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Old 06-09-2014, 23:12   #16
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Re: Shaft log replacement in Malaysia - Singapore

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Originally Posted by Alii View Post
Thanks everyone for the input. We aren't fiberglassing pros for sure, but have fussed with this boat for 17 years, lived aboard full-time for 13+, 2 prior refits, have closed old (3) and installed new (3) thru-hulls, and perhaps most relevant have changed out our portlights twice, the last time closing in and fairing the deck house before cutting out smaller holes for smaller frames. We are using all International products (AUS and UK formulations) and have a variety of cloth weights, woven roving and chopped mat. And the West manuals and other how-to guides.

The Centek fiberglass shaft log that will accommodate my shaft and Volvo seal is only 1/8" thick. Is this thick enough? This only matters for the part of the tube exposed between the seal and interior lay-up, but there could be no worse place to have a crack.

Another question re fiberglass logs -- is standard antifouling (we use Ultra) enough to keep marine growth from choking them up? Am I wrong that stainless would/should inhibit growth better, allowing more water flow to the seal? One thing I'll say about the old stainless tube, we never had a fouling problem in it (clean the bottom at least monthly) and didn't paint it with antifouling.

As for what caused the corrosion in the old shaft log, it hasn't been exposed to stagnant water. We are usually on the move, or most recently on a 4-point mooring. We have motor-driven refrigeration and rely on the alternator to charge our batteries (no wind, only small token solar) so every day we run the motor at least twice and in gear (even if on the mooring). The tube is not in contact with the AquaDrive or with any other metal on the boat.

Thanks again for the input,
Laura
1/8' of an inch wall thickness does seem a bit light,though there is no real pressure on it apart from the clamp on the volvo seal.

a larger 1/4' section would be better in terms of robustness,if you can find the tolerance.
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Old 07-09-2014, 00:48   #17
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Re: Shaft log replacement in Malaysia - Singapore

Sounds like you have plenty enough fiberglassing experience.

The 1/8" fiberglass tube wall thickness should be fine, these are typically made with epoxy and fine, numerous layers of cloth. Think windsurfer mast, not boat hull. Or you could get a 1/4 wall thickness tube and have it machined down in just the area of the hose. Or a different size (or reducer) hose may be available. I understand your concern, and would probably try to find an adaptor type hose to fit the 1/4" wall tube and failing that, would probably just go with the 1/8". (I'm overkill prone, but pragmatic when push comes to shove...)

As far as I know the fiberglass tube should be compatible with any kind of antifouling.

As for the antifouling properties of stainless, I'm not aware of any, it brings to mind a stainless steel boarding ladder a friend of mind had hung off his dock, in open tidal water, that had 9 months of barnacles and zebra mussels on it. The mussels had killed (suffocated?) the barnacles, but under them were circles of corrosion and in some cases holes all the way through the metal (though the metal was rather thin and of unknown grade).

The cause of the corrosion is certainly mysterious. I know a little about electricity, but enough to know that it is difficult to imagine all the scenarios that can induce enough current to cause corrosion. There doesn't have to be actual metal to metal contact. This isn't to say that this is the problem though.

As for stagnant-water-caused crevice corrosion, all the engine usage and moving around would seem to preclude it, but not necessarily. I seem to recall that in times past (and probably still) people would inhibit marine growth in their kept-in-the- water boats' centerboard trunks by pouring various liquids in them, where they were retained by differences in specific gravity.

Guess that's not much help though.

But if you do decide to do this yourself, and regardless of tube material, just a few suggestions.

I don't think it likely that the old tube can be taken out with ease, it is meant to be permanent. If you can get it out easily (without cutting into the boat), while I'm sort of a fan of 5200, popping a new stern tube in with a load of it just doesn't seem kosher to me. Maybe properly thickened epoxy is the better route.

If you do have to grind or cut the tube out, I'd start by trying to cut along the length of the tube, a little below the halfway point, along both sides and joining together where the tube meets the hull, leaving a kind of clamshell that can be (hopefully) popped off with a hammer and chisel, leaving a saddle like affair to bed the new log in. Tool of choice would be 4.5 inch angle grinder with 1/16" thick abrasive disc or thinnest diamond blade I could get, or maybe what we call a sawzall around here (reciprocating saw) with a medium fine 6-8 inch metal cutting blade.

Use epoxy and the proper fillers to install the tube.

Duct tape is the best shim to hold the tube centered on the shaft. (possibly even the best use for duct tape) Wind the tape evenly around the shaft until it is the same size as the ID of the log and slide the log over it. Do it at both ends of the log and it is aligned, if you really want to get anal about it, make sure you start and stop the tape wraps at the same place. (Use the same technique with aluminum tape (properly wound in the right direction) on drill bits to make drill jig bushings to center drill bolts broken off below the surface.)

