning to
build a partially decked 15' rower / daysailer similar to Devlin's Egret.
I've downloaded the HULL chine design program and played with traditional
dory designs.

I find that if I use a v bottom at 20 degrees heel, the resulting righting
moment goes up 50 percent compared to a traditional flat bottom dory.

1. a v-bottomed dory is really a skiff, right?
2. aside from losing the ability to easily beach the boat, are there any
downsides to building with a v bottom? My goal is to increase ultimate
stability, and I think I can live with a little additional initial
tenderness
3. the primary job of this boat is as a rowboat. Will a v bottom hurt in
this regard?

I have the .hul file, if that would be helpful in providing advice.

Careful on those calcs ...flat bottom boats will generally have a higher
righting moment than V-bottom boats. If you are making an assumption about
the waterline being fixed at a particular location on the side of the boat,
then 'moving' the bottom deeper into the water to create the V-hull also
greatly increases the boat's displacement. The displacement is a constant,
or close to it. Since a righting moment is the righting arm times the
boat's displacement, you might find that looking at the righting ARM graphed
against the degrees of heel would be more useful to you ...and industry
standard. I don't know anything about the Hulls program, but if it lets
you, you should use the free-floating (trim and heel) setting so that the
s/w tells you what the hydrostatics and waterline turn out to be.

Brian D



"Lumberjack" wrote in message
...
Okay, I know that this is a stupid newbie question, but I'm planning to
build a partially decked 15' rower / daysailer similar to Devlin's Egret.
I've downloaded the HULL chine design program and played with traditional
dory designs.

I find that if I use a v bottom at 20 degrees heel, the resulting righting
moment goes up 50 percent compared to a traditional flat bottom dory.

1. a v-bottomed dory is really a skiff, right?
2. aside from losing the ability to easily beach the boat, are there any
downsides to building with a v bottom? My goal is to increase ultimate
stability, and I think I can live with a little additional initial
tenderness
3. the primary job of this boat is as a rowboat. Will a v bottom hurt in
this regard?

I have the .hul file, if that would be helpful in providing advice.

I am sure it varies depending on location.....here in Maine, a skiff has a
flat bottom usually with a little rocker.
Dave

The difference will be mostly in the complication of building. As for
performance there could be a bit of additional drag due to increased
wetted surface. It depends on how wide the dory bottom is. Fishing dories
had very narrow bottoms which made them quite tender. It would make no
difference to have a "V" bottom. "Batteau" dories were more like barges
with wide bottoms and low sides. What makes a boat a dory is basically the
way a large board is bent 'round a middle form on a flat bottom. Raking
the sides out is what gives the bottom rocker. The side boards are usually
shaved down at the lower ends to reduce the rocker. The computer program
you are using calculates wetted surface. It can also do the (hydrostatic)
calculations for different angles of heel but one assumes a rowboat is not
heeled as that makes rowing uncomfortable.

--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-FreeNet email must have "notspam" in subject or it's returned

Flat bottoms are easier and faster. Vee bottoms are smoother in rough
water and faster in rough water, but you row boat isn't going to go
fast enough to take advantage of that.

A flat bottom is way more stable than a vee bottom which means it
isn't going to be in the position of needing to be righted. So it has
pretty much no righting ability because it has no heeling ability.
When she goes she's gone.

As far as sailboats go a flat bottom is not so great. The vee will
help the boat resist getting pushed sideways by the wind. A flat
bottom will work but will need more center board than a vee hull. Also
the vee helps the boat heel over some and allows wind to escape up the
sail. So it dumps off the excess wind of a gust a little better. When
a flat boat goes over it goes fast and you will have a rough time
righting it. Because the initial force to tip it is much greater and
so when it happens the boat goes all the way.

I believe the difference in a dory and a skiff are the dory has less
rocker and the sides angle away from the boat more. Rocker is nice for
rough water but I don't think you will need much on a fifteen foot
boat. It won't be happy sailing in winds much over 15 mph and the
water is just beginning to roughen up in that wind.

Bottom line, if you want to row, go flat. But if you have never sailed
much go vee, because you are going to like sailing. You will row for
exercise and sail for fun. So a vee is not going to bother you.

On Thu, 05 May 2005 00:27:39 -0500, Lumberjack
wrote:

Okay, I know that this is a stupid newbie question, but I'm planning to
build a partially decked 15' rower / daysailer similar to Devlin's Egret.
I've downloaded the HULL chine design program and played with traditional
dory designs.

I find that if I use a v bottom at 20 degrees heel, the resulting righting
moment goes up 50 percent compared to a traditional flat bottom dory.

1. a v-bottomed dory is really a skiff, right?
2. aside from losing the ability to easily beach the boat, are there any
downsides to building with a v bottom? My goal is to increase ultimate
stability, and I think I can live with a little additional initial
tenderness
3. the primary job of this boat is as a rowboat. Will a v bottom hurt in
this regard?

I have the .hul file, if that would be helpful in providing advice.