Screwing into wood under the waterline

Good evening, I've been working on my nesting dinghy all winter and am coming close to the end. The keel is made of a pine 1x4 and you can see it on the stern half of the boat in the background. I've fiberglassed over it, then an extra coat or two of epoxy, then primer, then 2 coats of paint. Now I'd like to add an aluminum strip on top of it with several stainless screws. My question is, what is the best way to put in screws so that water won't get in and rot the wood?

I don't want to use bolts, and I'd rather not use 5200 b/c I'd like to remove it easier for repairs if needed. I'll be drilling holes about every 6 inches in the aluminum guard and putting a stainless screw through it into the wood.

 

Your nesting dinghy looks very impressive Jake, a labour of love for sure - what design is she please?
Re attaching your aluminium keel plate, if you do use 5200 and you want to take it off at some stage in the future you should be able to heat the plate with a hot air gun to release the 5200.
Alternatively, if you are using S/S screws, it should be ok if you bed the plate down liberally on a suitable non-adhesive sealant, ensuring that you fill the screw holes as well with sealant.

 

Thanks bajansailor. This is actually my own design. I scaled down this free design for a 15' fishing punt, then hijacked elements of the Chameleon nesting dinghy by looking at pics of it online, but I never got my hands on any Chameleon designs. This is my first boat so there's no telling how she'll actually row and sail, but I had a lot of fun drawing up plans on my own. I do plan to eventually make some videos from the build and posting the plans for free. I also tracked how many hours it's taken (166 so far) and money ($1065), etc. I've already got the oars, spar, mast, rudder, and daggerboard built. Just need to build the sail and install some hardware.

 

Brilliant! She does look very impressive.
How long is she?
Have you dared to weigh the two halves yet?

For background reference for other readers, here are a few links re Chameleon.
Chameleon https://duckworksmagazine.com/04/s/designs/greene/cham/

A nice article in Good Old Boat about a Chameleon -
https://www.goodoldboat.com/promo_pdfs/March12_Promo.pdf

And an article about Robbie -
Building Robbie https://www.sailorgirl.com/adventures/building-robbie/

I also have a soft spot for Chameleons - I drew up a smaller version (7' 6" long) 22 years ago (based on the drawing shown in the Duckworks link above) and built her in cheap ply as an experiment - I was very impressed by her rowing qualities in the relatively limited time I had before the plywood got eaten out by termites. A pal and I did manage to take a mould off her before this happened, and we each have a GRP version now.

 

Fit the strip, drill the holes into the strip and wood, mark alignment. Remove strip, enlarge and deepen holes with a drillbit several sizes larger. Fill holes with epoxy thickened with microfibres. Reinstall strip, redrill the holes into the epoxy plugs with drillbit apropiate for fastener size, install strip on bedding (butil tape, or thickened epoxy).

 

I'd second Rumar's suggestion. I'll post a photo of how I do this below. The picture is for installation of a 1/4-20 bolt so your grommet will be much smaller but the idea is the same.

 

She's 10' long. I haven't weighed her yet, but I was able to carry each side on my own onto the lawn for some outdoor sanding before I painted her.

I know how to do the drill, fill with epoxy, re-drill method for bolts, but I don't know how well this works for screws. In my mind a screw would just crack the thickened epoxy as the threads bite into the sides. Any thoughts on that? I don't want to use bolts and nuts b/c then I'd have to have nuts on the deck of the boat along the center-line.

 

You should be OK with screws. You're just using a thin strip of aluminum, right? Probably 1/8"? You know how to fit the aluminum and drill, fill, drill. Leave your pilot holes a little snug, enough to hold everything together. When putting your screws in the final time you can dip them in a little thickened epoxy and run them in. Once the epoxy coating cures they won't be going anywhere. You could probably use a little bedding material like Sika 291 as well. Either way you'll be fine. Nice job on that one. I'm doing a similar project just have to finish paint her this spring. Have fun!
To put your mind at ease, I never did this with wood screws but years ago I did the drill, fill, drill just like I described with some 1-1/4 inch lag bolts holding some stanchions onto a flybridge. They've never moved.

MIA

 

Jake,

Drill fill drill
Forgot about it
Since you probably won't be leaving it in the water for extended periods of time. Even simple unsealed screwing would suffice.

However' drill fill screw is that extra mile of love that will yeld extra longevity

 

Perfect solution!

 

If you use the correct pilot drill for the fastener size it will be fine. If you are concerned you can use machine screws and tap the epoxy plugs. Or as sugested just use some liquid epoxy with a snug hole, or make a hole the fasteners diameter and use some thickened epoxy. All methods work, with wood or machine screws, you can try them beforehand on a piece of scrap. To disassemble if epoxy glued use a soldering iron on the fastener head.

 

the only thing I might change is I'd put a little 3M 4200 into the screw holes just in case your overbore cracks or is drilled into or near the wood

 

Traditionally one simply dipped the screw in varnish before inserting it, which both lubricated the job and provided water resistance. There are some very ingenious suggestions here, which I'm sure will work, but might be rgarded as a little OTT for a boat that won't stay on the water.

 

almost all boat damages from ingress are caused by thinking overholing and rebedding is ott

 

Sure, varnish used to be used but that was in the days prior to the development of newer technologies. One thing I learned in doing a restoration and actually using the boat these past 6 years is that the water the boat actually sits in is only one factor and usually not the main one at that. I've found that dampness and condensation are larger issues. When I get up in the morning and go out on the back deck, everything is wet from dew, same for the flybridge.. All that work I did sealing every single hole I made has kept all of that water at bay. My boat (thanks to properly installed thruhulls and a PSS is tight as a drum. Even so there is water in the bilge every few days that I mop up from condensation. So even if your dink is stored on deck it's still wet for a good part of the day. Seal those holes up and pay attention to your paint. You'll be glad you did.