Cored decks and mounting hardware

[HeadedToTexas]

I am adding a couple cleats to the swim platform of my 2007 Mariner 37 for temporary use with my dinghy while loading and unloading. Is the swim platform cored, and assuming so, how close to the edge does that core extend? Any way to know where the core ends and solid material begins?

On a similar note, my dinghy davit system requires a few components to be through bolted and mounted with backing plates on the bridge deck overhang. Any way to know where the core ends and the solid material begins?

 

[DavidM]

Tap it with a screwdriver handle and you may hear the transition from solid to core, but I wouldn't expect the solid to extend far- less than an inch.

Here is a great series of articles on how to install hardware on cored hulls: https://marinehowto.com/category/hardware/

David

 

[FWT]

Betcha Scott Helker at Helmsman Trawlers could tell you.

Contact info from the website:

trawlers@helmsmantrawlers.com

206 282 0110

 

[Comodave]

Tap it with a screwdriver handle and you may hear the transition from solid to core, but I wouldn't expect the solid to extend far- less than an inch.

Here is a great series of articles on how to install hardware on cored hulls: https://marinehowto.com/category/hardware/

David

That is the way I like to mount hardware. Excellent article.

 

[FWT]

Tap it with a screwdriver handle and you may hear the transition from solid to core, but I wouldn't expect the solid to extend far- less than an inch.

Here is a great series of articles on how to install hardware on cored hulls: https://marinehowto.com/category/hardware/

David

Indeed. Good piece.

The piece is working on hardware with backing plates, and the advice is to not spin the bolts. I am wondering about a good procedure when lagging into solid material with no core, no backing plates. Suggestions?

 

[HeadedToTexas]

Am I reading the right article? Beveling or countersinking the holes makes sense to prevent gel coat cracking, but that will not prevent the long term wear eventually compressing the core and leading to leaks. Or at least that is my understanding.

Do those top builders simply bevel the bolt holes, form a seal with tape, bolt it tight the first time, and not worry about compressing the core?

 

[Comodave]

Did you skip the part about reefing out the core and filling with thickened epoxy?

Read this.
Sealing Deck Penetrations To Prevent Core Rot

 

[Jeff F]

Do those top builders simply bevel the bolt holes, form a seal with tape, bolt it tight the first time, and not worry about compressing the core?

Top builders know in advance where the hardware will be mounted, and will use solid glass or non compressible core material in that area.

 

[dhays]

I am adding a couple cleats to the swim platform of my 2007 Mariner 37 for temporary use with my dinghy while loading and unloading. Is the swim platform cored, and assuming so, how close to the edge does that core extend? Any way to know where the core ends and solid material begins?



On a similar note, my dinghy davit system requires a few components to be through bolted and mounted with backing plates on the bridge deck overhang. Any way to know where the core ends and the solid material begins?

I asked a similar question and got a lot of good advice.

https://www.trawlerforum.com/forums/s32/screw-mounting-cored-deck-58361.html

 

[HeadedToTexas]

Did you skip the part about reefing out the core and filling with thickened epoxy?

Read this.
Sealing Deck Penetrations To Prevent Core Rot

Apparently I did! Thanks, Dave. That makes a lot more sense.

 

[Comodave]

No problem, his articles are really good.

 

[HeadedToTexas]

Does MarineTex qualify as suitable expoxy for this application?

 

[lwarden]

I've usually done a derivative of the process described in the video. Rather than use a Dremel to remove the core material I use a bent nail on a drill to break up the core around the hole and then vacuum out the bits. If it's a new hole don't drill all the way through, if it's an existing hole cover the lower hole with duct tape. Having the lower hole open allows easier removal of the bits though. Using this method you can remove more of the core material and this means a better bond to the skins and better resistance to compression when tightening the fasteners.

 

[Datenight]

H to T,

I just added pad eyes to the fly bridge of our North Pacific for dinghy tie downs. They are over the cockpit.

First I found the pad eye location, taped it off and drilled holes from fly bridge through to the overhead of the cockpit with a long 1/4" bit.

Next cut out a square around the holes then with a hole saw drilled carefully up to the fiberglass skin.

Then cleaned out the core in each hole.

Mixed epoxy to about peanut butter, buttered the back of a piece of G-10 and stuck it up. used an extendable boat pole to hold it while the epoxy cured. I also filled a syringe and injected epoxy from the top to be sure there were no voids.

The next day I drilled from the top again through the epoxy filled core and G-10. The holes were counter sunk from the top and the pad eyes set in sealant.

I was going to put inspection ports in the overhead to cover the holes but ended up making covers out of 1/4" Corian and gluing them up with Phenoseal. I think they look better and are easy to remove if needed with a little help from a heat gun.

