In article ,
says...


In article . com,
"beaufortnc" wrote:

I'm prepping the bottom of my sailboat for barrier coat then ablative
bottom paint.

I'm thinking, however, that it might be a good idea to paint the prop
with something like Trinidad instead of ablative. It seems to me that
the ablative won't last long on the prop.

What's the conventional wisdom here?

I suspect something came up in the replies, but gave up when the thread
took a strange turn.

I've tried ablative, hard, "outboard" (TNT) and other options over the
years and have yet to find something that actually kept our prop clean
throughout the season.

I'm about to try something that scares the living dickens out of me, but
was recommended by the shop that installed our engine: NOTHING. No zinc,
no copper or tin-based paints. The theory is that the slight electrical
imbalance between the SS shaft and bronze prop will be sufficient to
keep both clean.

Since our shaft is isolated from everything else in the boat, the only
thing eating away half of our zincs each year is the SS/Bronze imbalance.

Put a donut zinc between the strut and the prop.

Evan Gatehouse wrote:

Rosalie B. wrote:

Some people can do quite well free-diving. My SIL does this for the
lobster season in FL, and can stay down for a considerable time. Even
I can dive on the prop and do some work on it if I wear fins. It is
not that hard if you practice and it makes a reasonable workout. The
only time I can't do too much is if the water is cold - I can't stay
in too long in cold water, and if I wear a wet suit, I am too buoyant
to stay down.

It sounds to me like the guy in Costa Rica didn't have a dive flag or
take appropriate safety measures - like having someone watching.

It was reported in Lat 38's Electronic Latitude that he was
the victim of shallow water blackout, not having a boat
above him.

That sounds more reasonable. After all - if the power boat wasn't
there when he went down there, the power boat would be moving - he
wouldn't be caught under it although he might be cut up.

Shallow water blackout occurs when you hyperventilate too
much before a freedive, and then when down, you run out of
O2. Your body uses increasing levels of CO2 to tell you
when to breathe, and hyperventilating reduces blood CO2. So
you don't get the urge to breathe, and pass out underwater.

I've come close a few times (black spots as I come up).
Now I only ever hyperventilate 3 deep breaths before a dive.
Diving with a buddy close by might save you, but by the
time they notice a problem you might be 20' deep and sinking...

In my case, I wouldn't sink I don't think. Even when I breathe out as
far as possible, I still float. I might come up under our boat
though. So having Bob in the dinghy watching (and in cases when I
would do this, the water would be clear enough to see me - our prop
isn't that far down) would be a help.

It reduces my bottom time slightly but I feel a lot safer

I've never been that close to blacking out. Or if I was, I didn't
have any warning like black spots.

grandma Rosalie

why don't you treat the problem and not the cause???
"Gogarty" wrote in message
...
In article
,
says...


In article
. com,
"beaufortnc" wrote:

I'm prepping the bottom of my sailboat for barrier coat
then ablative
bottom paint.

I'm thinking, however, that it might be a good idea to
paint the prop
with something like Trinidad instead of ablative. It
seems to me that
the ablative won't last long on the prop.

What's the conventional wisdom here?

I suspect something came up in the replies, but gave up
when the thread
took a strange turn.

I've tried ablative, hard, "outboard" (TNT) and other
options over the
years and have yet to find something that actually kept our
prop clean
throughout the season.

I'm about to try something that scares the living dickens
out of me, but
was recommended by the shop that installed our engine:
NOTHING. No zinc,
no copper or tin-based paints. The theory is that the
slight electrical
imbalance between the SS shaft and bronze prop will be
sufficient to
keep both clean.

Since our shaft is isolated from everything else in the
boat, the only
thing eating away half of our zincs each year is the
SS/Bronze imbalance.

Put a donut zinc between the strut and the prop.

"Gogarty" wrote in message

Put a donut zinc between the strut and the prop.

Uhhh, We HAVE had a zinc on the shaft and the MaxProp's hub as well.
Both get half eaten each year. Before the MaxProp & its zinc, we lost
the same half of the shaft zinc.

In article ,
"Boots" wrote:

why don't you treat the problem and not the cause???

We have no AC connection to dock power. There is no electrical
connection to the shaft or strut; the shaft is isolated by a plastic
drive-saver; electrical resistance between boat ground and shaft is
essentially infinite, so it's not from the battery.

It happened while we were in the mooring field.

Thus, I believe we solved what you believe is the problem already.

The *only* thing it can be is the difference in potential between bronze
and stainless steel.

OR... the potential difference between both steel & bronze and zinc, and
that's what I've been thinking for the past few years.

Truth be told, I *have* thought about switching out the shaft for
bronze. If the zinc still disappears, it's the zinc's problem as there's
nothing left. My only problem with this solution is that bronze bends
quite a bit easier than SS, and I'm more concerned about proper shaft
straightness and alignment than the loss of relatively cheap zincs.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Dave wrote:
On Thu, 24 Nov 2005 01:05:21 GMT, Gary said:


This schmuck is a Navy diver. How about you?


Spent 3 years as a helium hardhat diver on an ASR.

Then you should know that your lungs are not going up the hose!

Dave wrote:
On Mon, 28 Nov 2005 02:18:04 GMT, Gary said:


Then you should know that your lungs are not going up the hose!


That's not the issue. Your claim is that if the hose is not reinforced, it
will collapse, sealing the air below it, including the air in your lungs.
Think of a thin rubber tube, or a plastic bag, you can't submerge them
at all without them collapsing.

