replacing prop shaft strut on O'day 40

[rlg]

My prop shaft strut is cracked on both side the length of it. Small crack but there is some movement noticeable. It is bronze. I discovered this today after hauling yesterday. I am trying to get my head around this and really could use some of the experience and generosity of this forum about now.

Apparently new ones are reasonably available but thats about all the good news. And that I was hauling to replace the rudder so it is a little easier. I guess 30 years of heavy use is enough to expect from these components.

Im specifically wondering about how to remove it? Is it bolted??

Is there any other options?

Im in Stuart Fl btw

Thanks very much,
Rob

[Mischief_Inc]

Yes, they're normally bolted on, with the bolts & a backing plate for it being in the bilges. And usually the only "trick" to getting a new one is ensuring that the angle through which the shaft passes is correct when the new one is in place. Also, you might consider getting one with a V profile, instead of just a straight leg. That way you have 2 struts connected to the bearing itself, thus lending more strength to things.
Some of what you choose depends on how snag prone your boat, & favored waters are.


Edit: Some guys will incorporate a line cutting blade into the leading edge of their struts. Fixed, or replaceable. But if you do, be sure to warn all divers & swimmers of such. And now's as good a time as any to add a line cutter to your prop shaft if you desire one.

[Pizzazz]

They are bolted on the O'day. Find the nuts on the inside (they may be glassed), unbolt and remove the strut (take pictures of the angle, etc.). Put the new strut it and position with shims. You want the shaft to be centered in the PSS (or packing gland - I strongly recommend to install a PSS at this point since you have done most of the work).

When you position the shims you want to make sure that the shaft rotates freely. If it is at an angle to the strut you will feel resistance. Adjust. Bolt tightly with the shims, run the engine for a minute (or just use the starter to rotate the shaft a few times with fuel cutoff). Check everything again. When comfortable, fix with Sikaflex-291.

If you take your time you can do a great job. Talk to others in the boatyard as well. Typically they will give you great advice.

[Mischief_Inc]

Originally Posted by Pizzazz

They are bolted on the O'day. Find the nuts on the inside (they may be glassed), unbolt and remove the strut (take pictures of the angle, etc.). Put the new strut it and position with shims. You want the shaft to be centered in the PSS (or packing gland - I strongly recommend to install a PSS at this point since you have done most of the work).

When you position the shims you want to make sure that the shaft rotates freely. If it is at an angle to the strut you will feel resistance. Adjust. Bolt tightly with the shims, run the engine for a minute (or just use the starter to rotate the shaft a few times with fuel cutoff). Check everything again. When comfortable, fix with Sikaflex-291.

If you take your time you can do a great job. Talk to others in the boatyard as well. Typically they will give you great advice.

I'm curious, have you ever bedded a strut in bog (epoxy, & milled fibers) so as to get the angle perfect? Obviously you'd only tighten the bolts finger tight until everything cured. And then you'd recheck the alignment, prior to doing the final bedding. But that way, in theory at least, you'd have custom made, fixed, shims. I mean it works for bedding keels, the technique & materials that is, so I'd figure it'd work for struts, non?


And yes, once everything is "permanently" bolted into place, it pays to run things for a bit in the slip, to ensure that the alignment is perfect. And that nothing's prone to vibrating loose. Do the same prior to splashing the boat, only without running the engine such that it hurts itself. Basically a spin check. Most of which can really be done by hand.

[Pizzazz]

Originally Posted by Mischief_Inc

I'm curious, have you ever bedded a strut in bog (epoxy, & milled fibers) so as to get the angle perfect?

I just followed what they do in the boatyard. They bed as much as possible in Sikaflex. Not 5200, not epoxy. Sikaflex finds its way into all the small holes and beds nicely. If you mess it up, it can be redone easily. In my case, both the shaft and the strut were bent. So I replaced both, in the process had to lift the engine up to pull the new shaft underneath. Instead of shims I used stainless steel washers on the bolts. I had something like 5 on one bolt, 6 on the other, 7 on the last two. Then you tighten the bolts and the strut is fixed in place, it will not move without any Sikaflex. Next I installed the shaft and run the engine for a few minutes so that it positioned itself on the mounts correctly. Checked if the shaft was centered and rotating freely. Realigned the strut, checked for free movement and fixed it with Sikaflex. Next, once the boat was in the water, released the engine mounts a bit, ran the engine, then tightened again, then aligned the engine. It took me about 6 hours to complete the procedure (I even had to lift the engine twice because the first time I forgot one of the PSS parts. It was my first time doing it but it worked out OK.

A few weeks later I called a mechanic to do a professional alignment, he came, ran the engine, checked the tolerances and said: "I would be happy to take your money and realign the engine but I have never seen a better aligned engine and I do not think I could do a better job." So, he charged me for half an hour of his time and left.

The moral of the story is, take your time and experiment with the angles. Once you think it is aligned, misalign it deliberately to see for yourself that it is worse, then go back to original alignment.

[Mischief_Inc]

I'm assuming that you're referring to using stainless steel washers in between the bracket & the hull in order to get it's alignment as close to perfect as is possible. And that the Sikaflex is just being used as a sealant.

