Mounting a electric control box on transom inside lazaretto

[HeadedToTexas]

I need to mount a box inside the lazarette on the transom of my Mariner 37 to house a solenoid and some connections for my dinghy lift. The transom has a few points where it's probably fine to use screws, but it still gives me the willies to drill holes so close to the waterline. What about using 5200 to mount the box?

 

[DWJensen]

As long as you're looking for a permanent mount I don't see why that wouldn't work.

 

[hollywood8118]

I need to mount a box inside the lazarette on the transom of my Mariner 37 to house a solenoid and some connections for my dinghy lift. The transom has a few points where it's probably fine to use screws, but it still gives me the willies to drill holes so close to the waterline. What about using 5200 to mount the box?

fiberglass a 3/4" plywood block to the transom, then mount to the block
Hollywood

 

[Comodave]

fiberglass a 3/4" plywood block to the transom, then mount to the block
Hollywood

That is what I would do. You can use thickened epoxy to hold the plywood or completely enclose it with glass. The thickened epoxy is quick and simple.

 

[HeadedToTexas]

Guessing you guys are far more comfortable than me with glass and resin. My career skills have given me a comfort level with 5200 and its lesser cousins. Is it a preference thing, or does glassed in plywood offer a stability for security benefit?

 

[Comodave]

Yes, I use fiberglass and epoxy all the time. I use 5200 sparingly and only when absolutely necessary. So I don’t like to open a tube and use a small amount since by the time I will use it again the tube will have gone bad. With epoxy I can mix a small amount if that is all I need.

 

[HeadedToTexas]

Perhaps this is the project that introduces me to fiberglass? If I thoroughly clean the white gelcoat surface inside the lazarette, will a thick smear of epoxy permanently mount a roughly 8x10 inch slab of ¾" marine plywood if that slab of plywood is not glassed over?

 

[Scottwb96]

I 2nd the use of epoxy over 5200... I would also paint the plywood with marine/bilge paint to seal it up as well. Make sure you get the edges with a few heavy coats...

 

[Comodave]

I usually use Bilge Kote to seal up the plywood. Then sand the area to be glued to to give it some tooth for the epoxy to stick to. I use West 404 thickener to thicken the epoxy as it is a structural filler. Mix the epoxy completely then start adding some filler and stir it until it is evenly mixed. Keep adding thickener until you get a peanut butter or slightly thicker mix. Smear a blob on the plywood and squeeze it in place. Tape it in place until it has gone off, depends on temperature. You are done. It sounds complicated but once you have done it you will find it very easy to do. My wife usually does the mixing and I do the install work. Good luck!

 

[CharlieO.]

^^What they said^^ Also will be able to remove the mounted box from the plywood if needed.

 

[angus99]

Perhaps this is the project that introduces me to fiberglass? If I thoroughly clean the white gelcoat surface inside the lazarette, will a thick smear of epoxy permanently mount a roughly 8x10 inch slab of ¾" marine plywood if that slab of plywood is not glassed over?

I was leery of this dark art initially as well, but it’s much easier than I thought. If you buy the metered pumps from West Systems or others and add in a filler to thicken the mixture, the job is surprisingly easy. Tons of how-tos on YouTube. I do wear a mask and ventilate well. Some of the fillers are easily made airborne. Epoxy and plywood are ideal for what you’re doing. Hope you’ll post the full install when you’re done.

 

[Bacchus]

If fiberglassing scares you, I this case, just think of it as using atwo part adhesive.
Then coat over the plywood with the same 2 part coating.

 

[HeadedToTexas]

You guys do make it sound not so bad. A few questions.

1. I need less than 1 square foot of marine plywood. Where can I buy less than a huge sheet?
2. Is coating the wood with resin better than painting it?
3. If coating with resin, can I mix a batch of resin, reserve some for coating, then add the thickener to peanut butter consistency, "glue" the board in place, then use the unthickened to coat the exposed surfaces?

 

[Comodave]

You guys do make it sound not so bad. A few questions.

