Compression Post and Support design

Hi all,

New member looking for specific information.

I have a 1979 Irwin 37 center cockpit. I'm refitting the boat and looking to make upgrades or improvements. My boat was designed with a deck stepped mast. So from top to bottom the below mast components are in order:

A deck top mast step.

A tubular aluminum compression post spanning the inside deck surface to the floor.

A steel Pi shaped compression post support spanning two side to side floor ribs and bolted to those ribs.

On my boat corrosion is an issue. The bottom of the compression post is badly corroded. The entire compression post support is so badly corroded it can not be saved. The floor ribs used to attach the compression post support are water damaged.

I've removed the mast step, compression post and compression post support. I'm accessing the ribs to repair those.

My question is replacement.

I'm considering a few different paths:

Path one;
The area below the compression post below the floor is bilge area. It is about one foot deep below the hole in the floor for the compression post. With the compression post support removed the area is clear from the floor to the flat top of the lead keel. I'm considering modifying the round aluminum compression post to make it longer so that it sits directly on the keel. Eliminating the compression post support entirely. I would sit the compression post on some sort of a teflon washer so that the lead keel and aluminum compression post are cushioned. This would in effect support the mast step directly to the keel.

Path two;
Again the area below the compression post below the floor is bilge area. About one foot deep below the hole in the floor. The area below is clear to the keel. I'm considering replacing the compression post with a one piece hard wood 4X4. In the year or so prior to my boat building Irwin used wooden compression posts. I would sit the hardwood compression post on some sort of a teflon washer for cushion. Again supporting the mast step directly to the keel.

I'm in favor of the 'Path Two' as it would be cheaper.

I'm open to ideas and criticisms. I'd like to do this job once and only once. I'd also like to have the strongest most durable constructed boat afloat!

Thank you for reading...

 

Nothing lasts long in a wet bilge. Think twice before you locate anything in the bilge.

Post a picture of your proposal for better comments

 

Oh I've got lots of pics!!!

Compression post top.

 

Compression post bottom

 

The area under the compression post. This is the forward most section of the bilge. The bilge actually goes much lower than this as it goes aft. The bilge pump is in the lower sections of course. I don't believe the area of the bilge in question 'stays' wet, but the chain locker and forward shower drain through this area.

 

The bottom of the compression post support. I placed a mirror on the keel section below and took the picture looking up. The support is out of the boat now.

 

The bottom of the deck where the compression post joins to the mast step above.

 

The floor.

 

The mast step hole on the deck.

 

The compression post support removed, sitting in my cockpit.

 

Looking down through the hole in the floor to the keel.

 

If you re-do it the same and it lasts over thirty years again, will you still own the boat? If you won't, then keeping it the same is the way to go. You could use stainless or bronze for the new post without any major difference in price.

 

Irwin changed the step and compression post configuration a few times, to address the issues you currently have. The best setup would be to use the all metal arrangement, but consider a surface coating to offer more protection, then was available to Irwin in the day. The obvious choices are powder coating, truck bed liner and epoxy. If it was me, I'd put at least a 10 mil epoxy coating on everything in the bilge and extending a few inches above it. Then I'd use truck bed liner over this to offer some abrasion protection.

Don't place a hollow circular section directly on the keel. The step spreads the rather narrowly focused loads from this type of shape to a much wider area, so point loading is diminished. The wooden block arrangement was the very first step setup Irwin used and it was quickly discarded, because the rigging loads crushed it fairly quickly. If you changed the wooden block every couple of years, you'll get good service from it, but if you installed it and forget about it, you'll run out of rigging screw adjustment in no time.