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Hollow transom, re-core or not?

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  • Hollow transom, re-core or not?

    Hello guys and gals,

    I need your expertise helping me decide whether I need to immediately re-core the transom of my 1991 261 or not. While rebedding the swim platforms I noticed one of pass-thru screws was rusted. After removing it I noticed the wood inside was gone, it was just a wet paste, no fibers... nothing solid. I then open a few more probe holes from inside and the core wood is gone pretty much in the whole starboard portion of the transom. There is some wood/plywood lose in there but must of it just transformed in this wet paste that, once dry, get hard again. From the outside there is no signs of the transom failing or cracking, no spider webs, no cracks. I'm not sure how long this boat have been like this. I purchased it two years ago and I have added maybe 50 hours of use. Basically at this point the transom is totally hollow with the inner and outer layer of glass holding it together.

    Is it OK to use the boat like this or is it imperative to re-core the transom? If re-coring is necessary would it be fine to do the chain saw method from the cap of the transom and pour Seacast/Nidacore/Arjay pourable compound to re-core?

    Here are some pictures of the probe holes and the view of the transom from outside:









  • #2
    On my 231 I had a similar situation on both port and starboard of the transom cutout. Amazingly the plywood core between the transom cutout was in very good shape. No visible cracks or indications of problems. Tapping glass surveyor style was indicative but not as revealing as probing. Port side I found water ingress was a result of the baitwell overflow thruhull where mako sealed and tightened the nut against the rear side box liner NOT the actual inner side of transom. Also a PO removed port swim platform but marinetexed holes so may have leaked in there too. Starboard side was hard to figure exact ingress points. Boat had no trim tabs.

    The gelcoat putty that makes up the top of the transom under the aluminum trim is VERY likely cracked as mine had no cloth reinforcement between hull and liner. The aluminum trim is hiding the crack that is likely but not terribly srtuctural (unless creeping out corners) but a serious water ingrees issue.

    The reality is core material is primarily for compressive strength (many posters on here will strongly disagree) and most real strength is from the I-beam effect and load spread by the laminates.

    There are pourable materials and concoctions (eg 16 LB foam or pumice/cabosil/loose fiber/resin blend) to fill voids. Some commercial pourable fixes can be found by google searching.

    I think you need to take out all easy penetrations like drain plug, trim tabs and see what drains out and probe core. Then pull engine loose enough to get the trim plate off to probe the likely crack and trim screw holes. Transom thru hulls would be next to pull and check if necessary.

    I believe when you pull that stupid aluminium trim piece (and likely grinding putty out to expose skins and core )you will find your answer as the need to recore or bandaid.

    After getting a good handle on extent of rot then look again at options. Also as friendly, skilled and good intended as most posters on classic mako are, there are few if any on here I would call true professional boat builders or professional boat body work men. I would seek out a local professional (look for 20+ years experience and old school ways) to discuss your findings. The professional will be able to explain what the real risks from doing nothing to void filling.

    Where are you located?

    Putting my flame suit on now.
    Jupiter, Fla[br]1988 Mako 231 (new to me)[br]1988 Wellcraft Coastal 230 (Parted out and landfilled)[br]Several others in the past 30 years.[br]

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    • #3
      Forgoto to mention there are a few builders that do not core gunwhal to gunwhale only just the engine cutout. A professional boat builder could can explain the theory and practice of transom construction (eg race boats may have NO core). BTW I was not terriblly impressed with thickness and cloth of my mako factory transom skins.
      Jupiter, Fla[br]1988 Mako 231 (new to me)[br]1988 Wellcraft Coastal 230 (Parted out and landfilled)[br]Several others in the past 30 years.[br]

      Comment


      • #4
        Thanks for your feedback. I'm in Miami...

        Based on the years of use of this boat and the condition of the transom core it is quite difficult to believe the transom didn't crack already. As you said, the only explanation is that the real structural strength comes from the glass laminating.

        The key for me at this point is to find the water penetration area that very well could be from beneath the aluminum piece. Tomorrow I'm planning on removing the easy stuff... the thru-hull, the deck overflow, drain hole, etc. It seems to be solid fiberglass where the trim tab actuator is screwed to the hull. I need to poke more around to find the culprit.

        In reference to the thickness of the lamination in the inner transom walls, I'm not sure what's considered thick enough but here are two sample from the holes I opened.... they look pretty heavy to me.