1. I need less than 1 square foot of marine plywood. Where can I buy less than a huge sheet?
2. Is coating the wood with resin better than painting it?
3. If coating with resin, can I mix a batch of resin, reserve some for coating, then add the thickener to peanut butter consistency, "glue" the board in place, then use the unthickened to coat the exposed surfaces?

For mounting a box I use Baltic Birch plywood. There are places online that you can buy it in a box. It comes in full sheet size of 5’x5’. I bought a box of it and use it whenever I have small projects to do.

I paint the plywood rather than using resin unless it will be exposed to water frequently.

If you do coat it with resin only mix what you are going to use immediately. Don’t try to keep mixed resin for any amount of time as it will start to go off. You use metered pumps to dispense the resin and hardner so you can easily mix small batches. With the West System you pump say 2 pumps with the resin and 2 pumps with the hardner. You can do 1 pump of each for small batches.

If you are going to resin coat the plywood coat it and let it go off. Then wash it off with water to remove the amine blush, it is water soluble. Then mix the thickened epoxy and put the plywood up.

It sounds like a lot of work but it is really easy once you have done it. I always keep epoxy and fiberglass supplies on hand so I can do a little project if need be. I buy the gallon size of epoxy but I tend to do a lot of projects and the gallon size lasts me around a year. Epoxy doesn’t really go bad if you keep it for several years like polyester resin does, about a year for poly and it isn’t good.

 

[Bacchus]

Repeating my post in another thread
If coatings wood I use a first coat resin only thinned w acetone.
Don't leave puddles but I've added additional where itvsoaks in quickly. Let set / dry and add a second coat resin w catalyst & thickener, if desired.
The initial coats soaks in and provides a better grip than one that is thick,, sits on surface and cures rapidly.
Ratios c are important so I wouldn't try to save a partial batch.
I wouldn't worry about getting marine ply... just get a partial sheet of ply at local big box store and coat it after mounting. It's not like it's submerged!

 

[DWJensen]

Lots of good advice here if you're looking to make a nice solid mounting board - BUT, if all you want is to permanently stick a box on the transom, then a blob of 5200 is the easiest way to do it. It may not be the prettiest and it won't be removeable, but it will be easy and you won't have to buy plywood and resin and mix/thin, paint, etc.. It all depends on what you want the end result to be and what effort you want to put into the project. I've done both methods, and IMO they both have their place.

 

[rgano]

I 2nd the use of epoxy over 5200... I would also paint the plywood with marine/bilge paint to seal it up as well. Make sure you get the edges with a few heavy coats...

I use Clear Penetrating Epoxy Sealer (CPES) of all wood prjects on the boat. I would have no issue useing 5200 to mount a block of wood soaked with CPES. Fiberglassing over it would be optional unless the mounted item is pretty heavy.

 

[HeadedToTexas]

The solenoid and wires in this box weigh less than a pound.

 

[KnotYet]

Rather than any permanent chemicals or plywood I would use heavy duty Velcro.
The adhesive on the 2" and wider coarse Velcro will stick well to CLEAN fiberglass.

It is so durable that I used it to mount my front license plate to the bumper of my FJ40.

 

[HeadedToTexas]

Where can one buy marine plywood in sizes smaller than 4x8 sheets, or is that the standard minimum size available in the retail world?

 

[Dougcole]

Where can one buy marine plywood in sizes smaller than 4x8 sheets, or is that the standard minimum size available in the retail world?

Personally, at the risk of TF heresy, I wouldn't mess with marine plywood for this application. The plywood for this job is in no way structural and has no aesthetic value. A few voids in the plywood are no big deal. If it rots sometime in the (very) distant future (unlikely, given that it is not in a wet place, and will be sealed) just tear it off and replace it with another dirt cheap scrap of plywood.


Given how light the box is, I might even go with 1/2" or whatever scrap I had lying around. You don't need a very long screw to hold up less than a pound.


The velcro suggestion might work as well. Very little risk in trying it, you could always go back and use a plywood block (or 5200) if it fails.

 

[HeadedToTexas]

Marine plywood glassed over and epoxied inside the lazarette just to hold a small junction box with some light components inside does seem very thoroughly engineered. I appreciate the perspective.

