Strut repair

Discussion in 'Fiberglass and Composite Boat Building' started by Aaron Darby, Feb 2, 2021.

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  1. Aaron Darby
    Joined: Feb 2021
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    Aaron Darby Junior Member

    New here, did a little searching but didn’t find anything on how to repair a leaking strut. I’m helping a friend on his 64’ Harkers Islans Kingfisher. The STBD strut leaks, so we pulled her out of the water and I’ve gone to work. Of the 6 bolts that hold the strut on to the hull one is spun out and two look like they are leaking water since they are corroded even though they are stainless. I’ve removed the stainless backing plate and of course the spun bolt looks like it may have been leaking. The strut has been faired on the hull and when I ground out material to access the three bolts heads that I assume are potential leaks I noticed that the fairing compound didn’t stick to the strut, there is a void between the strut and fairing compound and water can reach the bolt heads, probably all of them. I’ve done a little research and assume the strut was bedded to the hull so my plan is to grind out all the faring material starting at the strut and working towards the hull until I can verify good solid contact. I’ll remove all the bolts, clean them or get new ones and install (backing plate as well) with plenty of 5200. I’ve done some epoxy work and feel confident in my skills but never have worked with a brass strut or hardware and epoxy before. Is a good thorough cleaning with a coat of epoxy and then fairing compound all I need or do I need to etch it, maybe prime it first. Any help and suggestions would be greatly appreciated.
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Welcome to the Forum Aaron.
    Is your friend's boat like a bigger version of this 50' Harkers Island sportsfisherman?
    Harkers Island Sportfish Charter Yacht for Sale, | Viva Boats https://www.vivaboats.com/-harkers-island-sportfish-charter-yacht/Power-boats/14858

    Is there still any bedding compound between the strut baseplate and the hull?
    Your proposal sounds reasonable - although the strut will be what everybody knows as bronze, rather than brass (but anybody pedantic might say it is a type of brass).
    Would it be possible / feasible to undo all the bolts, and slide the strut aft on the shaft (assuming that the shaft is still installed?)?
    That would make it easier perhaps to apply new bedding compound (5200?) between the base and the hull?
    I presume that this is the larger main strut, rather than a smaller intermediate strut?

    Do you have any photos of the strut?
    And a couple of photos of the boat herself would be nice as well - I presume that she has a legendary flared Carolina bow?
     
  3. gonzo
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    gonzo Senior Member

    Stainless bolts below the waterline is a no-no. You should install either bronze or monel. What you are seeing is the typical crevice corrosion in stainless. 316 passivated stainless is an option, but the price is probably not worth it. Also, any scratch or even the friction from the nut may remove the passivated layer.
     
  4. Aaron Darby
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    Aaron Darby Junior Member

  5. Aaron Darby
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    Aaron Darby Junior Member

    Seems all I have are pictures of all the broken parts. Ill get a picture of her up. Probably start a thread dedicated to the boat, The Grace.

    If I do go with Bronze or Monel bolts do I need to change the back plate that is currently stainless steel?
     
  6. bajansailor
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    bajansailor Marine Surveyor

    Yes please re a photo or two of the boat as well - and a thread on here all about The Grace would be even better!

    You have a couple of S/S bolts there that are textbook corrosion examples - very impressive!
    It would definitely be a good idea to change the bolts (and nuts and washers) for bronze or monel (if you can find monel).
    If your S/S backing plates are still in good condition, you should be able to keep them - how thick are they?

    Re how there are two holes in the longitudinal stringer for accessing the nuts on the bolts - this is rather poor design.
    Does the top flange of each strut have six bolts in total, aligned 3 transversely and two longitudinally?

    I think that I would be inclined to grind away all the fairing around the top flanges of the struts, and live with the slight amount of extra resistance - this would make it much easier to re-bed the flanges, and easier for future routine inspections.
     
    Last edited: Feb 4, 2021
  7. Aaron Darby
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    Aaron Darby Junior Member

    6 bolts total, 3 on each side of the strut
    The backing plate is 1/2 stainless and with exception of a little surface rust seems in good condition.
    I’m trying to source Monel or bronze bolts, they are 1/2-14 5” long pan head. I was wondering about the forces and load the bolts have to carry. Guessing it isn’t much, the shaft forces are rotational and any movement would have to move the engine and transmission. Being worried that a bronze bolt would fail is probably unfounded?
     
