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pastelblack
#1 Posted : Monday, March 14, 2011 3:59:43 AM(UTC)
pastelblack

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Hi All
Last year I isolated my rudder and shaft through the strut with the phenolic brgs from Marinette. I also isolated the shaft from the engine using the spacer/coupling and nylon bolt isolation from Marineete. I am still picking up resistence between the hull and the shaft, apparently indicating there is still some connection between the shaft and hull.

The only corrosion I have on my UNPAINTED hull is in two small locations. 1) at the freshwater intake; and 2) on the hull in close proximity to the rudder shaft where it goes through the hull.

I have removed the bronze Groco seacok and bronze intake and am replacing with Marelon. I feel confident that this will take care of the corrosion at that location (famous last words).

However, I am perplexed by the corrosion at the rudder (and also a little on the strut).

I have the appropriate length of anode on my keel and trim tabs fro a 26' boat according to Pluckebaum Houseboats and Marinette (8' total - 3' either side of keel + 1' each trim tab) and the typical 4" round anode on the SS rudder. All anodes are mg. My thoughts to combat this problem are as follows:

1)Paint the prop with epxy paint or similar (POR15 etc.).
2) Install larger diameter rudder anode if available.
3) Install one or two shaft anodes.

Any ideas, comments or suggestions would be oh so welcome.!!
Thanks guys....
Bob
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fastjeff
#2 Posted : Monday, March 14, 2011 4:36:39 AM(UTC)
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1. I suggest you add a block of magnesium (fresh water?) atop a trim tab. That will get the readings up.

2. The shaft isolation requires a nylon washer under each bolt head (as you've seen) PLUS a tube-like isolator around the bolt, to prevent contact. You can remove the bolts and see if the conductivity is gone, then add a bolt at a time until you find the problem.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
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Red5
#3 Posted : Friday, May 27, 2011 11:24:42 AM(UTC)
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fastjeff;22882 wrote:
1. I suggest you add a block of magnesium (fresh water?) atop a trim tab. That will get the readings up.

2. The shaft isolation requires a nylon washer under each bolt head (as you've seen) PLUS a tube-like isolator around the bolt, to prevent contact. You can remove the bolts and see if the conductivity is gone, then add a bolt at a time until you find the problem.

Jeff



How do I test to see if my boat is properly isolated?
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fastjeff
#4 Posted : Friday, May 27, 2011 11:35:08 AM(UTC)
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You have to make up a corrosion tester. The probe is about 70 bucks. You'll need a volt meter (5 bucks at Harbor Freight) some cabling, and an alligator clip to ground to your railing.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
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Neal Weatherman
#5 Posted : Friday, May 27, 2011 2:07:16 PM(UTC)
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Possible outside chance that the shaft is coming in contact with the thru-hull, is the boat on the hard or has it been hauled recently?
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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Barkleydave
#6 Posted : Friday, May 27, 2011 4:13:03 PM(UTC)
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I assume you are checking isolation with a digital OHM meter.

These meters are exteremely sensitive and will NOT real OL (unlimited resitance) There is always very small current flow through water to the hull.

Here is what you can do to confirm you are good.

1. Use only the beep function or continuity checker. If it beeps there is too much continuity.
2. If your CAPAC is working use the following recommended Big M test.

Have helper push button on CAPAC while you take a jumper wire and ground Shaft to Hull. If meter deflects downward this is an indication of inadequate isolation.

Even with fresh anodes my boat always reads on the low side in fresh water. I use a mag guppy over the side while in the slip and it keeps the numbers in the proper range and no corrosion observed over the past 6 years in the water.

