Commander Compression Post Discussions

[Rico]

Perhaps we are missing something in the communication... but...

You say that there is no failure now... Unless you are planning a drastic remodel why would you need to move the post in the future??? Besides - the addition of this solid pad would NOT prevent you from doing anything you can do now as this modification does not change the manner of attachment of the post/cabintop connection...

Perhaps you are not confident of the strength/durability of the suggested repair?

Consider that the original cored construction has done quite well all these years...

Solid epoxy is much stronger... And it is as excellent material for compressive resistance...

Let's consider:
The top of your post has a metal bearing plate which is some 6" in diameter. (The mast base is 8" - but let's consider the smallest area as an example as it is the weak element in this scenario)...
This plate bears on the inside of the cabintop below the Balsa core (which is already solid FG and will remain. You'll only remove the balsa core and will replace the FG layer at top.)

The compressive strength of epoxy varies a bit depending on the product, type of product, and manner of application, but it will range between 5,000 and 10,000 lbs/sq-in. Glass makes it stronger, but let's ignore that...

Let's say that you use bad epoxy and your install is full of holes and poorly applied... so we'll use 5,000 lbs/sq-in.

The bearing strength under these circumstances for the solid epoxy pad will be as follows:
The Area of the 6" plate at top of post 28.26 sq-in x 5,000 lbs/Sq-in = 141,300 lbs

So you see - the pad is actually the support system's new strongest point - far from being the weakest... the mast will crumble, the compression post will become a pancake, and everything -including the keel - would be pushed out the bottom of the boat WAAAY before the bearing pad you build even starts to consider failing....

[John]

I have a dremel like tool and for it I have 1 in + fiberglass reinforced cut off wheels. Can I use those to cut the deck to open up the void? Or am I better off going to Walmart and get their $29 angle grinder for that job?

[Rico]

Ahhh... I see.
I would suggest that you bring the cabin-top to its intended position for a proper repair job. The subsidence is due to the failure of the core and even though you would eliminate further deformation by making the repair where the pieces sit now, the best solution is to do it right. After all, once your commander is all shippy, you will not want to see that issue at the top of the post. It will not look right.

I imagine that if the cabintop does not pop back-up on its own, you can help prop it up into position fairly easily... Then do the repair as suggested. This is an important area, but it will not be hard to get it sorted out.

Your dermel-like tool may do the job, but it is a great big job for it... Not the best tool for this application. An Angle grinder with a cutting wheel, or even a skill saw with the proper blade would serve you best. Angle grinders are quite versatile. I'm sure you'll use it a lot if you cannot borrow one for the job, and end-up buying one...

BE careful with it though... They are powerful and can do lots of damage! (I am working on healing a nasty abrasion from one at the moment!)

[John]

Rico,

I am about to make the big leap, take a header off the tops, cut a hole in deck. I have a friend that is going to loan me his 6" angle grinder. Mask is at hand. Power to the boat. Can I cut a 5 in. diameter circle in the deck.? Can I mix up a gallon of epoxy to fill the void? Curious minds want to know.

[Commander 147]

John

I would like to offer a few suggestions that might make your job easier.

1.) For the small area you are working in a 6" grinder might be to large. I use a 4" grinder to grind in the bevel around the hole after I have cut it and even that seems a bit large at times.

2.) To cut the hole I often times use a small trim router similar to the one at this link. It allows me to control with a high degree of precision the depth of cut.

http://www.google.com/products/catal...CAcQ8wIwADgA#p

3.) If there is any balsa core intact under the cutout remove it carefully. It was bonded pretty well to the bottom skin which is often times very thin and fragile. Don't try to rush it just get it up slow and easy.

4.) Epoxy resin by itself is very brittle. You need the glass reinforcing to make this area strong. So cut all of your glass fabric pieces before you start putting things back together again.

5.) To keep a lot of resin from running down through the two holes that the mast step bolts through and dripping on your cabin floor you can wet out the top of the bottom deck skin and on a piece of visqueen (plastic) wet out the bottom piece of glass you will be putting in the hole. Then put the glass in the hole and make sure there are no air bubbles under it. Then let that start to kick and set up before you proceed with the rest of the glass. In addition I would use a couple of pieces of tape on the bottom of the holes to make sure nothing drips on the cabin sole.

6.) This repair will really take a small amount of epoxy. So mix small batches of epoxy so you don't waste it and it does not set up on you before you can use it all.

I hope this helps and I wish you the best on your project.