Transom Leak - NOT Bellows

vwduud

Cadet
Joined
Jul 15, 2009
Messages
9
I've owned this boat for about 3 years (17' Larson with 3.0 Liter, Alpha One). Until this summer, it has seen little use (few times a year). Although I knew I had a leak in the bilge, I paid little attention to it until recently. Until I began searching for reason a for the leak, I also knew very little about the periodic maintenance required of the bellows etc.

Long story, short, my bellows are long overdue replacement. However, that does not appear to be the source of my present leak.

During my research, a local boat repair shop mentioned transom rot. After a little digging in the bilge and pushing on the lower inner transom, I did in fact find some soft spots in the lower port side transom area. This combined with the 'mush' I found in the bottom of the bilge area led me to realize that I have transom rot.

Fortunately, the gel coat on the back of the boat shows no signs of cracking. Yet, I could move the sterndrive by hand, with a finger touching the Gimbal Housing and the transom and feel just a little movement on the lower port side. Yet another indication that the transom is less than sturdy in this area.

With a boating vacation in 2 weeks, where I had planned on leaving the boat in the water, I did not see transom repair as a possibility in such a short time frame. Not wanting to completely depend upon my battery, float switch and bilge pump to keep my boat afloat, I was in search of a temporary (AKA 'quick') solution to this leaking problem.

As mentioned above, the initial inspection of the bellows were negative. Not only could I NOT find any obvious tears or rips, they still felt and look fairly new (supple and 'rubbery').

This left a possible leak at the Gimbal Housing seal where it meets the outer transom wall. To test that theory (and possibly provide me with a temporary fix), I placed a bead of silicon around the outer edge of the Gimbal Housing where it meets the transom.

The initial results of this test were very promising. Where I was pumping close to a gallon of water every half hour out of the bilge, I now had NO water coming in. This was after an hour of floating, idling and riding on plane.

Needless to say, I will still make sure my bilge, float switch and battery are in good working order as well as some periodic checks during this vacation. My precaution with this had even prompted me to buy a second bilge pump wired to my second battery that is NOT sitting in the bilge (as a 'fresh' backup); where I can 'throw' it in the bilge to pump in the event the main bilge pump system should fail.

This will hopefully allow me to enjoy my vacation and not sink my boat. This also has me lined up for a challenging project after this vacation (and hopefully after the summer is over). Looks like a full engine/sterndrive pull for transom repair and some long overdue maintenance on the drivetrain.
 

danond

Lieutenant Junior Grade
Joined
Jun 11, 2007
Messages
1,118
Re: Transom Leak - NOT Bellows

Did you post this for the purpose of getting a question answered?

Check my site for info on I/O transom replacement. It's not that hard, mostly time consuming and messy.
 

vwduud

Cadet
Joined
Jul 15, 2009
Messages
9
Re: Transom Leak - NOT Bellows

Did you post this for the purpose of getting a question answered?

Check my site for info on I/O transom replacement. It's not that hard, mostly time consuming and messy.

Hey, thanks for the info. I had already found your site and read through most all of it. Great information. Agreed, not difficult work.

And no, I didn't have a question. When researching possibilities for my leak, I was getting mostly "bellows" type results. Very few threads discussed the possibility of a leak at the Gimbal Housing due to transom rot. As I began to plan bellows replacement, I wanted to make sure that that effort would solve my leak problem. It's frustrating to take on hours of labor and spend money on parts and NOT solve the problem you were chasing.

So, before I broke out the tools, I wanted to perform this simple test of the Gimbal Housing leak at the transom. Glad I did. It relieved me of the anxiety of operating my boat with water in the Gimbal Bearing/Driveshaft area for the rest of the summer AND afforded me a quick and inexpensive solution (cost of a tube of silicon). Now when I address the real problem, I will be better prepared to address the transom rot AND overdue maintenance issues at one time.

