Transom maintenance

[SkunkBoat]

A project this spring was removing the lower motor bolts and putting some glass “eyepatches” over the inside holes, redrilling, and installing ¼” aluminum plates across inside lower bolt s.
New 316 SS ½” bolts. 5” was correct length with plates and 1/8” SS washers. Boltdepot.com is good source for 316 SS hardware

The motors were replaced in 2020. Work done by dealer. The aluminum cap was well sealed so I did not have that done. That would have delayed the season.

End of last year I noticed a rust drip inside lower bolts. Not too happy with the work I found. They left the washers from the old yamahas. They had cut into the glass a bit. I think they should have told me “hey, you should patch the holes and put on plates to spread the force out so washers won’t cut the glass”

They put bolts with new washers thru the old washers and a blob of sealant. They inserted the bottom bolts from inside-out. Nut on outside. I think the bottom bolts should go in from outside. Nuts inside. That way the thread goes in clean and the hole sealant pulls from outside/in, sealing the hole. (lower bolts are underwater)

Unlike the top bolts, where the washers are up against smooth gelcoat, the bottom washers are up against rough uneven glass. Grady is worse at that than some other boats I’ve seen. Tightening the bolt eventually pulls the washer into the glass. Seeing what I have seen, I think it would be wise to always use plates inside lower bolts.

The wood was still solid in all the bolt holes. I sanded and cleaned up with acetone. Used West epoxy, High density filler, and some glass I had leftover from other projects.
To re-drill holes with motors still in place you need a LONG 1/2" bit. I got an 18" bit at Home depot
Sealed with SikaFLex 291

 

[steveditt]

Last year needing a transom replacement it was recommended to install a plate on the top bolts and lower would be better , Transom was replaced this winter he reinstalled the plates when finished .

 

[dogdoc]

do you buy or make plate?

 

[Hookup1]

Are those bedded in 3M5200? Looks like good insurance. Spread the load out. Probably do mine what I rebuild my transom.

 

[seasick]

If they used SS bolts and washers on aluminum plate without some sort of sealant as an insulator , there will be corrosion issues . Although the new bolts and plates looks nice and clean, I would rather see sealant ooze to insure sealant was applied.

 

[SkunkBoat]

I got the plates made at Atlantic Coastal Welding. $30 a piece but they did them in a day. Made them to my spec. I wanted them wide but have to fit above stringers.
3" wide. 1/4" plate. Standard 9 7/8" bottom hole spread. I looked at amazon. They have CAST aluminum 2" wide. I had a cast one crack on an older boat.

I used Sikeflex 291 sealant. First time I've used the brand. Comparable to 4200. I did not bed the length of plates.I don't think that would do anything but make it hard to remove.
I measured how much thread would come thru transom, covered bolt with sealant to that, inserted from outside-in. That makes the sealant seal the OUTSIDE hole on its way in. I worked the bolt in then back out a bit and more sealant and back in. Then a good donut of sealant were it comes thru inside. The plates squish it around the bolt.. This way the threads that are used for the nut are clean.
Remember, that water is on the OUTSIDE. Gobs of sealant inside don't do anything ....but hide fact that the washers are cutting into the glass.

As for SS against aluminum...my motors are aluminum with hundreds of SS bolts in them, and shafts and props, and steering cylinder and tie rods.....

 

[seasick]

You must have better luck than I do, I have often broken off SS screws on motor parts, like brackets, anodes, ground lugs etc.

 

[Gulffisher]

Uncoated aluminum and stainless steel in contact with one another WILL NOT play well together. But with 1/2" or larger bolts/washers in contact with 1/4" aluminum plate, it will be a long time before the aluminum corrosion results in failure.

 

[SkunkBoat]

So, having my head in there all that time I learned a few things.
There is an aluminum bar about 1/2" thick inside the upper transom. You can see it in the pictureswhere the motorwell joins the transom. Just above the plate that I put in.


You can see the adhesive filler that oozed out when Grady squished the cap to the hull. It is not uniform. There are gaps and eventually pieces of blobs fall off.
That area is right where the motorwell scuppers are drilled thru. They drill thru the 1/2" aluminum and the filler and the empty space.


It is easy for the old compromised brass tubes to drip into the bilge.
I noticed that the three brass scupper tubes are at different heights. the starboard one being right down in the corner. In my case it was mounted so low that it eventually made a hairline crack in the motorwell bottom corner and there was a very tiny drip into the bilge.

---

I used a sawsall with metal blade to cut a line in the brass tubes and then bent them in and pulled them out. Wood inside was solid. Made me feel good to know that.
If you have old brass tubes, get them out and look in there. Do it.




I fixed up the holes with epoxy and replaced the brass with plastic tubes (SeaChoice 1 1/4"). https://www.amazon.com/dp/B0006ZCG10?psc=1&ref=ppx_yo2ov_dt_b_product_details
Sealed with Sikaflex 291.
Covered outside with new 2 7/8" rubber flaps https://www.amazon.com/dp/B0019M5JPY?psc=1&ref=ppx_yo2ov_dt_b_product_details




In the past I replaced the POP-out Beckson pie holes with screw type Beckson pieholes. You don't need old 6" pieholes popping out in your motorwell.....

 

[Sardinia306Canyon]

In the past I replaced the POP-out Beckson pie holes with screw type Beckson pieholes. You don't need old 6" pieholes popping out in your motorwell.....

Thanks for your detailed how-to, very good information.

One annotation, I had the screw in pie holes on my Panga and they were a PITA to unscrew after some time.
I tried greasing the treads what led to even more tight seat and more power needed to screw them open.

Finally I welded a special handle to wrench open the cover.

Chris

 

[Ekea]

did you put any caulk behind the aluminum plate? if not, you may be susceptible to crevice corrosion. if water (condensation) were to get behind the plate, it would likely either dry very slowly or not dry. aluminum likes to be able to get dry to protect itself. this is why foaming in aluminum gas tanks is not recommended anymore and an air gap is the way to go. a nice smear of silicone caulk would prevent the back side of the plate from getting wet in the first place. using silicone shouldnt make any future removal that difficult either.

 

[49pan]

Just a thought . I would have used a stainless plate . It would have been much less susceptible to corrosion.

 

[SkunkBoat]

I was not concerned at all about corrosion. It is a giant 1/4" thick washer. No one ever sees it. It will function as a washer for longer than the motors will last.