Compression post base

[mikebikeboy]

I'm in the process of gathering materials for a compression post I'll be fabricating. I'm using stainless tube mounted onto a thick steel plate.

My question is what to make the base out of. I don't want to use wood because the base will be sitting in the bilges. My first thought was to make the base with epoxy / fiberglass soup. The reason being I could make a form and pour it in. I'm cutting a hole in the cabin sole and in the interest of cutting as little as possible, was thinking to make a form and make this base out of something liquid which would conform to the uneven surface of the bilge. That's why I thought epoxy / fiberglass soup. But I don't know if that has the compression strength I need.

Any advice?

[Artey]

I would use G10 epoxied in place, this needs to be quite the tight fit if you aren't going to plan on using mechanical fasteners between the hull and the base. Let that setup then on the bottom of your post use another steel plate screwed into the G10. I did something similar but used 6061 aluminum post/plates. Thickened epoxy with cabosil is what I used to set my top and bottom bases.

If you are really worried about only using epoxy to set the G10, you could also slope the edges and then fillet with epoxy and lay actual glass over the G10 and out into the bilge area where it sits. Remember glass doesn't like 90 degree angles, so having the edge of that G10 chamfered and a good fillet to complete the rest of the slop is very important so you don't end up with weak air pockets at that joint between G10 and bilge area

[mikebikeboy]

Thanks Artey, good information. Is this the product you are referring to?

https://www.mcmaster.com/garolite/mu...eets-and-bars/

Where do you source your g10 product?

[Artey]

Yep that's the stuff! McMaster is good but pricey usually. I have gotten it from well reviewed ebay sellers in the past.

[mikebikeboy]

Wow Artey thanks a lot for that tip. I've now found G10 for 1/3 the price of McMaster. Much appreciated.

[mikebikeboy]

FOr any0ne who's interested I'm going to make the compression post from this article:

Main Mast Support

I've got the Acme threaded rod and nut, next I'll be buying the pole and some steel plate and then find a welder to put it all together

will post pics

[Cheechako]

-A fiberglass layup with plenty of cloth will work. I guess that's what you mean by "soup", just have plenty of glass in it.
-A gallon of "kitty hair".
-Cement will work if you have a way to enclose it while you pour it.

There is nothing wrong with wood for a compression post and it's readily do able without hiring people.

[DougR]

Back when I sailed a Tartan 30, the keel stepped mast sat on a wood support that was shaped to conform to the hull and encapsulated in glass with the aluminum mast step screwed to that support. Plenty strong to take the mast compression load.

Given that G10 has a compression strength of around 60000 lbs./sq inch I feel confident that it will work fine to take the load of your mast. Shape it to conform to the hull and glass it in place. Make sure the top is level in all directions.

[mikebikeboy]

I found some 1 inch thick g10 for $15 bucks on ebay thanks to Artey's tip

I would be interested in using wood but space is limited, I need the profile as slender as possible. With wood I'd have to beef up which I don't have an option in my case

Unfortunately the post comes down right in the middle of the pass-thru between salon to v-birth

As long as I keep my waistline in check it's not hard to slip past

I pondered doing an arch but the amount of tear out / glassing is too much for me. This is an easier fix

[Cheechako]

Hmmmm, a post in the middle of your walkway is going to devalue the boat. Not possible to offset the post and have a large support plate at the top? Not sure why you would need to glass anything. You just need to support the deck/cabin top. Or an arch over the door way with a smaller post each side of the doorway?
This is a CD27, does yours have both those posts?

[mikebikeboy]

Hi Cheechako,

That was my plan in the beginning but upon inspecting those posts, they don't seem to be doing anything. They are not tied into the deck, and in fact one of them is hovering 1/4 inch above the floor, doing nothing.

I am going the post route because it's easy, and it provides a way to jack it up if I need to. Currently there's a bulging down, which I plan to slowly jack back up over time.

I paid almost nothing for this boat so it's resale value is not an issue for me. Which also means I want to invest as little as possible in the boat as well.

[mikebikeboy]

I'm trying to decide whether to use kitty hair or thickened epoxy w/ strands of fiberglass mixed manually, for setting the compression post base onto. The base is a 6x6x1 inch thick piece of g10. The stringer it's going to sit on is not exactly flat, it falls about 1/4 inch over the span of 6 inches so at thickest, whatever I bed it with will be 1/4 inch thick.

Any ideas of which is stronger?

Trying to save money---I already have the supplies to make my own thickened epoxy + fiberglass strands and don't want to spend another $40 bucks on a quart of kitty hair if I don't have to

But if kitty hair has enough advantages I'd be willing to buy it.

[mikebikeboy]

Ended up making my own. Seems to have worked fine.

[mikebikeboy]

Got the compression post base installed. Thanks for all suggestions and help. Here are some pics.

I cut a hole in the floor. Below the floor appears to be a horizontal stringer covered in fiberglass. Feels very solid. It drops off aft about 1.75 inches so I needed to build that up.






Homemade Kitten Hair


Built up piece in place. This is g10 I bought from ebay for pretty cheap. Thanks Artey


A couple days later I went back and installed the compression post footer, also a slab of 1-inch thick g10:


I used the same homemade kitty hair which was epoxy, 2 inch long strands of fiberglass, and some silica filler to thicken and prevent epoxy from oozing.