I have your site bookmarked and will refer back to it. Until I get the motor and floor out of the way, I am undecided on whether I will use Seacast or wood in my repairs. My stringers are also in bad shape.

Thanks again - Jim
 

cr2k

Captain
Joined
Mar 19, 2009
Messages
3,730
Re: Transom Leak - NOT Bellows

See if you can get to the bolts that bolt the transom plates together (inside to outside). Tighten them if you can, this may help slow the leaks along with the silicone bead you ran. If the mount is loose it will eventually work on the silicone bead and you will be back to leaks.
 

vwduud

Cadet
Joined
Jul 15, 2009
Messages
9
Re: Transom Leak - NOT Bellows

See if you can get to the bolts that bolt the transom plates together (inside to outside). Tighten them if you can, this may help slow the leaks along with the silicone bead you ran. If the mount is loose it will eventually work on the silicone bead and you will be back to leaks.

Yea, I contemplated that - had the tools in hand on my way in to tighten...

This was when I found a little more of the "soft spot" of the rotted wood (poking around on the inner transom wall). I got to thinking about the additional pressure to the fiberglass "shells" of my transom with no "filler" (wood - now gone due to rot). Although I am sure I could have tightened things up slightly, I elected to leave the bolts as they were and just silicon the around the mount.

I am banking on the silicon to "give" a little when the mount flexes on the transom. After first test in the water, the silicon seemed to have held up. With this being a short term solution (just to the end of the season), I will keep a tube of silicon handy to re-seal should it rip or crack due to movement.
 

scbolling

Cadet
Joined
Apr 7, 2003
Messages
14
Re: Transom Leak - NOT Bellows

Try running a bead of 3M 4200 adhesive around the transom plate. I had a slight leak from my tansom and found the transom plate had 2 hairline cracks in it. A very isolated problem. Anyway, I put the 4200 adhesive on the hairline cracks and that nearly stopped it. Then I put a bead of the 4200 completely around the transom plate and that fixed the problem. I've got over 80 hours on the repair and the bilge is still dry.
This may give you the temporary repair you're looking for.
 

vwduud

Cadet
Joined
Jul 15, 2009
Messages
9
Re: Transom Leak - NOT Bellows

Try running a bead of 3M 4200 adhesive around the transom plate. I had a slight leak from my tansom and found the transom plate had 2 hairline cracks in it. A very isolated problem. Anyway, I put the 4200 adhesive on the hairline cracks and that nearly stopped it. Then I put a bead of the 4200 completely around the transom plate and that fixed the problem. I've got over 80 hours on the repair and the bilge is still dry.
This may give you the temporary repair you're looking for.

Thanks. Silicon seems to have held up for first outing. Should it fail as a temp fix, I'll try the 3M 4200.

Thanks again - Jim

Oh, and by "hairline cracks in transom plate", are you referring to the Gimbal Housing "plate" (not the fiberglass "transom" itself)?
 

skeat

Petty Officer 2nd Class
Joined
Oct 1, 2007
Messages
110
Re: Transom Leak - NOT Bellows

Silicone might slow down the leak but doesn't fix a dangerous problem. The bolts are almost impossible to get to and won't accomplish anything because there is nothing there to tighten up against. The 4200 is an excellent sealant but it is very difficult to remove so that may be a consideration. A couple of years ago I had to replace the transom in my '89 Four Winns it took me about month of weekends but it doesn't leak a drop now, doesn't need any sealant and I don't have to worry about the back of the boat breaking apart. As danond said it is a messy, time consuming job but there really is no easy answer.

Good Luck,
Shawn
 

danond

Lieutenant Junior Grade
Joined
Jun 11, 2007
Messages
1,118
Re: Transom Leak - NOT Bellows

Your transom could very well be more rotten than you think. You may find that one day you punch the throttle and the drive busts through, or the leak suddenly goes from very bad to totally uncontrollable.

I'd say you're done for the season. Tear it apart, and be happy you have a boat with a rotten transom on the trailer, not one at the bottom of the lake.
 
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