Good luck with it and best regards,
Jim
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Old 07-09-2014, 01:16   #18
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Re: Shaft log replacement in Malaysia - Singapore

Thank you, atoll and Jim. My concern about the sturdiness of the tube is amplified by the fact that this stern tube is situated directly under the companionway entry from the aft cockpit. Someone could accidentally step directly on the tube when coming down the steep ladder while the floor board was pulled up for some reason (bright sunlight into dark interior, wouldn't be able to see that floor is missing). This is probably more of a concern while we're on the hard as this piece of floor will be removed while we run new Teleflex cables, etc., but there's still some risk after relaunch (as when floorboards are removed for cleaning).

I'll see if Centek can give an opinion on the minimum wall thickness I should use.

Perhaps I should start a separate thread on this, but as you already know the background: Is there any rule-of-thumb or standard about how true the bore in the p-strut should be? When I measure the ID of mine I get anything from 47-47.9mm depending on the position (noon-6, 1-7 o'clock, etc.). The bore is 140mm long. If I take a cylinder hone to this can I achieve more consistent roundness?
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Old 07-09-2014, 18:56   #19
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Re: Shaft log replacement in Malaysia - Singapore

Not able to get HT120 glue powder so will need to use West fillers. What do u suggest - 404? 406?

Turns out that none of the Centek tubes are a workable size so back to square one on that issue.

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Old 07-09-2014, 21:52   #20
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Re: Shaft log replacement in Malaysia - Singapore

Either 403, 404 or 406 are good, 406 smooths out best and seems to be easiest to grind to a laminate-able surface if you don't initially fair it in enough.

Regarding eccentricity in the strut, how far inside are you measuring? To hone out a millimeter would be a lot of honing, and you might wind up making the fit too loose. I'm assuming the brg is an interference fit? If you can get an opinion from the bearing supplier or manufacturer, I'd go with that, but if you're replacing like for like, it seems to me that you'll be ok with it as is.

And back to the root problem. Is this your Volvo seal?



After looking again at the holes in the tube, I wonder if the clamp was slightly loose, allowing enough water to seep in and corrode it from the inside, under the clamp and rubber? Can you tell? If so, maybe the easiest solution is to go back with a SS tube and tighten the crap out of the seal clamp regularly.

Personally though, I'd try and find a way to use the glass tube. That would mean replacing the Volvo seal with something more standard sized (I could only find one source for 54mm tube, minimum order 10000 ft) or getting an oversized G10 tube and having it machined down to fit the Volvo seal. There's one here that's 2.25 od x 1.5 id x 48" but it's 351.00:

G10 FR4 Tube and Tubes | Cross Nail Laminates

I would be uncomfortable with 1/16" wall tube thickness too.

While I like Volvo for their general high quality and durability (I've got 2), their insistence on making things proprietary to them and high prices can get a bit annoying... though the price for the seal at least is sorta reasonable.

Seems like nothing's ever simple, I guess at least it's interesting though.

Regards
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Old 08-09-2014, 01:41   #21
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Re: Shaft log replacement in Malaysia - Singapore

Thanks, Jim.

- 403 is what I can get my hands on.

- My calipers only reach about an inch inside each end of the strut. As the ends of the strut bore are angled, not square, I know I'm not getting particularly exact measurements -- but also that the bore isn't exactly round. I'm thinking of doing a light hone just to clean it up, nothing so aggressive that I could knock it even more out of round. If I can enlarge this ID at all it will mean less lathing down the sleeve of the cutless bearing to fit. Have been using Duramax brass-sleeved bearings for a 1 3/8" shaft and 1 7/8" strut ID. Apparently "like for like" no longer available. The sleeve thickness of the old one we just pulled out was at least 8mm thick but the ones on the market now are only 3mm, meaning about .5 needs to be shaved off.

- Yep, that's the seal. We've never had a drop of water out of either end of the seal except when burping it, but I guess water could have gotten in between the first two ridges of the seal body, leaving just the third keeping the water in, and in contact with the tube. The tube OD tolerance of the Volvo seal is 53.7-54.5. I'll make sure my tube is all of 54.5 for the tightest fit.

- Thank you for the lead on the G10 tube. $352 hurts but not as much as getting rid of my 2 Volvo seals (value about $352) plus needing to buy another type of seal. The kicker will be the expense of having a 4-ft tube shipped. Perhaps I can get G10 to cut it in half and ship it that way. I'll have a spare for next time.
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