Commander Compression Post Discussions

[Doug]

Working on the mast for Ariel #400....and looking for some advise
Removing the through bolts for both the spreaders and uppers - I found that there are no compression posts for these bolts to prevent the mast from being distorted or crushed. Is this the normal state of things?
I am also busy trying to remove the mast base to adapt a mast hinge - has anyone used a slide hammer to whale away at the base?

[commanderpete]

Don't think a post is needed. The load is pretty spread out and probably not too great.

[Rico]

While I had my mast down, I decided to retrofit compression pipes at the spreader brackets on the mast.

You can read-up on the concept, and can see the pictures of the install here (post #87+):
http://www.pearsonariel.org/discussi...ead.php?t=1552

[Chance]

Hello all,
I have experience removing and working the area of the compression posts on Commanders, don't know if there are any outstanding questions that I can help shed some light on. Here's a couple of points though:

1) The compression post is schedule 80 anodized aluminum.
2) The sole was installed first, then the post lowered down through the forward hatch and inserted into the cabin sole hole at a slight angle.
3) The lower end of the post sits on a built up fiberglass base in the bildge. Most likely with wood somewhere inside. The post itself is not glassed in.
4) The wooden wedge between the top of the post and the underside of the cabin is made of teak. The wedge is necessary for the same reasons the mast base has a slope to it.
5) Pearson cored the entire cabin roof, to include (unfortunately) the area immediatedly under the mast step.
6) The core is 3/8 inch end grain balsa.
7) Any detected movement is a sure sign that the balsa's integrity has been compromised. ie, water intrusion followed by rot / decay.
8) No work should be attempted with the spar (mast) up.
9) To remove the compression post strip away the very light tabbing around top of the post and with a block of wood drive the top of the post directly forward. Remember, the post was installed through the cabin sole hole at an angle and will come out at an angle. The biggest challenge will of course be in overcoming any downward movement the cabin roof made due the core failure.

I'll leave it at that for now, unless there are more questions of repair, etc..

Thanks,
Chance.

[Commander 147]

I appreciate your post.

Have you replaced the compression post with a laminated support beam yet? If so is the process detailed here someplace?

[Chance]

Your welcome.
No, I'm not replacing the standard compression post for a built up beam of some sort. On the commander, it is my belief that the compression post is the best way to go. If one were to say, want to remove it and do something like the Ariels set up, it would take major interior redesign and careful calculations to address the tremendous loads that the compression post carries, then where to fit everything in such a small cabin layout.
For an idea take a look at the Kittiwake's interior configuration, which is another Carl Alberg design. The cabin interior is small and there are what amounts to two load bearning posts on each side of the centerline cabin sole.

Thanks.