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        • #5
          Everyone that I have talked to that does fiberglass work in my area looks at me like I just farted when I ask them about a poured transom. All of them said to go with Plywood and do it right and it will last for years. Also I have never seen an old Mako in the Bahamas that had the transom redone and there are tons of old Mako's being used everyday over there.
          84 Mako 224/2011 200hp etec[br]Ocracoke Island NC

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          • #6
            Ask them if the still use wire nuts as well! The people I talked to about poured transom a said the same thing until they saw mine. Now they say go with a poured transom!
            1978 Mako 25 - Blind Hog
            1985 Mako 20c - sold
            Fort Walton Beach, FL
            https://forum.classicmako.com/forum/...og-bottom-time

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            • #7
              Plywood is rather inexpensive and provides them repeat business down the road, so no surprise they recommend.[]

              Newer boats are going synthetic transoms and a number of them are poured. After replacing my transom and going poured, I'd never consider wood. It's a nice feeling knowing the core cannot aborsorb water and sounds solid when tapping with a sounding mallet. Even if a bracket or swim platform was not sealed 100% correct and water makes contact with the core, nothing happens.

              D-
              Current Mqko - 1990 Mako 211 w/2006 250 E-TEC. http://www.classicmako.com/forum/topic.asp?TOPIC_ID=6226. [br]- Previous Makos 1987 20C, 1979 23\' IB, 1970s 17 Angler

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              • #8
                Coosa board is a good option to replace the wood core with.
                Billy[br]1974 Mako23 CC Cuddy IO[br]200hp Cummins Mercruiser Diesel w/ Bravo 3X Drive[br]Bellport Long Island NY[br]http://www.classicmako.com/forum/topic.asp?whichpage=1&TOPIC_ID=42355#319618[br][/URL][br]

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                • #9
                  For peace of mind I'd replace the transom. If you are capable of doing it yourself it wouldn't be an expensive job.

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                  • #10
                    If you decide to use plywood, you can extend its life and make fiberglass stick to it better by cutting out your pieces and coating them with polyester resin thinned 25% with styrene. Make sure that the plywood has been air dried and that you coat the edges. The thinned resin will soak into the wood, sealing it and providing a more compatible base for fiberglass.

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                    • #11
                      Oh, and don't forget the hardener.[8D]

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                      • #12
                        Everything is soaking wet, I'm doing it... while the transom structure is still in good shape. Most definitely will pour it, Arjay is available from FGCI locally for around $180 the 5 gal pail. I haven't found solid feedback about the efficacy of the chain saw from the cap method but I can't afford anything else so it has to suffice.

                        I'll try documenting the process.

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                        • #13
                          quote:


                          Originally posted by mesias


                          Everything is soaking wet, I'm doing it... while the transom structure is still in good shape. Most definitely will pour it, Arjay is available from FGCI locally for around $180 the 5 gal pail. I haven't found solid feedback about the efficacy of the chain saw from the cap method but I can't afford anything else so it has to suffice.


                          I'll try documenting the process.


                          If it's of any value, here's my poured transom project, starts about 3/4 the way down the page.

                          http://www.classicmako.com/forum/top....&whichpage=15

                          D-
                          Current Mqko - 1990 Mako 211 w/2006 250 E-TEC. http://www.classicmako.com/forum/topic.asp?TOPIC_ID=6226. [br]- Previous Makos 1987 20C, 1979 23\' IB, 1970s 17 Angler

                          Comment


                          • #14
                            Highly valuable... I went thru it before this, very informative. I'm still debating about the chain saw method... I haven't been able to find any feedback on neither success cases nor failed cases. Seacast shows it as a valid method and I have read about a few people doing it but no further details after the fact.

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                            • #15
                              I think it's nearly impossible to get the cavity clean and properly prepared going in from the top with a chain saw. you also can't be sure you have the inside skin sealed off so the material does not flow through a crack or hole into the bilge or under floor etc..

                              the method used for most of the poured transoms I've seen is with the outer skin removed. it requires some extra fairing and painting or gel-coat work but seems to be the best way to be sure the job is done correctly.

                              FWIW
                              76 25 \"Aenigma\"[br]73 17[br]Richland/Long Beach, MS[br]http://www.classicmako.com/forum/topic.asp?TOPIC_ID=14182[br][br]17 project[br]http://www.classicmako.com/forum/topic.asp?TOPIC_ID=56176

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