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Old 12-09-2014, 01:42   #16
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Re: Prop shaft log replacement

Quote:
Originally Posted by Alii View Post
Here is what the Aceon (the company in Selangor) can give me:

40mm ID / 55mm OD, "contact molded" (hand-laid) fiberglass and resin. They only do vinyl ester filament-wound for pipes over half a meter OD.

So, basically atoll's recipe but by professionals. Per Jim's analysis all I would need to do is skim the exterior but remove 2.5mm around the inside. If I need to go with this, what other questions should I ask Aceon? Same techniques and tools outlined for G10?

I have queries out re 316L stainless tubing, but so far have found only 304.
sounds good the GRP tube will give a 5mm wall thickness,should machine just as well as g10,and be plenty strong enough.

with the 316 if you can find it make sure it is unwelded seamless tube,though the GRP tube would be my choice.
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Old 12-09-2014, 03:41   #17
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Re: Prop shaft log replacement

My post was sloppy - I can't get VE since my OD is under half a meter, just regular hand-laid glass. This is plenty thick so next step would be making it thinner. Tq for pointers on my 316 shopping.

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Old 12-09-2014, 05:27   #18
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Re: Prop shaft log replacement

Like atoll, I really lean heavily toward the GRP, even if you can only get polyester lain-up tubing. (G10 uses epoxy) Tools and and techniques for working it would be the same as for G10.

Unless you can be sure of what caused the problem, to go back with the same setup pretty much guarantees you'll have it again.

Here is a quote about SS corrosion, specifically talking about 316L:

PITTING
This is an accelerated form of chemical attack in which the rate of corrosion is greater in some areas than others. It occurs when the corrosive environment penetrates the passivated film in only a few areas as opposed to the overall surface. As stated earlier, halogens will penetrate passivated stainless steel. Referring to the galvanic chart you'll note that passivated 316 stainless steel is located nine lines from the bottom and active 316 stainless steel is located thirteen lines from the top. Pit type corrosion is therefore simple galvanic corrosion, occuring as the small active area is being attacked by the large passivated area. This difference in relative areas accelerates the corrosion, causing the pits to penetrate deeper. The electrolyte fills the pits and prevents the oxygen from passivating the active metal so the problem gets even worse. This type of corrosion is often called "Concentrated cell corrosion". You'll also see it under rubber parts that keep oxygen away from the active metal parts, retarding the metal's ability to form the passivated layer.

The complete article can be read here:
Corrosion, stainless steel

And a link to s supplier of 316L tubing in KL:
Supreme Steelmakers | Stainless Steel Specialist - Laser Cutting, Waterjet Cutting, Metal Cut, Steel Malaysia
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Old 13-09-2014, 00:28   #19
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Re: Prop shaft log replacement

Is this a reasonable ready-made solution:

MAX-GAIN SYSTEMS, INC. : Fiberglass Price List

Buy both 2.25" and 2" OD, sleeve the smaller tube inside the larger with resin, open the ID up per Jim's guideline and skim the 2.25" to fit the Volvo shaft seal.

Seems I've found 3 possible sources, all offering a 2.25" OD / 1.5" ID tube:

1. Hand-made here in Malaysia with polyester -- probably around $150-170 including machining to specs but unknown companies, uncertain quality control

2. Mass-produced polyester tube from Max-Gain - $55 plus shipping from USA but I have a box coming already, can consolidate; add another $20 to machine here

3. G-10, $352 plus shipping to Malaysia (or to Jim, then Malaysia) + $20 machining -- not clear that it is worth 10x the price of option 2.

So, I'll have a sleep on it, but pretty sure I'll forget about 316 and order the MaxGain.
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Old 15-09-2014, 16:39   #20
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Re: Prop shaft log replacement

Laura,

Well, that is an ingenious solution and I would normally say go for it but for the following 3 reasons:

The Max-gain tubing is, as far as I can tell from their website, pultruded polyester. The main problem with pultrusion for this application is that the fibers are all run longitudinally, and with age this can result in something like what is shown in the attached picture. That's a pultruded polyester rake handle after replacing a concrete culvert in my driveway.

Bare polyester laminate is notoriously hydrophilic, I would be leery of both the interface where they are glued together and the inside of the smaller tube, mainly because of the constant immersion.

You don't want to do this again. It seems to me a false economy not to use the highest quality materials you can get.


And since I don't like pointing out a problem without offering a solution, here you go:

Instead of just using the internet, I picked up the phone and made 3 calls.

Vanderveer Industrial Plastics
Thermoplastic Plastic Machining & Fabricated Plastic Parts - Laminated Machined Plastic Products | Vanderveer Industrial Plastics
43mm ID x 52.98 mm od x 2' Domestic (U.S.) G10 - 33.60/ft. In stock
714 646 6489 Talk to Bob. This should work as is with no machining, but if you're worried about the final mm, laminate a single layer of 6 oz. cloth around it with epoxy.

Franklin fiber
www.franklinfibre.com
1.75" x 2.125" G10 17.55/ft
800 233 9739
This is not really a solution as delivery is 6-9 weeks and they have a 20 foot minimum order. (although the price would be about the same as for the 4' piece from Crossnail)

The third guy hasn't gotten back to me yet.

