"Dag Stenberg" wrote in message
...
WaIIy wrote:
On Sat, 15 Jan 2005 14:47:58 GMT, "Jim," wrote:
BillP wrote:
When we bought the boat there were only a few wedges in place, not
enough
for proper support. I understand how the SparTite system works but is
there another system that would work? Say just filling the partner with
silicon, would this allow to much flexing? How firm is the SparTite
after
it sets?, does it allow some movement or does it harden as a solid
rubber?

One of the guys in my YC seals the mast opening with a piece of line
jammed into place (ater adjusting the stays to give him proper rake),
then coats it with silicone. Since we have to drop the mast every year
for haulout, it seems to work well for him

Which brings me to a question. I know next to nothing about sailboats
and I notice in a marina near me (Cleveland) that some of the sailboats
take down the mast for winter and some don't.

Regarding the nuisance of taking the mast down, I would not like to have
my boat close to someone who did keeps the mast up, and is toppled over
by a strong wind. (In our harbour, everybody who uses a plastic tarp
lost theirs in the storm we had just before Christmas. I also saw some
tarp supports blown over, not to speak of small craft that were blown
partly from their supports).

In the marinas around here, hundreds of boats are hauled and blocked with
the masts up. In 10 years I have only seen one boat fall over and that was
due to the sand erroding out from under a stand during a particularly
heavy downpour. Winds during the winter here can reach up to 60mph.
We have had 2 hurricanse roll through here with no toppled boats
either, winds up tp 70mph. I guess it is all in how the boats are blocked.

Another thing is, if you leave the mast up, you have to loosen the
stays and shrouds anyway to prevent the stress on the hull from the
shortening of wire in cold, so the additional nuisance of taking the
whole thing out is not so big. And makes it easiedr to survey the whole
thing before the next season.

I've never heard of doing that around here. We keep our boat in the water
as do many boaters. But nobody loosens the rig that I have even seen.

All cranes in my area can lift yachts with the mast up (provoding the
aft stays are removed), so that is not an impossibility. It also seems
that there are no regulations against keeping the mast up. If I were an
insurance official, I would make it illegal because of the increased
risks of toppling or stresses on the hlul. After all, the leverage
imposed by a mast is much more than without.

That may be the difference. Nobody around here hauls boats with a
crane. All the yards that do hauling have Travelifts, forklifts, or
railways.

Mast wedges and the seal do not seem at all the same thing to me. Wedges
are there to take up stresses, and the seal to prevent leakage. If one
uses wedges instead of Spartite, one can easily change the position of
the mast, as trimming requires, by just moving the wedges. I understand
that this is impossible with Spartite.

That is true, but I've never seen anyone actually move the wedges once they
are in position. Spartite doesn't leak which is it's strong point.

Dag Stenberg

Doug
s/v Callista

Dave wrote:
On 18 Jan 2005 09:00:27 GMT, "Dag Stenberg"
said:

Another thing is, if you leave the mast up, you have to loosen the
stays and shrouds anyway to prevent the stress on the hull from the
shortening of wire in cold, so the additional nuisance of taking the
whole thing out is not so big.

How does the coefficient of expansion of aluminum compare to the coefficient
of expansion of stainless wire?

Good point! I found the following values (in m/m.K) from different sources:

Al 23.5 E-6
Al 23.7 E-6 Steel 12 E-6
Al 22.2 E-6 Steel 13.0 E-6
that last source Stainless steel (304) 17.3
Stainless steel (310) 14.4
Stainless steel (316) 16.0

"The thermal expansion coefficient of aluminum near room temperature is
about twice that of steel (the exact values depend on the type of
aluminum and the type of steel, but for most types it's around 24 ppm
per deg C for aluminum and 13 ppm per deg C for steel)"

OK, so we'll believe that pure aluminium has nearly double heat expansion
compared to stainless steel.

Aluminium alloy 6063 T6: 22 E-6, Stainless steel (306) 17 E-6

Aluminium alloys
(LM 25) 22 E-6
(6061) 24 E-6
(6082) 23 E-6

So we can still believe that aluminium alloys have much greater thermal
expansion than even stainless steel.

Where does that put us? I suppose one can then argue, that when it gets
colder, the aluminium mast shortens more than the stainless steel
shrouds, so those should actually loosen. Apparently I have been misled
earlier by incomplete information....

