easy there Doug. Jim has just figured out what 'ballast'
is, not sure if he's ready for 'displacement'.

SBV


"DSK" wrote in message
. ..
No reason why other boats couldn't have positive
flotation.


JimC wrote:
Actually, there is. If conventional boats with heavy,
weighted keels,
particularly those of heavy construction, had enough
positive flotation
to keep the boat afloat, there would be little room left
in the cabin.

Bull****.

How much volume does the boat have immersed (ie below the
waterline)? The is the exact amount, no more. "Heavy
weighted keel" or any other sort.

Now, if you're talking about a flush-deck boat with 2' of
freeboard, then maybe there wouldn't be much cabin room to
spare... there wouldn't be much in the first place.

DSK

"Scotty" wrote in message
. ..

I guess I'm spoiled. 2 minute motor out of the marina,
and
I'm sailing!

I'm so sorry. Such a long motor is the price some have to pay for being so
far from open water.

Since we've moved to the leeward side of the dock, on low-traffic days we
shove the boat manually out of the slip, sails raised, and sail out of the
marina. Sail back into the slip, too. Let the powerboaters brag all they
want about how 'green' they are using biodiesel.

Max

"Scotty" wrote in message
...
I singlehand mostly, 30' boat slipped in the middle of a
long fairway. No reason not to motor out.. I have nothing
to prove.

Yeah, but it's fun listening to all the powerboaters scream at you because
they know you have rights-of-way.

Max

"DSK" wrote in message
. ..
No reason why other boats couldn't have positive flotation.


JimC wrote:
Actually, there is. If conventional boats with heavy, weighted keels,
particularly those of heavy construction, had enough positive flotation
to keep the boat afloat, there would be little room left in the cabin.

Bull****.

How much volume does the boat have immersed (ie below the waterline)? The
is the exact amount, no more. "Heavy weighted keel" or any other sort.

You are correct, but I'd be interested to see the volume of flotation
material needed to compensate for that displacement of water. *The volume
of flotation material required to offset a given volume of water is not
necessarily same.* Lear Siegler, the builder of O'Day boats, published a
lengthy report some years ago about why larger boats don't have positive
flotation. It was written from an engineering point of view and made sense
to me at the time, albeit I'm no engineer. Their point was essentially what
Jim C was claiming--loss of interior volume in a marketplace demanding more
and more interior space. They even explored the concept of flotation that
could be inflated in crisis, but cited cost and space requirements for even
this more compact system. So I'm not quite sure Jim is wrong. Can you
provide some documentation to the contrary, beyond just your opinion?

Now, if you're talking about a flush-deck boat with 2' of freeboard, then
maybe there wouldn't be much cabin room to spare... there wouldn't be much
in the first place.

Positive flotation probably wouldn't be offered by manufacturers
voluntarily. It would most likely be the result of a government requirement
(there's that nanny state again, Doug), and it would have to be applied to
all boats, regardless of design. So according to your last paragraph, such
a ruling might eliminate a whole class of boats. Small class racers like
the Mumm 30 come to mind.

Max

"Maxprop" wrote in message ink.net...
|
| "DSK" wrote in message
| . ..
| No reason why other boats couldn't have positive flotation.
|
|
| JimC wrote:
| Actually, there is. If conventional boats with heavy, weighted keels,
| particularly those of heavy construction, had enough positive flotation
| to keep the boat afloat, there would be little room left in the cabin.
|
| Bull****.
|
| How much volume does the boat have immersed (ie below the waterline)? The
| is the exact amount, no more. "Heavy weighted keel" or any other sort.
|
| You are correct, but I'd be interested to see the volume of flotation
| material needed to compensate for that displacement of water. *The volume
| of flotation material required to offset a given volume of water is not
| necessarily same.* Lear Siegler, the builder of O'Day boats, published a
| lengthy report some years ago about why larger boats don't have positive
| flotation. It was written from an engineering point of view and made sense
| to me at the time, albeit I'm no engineer. Their point was essentially what
| Jim C was claiming--loss of interior volume in a marketplace demanding more
| and more interior space. They even explored the concept of flotation that
| could be inflated in crisis, but cited cost and space requirements for even
| this more compact system. So I'm not quite sure Jim is wrong. Can you
| provide some documentation to the contrary, beyond just your opinion?
|
| Now, if you're talking about a flush-deck boat with 2' of freeboard, then
| maybe there wouldn't be much cabin room to spare... there wouldn't be much
| in the first place.
|
| Positive flotation probably wouldn't be offered by manufacturers
| voluntarily. It would most likely be the result of a government requirement
| (there's that nanny state again, Doug), and it would have to be applied to
| all boats, regardless of design. So according to your last paragraph, such
| a ruling might eliminate a whole class of boats. Small class racers like
| the Mumm 30 come to mind.


Have you ever heard of ETAP? Their boats have positive flotation. They have a nice 28-footer just
out that's so fine. It's not hard to put positive flotation in sailing yachts. You loose some interior volume,
of course, but much of the space used is not much good for anything else, anyway.

http://www.etapyachting.com/index.cfm?Part=Yachts

When you do the math, you don't need as much flotation as you would expect. To figure it you must come
up with specific gravities of the various boat components. Fiberglass, for example is lighter under water
than above water. All the wood in boats is positive flotation already. Things like lead or iron ballast have
to be compensated for pound for pound but most of the other things boats are built out of you can weigh
them in the air and cut the weight in half for the pounds of flotation you must add to compensate for them.

