# Mullions / Pillars Calculation

Discussion in 'Boat Design' started by ToMeK, Sep 20, 2021.

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1. Joined: Jan 2005
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Location: Philippines

### rxcompositeSenior Member

Pillars/mullions are basically post under compression designed to carry part of the load on deck and or the deck above it. You need to find the total amount of load per spacing and divide it by 2 as there will be a pillar on the opposite end.

If it is a pillar(s) it will be the total amount of load divided by the pillar. The pillar is sometimes used to reduce the size of the transverse beam effective length. The load it will carry will be the Force/Area, with the force being in compression. Area being the solid surface that bounds the tube. For a post, I will use UD fiber as a core Wrapped on the outside with a WR to prevent the UD fibers from bulging/separating and a WR inside to prevent the walls from collapsing. Different fabrics then with different compressive properties. Use the basic formula but use only compressive properties.

If the pillar is located on the outermost part of the ship, it is usually canted inwards, an eccentric load. This is where the beam in page 2 is used. More UD is used in the inside part as there is more compression load. Note that side pressure load given by ISO or LR might be inadequate. It is a uniformly loaded pressure with a fixed ends. Note that you have to attach a plate.

For the front part, the windshield side, pressure is generally greater by 15 to 20% and the cant is greater. You must do double calculations. One for the top load and one for the front load (using the plate + stiffeners).

2. Joined: Jan 2005
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Location: Philippines

### rxcompositeSenior Member

That seems to be a permanent connection. How do you plan to make it a tight fit? These stiffeners, unless reinforced with a core would buckle when the bolt is tightened.

I would prefer a flange and screwed connection. You have to increase the thickness of the laminate at the area of connection and you have to add wood inside for the screw to grip. Fit the pillar, slide the flange, tack weld, remove then full weld.

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