Dag Stenberg

On 18 Jan 2005 12:31:23 -0600, Dave wrote:

On 18 Jan 2005 09:00:27 GMT, "Dag Stenberg"
said:

Another thing is, if you leave the mast up, you have to loosen the
stays and shrouds anyway to prevent the stress on the hull from the
shortening of wire in cold, so the additional nuisance of taking the
whole thing out is not so big.

How does the coefficient of expansion of aluminum compare to the coefficient
of expansion of stainless wire?

Thermal coeff of Aluminum is double that of Stainless, in round
numbers

Brian W

"Dag Stenberg" wrote in message
...
Dave wrote:
On 18 Jan 2005 09:00:27 GMT, "Dag Stenberg"
said:

Another thing is, if you leave the mast up, you have to loosen the
stays and shrouds anyway to prevent the stress on the hull from the
shortening of wire in cold, so the additional nuisance of taking the
whole thing out is not so big.

How does the coefficient of expansion of aluminum compare to the
coefficient
of expansion of stainless wire?

Good point! I found the following values (in m/m.K) from different
sources:

Al 23.5 E-6
Al 23.7 E-6 Steel 12 E-6
Al 22.2 E-6 Steel 13.0 E-6
that last source Stainless steel (304) 17.3
Stainless steel (310) 14.4
Stainless steel (316) 16.0

"The thermal expansion coefficient of aluminum near room temperature is
about twice that of steel (the exact values depend on the type of
aluminum and the type of steel, but for most types it's around 24 ppm
per deg C for aluminum and 13 ppm per deg C for steel)"

OK, so we'll believe that pure aluminium has nearly double heat expansion
compared to stainless steel.

Aluminium alloy 6063 T6: 22 E-6, Stainless steel (306) 17 E-6

Aluminium alloys
(LM 25) 22 E-6
(6061) 24 E-6
(6082) 23 E-6

So we can still believe that aluminium alloys have much greater thermal
expansion than even stainless steel.

Where does that put us? I suppose one can then argue, that when it gets
colder, the aluminium mast shortens more than the stainless steel
shrouds, so those should actually loosen. Apparently I have been misled
earlier by incomplete information....

This jives with what I have observed. Not so much that shrouds appeared
to be loose, but I have noticed occationally that forestays and backstays
appear a bit slack. I chauked this up to the fact that to be hauled with
a Travelift one often has to release either the backstay or forestay to fit
into the Travelift without hitting the crossbar. Once blocked, I assumed
that
the fore or backstay was not tightened as it would be for normal operation.

Dag Stenberg


Glad to learn something new and useful.

Doug
s/v Callista

Doug Dotson dougdotson@nospamcablespeednospamcom wrote:
"Dag Stenberg" wrote in message
...
... pure aluminium has nearly double heat expansion
compared to stainless steel.
Where does that put us? I suppose one can then argue, that when it gets
colder, the aluminium mast shortens more than the stainless steel
shrouds, so those should actually loosen. Apparently I have been misled
earlier by incomplete information....

This jives with what I have observed. Not so much that shrouds appeared
to be loose, but I have noticed occationally that forestays and backstays
appear a bit slack.

Yep, now I heard something from our club: somebody left the mast up, and
it started to wobble in the wind, putting more stress on the hull.

About the risk of toppling over - there seems to have been an occasion
in Cornwall about five years ago, when 50 boats toppled over, because
the gusts had rocked the supports, making them loose. They used logs for
supports, no cradle.

With the mast up, the rocking against the supports of the cradle will be
stronger than without the mast. I hear that one yacht in a marina close
by our place got one of the supports through the hull because of this.

So I remain happy with unstepping the mast for the winter.

Dag Stenberg

Dave wrote:
On 18 Jan 2005 20:08:50 GMT, "Dag Stenberg"
said:

Where does that put us? I suppose one can then argue, that when it gets
colder, the aluminium mast shortens more than the stainless steel
shrouds, so those should actually loosen. Apparently I have been misled
earlier by incomplete information....

Not really a matter of "one can argue." Should be pretty obvious from the
results of your research.

Yes, but I tried to make an allowance for unknown factors. Anyway, I
have learned that experimentation is more reliable than reflection.

Dag Stenberg

Dave wrote:
On Wed, 19 Jan 2005 00:52:07 GMT, Brian Whatcott
said:

How does the coefficient of expansion of aluminum compare to the coefficient
of expansion of stainless wire?

Thermal coeff of Aluminum is double that of Stainless, in round
numbers

Actually, it was a rhetorical question.

Maybe, but the same question was asked yesterday in our local newsgroup.

Dag Stenberg