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Steve's "Mobjack Bay" Skin-on-Frame Kayak Project - March, 2017

Dave Gentry's Mobjack Bay Kayak

Documenting the building of a Greenland-style Skin-on-Frame Kayak

In the spring of 2016 Sue and I built a skin-on-frame kayak for her use. It was based upon Brian Schulz's F1 design though it was built using frames and stringers vs. steam-bent ribs. You can check out the building of that boat here.

The Mobjack Bay was designed by Dave Gentry as a smaller Greenland-style kayak for lighter paddlers. The photo above is of Dave's prototype. It is definitely a low volume boat intended for day trips as opposed to camping or expeditions. There is not much storage space in this boat but I think it will suit the kind of paddling we do just fine. So, here we go!


Mobjack frame
The project began with cutting out the seven frames using full sized patterns provided with the plans. I was able to slightly modify the gunwales, keel and stringers I had prepared last year when building Sue's kayak. In the photo above you can see the basic frame layout. All those clamps at the bow are 'redirecting' the split gunwales to create the swoop of the shear of the bow.
Gunwale tips

Here is a closer look at that process. The gunwales were split (sawn) 54" back from their tips then bent upward to create the desired 'laminated' curve at the bow. The pine wood we're using is pretty stiff, even  at only 5/8" thickness, but this did work as the plans indicated it would with only about an inch or so of spring-back when the epoxy had cured.
 - March 5, 2017

Frame - March 9th
The gunwales and chines are permanently screwed and glued to the stems and frames. I am in the process of adding risers to fill the space between the tops of the gunwales and the top of the bow stem. This is according to the plans and should produce a nice even sweep at the bow. The boat project is on hold awaiting warmer weather. It takes a lot of firewood to bring the shop temperature up from low single digits that are forecast for the next week. The rivers are still pretty hard so that's OK.   - March 10, 2017
Gluing on bow risers
Today it finally warmed up enough (28 deg F.) to fire up the stove in the shop and epoxy the risers to the bow. Lots of clamps (21). Looking good.

As an aside, that red object under the saw horse is an inverted large, re-purposed plastic bucket that I use as a step-stool or seat. It is very handy since you can slide it into position with a gentle kick and it is super sturdy.
 - March 15, 2017

Risers & bow plate
After the epoxy holding the risers had cured I cut a recess for a small plywood bow plate. This piece is shaped to form a continuous curve with the tops of the risers and gives the bow its shape.
Hatch plate from side
I decided that it might be a good idea to have at least a little accessible storage space for things like a jacket, gloves, water bottle and lunch so I designed this hatch system to replace the aft deck beams. I added an additional cross piece and then screwed and glued the hatch plate (above) between the two frames behind the cockpit.

The covering fabric will go over the hatch plate and be sandwiched between the plate and the rim shown at left. The lid rests on a 5/8" lip inside the rim and will be held in place by a simple lip under the aft edge and by three large rare-earth magnets along the front edge. A small lift loop at the forward edge of the lid will allow it to be opened but shouldn't be in the way of a wet re-entry. By the way, this is not a water-tight compartment; dry-bags will protect my stuff. - March 18, 2017
Hatch with rim & cover
   hatch detail drawing
  This assembly is made from 1/4" Baltic birch plywood and adds 28 oz. to the weight of the boat.

Mobjack floor (seat)
Today's project was to complete the floor (seat). I deviated somewhat from the plans here by choosing to fasten the floor slats into two panels and then fasten them to the frames with simple hidden fasteners. 
Floor retaining clip
Cut masic
Here's another view of the floor showing Tom Yost-style mounting backup plates. With the floors in I was able to get into the boat for a test fit. For a couple of reasons I decided to go with a larger, more modern style coaming. Most  important  was that I had a hard time getting into the boat. With the traditional, round coaming you enter the boat by sitting on the back deck and sliding forward until you plop down into the seat. The clearance on the masic was too tight for comfort. Also, I felt that I would have a hard time doing a wet exit through the smaller coaming.
Coaming form on boat
So, here is the coaming laminating form from Sue's kayak sitting in position - it fits perfectly! I left remnants of the masic to at least temporarily stabilize the coming.
- March 20, 2017