How to glass mounting blocks to the hull

[glhotka]

We are doing a refit of our Gulfstar and as part of this we are wanting to "re-arrange" the engine room to make it more organized and also relocate the refrigerator compressor to the engine room.

One of my goals is to mount a small shelf (14" x 12") shelf in the engine room to mount the compressor on. I have built the shelf from wood and coated it all in epoxy. My goal was to mount this to the fore or aft engine room bulkheads but there is just not a good place to do that and still leave ample room to get into the engine room for matineance and move around.

My next thought is to glass in some mounting blocks to the inside of the hull, attach my shelf to those mounting blocks and then attach the DC refridgerator compressor to that shelf.

The problem is I have never done this and not sure how to. I see other small mounting blocks where water lines are attached to the hull so I figure it is a standard practice.

Do the questions are:
1) If I am going to do this what is the best wood to use. I assume some kind of hardwood, does that make sense?

2) Do I just put a bit of 5200 to hold it in place and then put a few layers of epoxy resin and glass matt over the block and out 5 inches or so around the block to the hull?

3) The inside of the hull appears to be painted, do I need to sand it down to raw glass before I can do this?

4) Lastly are their reasons why I should not even be considering this as an option?

Thanks in advance for those that have charted this course before me.

[Nemo55]

Yes,,to #2 and #3

[glhotka]

Thanks for the quick reply. Would love to hear from others who have done this or any photos you may have of the work you may have done.

[daddle]

Tab it on just like the nearby bulkheads are tabbed. Yes to sanding off any coatings. The 5200 is probably a waste of effort. Epoxy and glass is super strong. There should be some sort of brace under (or above) the shelf to take the load ... like a bookshelf in a house.

[bobofthenorth]

Building on what others have already said, I wouldn't bother with the 5200 either. I would use epoxy thickened with some colloidal filler for the adhesive and then cloth and resin to tie it into the hull. You're making a mechanical attachment to the hull as opposed to a chemically linked bond so you need to prepare the surface for mechanical adhesion. I would use a 4" angle grinder to remove the existing paint and roughen the surface over the entire area including some periphery for reinforcing cloth, the rougher the surface the better. I would dry fit the shelf that you have already built and grind it to get as close a fit as possible. When you are ready to actually fit it in place you should butter it with resin and filler mixed into a paste about the thickness of peanut butter. You'll need to have some way figured out to clamp it in place while it cures and you'll want to brace it as tightly against the hull as possible. I would paint both surfaces with resin, then butter the shelf and brace it in position, then lay well wetted cloth against the edges and along the top and bottom of the shelf. Make sure you work out all bubbles under the cloth. You can let one layer cure and still get a chemical bond to subsequent layers as long as you do it all within roughly 24 hours - check the allowable time with the supplier for whatever epoxy system you use. One thing to watch with epoxy brackets like you are building is to avoid sharp angles because they tend to become stress fracture points. Fillet out your corners with thickened epoxy to avoid sharp inside corners.

[delmarrey]

W/o writing up a long explanation you can go to my blog below and then to the last parts of the motors page. It shows how one can install mountings to the hull or bulkheads using epoxy filler, filling radius and tabbing over.

For a strong attachment you need to create a large surface area bonded and glassed over for max strength.