Was also thinking about your inquiry about the strut and remembered when I replaced my rudder shaft bearings with a material called Vesconite, which is also used for shaft tube bearings, They have an office in Singapore, I assume pretty close to where you are, that has the size you need in stock.

VB050x0351000 50mm od x35mm id x 1' Vesconite shaft brg

In stock in Singapore according to their stock list.

Singapore-VP Sea
65 6481 8728


Merry Xmas

JIm
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Old 15-09-2014, 16:43   #21
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Re: Prop shaft log replacement

This a glass boat? what numbskull designed a stainless stern tube? use glass..... if you cant find one over there a glass tube is easy to make. Just use an inner cardboard tube and wrap glass around that. Grind the OD at the end to fit your rubber hose. or if the sizing is right, use a hole saw on the OD of the laid up tube and it will shape it perfectly round..... if that makes sense....
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Old 15-09-2014, 19:18   #22
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Re: Prop shaft log replacement

Great stuff, Jim.

An Aussie surveyor who has been overseeing a refit here (but away the last few weeks on a delivery) stopped by to chat. When I told him about the sleeving idea he wasn't concerned about the polyester (although he did challenge me on exactly how I thought I would sleeve it) but his #1 choice was laying up my own tube a la atoll and Cheechako .

So when I asked what he recommended for ID, his choice was 45mm -- leaving 5mm clearance around the shaft. That is almost a 40% reduction in the cooling water available to the Volvo seal. As we were stooped right under the boat and he could see the configuration of the shaft log exit, his opinion was that any reduction in ID from the current 50mm would be cause for concern, and that I should plumb cooling water from the exhaust system into the tube.

Bummer -- this nullifies one of the top attributes of the Volvo seal, that I don't have extra hoses and tees and potential points of failure hidden in the engine compartment and bilge. The only way to avoid this underwater plumbing exercise would be to go back on the hunt for 316 pipe, but even international phone calls to yards that work regularly on Jonmeri's (e.g., Jamestown) have hit deadends.
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Old 16-09-2014, 05:23   #23
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Re: Prop shaft log replacement

Have nothing against making your own tube, done it plenty of times (never for a stern tube though). Thought you might be a little uncomfortable with it.

I'm not so sure how far I'd trust a surveyor who doesn't know about uncoated polyester laminate's hydrophilic properties. If you do make your own and use polyester resin, make sure you coat the inside with waxed gelcoat.

Which leads us back to the tube itself.

A traditional stuffing box for 1 3/8" shaft uses a tube OD of 2 1/2"; with 1/4 wall thickness you'd have 5/16" clearance all around. For most applications no extra cooling water is required. With Teflon impregnated packing they work very well, plus you can renew the packing without hauling the boat or diving. (Suppose it's not strictly necessary with the newer types of seals either, although a bit more involved...) Initial cost is about 140.00 here, cost for the packing itself is less than 5.00.

As for making your own tube, for a 2 1/2" OD epoxy tube with 1/4" wall:

20-25 oz resin 25.00
hardener 10.00
2' z 7' 6oz cloth 20.00
colloidal silica 10.00

65.00 total, minus the satisfaction of doing it yourself.

One technique for doing it singlehandedly: Prepare a 2"x 3' mandrel, 1 1/2" pvc (O.D. is 1.9") is about right, I'd wrap multiple layers of waxed paper tightly around it to get the OD closer to 2". For a 2' tube I'd use 26"-28" wide cloth. Do a dry run, lay out the cloth on a plastic covered piece of plywood, tape the width of the cloth to the length of the mandrel and roll it onto the mandrel until you have your 1/4" wall thickness, 6 or 7 feet of cloth is a guess. Unroll it, mix the epoxy (with silica), squeegee it out, and roll it up, not too tight, not too loose. Be liberal with the epoxy, this is not the place for a resin starved layup. Or air bubbles. (The reason for the silica is too keep the resin evenly distributed until it kicks) For the same reason, the fastest hardener you can get away with is best. Go have a couple of beers. When you get back (or maybe the next day), knock the pipe out, peel off the waxed paper stuck inside as best you can, cut an inch or so off to square it up, run a 2 3/4" hole saw (giving a 2 1/2" OD to the tube), a la Cheechako, down it, and you're ready to install it.

If you decide to go the water cooled route, make sure you take the water from before the heat exchanger, otherwise you'll probably be heating rather than cooling. (hope that's not being condescending)

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Old 16-09-2014, 16:46   #24
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Re: Prop shaft log replacement

Not condescending at all, but I kept my mouth shut when these plumbing instructions were presented (based on other examples where raw "cooling" water was plumbed into the shaft log tube using the Volvo seal):

Install T in pressure side of the anti-siphon loop we already have between the heat exchanger and the mixing elbow; run 3/8" hose to a fitting thread into the shaft log tube.

