Beneteau First 42 propeller strut repair

[SvNovia]

The strut has vertical movement/play of about 3/8”. The boat yard has estimated 56 hours labor with much of the hours involved in the job devoted to removing/reinstalling the steering, rudder and prop shaft. Removal of the strut itself will involve cutting off the top of the fiberglass strut housing, and cutting the horizontal securing bolt located above the glassed-in lateral support plywood squares. I have uploaded a starboard side pic of the strut housing:


The strut probably looks something like the 2nd upload but with a single through hole for the security bolt.

The boat yard has proposed removing, inspecting and re-securing the strut by bonding and reglassing within the existing fiberglass housing buildup. My concerns with this plan involve relying on the original marine plywood squares providing lateral support to the strut.

My questions to the community, besides wanting to hear all of your general thoughts or experiences with this type of repair, are what is the best strategy to assess the condition of the existing strut ( my surveyor believes it to be manganese bronze, subject to dezincification), and what known sources are there to get a new strut of this type if I need one?

I’ve also included a pdf from Bénéteau detailing the construction process.

[tkeithlu]

Welcome to the forum, SvNovia.

I'm impressed that Beneteau supplies such detailed instructions for this repair. I'm also impressed that your yard dues such a careful analysis of the task. The only thing that doesn't impress me is the original design of the strut - as long as they were casting it, a horizontal flnge with bolts would seem in order. Dezincification should be evident on close examination fo the lower part of the strut, if it exists. I can't help you on a source, but I am doubting that you need one.

With such careful instructions, are you considering doing this job yourself? It's long and complicated, but none of the individual tasks is challenging. You would determine whether the plywood triangles can be salvaged when you get down to them, and they are easy to replace if needed.

[tkeithlu]

What did you hit? I hope it wasn't one of Mark's blubber butt manatees.

[Manateeman]

Good morning original poster. Well, the first question would be : did you hit something or wrap the prop in a line? Since the builder has gone into great detail, is this a common problem with your model boat.
Are you asking our repair opinions because you wish to DIY or are you asking about the yard estimate.
The next question is simple. Is the strut loose in the hull or is the hull flexing.
Does the strut move side to side , fore and aft or only up and down.
Does the prop shaft turn more easily of you push up or down on the strut.
Did you have a lot of leaking past the stuffing box or any other symptoms which got you to look at the strut.
Well the Green Frog is correct. A “tee” shaped strut is a much stronger design. It spreads the load. So...let’s take a look at repair options...DIY.
You will make things a lot worse if everything is not kept in alignment...so let this be your priority. Remember the weight of your propeller or any mis alignment of your engine will defeat the repair so off goes the prop and disconnect the engine.
How far off is the engine with the strut loose. Can you prop up the strut so you are pretty closely aligned to the engine as is?
What we are trying to figure out is a fix without tearing the box surrounding the strut inside the hull, apart completely.
IF...and it’s a big IF, the strut is just loose in that “box” support thing inside the hull...and IF the shaft is centered in the tube, then it MIGHT be possible to fix it by epoxy injection. A few small holes drilled into the box till you hit the strut will tell you if the plywood is wet. If it is...then a simple repair no longer is possible.
You could add angled supports on the hull exterior or interior bolted both to the strut and hull but it would be a lot of work.
We don’t recommend rebuilding the box support system recommended by the builder. You can cut the box flat to the interior of the hull...have a tee shaped strut welded or cast . We’d lay up a nice wide area of reinforcement to the hull and bolt the new strut to bronze reinforcements inside the hull.
Please let us know if you intend to DIY.
My Green web footed friend exists on a diet of flying insects, lives on an unstable wet pad of dubious strength, and makes the beginning of a nice Cajun dinner...BUT ...he is very knowledgeable, kind and helpful. Thus we leave you in his capable hands as the manatee crew wishes you...happy trails.
Captain Mark

[SvNovia]

Thank you for your reply tkeithlu. I don't know if this is collision damage or just from normal wear. I may take on the task myself. Time is the biggest factor right now. I had the boat pulled just to put on a coat of bottom paint and upgrade my depth and speed through hole sensors so I hadn’t planned on tackling such a big job right now. My first step will be to sand and clean the strut to bright metal to determine the extent of the dezincification to assess if it is still sound. My thought is, if I am going to pay the yard to remove the strut for inspection I may as well have a new one, possibly cast out of bronze, installed. I’m meeting with the yard service manager in a few days to discuss the specifics on how much of the housing they intend to rebuild prior to re-bonding the strut into place.