safe boating,

dave
None
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jralbert
#7 Posted : Friday, May 27, 2011 11:08:30 PM(UTC)
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shaft zinc shouldn't be necesssary but it can't hurt to install one and observe if it wears out. If it does, that's a decent indication the shaft isn't isolated. Also, If you get some corrosion neasr Marelon thru hulls, it's ain't their fault. They are plastic, not metal.
Joel Albert, Potomac MD
"Charlie B" - 1988 32' FBS
Twin 318's/FWC/16x15 nibral props
docked Deale, MD
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fastjeff
#8 Posted : Saturday, May 28, 2011 5:49:51 AM(UTC)
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Shaft anodes ARE necessary. Mine are eaten up in a couple three years--just changed another one--so they are doing something.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
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jimski2
#10 Posted : Saturday, May 28, 2011 6:05:43 AM(UTC)
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The rudder also has isolation areas that need to be addressed. There is a nylon bearing sleeve for the steering cable attachment and I believe isolated cutlass bearings for it. The rudder packing nut needs isolation also I believe.
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jralbert
#9 Posted : Saturday, May 28, 2011 12:37:46 PM(UTC)
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fastjeff;23956 wrote:
Shaft anodes ARE necessary. Mine are eaten up in a couple three years--just changed another one--so they are doing something.Jeff
I don't make this stuff up...I read what I wrote in a galvanic corrosion manual put out by a galvanic product mfr. Long time ago, I posted that stuff on the site but I think it disappeared in the site transition. It makes sense. My shaft zincs showed no sign of wear for years. So I went down to a single one on ea shaft just to ward off evil spirits. Still no wear. My guess is that despite good readings on your PerryMeter there is some current leak in the shaft area. But your shaft zincs are doing their job. So, lean back and worry less.
Joel Albert, Potomac MD
"Charlie B" - 1988 32' FBS
Twin 318's/FWC/16x15 nibral props
docked Deale, MD
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Docsnow
#11 Posted : Saturday, May 28, 2011 4:45:42 PM(UTC)
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For $500 give or take a few $$$ (for twin eng.) replace them out of date isolators with Shaft Savers a one time fix unless U hit something pretty large but than it saves your trannys & shafts. So $500 compared to $2800 per eng. sounds like a pretty good trade off to me plus no more worry’s of eng. to shaft continuity. Problem solved than if your capac is reading low U can look at other places for A/C D/C voltage leaks. Next probable place your bilge pump wiring. Oh BTW if U have to use Magnisum to get your readings up to par U have a electrical leak somewhere d'oh!

The orange thing in the pic is the Shaft Saver

Norm,
argh!!

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Aquaholic
#12 Posted : Monday, May 30, 2011 5:42:27 PM(UTC)
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Does anyone know where can I get the tubes that go over the flange bolts? I seem to be missing all of them..
1979 Double cabin with 440's
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BCassedy
#14 Posted : Monday, May 30, 2011 9:33:31 PM(UTC)
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I don't know if this would work, or even if it should be tried, but could you use shrink wrap tubing over the coupler bolts? If one layer, when heat is applied (and the tubing shrinks down over the bolt length), might have room for a 2nd covering thus doubling up on the tube's thickness.

I'm not sure about abrasion from the threads while the bolt's in place and tightened down. I would think that plastic washers (on both sides of the coupling) would theoretically work to isolate the shafts. As the nut would be tightened, it would force shrink tubing back over the washer in a flange effect and this should provide the isolation we seek.

Just a thought...

Bill
Bill & Sharon Cassedy
" Sunset Seeker "
1988 32' Fly Bridge
Twin 318 Cu In / 240HP Chrysler power plants
Raw water cooling
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Rick100
#13 Posted : Tuesday, May 31, 2011 7:58:04 AM(UTC)
Rick100

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Aquaholic;23974 wrote:
Does anyone know where can I get the tubes that go over the flange bolts? I seem to be missing all of them..

McMaster Carr is the place to go for nylon tubing that fits the bolt and the i d of the flange. Rick
When I die I hope my wife sells my stuff for more than I told her I paid for it.
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fastjeff
#15 Posted : Tuesday, May 31, 2011 8:17:12 AM(UTC)
fastjeff

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Hey! I like that shrink wrap idea. On mine, I used PVC tubing and had to sand it down to get the bolt in. Shrink wrap makes a lot of sense.


Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
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Docsnow
#16 Posted : Tuesday, May 31, 2011 9:31:10 AM(UTC)
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Try it Jeffster, U’ll Love it. I’ve been using that method since John Simanella posted on the old site about 3 / 4 yrs ago. On a lot of different applications like when I redid the Pulpit & remounting the swim platform. Worked great in both instances.Applause

Norm,

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http://www.picturetrail.com/gid23690601 Try it now there's music to listen to while U view the Big M's

http://www.PictureTrail.com/club/club/index.php?clubID=20726 this one for the Pix club


 You'll have bad times, but they'll just wake you up to the good times you weren't paying attention to

Some people try to turn back their odometers.Not me, I want people to know "why" I look this way.I've traveled a long way and some of the roads weren't paved.
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