Hull Flexing
 

I had a odd experience yesterday. I went to the boat to finish winterizing, and saw my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3 trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled because the
door had never latched in his experience (he's had the boat a year and always locked with
an external padlock). After a while we were able to pry it open and figure out what had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough that the
latch, which had not recently engaged, now caught the latch plate. We estimate maybe 1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what the owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so much when
we unrigged her that it opened a deck leak."

Hull Flexing
 

Check the jack stands. Some fool probably has the ones in the
middle way too tight and doing most of the work and bending
the boat in the process.

S.Simon


"Jeff Morris" wrote in message ...
I had a odd experience yesterday. I went to the boat to finish winterizing, and saw my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3 trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled because the
door had never latched in his experience (he's had the boat a year and always locked with
an external padlock). After a while we were able to pry it open and figure out what had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough that the
latch, which had not recently engaged, now caught the latch plate. We estimate maybe 1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what the owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so much when
we unrigged her that it opened a deck leak."

Hull Flexing
 

Its a catamaran - it can rest on its two keels. Prouts can be stashed like that because
the keels are solid.

My keels, however, are "sacrificial" so its best to jack under the bridge, supporting most
of the weight under the bulkheads:

http://www.sv-loki.com/Along_the_Way/UnderBelly.jpg



"Simple Simon" wrote in message
...
Check the jack stands. Some fool probably has the ones in the
middle way too tight and doing most of the work and bending
the boat in the process.

S.Simon


"Jeff Morris" wrote in message
...
I had a odd experience yesterday. I went to the boat to finish winterizing, and saw
my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3
trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled because
the
door had never latched in his experience (he's had the boat a year and always locked
with
an external padlock). After a while we were able to pry it open and figure out what
had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough that
the
latch, which had not recently engaged, now caught the latch plate. We estimate maybe
1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what the
owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so much
when
we unrigged her that it opened a deck leak."

Hull Flexing
 

I see the problem. Those jack stands blocking up the
bridge deck are doing just the opposite of what that
area of the boat is supposed to do. If the stands are
taking too much weight the hulls are sort of hanging
from the bridge deck. In the water the hulls support
the bridge deck.

In the water viewed from the front the bridge deck
would have a tendency to be curved down a little in
the center portions. Jacked up as it shows the bridge
deck would be curved the opposite way. This would
warp the house in an abnormal manner.

S.Simon


"Jeff Morris" wrote in message ...
Its a catamaran - it can rest on its two keels. Prouts can be stashed like that because
the keels are solid.

My keels, however, are "sacrificial" so its best to jack under the bridge, supporting most
of the weight under the bulkheads:

http://www.sv-loki.com/Along_the_Way/UnderBelly.jpg



"Simple Simon" wrote in message
...
Check the jack stands. Some fool probably has the ones in the
middle way too tight and doing most of the work and bending
the boat in the process.

S.Simon


"Jeff Morris" wrote in message
...
I had a odd experience yesterday. I went to the boat to finish winterizing, and saw
my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3
trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled because
the
door had never latched in his experience (he's had the boat a year and always locked
with
an external padlock). After a while we were able to pry it open and figure out what
had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough that
the
latch, which had not recently engaged, now caught the latch plate. We estimate maybe
1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what the
owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so much
when
we unrigged her that it opened a deck leak."

Hull Flexing
 

Doesn't really matter what size the boat is, you will get some degree of
"flex", especially when you remove it from the water and put it on a
hard stand. BG you want to see flex, you should watch and listen to a
large tanker at sea, or watch one go from hog to sag when loading.

otn

Jeff Morris wrote:

I had a odd experience yesterday. I went to the boat to finish winterizing, and saw my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3 trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled because the
door had never latched in his experience (he's had the boat a year and always locked with
an external padlock). After a while we were able to pry it open and figure out what had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough that the
latch, which had not recently engaged, now caught the latch plate. We estimate maybe 1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what the owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so much when
we unrigged her that it opened a deck leak."