[Pauls]

Totally concur with both previous posts about Beneteau's design. Technically speaking, it's crap. If the existing strut has suffered sufficient dezincification to warrant replacement I second Manatee's recommendation.

If you find the strut to be in good condition you can convert it to a "T" type by welding plates to the existing strut. This will be much cheaper than casting, then machining, a new one.

However you go about it, I'd suggest that converting to a T strut is well worthwhile. I believe you'll find it will be easier than mucking about with the internals of your existing mounting box, and it will certainly be a superior product.

[Bowdrie]

Hopefully any repair process will enable the re-use of your existing strut.
That said, if circumstances preclude that, then you might want to at least take a look at other options.
The old "Buck Algonquin Co." made scores of fittings, they have been taken over by "Hydrasearch", but many of the designs are still being produced.
Here is a page'
https://catalog.hydrasearchrecreatio...egory/struts-1

[SvNovia]

Thanks for your reply Captain Mark. The strut mostly has vertical play. I will assess side to side movement tomorrow when I can get down to the yard. It appears to be still in horizontal alignment and I haven’t seen signs of hull flex or damage. The prop turns freely and the shaft seal wasn’t leaking. The loose strut was discovered while pushing up on the prop to check the cutlass bearing. The shaft is centered in the log horizontally but is closer to the bottom of the log. I attributed this to hull deformation due to its resting on the keel while on the hard. I have experience aligning a shaft flange to a motor. I did that job on another boat after replacing the cutlass bearing.

Thank you for your suggestion on drilling into the ply squares to test their integrity. From the Beneteau document it seems like the ply is initially installed to set alignment then also supply lateral support to the final build. Maybe sistering the squares with new glassed in ply on the outside of the existing housing would supply enough support? I feel the simplest “patch fix” would be to cut the top off of the glass strut housing, clean the inside as best as possible, realign the strut with the shaft in place and fill the housing with epoxy. The most complicated repair involves removing and rebuilding the entire strut housing as per the Beneteau publication. I’m assuming the yard is proposing something in the middle of those two extremes. Their description in the estimate was somewhat vague. As to whether I do this job myself or hire the yard I haven’t decided yet. Either way I want to understand and weigh all options.

[SvNovia]

Thank you for your replies Pauls and Bowdrie. I appreciate your advice and I am open to alternatives. If I am understanding, you are both suggesting a flanged strut through bolted to the bottom of the hull to a bedded backing plate on the inside? That does sound like a stronger solution than the original design. If I were to get a bronze replacement of the original strut cast I would be able to do the machining of the strut myself.

[Pauls]

Hi SV. Yes, that is correct. A flanged strut, thru bolted, with backing plates. It is not a complicated repair and you are correct, it will be significantly stronger.

[SvNovia]

Thanks Pauls. I will look into that as an option. It introduces new complications to setting proper shaft alignment and possibly requires modification of the inner hull? At least filling in the existing strut slot and glassing in a strengthening platform that would be sandwiched between the strut flange and backing plate? I’m also wondering how much modification would be needed to the outer hull.

[Bowdrie]

Originally Posted by SvNovia

I’m also wondering how much modification would be needed to the outer hull.

After reading thru the PDF, It's apparent that should you go with a "flanged" strut, (I agree with Pauls,) that the "inside" work would be much easier than the "factory way".
As for the outside, it's really not that big of deal, it's a matter of grinding the gel coat off in relatively small area, and using fiberglass/epoxy to build-up a tapered pad for the flange to bolt thru.
The rough alignment is done by using the propshaft/strut/bearing, being supported from below as the "gauge" for pad angle/thickness, allowing that a final "fine" alignment will need to done once all is secured.
Assuming reasonable access to inside I don't really see any hard difficulties in the job.
Like most boat work, careful/thoughtful prep work is key to success.
56 hours??, that seems excessive to me.
From your given location it seems that their must be a lot of good boatwrights that could knock that job out in much less time, no matter the path you choose.

[Bowdrie]

I need to add: I don't know if your hull is cored in that area, if it is then a flange mount becomes more complicated, and some "surgery" would be required.

[Searles]

All good imfo,the simplest way to me would to flush off the hull inside,and get or have made two 90dg bronze piece’s in g2 bronze ,bolt or weld to existing strut ,re fit re align ,bog in ,check alignment of shaft ,adjust if necessary ,clean up glass in with epoxy or vinalester,I would guess about 16 hrs work for a good shipwright.⛵️⚓️

[SvNovia]

Thanks Bowtrie. The hull is solid fiberglass construction. I’ll take measurements tomorrow and look into sourcing flanged strut.