Dan's I/O Boat Transom Repair

There just isn't enough information on the web with pictures related to the repair of transoms in I/O boats.  This site chronicles my adventures replacing the transom on my 1990 Starcraft 171SS I/O Bowrider.  Disclaimer: I am no expert.  I am using info I find on the web and from friends in this project.  I might be wrong, I might be right.  Use the info you find here at your own risk!

-- Dan Polk (danpolk@gmail.com)

My last update was on:

  • 2/28/09

Tools I've used so far:

  •  Sawzall
  • Rotozip
  • Prybars (varying sizes)
  • Dead-blow hammer
  • Cheap 4.5" grinder (with flapping wheel)
Products I mention:
  • Seacast

I bought a 1990 Starcraft 171SS I/O Bowrider in 2008.  Beautiful boat, with perfect interior and it looked well taken care of.  Shiny exterior, interior that smelled good, roller trailer with nice wheels, and 205 HP OMC Cobra 4.3 V6 and OMC Cobra drive.  I wasn't thrilled about the Cobra drive (they are out of business) but my local dealer supports and repairs them and I'm very mechanical so it was acceptable to me.  

After purchase I noticed it took on water after sitting in water for a while.  Not fast, but enough to bug me.  I knew the engine needed to come out anyway to replace the bilge pump (I know, what a pain right?) so I pulled the motor, and...found rot.  Horrid amounts of it, so bad that I could remove it with a spoon from the drive hole.  Interestingly enough, I couldn't "hear" this rot from the outside like most people suggest (knock on the transom and listen for different sound in specific areas).  Either way, I now knew the transom had to come out.

I chose to go the wood replacement route versus repairing with Seacast because Seacast is so freakin' expensive and seems very geared toward outboards.  The cost to go Seacast was around $600, cost for wood - $50.  If done right, wood will last longer than I'll ever own the boat, so I'm fine with it.  I also chose to replace the whole thing versus a partial repair because I'm like that.  A partial repair or a "patch job" would bother me to no end.

On to pictures.  These were taken with my Blackberry, so quality is so-so.  You'll get the drift, and I'll try to take pictures with a good camera when it counts.

 This image shows the stress cracks I noted while inspecting the boat.  I didn't know it at purchase, but these are cracks from WAY too much flexing.  If you have these in your transom, it's moving.  The only way it's moving enough to crack is if the wood in your transom is rotten.

In this picture, the engine and drive are removed and I've started cutting things away.  Tools I used were: sawzall with a short wood blade, rotozip with the general purpose bit, gasket scraper (mostly as a small pry bar), thin, strong pry bar (the kind used for removing trim and working with doors and such), a big tire iron (for leverage when I needed it), and a dead-blow hammer.

To get to the entire transom, I had to cut the stringers and battery trays back a bit (about 8" on the stringers, about 12 at the battery trays).  Stringers are the tall (approximately 6"x6" boxes) that run the length of the boat.   The engine probably sits on the stringers.  The battery trays are the flat surfaces to the sides of the engine.  Don't worry about cutting your stringers, but only cut back what you need to in order to access the transom.  Unless, as was with my boat, your stringers are rotten.  Then cut away, Jack.  You're not going to make anything worse.  I found a bunch of floatation foam under my battery trays.  It's not hard to remove, just stick a pry bar under it and shove, it'll come out in chunks.

My process for transom removal was simple.  I set the depth of the rotozip to just enough to go through the wood but not into the fiberglass, and cut grooves from top to bottom about 12" apart.  (this went through rotozip bits like CRAZY).  I then used the gasket scraper, pry bar and dead blow hammer to "chisel" enough away that I could fit the pry bar between the fiberglass skin and the wood and with enough pounding and moving the prybar around, I could eventually pop the transom out in chunks.   Removing the transom is no magical process.  You will fight, swear and bleed.  It'll come out though, just keep working at it.

This was typical of the crap that came out when I couldn't get big chunks of the transom out.  I had to settle too often for tiny pieces, but I stuck with it.

I used a rotozip around the perimeter of the transom, cutting away any fiberglass that was holding the transom to any part of the boat.  DO NOT underestimate how well a 1" high lip of fiberglass or even just resin can hold the wood in the boat.  Cut it away before trying to pry the transom parts out and you will save yourself a TON of work.

See the dark spot on the lower right?  That's where it was rotted the worst.  It was pretty bad around the bottom of the drive hole too, but was almost missing in that area to the right.  Gross.

Let's talk for a second about mounting things to the transom.  This picture shows the holes from the pitot tube mount.  Note the lack of silicon or additional sealant around the holes.  This is manufacturer installed, and I have no doubt this contributed to my rot.  If you just bought a boat, remove all the stuff on the transom and seal it with marine silicon.  When I removed the mount, water ran out of the holes.  Not a good sign!

2/22/09: I want to have this done by spring, so check back soon.  I'm going to be moving on to grinding the inside mounting surfaces down to the fiberglass, preparing a cardboard template and cutting out the boards I'm using to make the new transom.

Stay tuned!