Paladin
(Have Blue Water Positive Flotation Yacht - Will Travel)



--
Posted via a free Usenet account from http://www.teranews.com

... If conventional boats with heavy, weighted keels,
particularly those of heavy construction, had enough positive flotation
to keep the boat afloat, there would be little room left in the cabin.


Bull****.


Maxprop wrote:
You are correct, but I'd be interested to see the volume of flotation
material needed to compensate for that displacement of water. *The volume
of flotation material required to offset a given volume of water is not
necessarily same.*

I'm not sure what you mean, here.


... Lear Siegler, the builder of O'Day boats, published a
lengthy report some years ago about why larger boats don't have positive
flotation. It was written from an engineering point of view and made sense
to me at the time, albeit I'm no engineer. Their point was essentially what
Jim C was claiming--loss of interior volume in a marketplace demanding more
and more interior space.

Whoa... "marketplace" and "Engineering" are usually two
viewpoints in conflict.

From an engineering standpoint, there is less than no
reason at all why *any* boat shouldn't have positive
flotation. Just fill it all up with foam.

From a more practical standpoint of a useful cruising boat,
then you (as I believe you were driving at above) all you
need is a flotation volume equal to the difference between
the boat's volume of material and the immersed volume needed
to float that weight. I've worked out such figures for a
couple of production boats and the answer is that the volume
of the seat & berth cushions is pretty close to enough. Of
course, you need a safety margin, and that volume needs to
be both *secure* and also distributed in such a way that the
boat floats in it's proper attitude (ie not bow pointed
down, or leaned over 45 degrees) & has some stability.



... They even explored the concept of flotation that
could be inflated in crisis, but cited cost and space requirements for even
this more compact system.

There have been two such systems on the market, both went
out of business. People won't pay enough for such a
system... from a viewpoint of market analysis, a failure.
From a viewpoint of somebody who wants as much safety as
practical, and cares less about costs, it's a total success.

People buy cheap stuff. Why do think Wal-Mart does so well?


... So I'm not quite sure Jim is wrong.

From a marketing standpoint, sure. MacGregor can only
afford to offer positive floation because it's partially
installed anyway by their building method... and their foam
is the cheap stuff.



... Can you
provide some documentation to the contrary, beyond just your opinion?


Umm, show me a boat that doesn't float to start with, and
I'll show you one that probably can't have positive flotation.





Positive flotation probably wouldn't be offered by manufacturers
voluntarily.

It already is, by several. Sadler & Etap spring to mind.



... It would most likely be the result of a government requirement
(there's that nanny state again, Doug), and it would have to be applied to
all boats, regardless of design.

Show me where I suggested that it be mandated that all boats
be required to have positive flotation.


So according to your last paragraph, such
a ruling might eliminate a whole class of boats. Small class racers like
the Mumm 30 come to mind.


Heck, the Mumm 30 would be real easy to put positive
flotation in. Not much of a premium on cabin space, anyway.

The bottom line is that positive flotation is *definitely*
possible... as I said, all you need is to fill the boat with
foam up to the static waterline, and put your cabin floor
over that. Or apply that same volume of foam to a carefully
distributed set of unused voids & crannies.

Is it desirable? Depends. If I were going to do a lot of
ocean crossing, making passages along rough & rocky coasts,
etc etc, I would want it. There are tremendous advantages in
a boat that just plain will not ever sink. It's possible
that I would make it a high enough priority to put in
myself. Do I expect anybody else to? Not really, especially
the people who rave about the advantages of Wal-Mart type boats.

DSK

On Sun, 12 Nov 2006 11:48:01 -0500, DSK wrote:

Positive flotation probably wouldn't be offered by manufacturers
voluntarily.




It already is, by several. Sadler & Etap spring to mind.



http://www.mikelucasyachting.co.uk/story.htm

Positive flotation probably wouldn't be offered by manufacturers
voluntarily.


It already is, by several. Sadler & Etap spring to mind.


Goofball_star_dot_etal wrote:
http://www.mikelucasyachting.co.uk/story.htm


Cool link, thanks. Lots of info in there I didn't know
about. I had heard about the sailing-while-flooded test.

There are a couple of people who contribute once in a while
over at the rec.boats.cruising NG with Sadlers.

DSK

On Sun, 12 Nov 2006 12:15:22 -0500, DSK wrote:

Positive flotation probably wouldn't be offered by manufacturers
voluntarily.


It already is, by several. Sadler & Etap spring to mind.


Goofball_star_dot_etal wrote:
http://www.mikelucasyachting.co.uk/story.htm


Cool link, thanks. Lots of info in there I didn't know
about. I had heard about the sailing-while-flooded test.

There are a couple of people who contribute once in a while
over at the rec.boats.cruising NG with Sadlers.


There are more here amongst the locals than any other make. I was very
impressed with my trip on the 34.

I only sail with my friend a couple times a year so it is just for fun.
No hidden agenda in my message.

Scotty wrote:
I singlehand mostly, 30' boat slipped in the middle of a
long fairway. No reason not to motor out.. I have nothing
to prove.