I suggest a small experiment. Take a child's balloon and puff it up to just
ambient pressure so the rubber's stretch isn't a factor. Then take ahold of
the point opposite the inflation tube, hold the inflation tube shut, and put
the balloon under water, with the inflation tube up. Unseal the inflation
tube while holding the balloon at the opposite (now bottom) point with the
other hand. If your theory is correct, the inflation tube will be sealed by
water pressure, and the air will remain in the balloon.

To simulate your lungs, the balloon would have to be held closed at the
mouth of the inflation tube (your throat), not oppsite it and protected
by a cage (ribs). How do you think free divers work?
Wanna bet that will happen?

Jere Lull wrote:

"Gogarty" wrote in message


Put a donut zinc between the strut and the prop.


Uhhh, We HAVE had a zinc on the shaft and the MaxProp's hub as well.
Both get half eaten each year. Before the MaxProp & its zinc, we lost
the same half of the shaft zinc.

In article ,
"Boots" wrote:


why don't you treat the problem and not the cause???


We have no AC connection to dock power. There is no electrical
connection to the shaft or strut; the shaft is isolated by a plastic
drive-saver; electrical resistance between boat ground and shaft is
essentially infinite, so it's not from the battery.

It happened while we were in the mooring field.

Thus, I believe we solved what you believe is the problem already.

The *only* thing it can be is the difference in potential between bronze
and stainless steel.

OR... the potential difference between both steel & bronze and zinc, and
that's what I've been thinking for the past few years.

Truth be told, I *have* thought about switching out the shaft for
bronze. If the zinc still disappears, it's the zinc's problem as there's
nothing left. My only problem with this solution is that bronze bends
quite a bit easier than SS, and I'm more concerned about proper shaft
straightness and alignment than the loss of relatively cheap zincs.


Then you are left shopping for a stainless prop. Zincs may be
cheaper. Go without and watch the prop melt until thr money saved
on zinc offsets the cost of a prop. Or not. A thin insulating
bushing and washer between the shaft, prop and nut may serve you well.

On Mon, 28 Nov 2005 12:08:56 -0400, Terry Spragg
wrote:

Jere Lull wrote:

"Gogarty" wrote in message


Put a donut zinc between the strut and the prop.


Uhhh, We HAVE had a zinc on the shaft and the MaxProp's hub as well.
Both get half eaten each year. Before the MaxProp & its zinc, we lost
the same half of the shaft zinc.

In article ,
"Boots" wrote:


why don't you treat the problem and not the cause???


We have no AC connection to dock power. There is no electrical
connection to the shaft or strut; the shaft is isolated by a plastic
drive-saver; electrical resistance between boat ground and shaft is
essentially infinite, so it's not from the battery.

It happened while we were in the mooring field.

Thus, I believe we solved what you believe is the problem already.

The *only* thing it can be is the difference in potential between bronze
and stainless steel.

OR... the potential difference between both steel & bronze and zinc, and
that's what I've been thinking for the past few years.

Truth be told, I *have* thought about switching out the shaft for
bronze. If the zinc still disappears, it's the zinc's problem as there's
nothing left. My only problem with this solution is that bronze bends
quite a bit easier than SS, and I'm more concerned about proper shaft
straightness and alignment than the loss of relatively cheap zincs.


Then you are left shopping for a stainless prop. Zincs may be
cheaper. Go without and watch the prop melt until thr money saved
on zinc offsets the cost of a prop. Or not. A thin insulating
bushing and washer between the shaft, prop and nut may serve you well.


I guess I have mentioned this befo (Sir) Humphrey Davy sold the
British Navy a bill of goods to prevent erosion of their copper
bottoms. It was essentially electrolytic/cathodic protection.
The copper erosion stopped dead. But the marine growth started and
was overwhelming in months. So they dumped the cothodic protection.
The copper slowly dissolves and poisons the fauna.

So here's the scoop.

If you want to protect a lump of bronze from erosion, you could site
a lump of zinc close, or supply a lead or stainless anode close with a
one volt feed..

BUT
if you want to prevent marine growth on the bronze lump, you get rid
of the zinc or the protective anode current and let the copper slowly
dissolve. Yoiu get no marine growth.

OR if you want a really radical alternative to painting a bronze prop
on a stainless shaft, arrange for the shaft to be fed a small current
with say +1 volt wrt the prop. It may grow a garden, but it won't
dissolve, and won't need zincs.

Brian Whatcott Altus OK

In article ,
says...


"Gogarty" wrote in message

Put a donut zinc between the strut and the prop.

Uhhh, We HAVE had a zinc on the shaft and the MaxProp's hub as well.
Both get half eaten each year. Before the MaxProp & its zinc, we lost
the same half of the shaft zinc.

Well, of course the zinc gets eaten. That it gets assymetrically eaten
indicates a directional electrolysis current or whatever at your slip or
mooring. But that's odd too. Does your prop stop in the same position
every time?

But the point was preventing growth. Do you find that the zinc in close
proximity to the hub of the prop prevents or reduces growth on the hub? I
do.

In article ,
says...

OR if you want a really radical alternative to painting a bronze prop
on a stainless shaft, arrange for the shaft to be fed a small current
with say +1 volt wrt the prop. It may grow a garden, but it won't
dissolve, and won't need zincs.

We have a keel cooler refrigerator. The condenser is a sintered bronze block
on the bottom of the boat through which the refrigerant flows. The block is
direct connected to the negative side of the battery. It does not corrode.
But it sure grows a garden. I susepct my garden grows not only because copper
ions are completely suppressed but also because the block is warmer than the
surrounding territory. I mean those are eating size barnacles like no other.