Hull Flexing
 

Again, allow me to reiterate. This is a sailing newsgroup.
We talk sailing yachts here. Why do you keep butting in
with your motor vessel references which are not relevant?

S.Simon


"otnmbrd" wrote in message ink.net...
Doesn't really matter what size the boat is, you will get some degree of
"flex", especially when you remove it from the water and put it on a
hard stand. BG you want to see flex, you should watch and listen to a
large tanker at sea, or watch one go from hog to sag when loading.

otn

Jeff Morris wrote:

I had a odd experience yesterday. I went to the boat to finish winterizing, and saw my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3 trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled because the
door had never latched in his experience (he's had the boat a year and always locked with
an external padlock). After a while we were able to pry it open and figure out what had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough that the
latch, which had not recently engaged, now caught the latch plate. We estimate maybe 1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what the owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so much when
we unrigged her that it opened a deck leak."

Hull Flexing
 

Your theory might have merit except for a few details:

First of all, the pictures are of my boat, while the problem was different boat, a Prout
37. The Prout has a third, central hull, called a "nacelle," and it is impractical to
support like mine. It is sitting on its keels. At first, I wondered if the center of the
Prout had sagged and should be supported, but we concluded that in fact the center had
risen when the weight and stress of the mast had been removed.

My boat is supported according to the factory specs. Although the keels can support the
hull for a limited period, they are not intended to support the hull for extended periods.
Since the three timbers are directly un the three bulkheads, the hull is support with no
flexing.



"Simple Simon" wrote in message
...
I see the problem. Those jack stands blocking up the
bridge deck are doing just the opposite of what that
area of the boat is supposed to do. If the stands are
taking too much weight the hulls are sort of hanging
from the bridge deck. In the water the hulls support
the bridge deck.

In the water viewed from the front the bridge deck
would have a tendency to be curved down a little in
the center portions. Jacked up as it shows the bridge
deck would be curved the opposite way. This would
warp the house in an abnormal manner.

S.Simon


"Jeff Morris" wrote in message
...
Its a catamaran - it can rest on its two keels. Prouts can be stashed like that
because
the keels are solid.

My keels, however, are "sacrificial" so its best to jack under the bridge, supporting
most
of the weight under the bulkheads:

http://www.sv-loki.com/Along_the_Way/UnderBelly.jpg



"Simple Simon" wrote in message
...
Check the jack stands. Some fool probably has the ones in the
middle way too tight and doing most of the work and bending
the boat in the process.

S.Simon


"Jeff Morris" wrote in message
...
I had a odd experience yesterday. I went to the boat to finish winterizing, and
saw
my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3
trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled
because
the
door had never latched in his experience (he's had the boat a year and always
locked
with
an external padlock). After a while we were able to pry it open and figure out
what
had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough
that
the
latch, which had not recently engaged, now caught the latch plate. We estimate
maybe
1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what
the
owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so
much
when
we unrigged her that it opened a deck leak."

Hull Flexing
 

Subject: Hull Flexing
From: "Simple Simon"
Date: 11/09/2003 16:38 Pacific Standard Time
Message-id:

Again, allow me to reiterate. This is a sailing newsgroup.
We talk sailing yachts here. Why do you keep butting in
with your motor vessel references which are not relevant?

S.Simon


If you had a lick of common sense, you'd have noted the general, but related
sense to his comments.

Shen

Hull Flexing
 

Then it sounds like the Prout might be designed to incorporate
the rigging into the total package to stiffen things up. That's
a problem with catamarans - the downward force of mast and
rigging places maximum loading on the center of the bridge deck
as there is no hull there into which to step the mast and loading.

So one can easily picture the hulls being pulled up by the rigging
while the center of the bridge deck is being pushed down. When
their mast and rigging forces are removed the bridge deck can
then assume a more upward position causing the house to warp
somewhat. This might cause the doors to jam, etc.