 

[jgwinks]

Personally, at the risk of TF heresy, I wouldn't mess with marine plywood for this application. The plywood for this job is in no way structural and has no aesthetic value. A few voids in the plywood are no big deal. If it rots sometime in the (very) distant future (unlikely, given that it is not in a wet place, and will be sealed) just tear it off and replace it with another dirt cheap scrap of plywood

Correct. Marine ply uses the same adhesive as exterior (construction) grade. The only difference that makes it "Marine" is the number of plies and no voids. These have little bearing on the strength or durability of the plywood, they just ensure that the panel bends uniformly. Important if you're bending panels over a form to build a hull, but irrelevant in this application. Any exterior rated plywood will do, so just pick through the pile in the big box store and choose one with few voids. They have them down to about 2'x2' size for just a few dollars. Marine grade usually can only be found in full 4x8 sheets and it's real pricey.
On the other hand, if there's a plywood boat building shop in the area (pretty rare), they'll have lots of small Marine grade scraps laying around. Some shops even burn them for heat so would be really cheap. I once worked in such a shop, we didn't burn them there but one of the techs had a wood burner at home and took all the little scraps for that.

 

[koliver]

Rather than any permanent chemicals or plywood I would use heavy duty Velcro.
The adhesive on the 2" and wider coarse Velcro will stick well to CLEAN fiberglass.

It is so durable that I used it to mount my front license plate to the bumper of my FJ40.

Another great TF contribution, thanks!

Velcro will adhere well with a smear of epoxy on its back, to any clean surface.
I have a front license plate that permanently resides in the trunk, as my CLK500 has never had a front holder. Velcro may solve that issue, though this has been its issue since 2004, so the solution is not urgent.

The inside transom surface will likely be 1/8" or thicker Glass roving, over airex foam or plywood, so a short screw through less than the thickness of the core won't hurt anything, especially if you use 5200 or epoxy around or over the screw. That screw can attach your small box, or your strip of velcro. Once fastened, you can trust it all to remain in place without further ado.

 

[HeadedToTexas]

Any exterior rated plywood will do, so just pick through the pile in the big box store and choose one with few voids. They have them down to about 2'x2' size for just a few dollars.

Makes a ton of sense.

I appreciate the grip of Velcro, but if it’s okay to epoxy or 5200 the Velcro to the lazarette, why not just attach the box directly to the lazarette?

 

[guy with a boat]

Seems like this is getting over-engineered.

KnotYet made a great suggestion to use velcro. The stuff you want is industrial grade or heavy duty stuff. Both sides have the plastic hook stuff, there is no “fuzzy” side. It has serious peel-and-stick adhesive on the back, so you don’t need any epoxy or other additional adhesive. Clean the box and the transom surface and mount with the velcro tape. It will be there forever unless you want/need to remove, which will still be possible. You can still pull the box and reattach if needed. There is no need, IMO, for plywood or other mounting block. Look for 3M or Scotch brand on the velcro.

Another option for this type of thing is 3M VHB tape. Look it up if not familiar. It will mount that box with no penetrations or mixing stuff and the bond will way more strength than necessary for this application. This won’t remove without destroying the tape, but way easier than epoxy. The tape seems expensive for tape but is cheap for its capability.

A few more suggestions for future use:

1. 5200 has its place, but is very slow to cure (days) and is messy, expensive per use, and is much better suited to other uses. Almost always, 4200 is a better choice, but that debate can happen in another thread. Neither product is needed for this project.
2. When you do need a small amount of thickened epoxy, such as to mount a small block, its quick and easy to use a two-part kit from the hardware store. The cost and quantities are small and you can get it with thickener already in it. Its easy to store and easy to use. I have gallons of epoxy and multiple thickeners but its way too much trouble and mess for a very small job.
3. Penetrating epoxy and thinned epoxy for a first coat is a popular myth. The waterproofing comes from the epoxy layer, and thinning it just means you have to use more coats. Epoxy has tremendous bonding strength to a properly prepared surface so doesn’t need to “penetrate” for bonding. The penetrating aspect is for marketing, not because it is better. Skeptics should read manufacturers recommendations. They know how to best use their own products.

Now go mount that box with industrial strength velcro.

