Cutouts in bulkheads inadvisable?

[Randall S Anselmo]

I am thinking of making two small (about 3x8 inch) cutouts in bulkhead  number 2 (aft in main cabin), just below where the aft deck attaches, in order to flush mount my VHF and a stereo.  This would add a small but precious amount of space efficiency, but does anyone think it would cost me more dearly in structural integrity?

[Russell and Janet Puryear]

I would ask JWD, but if it were me, I'd do it.  There is a deck beam that reinforces the attachment of the deck to the bulkhead just above where you are thinking of cutting.  I would not cut into that beam.  You might laminate a 5 x 10 piece of plywood behind the bulkhead as reinforcement.

 

But ask JWD

[Duncan Clausen]

Hi Randall! I assume you are planning on placing them either side of the existing cutout and below the deck beam. A couple of thoughts on this: 1. If I understand you correctly, you will only have about 25 mm (1") of material on either side of the cutouts, therefore I would try and fit a narrow/taller VHF and stereo. 2. The aft beam is lashed down just behind bulkhead 2 although most of the loading is transfered to the hull sides some of this loading will pass through the bulkhead. 3. An engineering rule of thumb that might help you is, to reinforce any hole/penetration with a doubler of the same area as the hole (i.e.5x10 inch). 4. Avoid sharp corners in the cutout, use as big a radius as possible or drill 1 6mm (1/4") hole in each of the corners to reduce the stress concentration. 5. The inboard beam lashings carry more load, so if possible make the inboard cut out as small as possible or alternatively place VHF in one hull and the stereo in the other hull, making the cutouts nearest the outboard hull side.

That all said I would double the entire bulkhead from the deck beam down to the stringer in 9mm (3/8") ply. This will also give you some thing screw into. Again if you are worried check with JWD.

 

I hope this helps you.

[Randall S Anselmo]

Duncan,

Thanks, that all sounds like good advice.  I was considering mounting the units vertically, or at least diagonally, given the lines of stress.  I hadn't considered the fact of the inboard beam lashing carrying more load, but your advice to put the cutout on the outboard side makes perfect sense.  I'll also contact JWD and post their advice here.

Duncan Clausen said:

Hi Randall! I assume you are planning on placing them either side of the existing cutout and below the deck beam. A couple of thoughts on this: 1. If I understand you correctly, you will only have about 25 mm (1") of material on either side of the cutouts, therefore I would try and fit a narrow/taller VHF and stereo. 2. The aft beam is lashed down just behind bulkhead 2 although most of the loading is transfered to the hull sides some of this loading will pass through the bulkhead. 3. An engineering rule of thumb that might help you is, to reinforce any hole/penetration with a doubler of the same area as the hole (i.e.5x10 inch). 4. Avoid sharp corners in the cutout, use as big a radius as possible or drill 1 6mm (1/4") hole in each of the corners to reduce the stress concentration. 5. The inboard beam lashings carry more load, so if possible make the inboard cut out as small as possible or alternatively place VHF in one hull and the stereo in the other hull, making the cutouts nearest the outboard hull side.

That all said I would double the entire bulkhead from the deck beam down to the stringer in 9mm (3/8") ply. This will also give you some thing screw into. Again if you are worried check with JWD.

 

I hope this helps you.