Square versus triangular stanchion bases?

[Jaco Versfeld]

Good day,


I am busy with a project Flamenca 25 GRP boat. The boat had triangular stanchion bases. Three of these damaged the deck, so much so that triangular holes were in the deck. (I have now glassed and filled the holes).


However, there are two other Flamencas in the marina. One has similar problems, with nasty holes due to the triangular stanchion bases.


My question is: Are square / rectangular bases with 4 bolts inherently stronger?


Kind regards,
Jaco

[leecea]

I would imagine that what they are bolted too and what type of backing they have would be a bigger factor.

I wonder what forces were applied to the stanchions to cause such damage?

[markxengineerin]

My question is: Are square / rectangular bases with 4 bolts inherently stronger?

Yes, if you take the same outer dimensions of your triangle, but make it a square instead, it will put less localized pressure on the boat interface when the stanchion is subjected to a force. I don't know why they would have chosen triangles- maybe for beauty- or maybe there's a spot somewhere where a rectangle didn't fit, and they wanted to keep them all the same.

What you want is a big contact area with the boat, and bolts as far towards the outer perimeter (of whatever shape) as you can get.

Having backing plates is of course better, but the above applies in either case with or without.

[barnakiel]

Stanchion area problems are mostly due to poor design of stanchion area by the designer or else poor grp layup by the builder. But good news these errors can be easily fixed with some epoxy, quality plywood, and better stanchions.


You do want the new stanchions to be attached so that the forces are spread out over a bigger area. Avoid point loading / hard points. If the deck grp is flimsy - build up epoxy glass pads under the deck. It should be all solid - no core ! there.


If a grp pad can not be built there, you may still be able to back the new stanchions with quality marine grade plywood.


Make sure it is not only strong but also perfectly watertight - leaks thru stanchion area are common and PITA. Do it once, do it right, you will be happy ever after.


b.

[TrentePieds]

Jaco said: "My question is: Are square / rectangular bases with 4 bolts inherently stronger?"

That's the wrong question to ask, Jaco :-)

What you REALLY want to know is whether the DISTANCE from the centreline of the stanchion itself to the outer edges of the baseplate is big enough.

That's because when you lean on the stanchion top (or hit it hard), then it and the base plate form a pry bar! The greater that distance is in the direction away from where the impact is coming from the better the stanchion assembly can handle it.

The stanchion assembly will pivot on the deck at the edge of the base plate, and the opposite side of the baseplate will try to lift off the deck. The bolts on that side of the baseplate will try to pull through the deck. Therefore it's essential that there are backing plates UNDER the deck to match the base plates above, and that the deck lay-up itself is gutsy enough to handle the forces.

All the best :-)!

TrentePieds

[Bowdrie]

Originally Posted by Jaco Versfeld

Three of these damaged the deck, so much so that triangular holes were in the deck.

Others have pretty much covered it, so just a couple notes.
If you use some G10, (~3/8ths>1/2,) to make pads that are larger than the bases and fit them between base and deck, you'll eliminate a very common cause/source of leaks.
You'll also eliminate any tendency for the base to "imprint" on the deck.
And bases that are "sockets" for removable stanchions sure save a lot of headaches and work when you bend a stanchion.

[TrentePieds]

Bowdrie said: "And bases that are "sockets" for removable stanchions sure save a lot of headaches and work when you bend a stanchion."

Indeed! That's the way to do it. But penny-pinching cost accountants often nix sound construction of "mass produced" boats.

More's the shame!

TP

[GordMay]

Originally Posted by markxengineerin

Yes, if you take the same outer dimensions of your triangle, but make it a square instead, it will put less localized pressure on the boat interface when the stanchion is subjected to a force. I don't know why they would have chosen triangles- maybe for beauty- or maybe there's a spot somewhere where a rectangle didn't fit, and they wanted to keep them all the same.

What you want is a big contact area with the boat, and bolts as far towards the outer perimeter (of whatever shape) as you can get.

Having backing plates is of course better, but the above applies in either case with or without.

Indeed.