hi Powderpack, 

the reason is subtle, but it is supposed to help protect the boat in case you slide over a rock.

the soft bulkhead will 'give' a little and not act as a fulcrum against the bottom panel.  when a rock is being slid over, the bottom panel could crack adjacent to the bulkhead because it will stop flexing at that point. 

sometimes a bit of flex is stronger than all solid parts with a certain geometry.

that said, if you don't intend to be sliding over rocks, you could go with the sliding bulkhead.  and i suppose it would take pretty good rock strike right at the right location to see the effect.

that said, i have the 3 inch minicell bulkheads in several boats attached with 3M 5200 and have not had a problem with them decaying or leaking.  the boats have been used extensively over the years.  the main thing to prevent problems is to ensure you put away the boats dry.  and that's a good lesson regardless of the bulkhead material.

hope that helps

h

 Hi Hspira,

Thank you very much for your very informative answer. Now everything about minicell bulkheads makes sense.

Regards,

Powderpark

Personally, I am not a fan of foam bulkheads and use plywood in all of my boats.  I acknowledge that with ply there will be some stress concentration near the bulkheads during a major collision, but I paddle in an area (Florida) where those those types of collisions are unlikely.  Also, the deflection issue is really only a factor in close proximity to the bulkhead, so most of the hull flexes anyway. 

For me, there are two advantages of plywood bulheads that make them worth the small risk discussed above.  If made from ply, the rear bulhead adds a lot of strength to the cockpit opening where most paddlers put their weight when getting into and out of the boat.  Secondly, ply bulkheads give you firm attach points not available with foam.  Nearly all of my boats have fittings on the front of the aft bulkhead to hold items like a dry bag and/or water bladder.  On all my boats with sufski style footbraces, I use the forward bulkhead to mount cleats for adjustment of the rudder system.  Picture is the front of my Yukon prior to adding the deck. 

Lastly, I will point out the CLC include plywood bulkheads with the S&G Petrel Play kit.

   I use wood bulkheads in all my boats. Plywood in some and panels made from scrap strips in others. All are fiberglassed on both sides before installation.

But, I have also installed foam bulkheads in other boats, some wooden and some composite. To make a template I take a piece of stiff wire, wrap it around the boat in the area where the bulkhead will go, slide it off and trace the shape onto the foam. Then I'll cut it just a tad smaller to account for the hull thickness. As mentioned above I'll use 3M sealant to hold it in place.

The main downside I've seen is that if the boat is stored outside with no cockpit cover critters have been known to get inside and scrabble their way through the foam.

Both materials work fine in my opinion.

Dan