Your transom is usually the first part of the structure in a boat to go rotten and is also one of the most important structural parts of your boat - Not only does usually the most expensive investment get bolted to it, but it also ties a lot together and well without it... your swimming. So in no particular order, let's get into them!


1) The Old "Pour In Instant-Fix You Saw On The Internet”

    Ok so let’s start with the biggest cringe transom subject we get weekly! You don’t want to go to all that effort and itch to do it properly, so you saw this awesome product you just mix up and pour into the rotten areas of the transom. It sets hard and boom you bolt the outboard back on and drive past your local repair shop who quoted you more than the $200 including postage for the gypsie product that fixed your transom in about the same time it took to drink that 6 pack.

    So this is wrong on so many levels, firstly because you paid for a pretty label and false hopes when mixing resin with talc powder can achieve the same result. That result of course is pouring a band aid bog essentially into a cavity you created once you dug what you think is all the soft area of your transom and chances of it bonding to the rotten timber are slim to none, as soon as any flex or load is put on that area it will break free or worse just shatter and you are back to where you started from but worse… you now have to make up a story when you take it into the repairer on the guy who owned it before you must have put some bog in it to fix it.



    2) Sliding A New Transom In From The Top

      So your not as ruff as filling areas with bog, but you still don’t see yourself cutting the top deck off and getting super itchy, plus the weather is good over the next week so you want it done quick! The transom is only approx 40mm thick and the chainsaw blade is no where near that… here hold my beer, out it comes. You spend the best part of the day carefully jamming a chainsaw or chisel down in between the two transom skins until your confident “it’s as good as it’s gonna get”. Next comes the 2 pieces of ply you got from the hardware store… probably went all out on marine ply to justify it to yourself that it will be fine. Trim it to size and “glue it together” even with an epoxy bonding paste because the internet said epoxy was the best! Then with some sort of pure magic you got enough of the same epoxy adhesive to run down the inside face of the transom skins and what do you know, it just slides right down in there. Give it a good couple of bangs with a closed fist the next day and mate she is as solid as a rock! Now to spend the next 2 days trying to make the top section you cut off look pretty and glass it all back together to resemble something like what you cut out.

      After 2 trips to the reef if you have made the second trip… it now sounds drummy in areas and the sides of the top cap have strange cracking starting to form… that’s because it has literally sheared the transom away from either one or both of the skins and you may as well have just put a large aluminium plate on the area the engine bolts too. The timber is in mint condition and will make a perfect template or, even better could possibly still be used when you actually do the transom correctly.


      3) Using The Wrong Resin

        Let’s assume you have rolled your eyes at the top 2 and know that you are in for some itchy work but if done correctly will never have to be done again and you will have confidence in swinging the ponies off the back in some madddd chop. Number 3 is not a dodgy or something that is detrimental to the job, but more a classic mistake we see regularly and we want to be more of an awareness point. Figure out what resin your boat has been made with first, either by doing some tests, contacting the manufacturer or hit us up! The most commonly used resin in Australian made boats is Polyester ortho resin. Basically the blue stinky stuff commonly associated with fibreglassing that needs the hardener at 1%. This is handy to know as the same resin is ideal to use to carry out your tranome repair/replacement. The adhesion will be fine, the working time will be achievable to work with and you will be keeping it same/same. The most common resin we get asked to replace a transom with is epoxy. That is fine if you do not want a bar of the differences in resins and the group admin from your favourite social media site said he did his in epoxy so that’s what your going with, but keep in mind that once you do your transom with epoxy you then will find it super hard to transition back into poly or vinyl ester resin in the rest of the build, plus getting gelcoat/flowcoat to bond is now almost impossible. In a nut shell - epoxy is dearer per kg, takes longer to cure and you will need to change your laminate schedule (glass type used) to make it all work.

        As a little experiment, email or contact 10 of Australia’s leading boat manufacturers and ask them if they use epoxy in their builds. On the flip side, if you have an epoxy made boat, guess what… your using epoxy!



