On Jul 4, 7:52*am, wrote:
...
Well, at the risk of being simple. I still suggest it's the wrong boat
for the job. He just needs to start with the right boat. He can
justify, defend, and make any excuses he wants.. Still water,
whatever.. But once you leave the dock, things can change quickly to
something you have never seen before.
Anyway. Have a great fourth, go out in your boats for me Scotty

It wouldn't surprise me in the least to find that the boat was
originally sold in several configurations (eg. bow rider, 1/3 decked,
cuddy cruiser, etc.). So, if the guy wants to convert from one to the
other and enjoys doing the work the hull might well be adequate.
Since we've only got a pic of the deck it is a little hard to tell
what the hull form is, but given the bluff bow I'm guessing it's a
Whaler style. If so, he's got oodles of stability. In Hawaii many
small fishing boats have home built hard dodgers very like lobster
boat style cabins. They put them on to get some cover when operating
at sea and stability isn't typically an issue at all. If I were
making this kind of conversion I'd put a little cuddy over the
foredeck, build a hard dodger and run some rails off of that aft to
use as supports for a Bimini, surfboard racks and tent. I'd probably
also put a proper transom on the boat and build an external rack for
the outboard. The cuddy and the transom will make the boat much less
susceptible to swamping the result may be more seaworthy than the
original. Sure he can do some testing to see if stability is going to
be an issue. I like Roger's method and if he can secure the table and
weights he can even go out and do some dynamic testing. But, in the
end, I'd be amazed if a well constructed cuddy cabin would make the
boat dangerously unstable.

Happy 4th!

-- Tom.

"Roger Long" wrote
The mini houseboat fellow won't get very far trying to apply what he reads
about GM in a standard textbook to his problem.

My guess from the OP's photo is that he has a tri-hull, of typical heavy
60s-style construction. If he goes through with his hard-top plan, I'm
thinking he'll end up with something akin to a pontoon boat.

On Jul 4, 12:22*pm, "Ernest Scribbler"
wrote:
"Roger Long" wrote

The mini houseboat fellow won't get very far trying to apply what he reads
about GM in a standard textbook to his problem.

My guess from the OP's photo is that he has a tri-hull, of typical heavy
60s-style construction. If he goes through with his hard-top plan, I'm
thinking he'll end up with something akin to a pontoon boat.

Here is a neat program that will give you some pretty basic ideas of
rightingmoments, bouyancy, trim, etc..

http://carlsondesign.com/#Fun_Shareware

It's shareware, but for a quick idea of a design and it's capability,
it is ok..

On Thu, 03 Jul 2008 22:27:51 -0400, Matt Colie
wrote:

Every boat has the center of gravity above the center of buoyancy.

Why? Ever hear of heavy ballast keels? If the superstructure is heavy
that's one thing, but it doesn't have to be.

Casady

David wrote:

I've got an old boat very much like this one:

http://www.warnersdock.com/images/Fr...fores15yel.JPG

that I'm trying to make into a mini-houseboat,
sort of like a camper. I only expect to have
about 200-300 pounds in the roof and walls,
and the roof will only be about 48" above
the gunwale. The hull will weigh a *lot* more
than what is added, so shouldn't that alone
be enough to keep it from being top heavy
and flipping over? If I add weight, like a
couple hundred pound bags of sand down
in the hull to counterballance, shouldn't
that take care of it? If so, should they
be placed on the sides, or in the center?


Well, boat stability is a complex subject. Here
some loose thoughts (before my first cup of coffee,
so no guarantees that I get all things right. I'm
sure others will jump on the chance to correct my
worst blunders - maybe I can learn something too!)

I would recommend you read a bit more about it. The
"Nature of Boats" by Dave Gerr is a good all-around
introduction, and doesn't get too technical. Many
other books work as well.

When you add weight and windage high up, you reduce
the stability. That increases the risk that your boat
will capsize in high seas (or even in flat water). It
also changes the way the boat rolls in seas, which may
make it more or less comfortable to be inside.

You are right, you can compensate by adding weight (as
low as possible!). This will make the boat sit deeper
in the water. Maybe too deep.

It all depends what you are going to use the boat for.
With a solid house on it, and enough ballast to keep her
upright, she will not want to plane. If you can live with
moving her at hull speed (a few knots), you can make do
with *much* smaller engine, and use the weight difference
as ballast. If you do not plan to move her around much at
all, then you can afford to load he a bit deeper, as the
sailing characteristics won't matter.

You can probably get an idea of the stability by doing a
simple roll period test. Rock the boat sideways, it will
settle on some speed of rolling from side to side. If
this roll time (in seconds) is the same as your overall
beam (in meters), (or 10% more), you have what Gerr
describes a good initial stability. If the boar rolls
much faster, you have more (initial) stability for
good comfort - that would be good news for you. If,
after all the construction, your boat rolls slower than
this, you may want to add some ballast.

In any case, keep the structure as low as you can manage,
and build it light! It looks like a small boat to begin
with, so don't even try to build a large house on her.
Keep it small and simple, and might work well.

Remember that a boat is always a compromise. A heavily
modified boat is a compromise between the original
compromiseand a your new ideas. It is your own boat,
and it is you who will have to live with it. Don't let
us naysayers put you completely off. But watch out, it
is also your own life you are risking, and possibly your
dear ones as well!

Good luck!

-Heikki

On 2008-07-03 11:34:39 -0400, David dh@. said:

I've got an old boat very much like this one:

http://www.warnersdock.com/images/Fr...fores15yel.JPG

that I'm trying to make into a mini-houseboat, sort of like a camper. I
only expect to have about 200-300 pounds in the roof and walls, and the
roof will only be about 48" above the gunwale. The hull will weigh a
*lot* more than what is added, so shouldn't that alone be enough to
keep it from being top heavy and flipping over? If I add weight, like a
couple hundred pound bags of sand down in the hull to counterballance,
shouldn't that take care of it? If so, should they be placed on the
sides, or in the center?

Judging from friends' boats of about that configuration, I'd suggest
something quite a bit lighter: a light hard roof and tarps, screen and
plastic for removable "walls", a pop-top camper of sorts.

That said, a friend was for a time a "slum landlord" of a number of
"floating structures" in Key West that were about what I hear you
saying. They (mostly) stayed afloat for some years and weathered some
nasty weather.

Have to say that the inhabitants were not thought well of, though, and
the "boats" uniformly disliked by all. Ugly doesn't begin to say it.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/