Partial Rotten Transom

Discussion in 'Fiberglass and Composite Boat Building' started by troycomp14, Apr 15, 2009.

  1. troycomp14
    Joined: Apr 2009
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    Location: Sydney

    troycomp14 New Member

    Hi All,

    I have just purchased a Pongrass Surfmaster, I beleive they were built in the 80's. I have found rot in the transom, but it doesn't appear to have spread all the way through. I have looked at all the other posts and they seem to replace the whole transom as it is totally rotten. In my case I am only trying to replace the area of rot rather than the entire transom.

    The rot on my boat starts from the top and then stops about 4-5" from the bottom of the floor. The floor feels very solid so I don't think the stringers are rotten.

    This will be my very first boat repair but this is how I think I may be able to repair it.

    1. Cut 3" above the floor to remove all the rot. (the whole job will be done from the inside to maintian origninal look from outside)

    2. Remove the fibreglass from the remaining good areas of the transom to allow me to bond the new bit of fibreglassed ply to it.

    3. Cut the ply to suit the area required. Glass the ply and then glue to the transom fibreglass/gelcoat (not sure of the correct term).

    4. Fibreglass over the new and old ply to bond together.

    My concern is will this be strong enough? I will be putting a 55hp engine on the transom.

    Thanks in advance
    Troy
     
  2. milljfred
    Joined: Apr 2009
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    Location: Wisconsion

    milljfred New Member

    It should be strong enough if you used like 2 layers of 3/4 in plywood or a 3/4 and then something else. I assume the transom is a few inches thick right now before you work on it... If you try to recreate it the way it was it should be fine as long as the glue is adhered well and thoroughly to all surfaces that are being glued. I did a transom on a 23 comity boat that had a 100hp on it. I used 2 layers of 3/4 inch plywood as my base to ensure structural integrity. once you remove everything you will see what you will need. good luck
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Unfortunately. the rot will have traveled down the voids and cross grain layers, of the internal plies within the plywood. Once they start to show signs of softness, the amount of the damage is far greater then would appear from the outside.

    You really want the plywood core to have it's longitudinal grain layers intact, from side to side for maximum strength. You could scarf in a repair, but I suspect if you expose enough transom, you'll see much more rot then you think you have.

    In the end it's easier to remove the transom skin as a whole piece and replace the core, then to do multiple small repairs in different locations on the transom.

    I've done dozens of transoms and I can assure you, once they're soft, you've got major issues within the core. You can't know this until you remove enough of the skin to check. Drill fairly large test holes (3/4" or bigger). You can fill these with a properly sized dowel and thickened epoxy if the hole proves solid. The transom will two or three layers of plywood, so make sure you holes are deep enough to check both layers.
     
  4. troycomp14
    Joined: Apr 2009
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    Location: Sydney

    troycomp14 New Member

    Thanks Milljred and Par,

    Before I got a chance to read you replies I decided to dig around the transom with a chiesel and drill a couple of core wholes.

    Par, you were spot on the core wholes show rot in a large number of the core holes even when those areas seem hard as a rock from the top layer.

    I have a couple more questions though.
    1) Where does the transom get all its support from. I can't work out how it manages to hold a 60hp motor pluse all the forces while in the water.

    2) I will be "attempting" to cut the out the transom from the rear now. I have read a couple of places that you need to come in a couple of inches rather that cutting the entire transom out. Is this correct and if so why?

    thank very much.

    The knowledge from everyone is fantastic.
    Cheers,
    Troy
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Moisture usually gets into the transom through screw holes in the deck cap along the top (cleats, vents, etc.) and through the mounting bolt holes. These were once sealed with bedding compound (caulk) at one point, but this needs to be renewed every so often or it dies and lets in water.

    The moisture travels down to the bottom of the transom and rot generally works it's way up from thee.

    The transom is strong through several general engineering principles, the reasons are not so important as insuring it's integrity, when you're finished with the repair. It carries a lot of weight and resists a lot of thrust.

    The corners of the transom are a natural area of stiffness. If you don't have to rebuild these areas, don't, because it's a lot of material and making the corners smooth and straight again is troublesome for the novice.

    I leave at least 3" around the perimeter of the transom. It offers a few benefits. It retains the inherent strength of the area, helps keep the aft portions of the boat in the proper shape, provides a large area to blend the repair into without resorting to running fabric and goo around the corner and if you work neatly, you can repair the transom, repaint it, but not have to paint the sides of the boat too, saving a good bit of work.

    Your transom is 1.5" of core material, probably 2 layers of 3/4" plywood. After the skins are in places, it's around 2" thick.

    If you provide some pictures we can get a good look at what you got and offer approaches to it "cure". It would also be helpful to review the dozens of previous posts about transom core replacement.
     

  6. Stumble
    Joined: Oct 2008
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    Location: New Orleans

    Stumble Senior Member

    From what I am reading here it sounds like your entire transom core is suspect. Given that and the large amounts of rot I would seriously think about opening up the entire inside of it. If so you would need to cut away the entire inside layer of glass, leaving the 3" flange that Par was talking about and rebuilding it from there.

    To do this first you need to really clean out any remaining wet wood and let it really dry out well. Once you get the area clean and prepped I either just cut the plywood to shape, or in the event the core has any funny shapes to it that make the cutting difficult, I use a 2lb expanding foam to create a mold of the shape I need then take that over to a router with a flush trim bit and let it do the work for me.

    This ensures that you have an insert exacally the right size and shape to fit the existing transom remains. I then normally epoxy coat the new wood, drop it into place, and take the cut out fiberglass from the original transom and stick it back into place with a couple of layers of glass, and epoxy.
     
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