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Bayliner 4788 Strut Bolts: Are They Designed to Shear?

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    Bayliner 4788 Strut Bolts: Are They Designed to Shear?

    When we hit a submerged channel marker last week, it sheared our starboard strut right off. There seems to be no fiberglass damage, just six broken bolts.

    Is this what is supposed to happen?

    We've had a few people express surprise that the impact did not rip a hole in the bottom of our boat, or at the very least pull the bolts all the way through. But instead the bolts failed. Is this perhaps by design, to prevent worse damage?

    The mechanic who is working on the repairs said (I think - my Spanish is non-existent) that the current bolts were cheap and weak, and when he does the repairs he will use better bolts. Is this a good idea?

    What kind of bolts should be attaching the struts to the bottom of a Bayliner 4788?

    Thanks,

    - Chris
    The strut bolts sheared off when we hit a submerged channel marker.
    Chris & Cherie - www.technomadia.com
    "Y-Not" - 1999 Bayliner 4788
    "Zephyr" - 1961 GM PD4106 Vintage Bus RV Conversion

    Full-Time nomads since 2006.
    Now spending half of each year slowly doing the Great Loop in our 4788!

    #2
    Did you see the bolts? If so, were they corroded in the area that passed through the fiberglass? If so, the bolts suffered crevice corrosion. This occurs in stainless steel in areas where moisture collects and becomes stagnant, with no oxygen circulation. The bolts get pitted and lose cross-section. This weakens the attachment.

    https://www.boatdesign.net/attachmen...019-jpg.52160/
    1999 3788, Cummins 270 "Freedom"
    2013 Boston Whaler 130 SS
    Anacortes, WA

    Comment


      #3
      Seems to me that if the strut is bronze then the bolts should be also?? To prevent dissimilar metal corrosion??
      Chris I bet their is at least cracks/fractures in the fiberglass around the struts need to grind thru gelcoat and bottom paint,I would at least reinforce that area just for my own peace of mind....Good luck Brad
      Brad & Sharon
      Lady Jake
      1985 4550 EH 700TI /Twin Disc 502
      LaConner,Wa. (summer)
      2003 Scout CC 24' W/225 Yamaha
      kailua Kona,Hi (Winter)

      Comment


        #4
        You should remove and inspect the other strut hardware as it may be near failure as well.
        1997 Maxum 2400 SCR 5.7LX Bravo II

        Mike

        Comment


          #5
          Following your saga on your website. The definitive answer would come from the boat designer/engineer. Given the option of the bolts shearing or the hull being opened up, I think the former would be the preferred outcome. A quick dive under the boat (or a waterproof go pro on a stick) would have revealed the problem and given options of course of action. A breached hull with water coming faster than pumps can handle is an emergency situation. I don't believe they are true "shear bolts". A close inspection of the bolts should reveal if they were corroded to the point of failure. I would have them replaced with the original style bolts. Some strut bolts are bronze and some are stainless steel. Bronze is a much softer material. Not sure what material your bolts are, regardless, I would be cautious about replacing them with a tougher material. I have not heard of any breakage of these bolts under normal wear and tear.
          1980 Bayliner 3270 "Goose Bumps"
          Twin 4.3 V6
          Located Blaine Wa.

          Comment


            #6
            Don't think you have to worry. Every accident is different. You probably just had unique forces that caused the bolts to shear. Running aground at speed would push it up into the boat. And hitting something is anyone's game how and what gets affected. The hull is really strong in some force directions, and even stronger in some. My guess is the piling hit high up on the strut, with momentum, was too much for the bolts, but the glass wasn't affected due to direction of force.
            1985 3870 175hp Hino's

            Comment


              #7
              Originally posted by Ray_Stec View Post
              I would have them replaced with the original style bolts. Some strut bolts are bronze and some are stainless steel. Bronze is a much softer material. Not sure what material your bolts are, regardless, I would be cautious about replacing them with a tougher material.
              But that is my key question here. - what are the "original style bolts" for the struts on a Bayliner 4788?

              Cheers,

              - Chris
              Chris & Cherie - www.technomadia.com
              "Y-Not" - 1999 Bayliner 4788
              "Zephyr" - 1961 GM PD4106 Vintage Bus RV Conversion

              Full-Time nomads since 2006.
              Now spending half of each year slowly doing the Great Loop in our 4788!

              Comment


                #8
                Talk to marinehardware.com. Pretty sure they supplied the running gear for Bayliner.
                "Impasse". 2001 3988
                Cummins 330's
                Puget Sound

                "You don't want to be the richest guy in the nursing home..."

                Comment


                  #9
                  If Don is still at marine hardware, he has all the Bayliner answers.
                  "Impasse". 2001 3988
                  Cummins 330's
                  Puget Sound

                  "You don't want to be the richest guy in the nursing home..."

                  Comment


                    #10
                    It is listed right in the Bayliner parts manual for the 4788....5/8-18 X 2 1/4" GR.8 HCS, the backing washer is Bronze...(it's in the engine section).
                    Brad & Michelle
                    Bo, Jet & Maverick (we need a bigger boat!)
                    1993 3688 "the Kraken"
                    Hino W06 250HP
                    14' Avon RIB, 50hp Tohatsu
                    Moored at Shelter Bay
                    LaConner, WA

                    Comment


                      #11
                      I stand corrected..I'm not sure the parts manual has it listed (although they list the strut and the backing washers) I believe it is a SS Carriage bolt that attaches the strut. That is what's on my 3688 and I'm pretty sure that was on the 3988 I had.
                      Brad & Michelle
                      Bo, Jet & Maverick (we need a bigger boat!)
                      1993 3688 "the Kraken"
                      Hino W06 250HP
                      14' Avon RIB, 50hp Tohatsu
                      Moored at Shelter Bay
                      LaConner, WA

                      Comment


                        #12
                        Originally posted by Technomadia View Post

                        But that is my key question here. - what are the "original style bolts" for the struts on a Bayliner 4788?

                        Cheers,

                        - Chris
                        Chris,

                        Just look at the ones you removed. It will be obvious if they're SS or Bronze.
                        In my opinion it's better to shear the bolts than hole the hull.
                        I'm sure the bolts were engineered to maintain normal forces but give when put in shear.
                        The newer prop pods are designed to shear off if struck.
                        I wouldn't substitute a stronger bolt that would transfer the load to hull. Something has to give. Better the bolt.

                        Chris

                        Comment


                          #13
                          Chris, the strut bolts on my 2003 490 are stainless. The strut bolts on my former '91 4387 were also stainless. No idea if they have a specific shear rating.

                          Comment


                            #14
                            Nothing special about the bolts. Just make sure they are 316 stainless.
                            1985 3870 175hp Hino's

                            Comment


                              #15
                              If they were stainless - I suspect they had a crevice corrosion going as stated above.

                              There is no way that the stainless bolt should have failed and not done some damage in the fiberglass if it was of full strength.

                              I am going to have to look closer next time in the bilge - I thought mine were bronze bolts.
                              1989 3888
                              Nobody gets out alive.

                              Comment

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