Rob

 

[HeadedToTexas]

Very nice work, Rob. So your bridge deck overhand is thick enough to have a hollow void between the top and bottom "skins?" I have been assuming that my bridge deck is a single fiberglass plywood sandwich with no void inside as the whole deck is only 1-¾" thick, but I know what happens when one assumes...

 

[Datenight]

Very nice work, Rob. So your bridge deck overhand is thick enough to have a hollow void between the top and bottom "skins?" I have been assuming that my bridge deck is a single fiberglass plywood sandwich with no void inside as the whole deck is only 1-¾" thick, but I know what happens when one assumes...

Thank you. Yes, there is a void. I would guess the top tp bottom thickness is about 3". The fly bridge deck was glass-core glass with the core about 1/2" thick.

More to your project I installed Trick Davits on our NP 39 swim platform. There was about 1" of glass-core-glass, a void then another inch of glass-core-glass. I posted the project here in about 2013 or 14. If you like I can post the pictures again of how I removed the foam and replaced with solid blocking.

Rob

 

[HeadedToTexas]

I am still trying to arrive at the right epoxy product for this project. Right or wrong, I suspect the more formal world of West System products with their thickener mixing is just not for me. All of my epoxy experience has been J-B Weld style two part, be it tubes or a mixing syringe. Any problem with J-B MarineWeld?

 

[Datenight]

Headed to T,

I just checked. The post I did on the swim platform was May of 2018.

For epoxy I usually use products from LBI (Legnos Boatbuilding Inc.). They are here in Groton, CT, reasonably priced and have a great deal of technical expertise which they freely share.

Rob

 

[Comodave]

I am still trying to arrive at the right epoxy product for this project. Right or wrong, I suspect the more formal world of West System products with their thickener mixing is just not for me. All of my epoxy experience has been J-B Weld style two part, be it tubes or a mixing syringe. Any problem with J-B MarineWeld?

It is really very easy. If I am doing a project that needs strength then I use the 404 thickner. It is more of a structural thickner. Just mix the epoxy and stir in the thickener until you get a consistency that you like. Then put it in wherever you need it, simple. This way if you are trying to fill a hole you make it a bit runnier. Put it on the bottom of something and need it not to fall off, then make it thicker.

 

[fgarriso]

Top builders know in advance where the hardware will be mounted, and will use solid glass or non compressible core material in that area.

Don't forget about SS or aluminum backing plates.

 

[HeadedToTexas]

Roger that. And on that subject, what is the best approach for locking nuts, Nylock nuts and flat washers, or regular nuts and lock washers? And I don't read much about Loctite in the marine application. Is thread locking compound recommended?

 

[fgarriso]

SS nylocks for deck mounting hardware with backing plates under them.

 

[HeadedToTexas]

So is that a no on Loctite thread locker for marine applications?

 

[Datenight]

So is that a no on Loctite thread locker for marine applications?

WHAT?! Always Loctite! I guess I should say my wife was the head of marketing on the industrial side of (Henkel) Loctite.

Having said that the pad eye and backing plates I put in are secured with nylocs.

If you ever have a question which Loctite product to use the Lab at the Rocky Hill, CT is a wealth of information and happy to answer questions.

Rob

 

[HeadedToTexas]

So back at it after a 2-½ week hiatus fighting the Covid. Optimistic enough to drill holes in my deck, and that’s a big relief.

Turns out the Mariner 37 bridge deck is foam cored. Better than wood in some ways, but still needs drilled oversize, filled, then drilled at the right size once the filler is cured. That is today’s project. Two questions.

First, despite keen attention, my test holes were not square enough for the backing plate to fit over the four protruding bolt threads. What is the trick to getting the bolts to stay square enough to mate up to the backing plate?

Second, since the foam is already rough and not rotted, no additional hogging out of material is required to insure a clean bond with the filler resin, true? Thanks guys.

 

[HeadedToTexas]

So to question 1, I am going to say use a drill guide to ensure each hole is vertical relative to the surface. The curvature of my bridge deck over the short spacing between holes on the plates should not impact the distance between the holes a few inches down. Fingers are crossed.

 

[Comodave]

So to question 1, I am going to say use a drill guide to ensure each hole is vertical relative to the surface. The curvature of my bridge deck over the short spacing between holes on the plates should not impact the distance between the holes a few inches down. Fingers are crossed.

Not sure exactly how the bolts are going to be mounted. You can always over drill the holes in the backing plate one size. That should give you a bit of room for error in the drilling of the holes. A washer and nut will cover the over size holes. Good luck.

 

[HeadedToTexas]

Big weekend. I got 12 holes drilled out to ¾” and filled with Marine-Tex. It should be cured and ready to sand soon. Once flat and acceptably similar to the surrounding deck, I will mark and drill the ¼” holes for the hardware. My strategy is to use a drill guide to keep each hole perpendicular to the deck surface. Fingers will be crossed.