Drilling holes for transom assembly

[Fishermark]

I am just about finished with the installation of my new transom on my Wellcraft with a Mercruiser Alpha outdrive. I have the new plywood encapsulated in fiberglass resin and glued in. I have not yet tabbed the fiberglass cloth nor made the final covering with fiberglass mat.

When it comes to drilling the holes for the transom assembly.... a couple of questions.

1. Is it best to wait till the very last, then drill the holes? Or is it better to do it now so they can be coated somehow?

2. If the holes are coated, what is the best procedure for doing so?

3. Is there an easy way or technique without special tools to drill the holes at 90 degrees? (I can certainly "eyeball" it with the drill - just curious if there is a better way).

 

[gm280]

Re: Drilling holes for transom assembly

If you have any drill press of any sort, you could make a template on the drill press out of a solid piece of wood (or even a thick piece of metal) that would hold the drill bits at the perfect right angle while drilling into the transom. Simple drill straight holes into the wood on any drill press and then use that template as your guide while drilling into the transom or whatever. The template will force you to drill perfectly straight holes into whatever you are drilling in to... Also, there is a thread on here that talks about drilling transom holes larger then the bolt sizes and fill them in with PB and resin. Once hardened, you sand them flush again and re-drill the correct size out again giving you holes surrounded by PB and resin and there will be zero water intrusion into the transom wood... JMHO!

 

[Woodonglass]

Re: Drilling holes for transom assembly

Due to the close proximity of the holes to the keyhole I don't think oversized holes would be a good idea but that's just me. To drill the holes you can use a store bought drill guide for your 3/8" drill or make your own from a piece of 1" hardwood. Just need some thing to keep the drill at the proper angle. If you coat the holes and bolts with 3M 4200 at the time of installation you should not have any issues with water intrusion in the future as long as you have due diligence with maintenance and care.

 

[JASinIL2006]

Re: Drilling holes for transom assembly

I waited and drilled the holes after doing all the 'glassing. I didn't see any point in letting the holes get filled with resin while skinning the transom; I was afraid it might be hard to ream them out and not mess up the holes.

I almost bought a drill alignment tool, but I figured I would be unlikely to use it much after this project. Instead, I had several 6"x6" sqares of 3/4" plywood left over from the transom, so I glued them together to make a nice thick block of wood. I drilled several guide holes into my plywood block (using my drillpress), and then I clamped that up to the transom and used the guide holes to keep the bit perpendicular to the transom. I worked pretty well. I only used each guide hole twice because I was concerned the holes might get a bit misshapen as I was drilling into the transom, and I didn't want to use a bunged-up guide hole to drill into my lovely new transom!

I used some fat pipe cleaners to coat the insides of the holes with resin. Worked really well. I mixed it a little light so it would soak in well before it kicked. Did that twice.

Good luck!

Jim

 

[Fishermark]

Re: Drilling holes for transom assembly

Thanks for all the recommendations. Some good ideas I will put to use!

 

[oldboat1]

Re: Drilling holes for transom assembly

I'm with JL, above, on waiting to drill, then coating the raw wood as he describes. I use epoxy, but it's the waterproofing that counts. I would add that it's a good idea to predrill with a smaller bit just to make sure of the location, and to help insure that the larger bit tracks correctly.

 

[JASinIL2006]

Re: Drilling holes for transom assembly

I'm with JL, above, on waiting to drill, then coating the raw wood as he describes. I use epoxy, but it's the waterproofing that counts. I would add that it's a good idea to predrill with a smaller bit just to make sure of the location, and to help insure that the larger bit tracks correctly.

VERY good idea!

 

[fishrdan]

Re: Drilling holes for transom assembly

I had several 6"x6" sqares of 3/4" plywood left over from the transom, so I glued them together to make a nice thick block of wood. I drilled several guide holes into my plywood block (using my drillpress), and then I clamped that up to the transom and used the guide holes to keep the bit perpendicular to the transom.

I would add that it's a good idea to predrill with a smaller bit just to make sure of the location, and to help insure that the larger bit tracks correctly.