 

[Dougcole]

Seems like this is getting over-engineered.

KnotYet made a great suggestion to use velcro. The stuff you want is industrial grade or heavy duty stuff. Both sides have the plastic hook stuff, there is no “fuzzy” side. It has serious peel-and-stick adhesive on the back, so you don’t need any epoxy or other additional adhesive. Clean the box and the transom surface and mount with the velcro tape. It will be there forever unless you want/need to remove, which will still be possible. You can still pull the box and reattach if needed. There is no need, IMO, for plywood or other mounting block. Look for 3M or Scotch brand on the velcro.

Another option for this type of thing is 3M VHB tape. Look it up if not familiar. It will mount that box with no penetrations or mixing stuff and the bond will way more strength than necessary for this application. This won’t remove without destroying the tape, but way easier than epoxy. The tape seems expensive for tape but is cheap for its capability.

A few more suggestions for future use:

1. 5200 has its place, but is very slow to cure (days) and is messy, expensive per use, and is much better suited to other uses. Almost always, 4200 is a better choice, but that debate can happen in another thread. Neither product is needed for this project.
2. When you do need a small amount of thickened epoxy, such as to mount a small block, its quick and easy to use a two-part kit from the hardware store. The cost and quantities are small and you can get it with thickener already in it. Its easy to store and easy to use. I have gallons of epoxy and multiple thickeners but its way too much trouble and mess for a very small job.
3. Penetrating epoxy and thinned epoxy for a first coat is a popular myth. The waterproofing comes from the epoxy layer, and thinning it just means you have to use more coats. Epoxy has tremendous bonding strength to a properly prepared surface so doesn’t need to “penetrate” for bonding. The penetrating aspect is for marketing, not because it is better. Skeptics should read manufacturers recommendations. They know how to best use their own products.

Now go mount that box with industrial strength velcro.

This.

 

[rgano]

3. Penetrating epoxy and thinned epoxy for a first coat is a popular myth. The waterproofing comes from the epoxy layer, and thinning it just means you have to use more coats. Epoxy has tremendous bonding strength to a properly prepared surface so doesn’t need to “penetrate” for bonding. The penetrating aspect is for marketing, not because it is better. Skeptics should read manufacturers recommendations. They know how to best use their own products.
.

As a long time user of the real Clear Penetrating Epoxy Sealer, it is clear to me that you have no familiarity with the product. It does NOT behave like thinned Epoxy. No myth, it will waterproof wood. Look it up.

I certainly agree with your other suggestions to go KISS on this nearly weightless box.

 

[guy with a boat]

As a long time user of the real Clear Penetrating Epoxy Sealer, it is clear to me that you have no familiarity with the product. It does NOT behave like thinned Epoxy. No myth, it will waterproof wood. Look it up.

I certainly agree with your other suggestions to go KISS on this nearly weightless box.

If you mean the TotalBoat product, then I am somewhat familiar with it. They promote it to firm up rotted wood, which is a project that I’m not likely to undertake. If you mean another brand name, I would expect from the name that it is still a penetrating epoxy.

The context here is waterproofing the wood block that was discussed earlier. I’m sure the penetrating stuff will eventually get the job done, but testing consistently says full strength resin is better. Here is one test and discussion by a chemist at Gougeon Bros/West System:

https://www.epoxyworks.com/index.php/penetrating-epoxy-legend-myth/

You aren’t alone in being happy with the penetrating epoxy and its fine if it works for you. I spend enough time hanging out where boatbuilders and chemists overlap that I have a hard time staying quiet when the stuff is recommended. I’m really not trying to change your mind, but at least have a look at the research if you are interested.

 

[Circumnavigator]

Where can one buy marine plywood in sizes smaller than 4x8 sheets, or is that the standard minimum size available in the retail world?

Unless you're using it for the hull, there's no need to use marine plywood. Simply coat all sides and edges with West System epoxy and it will be fine.


Home Depot sells plywood in several sizes cut from a 4x8.


If you insist on using marine plywood, Boulter Plywood sells 2x4 and 4x4 pieces. https://www.boulterplywood.com/. I've done business with them for 50+ years -- good people.



Jim