So yes it seems strange that I'm told to take water heated by the motor to "cool" the seal, but this appears to be what at least one other seal manufacturer wants, see e.g. pages 9-11 of http://www.tidesmarine.co.uk/downloa...llation-manual.

If I was to install the PSS seal, all I would plumb would be a vent line not a pressurized water source. And the PSS line envisions a shaft log ID as small as 45mm for a 35mm shaft. Does this suggest an option for me in reducing the ID from 50mm to 45mm with the Volvo seal?
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Old 16-09-2014, 19:00   #25
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Re: Prop shaft log replacement

After scratching my head about Tide's manual, it appears to me that they're more concerned with lubrication than cooling. It also seems, based on their list of take-off points by preference on page 9, that they're mainly concerned with not causing the engine to over-heat by diverting too much water away for the shaft seals. If I were trying to provide cooling water, my first choice would be their position 3. The water that comes out of the heat exchanger of my MD2020 when under load is pretty warm, way above the 90F ABS approval upper temp rating.

As for venting the Volvo seal to promote water flow in a reduced clearance tube/shaft situation, it's hard to say if it would help. My gut instinct is that there would be no difference.

But if you're worried about water flow, I don't see any reason why you couldn't tap into the stern tube at some place close to the seal end and supply a little pressurized water. (Well, besides the complications of doing it and the added headache of maintaining and worrying about another below-the-water-line source of (potentially catastrophic) flooding.)

Simplicity is your friend.
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Old 16-09-2014, 19:23   #26
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Re: Prop shaft log replacement

Yes, and simple is my current set-up with the no-hassle Volvo seal, no extra plumbing, and thin-walled 50mm ID 54mm OD tube. Except that the tube is stainless, and after 28 years has corroded.

I got this seal thru Vosbury Marine -- I'm going to call them and see if they endorse flooding with any water downstream of the oil cooler. Seems to me it can't be good for the all-rubber seal, and finding skinny hose that won't melt carrying 80C water from the engine will be tough.

As for take-off point #3 -- I have all-new Yanmar pipes and hoses ready to be installed in the cooling sea water system. There is a very small outlet to drain the system in the pipe running between the pump and oil cooler (part #1 in Fig 26 if my efforts to attach this .pdf succeed). In the past we have plugged this outlet, haven't used the #1 drain cock, as it has always leaked (right on top of a wiring harness) and we didn't see the use. As I read the parts list, this outlet is meant to feed a 7mm drain hose (although not under pressure). Perhaps this is a suitable extraction point?
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Old 16-09-2014, 21:29   #27
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Re: Prop shaft log replacement

This threaded outlet is 8.5mm ID, so will allow just a trickle once a fitting is screwed in. Is this enough to help the Volvo seal without screwing up flow to the Yanmar? I'm very hesitant to mess with the cooling system hydraulics -- we have a SeaFrost condenser upstream of the sea water pump and changes to the existing set-up have caused unanticipated problems (e.g., tried the Johnson OEM impeller and the softer vanes flipped backwards).

I think I'm wandering off into the engines forum terrain.
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Old 17-09-2014, 04:15   #28
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Re: Prop shaft log replacement

Well in my opinion, Jonmeri's simple solution is actually a pretty serious design flaw. Along with Volvo's if they spec a 2mm wall thickness for use in this critical, hard to get at area.

Kind of a moot point now though.

It'll be interesting to see what Vosbury says. If you take water from any point after the seawater pump, but before any heat exchangers, the water will be at ambient temperature, probably 85-90F in your location, hardly cool, but cool enough. The drain cock you propose seems ideally located for this application, I'm not so sure that that is not what it is intended for. A plus is that the drain cock is actually a valve, and as such can be used to adjust the flow rate.

Regarding flow, that is very idiosyncratic. A 4mm orifice under the pressure of a properly operating seawater pump will throw a bunch of water (how's that for a scientific term?). Gut instinct? Unless Yanmar has cut their cooling tolerances way too close, the amount of water taken to cool the seal shouldn't matter.

You're probably tired of hearing it, but for me the solution is simple. Get or make a 2.5" x 2" frp tube, couple it to an old fashioned bronze stuffing box with new fashioned Teflon packing, and there's no need for water injection. Sure you might have to adjust it now and then, but you should be inspecting this area at least every month or so anyway. Properly adjusted, they can run for years (depending on actual usage of course). Although I only use mine about once a week, I never needed to adjust it in more than 3 years. Had it out in May, shaft looked fine, packing looked ok, but I changed it since I was in there anyway. Checking the box consists of looking at it, and after running for a mile or so, feeling it's temperature. And, while 'they' say that stuffing boxes are supposed to drip while running, if mine does, it is very minimally. Think it has something to do with the Teflon packing.
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Old 17-09-2014, 08:20   #29
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Re: Prop shaft log replacement

The guys at Vosbury Marine are quite adamant that I should have no problem with the Volvo seal by reducing the shaft log ID from 50 to 45mm, no need to introduce a pressurized water source. I'm going for it, and ordering the G10 tubing from Vanderveer.
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Old 17-09-2014, 08:42   #30
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Re: Prop shaft log replacement

Finally good news. Let us know how it turns out.
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