  8. bajansailor
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    bajansailor Marine Surveyor

    Re 5" x 1/2" bronze bolts, I tried Classic Marine in the UK, but they only have 4" x 1/2" hex-head bolts -
    https://shop.classicmarine.co.uk/fa...rs/bronze-bolts-nuts-washers-12-inch-unc.html

    Similarly McMaster Carr in the USA -
    McMaster-Carr https://www.mcmaster.com/bronze-machine-screws/bronze-hex-head-screws/

    Jamestown Distributors have 6" x 1/2" csk hd machine screws on their website at $24 each - but no 5", and they are currently out stock of the 6" screws.
    It would be worthwhile contacting them though?
    Jamestown Distributors https://www.jamestowndistributors.com/product/product-detail/1276
     
  9. Aaron Darby
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    Aaron Darby Junior Member

    I’ve got new silicone bronze bolts, washers, and nuts. Other then 5200 and using TedGel should I be concerned about the stainless steel plate and bronze where they meet? Perhaps a thin fiber washer between the two or a maybe a wooden block?
     
  10. bajansailor
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    bajansailor Marine Surveyor

  11. Aaron Darby
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    Aaron Darby Junior Member

    27934D49-7C8D-4CCA-AA3D-2CAF96BCC468.jpeg D7ABED43-99A7-4807-A789-3DBD02C55D52.jpeg I’ve exposed the base of the strut and as always it looks like more work, exposed a void and not sure how bad it is yet. Had to stop and dump dust out of my eyes. Headed to pick up a full face respirator, this half mask and goggles ain’t cutting it.
     
    Last edited: Feb 5, 2021
  12. Aaron Darby
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    Aaron Darby Junior Member

    bajansailor likes this.
  13. Aaron Darby
    Joined: Feb 2021
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    Aaron Darby Junior Member

    B023738E-8D3A-44B4-8D82-AE7B7749B10E.jpeg C502FA43-5FCA-40F9-A3DA-2EC9256598BD.jpeg 06E4D8FA-B42F-41F6-B8F7-872715C7BD69.jpeg 10D41FEE-CA57-46D5-8266-00935970B3BA.jpeg 2AECD801-64F2-4607-87F9-67D5612BB2F9.jpeg 872C4A0E-BA8A-4E9B-A7DA-40C18031DB06.jpeg
    Figured out how to add pics to the post. After a few hours of chasing voided I’ve exposed a few problems. The strut appears properly bedded but water has been past the strut and into voids between the structural hull and the fairing materials. I believe they used wood and plywood so they didn’t have to apply 2” of fairing compound and this wood looks to have been exposed to saltwater.
     
  14. bajansailor
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    bajansailor Marine Surveyor

    Impressive photos Aaron - they look like works of modern art!
    Except that the black / mouldy looking areas do look rather ominous.

    I think it is time to make a decision to do a 'proper' job - and that would probably involves removing the propellers, withdrawing the shafts (can you do this with the rudders in place?) and completely removing the struts.
    Clean up both areas (get rid of that old wood and other bedding materials) and then use proper materials (not wood!) as backing pads under the strut bases.

    I think that you ideally want to use something like Chockfast (or similar) to form the backing pads -
    Chockfast Products | High-performance epoxy grouting https://itwperformancepolymers.com/products/chockfast

    Others on here will have more experience than me with this product (I have none) and can advise you better.
    But it might be feasible to re-assemble each strut with the securing bolts, leaving a gap between the base and the hull, such that you still have pretty good alignment of the cutless bearing in the strut with the engine shaft line.
    Can you get hold of a laser to help line it up?
    Otherwise use a tight string - but a laser would be easier.
    If you can build a dam around three sides of the strut base, then it might be possible to pour liquid resin in to the aperture (between base and hull) from the 'up-hill' side to form the new backing / bedding pads?
    If this is not feasible, then it might be possible to just use say 3 bolts for securing each strut base (in a triangulated formation), and then pouring resin in through the other 3 bolt holes?
    This is just a wild suggestion, and I would welcome constructive criticism re improving this method.

    Be aware that you would still have to carefully re-align the engines at the end, as the struts will not be in the same positions as they were before (and they might not have been perfectly aligned before you started this repair anyway).
     

  15. Aaron Darby
    Joined: Feb 2021
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    Aaron Darby Junior Member

    I’ve heard of Chokfast but at this point I think the strut and bedding compound are sound. I will investigate further, the bedding compound appears to be discolored but solid and undamaged. I will be sure to grind it just a little to ensure it hasn't been compromised.

    The water intrusion has caused damage to the fairing materials, a combination of plywood and other wood pieces surrounding the strut (blue on my drawing). It also looks like it has run between the hull and the fairing material, for how far I am not sure. I like the idea of a proper job, start removing fairing materials until I run out of damage and replace it all.

    This is my delima, like a thread on a sweater I feel like when I start removing the fairing materials I may end up in the bow without a sweater.

    It sounds like the plan is to dry it out like you describe with the chine work, clean it up a bit more and liberally inject epoxy mixed with Acetone (ill double check that, something that helps the epoxy wick into the wood?). After a few solid coats of epoxy, re-fair and we get to keep the sweater. It kills me because I will never know how far the damage went. Strut2.jpg
     
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