What I'm getting at is using bog in place of washers, so as to make a perfectly formed, custom bed for the strut where it meets the hull. Thus no shimming would be required. Or as close to none as is possible. Much as I cast bases for all sorts of other hardware onboard. Including things that have to be perfect, such as flat & level bases for deck hatches. Though they too still get bolted, once their bases are cast, & they recieve a dose of Sikaflex or similar.

The idea behind using bog for this is that you get 100% contact over the full base of the bracket, instead of just small areas around the washers. Make sense? And that way there's also no concern about metal + salt water = bad.

Albeit some brackets are set into shallow recesses within the hull. And once bolted in place, get faired over. Or even recieve both shims & bog underneath, in addition to being faired over.

[Pizzazz]

I see your point. Your approach would be even better as long as you can position it well. When I was removing the old strut it basically fell off together with its nice custom bed which is what you are describing. I do not think this bed was actually providing any structural support. It does spread the compression loads better than the washers but my thinking was that when the shaft is rotating it wants to move the strut it all directions and I felt that all the stress loads should be carried by the four bolts in both compression and expansion. But I agree that it can only help if done right. Thank you.

[Mischief_Inc]

By bog, I mean epoxy that's thick with milled, & even chopped fibers. Some up to 6-10mm long if possible, but a bit shorter works. And only enough epoxy so that things are wet & spreadable. Spreadable like peanut butter fresh out of the fridge. Though a bit thinner tends to work for most things, as does a touch less filler.
Regardless, it's definitely structural, in terms of support. And becomes a part of the hull too, properly applied. Since for all intents & purposes it's a DIY custom blended Marine-Tex (putty). With properties similar to same.

I use a layer of clear packing tape, PVA, or both, as a release. So that barring any big mechanical interlocks when things cure, at most it takes a few taps with a mallet to free up the part. Though usually just a touch of forceful wiggling does the trick. Then if it's a critical fit, I'll use a marking agent on the part, & re-seat it to see how much & where the gaps are, if any. And I suppose that on some things like this, that would be a good tool for checking alignment. To see if it needs a 2nd thin coat of bog, or a small shim somewhere.

One thing worth mentioning for those new to such tasks, is to check your alignment after the boat's been in the water for a week or three. As the hull will change shape a bit after having been on land. Which alters the engine's relation to the prop shaft. Something usually fixable by adjusting the mounts a bit, knock on wood. And it's also a good time to make sure that the hose in the shaft fitting isn't rubbing on the shaft due to any inherent curvature in the hose. Since that's a good way to wind up overloading your bilge pumps at an inconvenient time (sink her).

Edit: I reckon that G-10 would make some decent shim stock for this, assuming that you can grind it into wedges without it slicing your fingertips off Since it's easy enough to bond to, doesn't absorb water, & handles compression loads well. But any FRP plate with similar properties should work, knock on wood. So long as it's got good numbers, & doesn't absorb water. You can always check at matweb.com

[rlg]

Thanks very much for your responses. It sounds pretty straightforward. I saw somewhere a person recommended building a wood "strut" to put up against the hull to use as a measure for the new strut placement.

Anyone who has done this job please feel free to add their thoughts.

Any suggestions for the proper tool and method to grind out the old one neatly?

Rob

[Mischief_Inc]

I would think that once you have the old one off, & a flat hull to work with, you can make a mockup using some plywood, pvc, & a hot glue gun. Though if there's a foundry in your area that does any boat parts, they'd be the go to folks on this for info. Much as in any boabuilding town. Since they can custom build them from scratch, or modify an existing pattern to fit your boat. Which, it's worth contacting the original builders if they're still in business, as well as some of the better known foundries as well. Such as the one in Port Townsend, WA.

[Mischief_Inc]

Edit: Given that you’ve already got a bracket in your hands which is a perfect fit, that should be a pretty good model to work with in terms of getting another one made/purchased. But measure all of the angles & dimensions on it precisely, just to be safe.

Then I’d talk to a foundry, as they’ll know 20x more on this topic than most anyone else. Including whether or not they can use the current one to fabricate a mold for the new one. And if you should have the current one temporarily brazed up to maintain it’s integrity from the perspective of it being dimensionally accurate. Which, if you do get it brazed, I’d reckon they should put it in a jig while doing so, so that none of the angles or dimensions change.
That, or perhaps temporarily bolt it together with some straps? To the same effect.

A couple of other options are to make/have made, a composite one. Which is easier than it sounds, & gets done all the time, including on some production boats.
And you might look into having one made out of steel, & then salt bath nitrided. So that it winds up with a super corrosion resistant finish which is actually part of the metal. Though I don’t know if such a finish is appropriate in said environment & application. Nor if it would make things too brittle or not. And if the welding would hold up to the heat which is part of the nitriding process. But it’s surely worth checking. As in the proper applications, said “finish” is hands down, ultra corrosion resistant. WAY more so than stainless. So do some checking.

[rlg]

Im trying to find out what design and model or manufacture my strut is. Got the seized quadrant rudder bolt out today, thanks to bob and a 4inch grinding wheel.

Ill be digging in to try and move the fuel tank out of the way now that theres some room.

Still would love to hear from anyone who may have done this. Thanks