        4) Using The Wrong Substrate

          Ply has obviously been around longer than the Composite Core vs Marine Ply debate, however among the tried and tested substrates available on the market, there are also some not so recommended boards. Structural Ply and marine ply are readily available from most hardware shops, but make sure they are not treated with anything! You do not want any funny coloured ends or coatings on the board. The resin will not adhere to these treated boards (even epoxy) and you will end up with a good work bench to use to cut your non treated ply. If you have access to form ply from the job site that no one will know you’ve knocked off, cool… use it as a workbench also as the nice shiny smooth finish either side will work as a mould face and nothing will stick. Some form ply also has water proofing products in it, so avoid knocking it off for your transom and keep it for forming up your esky or new seat boxes! Honeycomb or PP sheets are an amazing lightweight product for your floor or hatches etc, but are no good for your transom due to it’s sheer strength and cell structure being easily compromised in a transom application.. Plus it’s resin up take is pretty high so what you would save on the price of the sheet would go in the amount of resin it eats up. PVC boards are an awesome option and are commonly used in Aussie made boats and the yanks have been using it for years. It is super easy to work with, comes in a bunch of densities and all resin types adhere to it. Here is the kicker.. you can get 2 types of PVC boards, the board that has a polished surface actually works the same as the form ply and nothing will stick to it so make sure you ask for a pvc board suitable for fibreglassing. Keep the polished board for your fit out applications!

          Last but no least is Thermo-lite and similar products. These boards fall under their own category in a league of their own with the benefits they offer. We will go over the Thermo-lite board in another blog, however in a nutshell this product offers a versatile, high density, waterproof, acid proof, fuel proof structural board with acceptance of all resin types.



          5) Cutting It Out From The Back

            If you have done it this way already you will disagree with what I am about to write and probably do a pffff easy for them to say type comment to yourself. I have left this to second last so that hopefully it is the last point that sticks in your mind, however it is probably the most important point of them all!

            Cutting your transom out from the back of your boat opposed to from the inside leaving the outer skin intact, is one of the most touch and go repairs I feel you can do. When a transom is put into a boat, no matter what brand or size, it is completed from the inside.

            The gelcoat is laid in the mould, then backed up with the laminate (layers of glass that make the hull) then let cure. The transom is then made outside the boat separately, whether it be a one-piece transom or multiple substrates laminated together to form one. Once the transom structure has been made it is then laminated into the boat from the inside and usually clamped off using large U-shaped clamps. Once cured a lamination is the placed over the front face of the transom and all stringers etc butt up against this to begin forming the structure of the hull. The front face laminate usually only goes across the face of the transom and back onto the inside of the hull approx 150-200 mm. This then sandwiches the transom between the 2 laminates and in theory you glass up and over the top section of the transom and finish it neatly on the back side. (but a lot of boat builders still do not do it, instead screw an alloy cap to the top)



            When you cut it out from the back you still have to dig the rotten timber out like you would from the inside, but you now also have a hard time trying to clamp it off as the top deck is in the way and the laminate of 150 -200 minimum now has to go around the back and down the sides of the hull and keel to laminate it back in. So amongst lamination issues and getting precise thicknesses as you only have the old thickness to work with depth wise, you also now have to spend, in my opinion, 3 times longer sorting out the cosmetics of the rear section of your transom and back section of your hull in general to achieve a smooth gelcoat finish, that will never match the rest of the boats hull colour or finish. If the transom needs to be done then there is a large chance the rear sections of your stringers need to be sorted out also. If you are happy to do the transom from the outside but then jump inside to do the stringers then I think you are going to be in a world of disappointment once the rebuild is finished compared to doing it all from the inside the way it was done from the factory.

            What it may cost you in time or to pay someone through a shop to take the rear section of the cap off to do the transom from the inside, will completely outweigh the cost of you or a shop getting it to all look pretty with a guaranteed laminate that will not fail from the outside. Look at your rebuilt boat now… does it have strange cracks appearing approx 15-20mm in from all the edges on the backside of the transom? Which way do you think your new transom was put into the boat?



            6) Not Waxing The Back Of The Transom

              Exactly that, when doing your transom from the inside, wax the outside skin of the transom thoroughly and tape up old bolt holes, transducer holes etc. When you put the new transom in and clamp it off, you should see the resin ooze out of the top and any holes on the transom skin. Oozing resin is a good thing and means it has enough pressure applied to compress the laminate. Once all is cured you can simply peel the tape off the holes, which will now be flat and flick any excess resin drips that have ran down the transom off with a paint scraper or plastic wedge. Any holes that need to be kept, you can re drill and with the excess wax, give it a wipe with some acetone or wax and grease remover to have a nice clean transom to continue your build!

              I hope these 6 topics shed some light on your transom rebuild decisions and remind you that cutting corners at this stage can be a world of hurt once its back on the water. I assure you the hottest debate will be over which way to replace the transom and a lot of builders/repairers may argue black and blue they have been doing it for years from the back of the boat. If you seek advice through Fibrefinish we will always recommend replacing it from the inside and happy to discuss all these topics more in depth if need be.

              Please give us feedback on what other topics you would like us to cover? Get in touch and let us know. Until then, thanks for reading and we look forward to helping you out with your project!


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