Mast compression post calculations.

[GILow]

Originally Posted by Wotname

I suppose if the old one comes out (with or without the acro props) then the new one should go in, especially as the new one will be 'smaller' but not shorter.

Unless I measure wrong…. then bring out the acro props.

[GILow]

Originally Posted by MicHughV

I'm a retired structural marine engineer....



All this math talk is hurtin' mah head...

I’m a professional mathematician and all this maths talk is hurting MY head.

[GILow]

Originally Posted by chris95040

This is a fantastic point. When I had mine replaced I had the welder make it 2 inches short, now it sits on g10 plates. I did it so that every trickle of water in the bilge wouldn't run past it and rust it away like the original, but it certainly made installation easier too!

Neat trick. I will see if that should be done on mine.

[GILow]

Originally Posted by El Pinguino

Mine is 2.5 inch diameter.
Ping, Ecuador.

Now you are just boasting.

But are you actually in Ecuador now?

[GILow]

Originally Posted by MicHughV

I've done a wood (teak)compression post installation twice now.
First on my steel boat, I welded the base plate to a frame, so it was well clear of any bilge water. The teak post had a groove cut thru' the middle of the top end, this allowed me to place the post on the plate and rotate the post and slide the post thru' a steel member, where it was bolted into place. Then I jammed some teak shims between the top of the post and underneath side of the deck. The bottom I kept in place by bolting some teak strips around the post on the bottom plate.
The second one was similar, but a fiberglass boat, so this time I fabricate a teak plate which was fixed to the to the top of the keel ballast, as the ballast surface area was a bit wonky. As before, I rotated the post into position and used shims to fill the space between top of post and underside of deck. The bottom was held in place as before.
Never had a problem with either installation.

Given I am stripping a Kelly Peterson back to a bare hull, I may well end up with a bit of teak lying around for this job.

But my current thinking is to build the post in situ, tack welding it all into the correct shape before pulling it out (carefully) and getting someone with a bigger welder to zap it properly.

[Bowdrie]

What is the displacement and sail area of your KP44?
The Westsail 42/43s were available with a tall double-spreader rig and they are in the 34>35K in displacement.
IIRC they used a stainless tube ~3.5 or so in diameter, I don't remember if it was a schedule 80, (Heavy wall,) or 160, (Extra heavy wall).
A stainless tube will always look better than some box-section contrivance.
The Westsail forum will have the answers.

[GILow]

Originally Posted by Bowdrie

What is the displacement and sail area of your KP44?
The Westsail 42/43s were available with a tall double-spreader rig and they are in the 34>35K in displacement.
IIRC they used a stainless tube ~3.5 or so in diameter, I don't remember if it was a schedule 80, (Heavy wall,) or 160, (Extra heavy wall).
A stainless tube will always look better than some box-section contrivance.
The Westsail forum will have the answers.

According to sailboat data she’s 30,000 lbs with 700 square feet of sail. But I’d take all that with a big grain of salt.

But your report tallies well with El Ping’s Westerly Seaslug, suggesting that the six inch pipe on the Swanson 42 is serious overkill.

As for stainless… a good idea and yes, it can look nice, but another bit to polish… I think it would stress me out. Galvanised and painted is more my cup of tea.

[Cheechako]

In round numbers, a 3" diameter 1/8" thick wall AISI 1020 steel tube is far more than enough for the task, neglecting the Slenderness Ratio i mentioned earlier. It's a short tube with fixed ends.
There is 1.13 sq in of steel in the tube cross section.
The yield strength (not the ultimate strength) is about 50800 psi.
So in just shirtsleeve calculations/round terms: if your boat could be balanced on it, it would be more than enough for that task even. (57404 lbs)

A common Fir 4 x 4 would be plenty up to the task. In compression it's good for 7230 pounds per square inch!

[El Pinguino]

Originally Posted by GILow

Now you are just boasting.

But are you actually in Ecuador now?

Yes I am , arrived at the boat 1600 Monday local time after 49 hours in transit. Boat back in the water one hour ago after 3 days shy of two and a half years on the hard.

[GILow]

Originally Posted by El Pinguino

Yes I am , arrived at the boat 1600 Monday local time after 49 hours in transit. Boat back in the water one hour ago after 3 days shy of two and a half years on the hard.

Very happy for you, it has been way too long.

[GILow]

Originally Posted by Cheechako

In round numbers, a 3" diameter 1/8" thick wall AISI 1020 steel tube is far more than enough for the task, neglecting the Slenderness Ratio i mentioned earlier. It's a short tube with fixed ends.
There is 1.13 sq in of steel in the tube cross section.
The yield strength (not the ultimate strength) is about 50800 psi.
So in just shirtsleeve calculations/round terms: if your boat could be balanced on it, it would be more than enough for that task even. (57404 lbs)

A common Fir 4 x 4 would be plenty up to the task. In compression it's good for 7230 pounds per square inch!

Another view suggesting, as suspected, that the Swanson is way over-sized.

[El Pinguino]

Originally Posted by GILow

Now you are just boasting.

But are you actually in Ecuador now?

Well maybe I have something to boast about

2.5 inch diam is also ideal for stowing Thai stubby holders on.

[Jim Cate]

Originally Posted by El Pinguino

Yes I am , arrived at the boat 1600 Monday local time after 49 hours in transit. Boat back in the water one hour ago after 3 days shy of two and a half years on the hard.

Mazel tov, mate! Happy days ahead...

73,

Jim

[Jolly Roger]

You might like to read how I changed my ketch to a schooner and overcame the same problem of the main coming through the center of the saloon.
CHANGE OF RIG (schooner-britannia.com)
My main was originally keel stepped and I didn’t want the large section through he saloon, so I spliced a 4” square steel tube to the mast and continued it to the keelson, then clad it with teak. It is now a keel-stepped, mast and stronger than the original section.
Another question should be the plate size and thickness to transfer the mast load to the post in the ceiling. It obviously needs to carry the load of the mast which will be bigger than the post
JR.

[GILow]

Originally Posted by Jolly Roger

…

Another question should be the plate size and thickness to transfer the mast load to the post in the ceiling. It obviously needs to carry the load of the mast which will be bigger than the post

JR.

Yes, that bit is tricky, not least because it is greatly affected by the chosen pipe radius AND the style of gusset used in attaching the plate to the pipe. No hard and fast rules there I suspect.

Again, I’m inclined to copy the Swanson to some degree.