I did both of the above. Glued up some MDF to make a block for a drill bit guide and used 4 different sized holes to step up in bit sizes. Worked well and the holes were right on the money.

I'll add, back the bit out often to clear the chips out of the drill bit, keeps the wood chips from deforming the hole.

 

[oldboat1]

Re: Drilling holes for transom assembly

All right! Good to go -- strong, safe transom.

 

[JASinIL2006]

Re: Drilling holes for transom assembly

Backing out the drill bit frequently is a good tip, too.

I think I only used a couple of different drill bit sizes when I drilled mine. I did avoid the super-aggressive drill bits you sometimes can find for wood. Those seem to chew through wood very aggressively, often at the expense of a nice clean, straight hole. I just used standard twist drill bits wood.

 

[Mud Puppy]

Re: Drilling holes for transom assembly

If you coat the holes and bolts with 3M 4200 at the time of installation you should not have any issues with water intrusion in the future as long as you have due diligence with maintenance and care.

Don't forget to seal the bolts/ studs (even above the waterline) like Wood said or all your work will be for naught.

 

[JASinIL2006]

Re: Drilling holes for transom assembly

Don't forget to seal the bolts/ studs (even above the waterline) like Wood said or all your work will be for naught.

Is this common practice -- sealing the studs and holes with 4200? When I was putting mine back together, I am pretty sure I didn't use any.... I don't recall seeing many other restorations where that was done. I thought the idea was the tubular rubber seal around the gimbal housing is supposed to keep that area dry...

I sealed the holes with resin, but now I'm worried I missed something....

 

[fishrdan]

Re: Drilling holes for transom assembly

I would seal the holes prior to installing the transom assembly.

BUT, I wouldn't seal the studs going through the transom as it will be darn near impossible to remove the transom assembly again if needed,,, due to all the studs being glued into their holes. The gimble housing gasket seals out water, so there's no need to use sealant on the studs going through the transom.

 

[Mud Puppy]

Re: Drilling holes for transom assembly

IMHO, Seals fail/ shrink and it is just one more layer of protection on your investment.

All along I thought all of my issues were bad floor related but it was actually a bad transom mount and gimbal ring seal and deteriorated bolts. Took years for it to show up; by then it was too late. Rotted out my transom and that compounded the problem with the seal. The floor was just the only readily visible damage.

 

[Woodonglass]

Re: Drilling holes for transom assembly

I'm NOT an I/O guy soooo...I'm NO EXPERT on this topic. I just thought I'd read somewhere it was a good idea to seal the bolts with 4200 but after further research I have discovered that in fact it goes on Dry and the seals do all the work. No other sealants required or desired. If done properly you should have no issues. Drill the holes 1/32" over sized and coat with epoxy and then install dry. Proper care and maintenance should ensure long life. Sorry for the Mis-Information.:facepalm:

 

[JASinIL2006]

Re: Drilling holes for transom assembly

Whew... For a minute there, I was getting a little worried. :faint2:

 

[Fishermark]

Re: Drilling holes for transom assembly

Yep - a transom assembly can be tough enough to remove WITHOUT any sealer on the studs. There is no way I would recommend putting anything on the studs themselves. You would need to cut out the assembly with a sawsall in the future if it ever needed to be removed.

 

[gm280]

Re: Drilling holes for transom assembly

Just remember to tighten ALL the bolt and nuts after installing any I/O or O/B engine/drive. Sounds like a "DUH" issue. But my first boat that I bought through a dealer, they installed everything and I drove that boat around for a year or two not knowing they didn't tighten the lower nuts on the bolts below the cap of the boat. When I found that out, I was really worried that something serious could have happen. I tighten them and boated on.

Also If you do drill larger holes and epoxy them closed again and then redrill them the proper size. There really isn't any reason to put anything on the bolts going through those holes. It is like a solid epoxy frame with just a small hole through it. So water can't even begin to intrude... Maybe a little silicon sealer to stop water from bypassing the bolt into the inside of the boat, but that isn't something to damage anything either.