It fits my theory about how a properly stayed vessel is a
much stronger system then say a Nonsuch with an unstayed
mast.

S.Simon


"Jeff Morris" wrote in message ...
Your theory might have merit except for a few details:

First of all, the pictures are of my boat, while the problem was different boat, a Prout
37. The Prout has a third, central hull, called a "nacelle," and it is impractical to
support like mine. It is sitting on its keels. At first, I wondered if the center of the
Prout had sagged and should be supported, but we concluded that in fact the center had
risen when the weight and stress of the mast had been removed.

My boat is supported according to the factory specs. Although the keels can support the
hull for a limited period, they are not intended to support the hull for extended periods.
Since the three timbers are directly un the three bulkheads, the hull is support with no
flexing.



"Simple Simon" wrote in message
...
I see the problem. Those jack stands blocking up the
bridge deck are doing just the opposite of what that
area of the boat is supposed to do. If the stands are
taking too much weight the hulls are sort of hanging
from the bridge deck. In the water the hulls support
the bridge deck.

In the water viewed from the front the bridge deck
would have a tendency to be curved down a little in
the center portions. Jacked up as it shows the bridge
deck would be curved the opposite way. This would
warp the house in an abnormal manner.

S.Simon


"Jeff Morris" wrote in message
...
Its a catamaran - it can rest on its two keels. Prouts can be stashed like that
because
the keels are solid.

My keels, however, are "sacrificial" so its best to jack under the bridge, supporting
most
of the weight under the bulkheads:

http://www.sv-loki.com/Along_the_Way/UnderBelly.jpg



"Simple Simon" wrote in message
...
Check the jack stands. Some fool probably has the ones in the
middle way too tight and doing most of the work and bending
the boat in the process.

S.Simon


"Jeff Morris" wrote in message
...
I had a odd experience yesterday. I went to the boat to finish winterizing, and
saw
my
neighbor trying to get into his boat, a Prout 37 (which, BTW, has done 3
trans-Atlantic
crossings). The companionway door was latched and locked - he was baffled
because
the
door had never latched in his experience (he's had the boat a year and always
locked
with
an external padlock). After a while we were able to pry it open and figure out
what
had
happened.

On Thursday the mast had been pulled. This seems to have relaxed the hull enough
that
the
latch, which had not recently engaged, now caught the latch plate. We estimate
maybe
1/16
inch of flexing.

Before you jump on the fact that a catamaran hull had a bit of flex, here's what
the
owner
said "I surprised there would be any flex at all - but my old C&C 37 flexed so
much
when
we unrigged her that it opened a deck leak."

Hull Flexing
 

otnmbrd wrote:

Doesn't really matter what size the boat is, you will get some degree of
"flex", especially when you remove it from the water and put it on a
hard stand. BG you want to see flex, you should watch and listen to a
large tanker at sea, or watch one go from hog to sag when loading.

Sure. Why else would they build expansion joints into the upper decks of big (or even
medium-sized) ships?

The only way to have zero flex would be to have literally infinite rigidity. The question is,
how much is too much, and how much is marginally greater rigidity worth the other sacrifices
made to increase it?

1/16" doesn't sound like a problem to me, although the latch sounds like a PITA. Another issue
is that fiberglass does lose a bit of torsional strength as it flexes many times... just like
any other material. The nice thing about fiberglass is that it has a very high number of load &
flex cycles to fatigue failure. Great engineering material, pity it's so heavy.

I remember reading about a New Orleans Marine hotshot racing boat built back in the 1980s, which
had a hull & deck of uncored glass & mat with a subimposed grid of straight S-glass. Everybody
guffawed and said "Those hicks sure don't know how to build racing boats, shoulda used foam
core" but the builder shrugged and said that they measured the bend in the hull/deck with
15,000# tension on the backstay.... it was 4 thousands of an inch....

Fresh Breezes- Doug King