Longeron attachment on Pontune boat?

Quite recent i decided to build a pontoon boat, it's not going to be a big one, about 3 meters maybe. I'm going to do a small one first to get experience before building a larger one and spending a lot.

Today i was researching on how to connect the floats to the deck area. I suspect that this is a point where the most stress will occur (for example when boating over some waves).

I bumped into a few old plans on the svensons.com ( Novelty Pontune http://www.svensons.com/boat/?p=Novelty/Pontune ) site and studied them for a while.

But one thing i can't figure out how they connect the longerons to the floats. You can see the longerons on the following image:
http://www.svensons.com/boat/?f=Novelty/Pontune/pontune3.jpg (bottom left corner of image, between the floats underneath the deck)

A image can be found here:
http://www.svensons.com/boat/?f=Novelty/Pontune/pontune5.jpg
(underneath the deck beams there is another beam that's a longeron)

Is it correct to assume that the longerons are there for extra strength to reduce the stress on the carriage bolts (the bolt holding the deck beams on to the floats).

Cheers for the ideas!

 

Looking at my post i saw the section below my post named "similar threads". This post gives a nice solution on how to attach the floats to the deck:
Catamaran Beam To Hull Attachment

Interesting for sure! Going to do a bit more browsing through the "similar threads"
Thumbs up for the valuable information on this forum!