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Marisa Build Sequence

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I am trying to visualise the Marisa build sequence. I have looked at lots of pictures and build threads but still can’t quite work it out. 


I have built 2 previous “stitch and glue” designs where when the boat was flipped (having glassed the outside), the frames/ stringers which had acted as temporary molds were removed, then the inside was sheathed in glass, and then the frames and stringers were glued and taped into place over this. In some ways it seemed a laborious approach but the boats went together quite fast.


Am I correct in assuming that with the Marisa the hull panels are glued to the stringers and frames when the boat is upside down? 

Then you flip it.


What happens at this stage? Do you fillet around all the frames and stringers, and do they get taped in place?


Does all plywood on the inside between the frames get a layer of glass? 


Edited by Thomas Dames
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Yes you are imagining it correctly. The Marissa uses only her actual permanent bulkheads to define the shape and the bottom and side panels are glued to these as well as the keel, chine batten and side stringer. We also use the cockpit sole panels as part of jig sitting on a pair of saw horses to keep the frames square to one another and to ensure the cockpit goes in perfectly. This is covered with plastic and then after flipping up right is pulled out so the interior can be glassed and epoxy coated. All of the interior gets a layer of 10oz glass (with extra glass on the chines). The frames and bottom stringers can be pre coated with 2 coats of epoxy and sanded prior to assembly but if done carefully the entire inside can be completed with almost no sanding. The key is to not get ahead of yourself and work neatly. Do one bay fully then move to the next always hot coating until you have the glass and 3 coats of epoxy done. Here is a short jig setup sequence. 



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Thanks Alan - I must admit that seeing the sole in place in lots of build photos I had looked at - prior to the addition of the hull panels is probably what was confusing me the most. Now that I understand this is a removable “component” of the jig it makes sense. 

Is the sequence similar for the Ocracoke series? 

Is this build sequence faster than the one I had described or is it’s main advantage in that the frames define the hill shape more accurately - as you mentioned?


I am going to assume weight/ strength wise they would be comparable? 

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The Ocracoke build sequence is similar but we use a strong back that the frames are set up on and some completely temporary frames (green) which are removed and tossed after the boat is flipped upright. Also since the Ocracoke topsides are strip planked those boats (the ocracoke and outer banks series) must be built upside down on a jig and couldn't be stitch and glued. Marissa is all developed panels bottom and sides. Below is the Ocracoke bottom planking going onto the jig. 


In contrast, the Marissa was designed to be easier to build and thus not require the strong back hence the use of the cockpit sole. I'm not sure it's a matter of faster so much as necessary for a boat in this size range since Marissa's Hull is only 9mm plywood. If the boat was built up right you'd need just as much support in the form of exterior cradles to define the shape to keep it fair which would entail a lot of extra cradle parts and add to the cost. Why do that when you can just use the permanent frames and be done with it. Additionally the boat is already upside down so the bottom can be finished, glassed, faired, primed, painted and bottom paint and keel protection applied all before the flip. That way only one flip needs to happen whereas an upright build needs to be flipped twice at the minimum. 


I think the Marissa could be built upright with cradles as described and another designer and friend Adam from salt boatworks builds his kits this way. Here is a picture of his latest 18 foot kit. But you can see the extra cradle parts i mentioned. This build is simliar to our sailboat builds such as the Core Sound 17, 20 and the Mark 3 designs and could be adapted for the Marissa but the Ocracoke with it's strip planked sides would always need to be built upside down. 


Below, screenshot from saltboatworks 18' design. 





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I just want to clarify a couple points to avoid confusion. The sides of the Ocracoke and Outer Banks designs are planked with two layers thin plywood glued together after the 4 x 8 sheets are cut into narrower strips and fitted. This is done because the sides have compound curves (curved in two directions) to get the flare. This method is called cold molding. This is not to be confused with strip planking which is a very common construction method consisting of thin strips of solid wood edge glued over the hull.


The term developable means that a flat sheet can be bent in one piece to the desired shape without stretching the edges or shrinking the middle. As an example you can take a sheet of paper and roll it into a cylinder or a cone. It can be heavily curved on one axis but must be straight on the other axis. Now try to wrap that sheet of paper over a globe and it will be instantly obvious that it cannot go without crumpling the edges or cutting darts.


Developed panels are used in many of our designs and by carefully manipulating the surfaces you can get some excellent shapes, coupled with stitch and glue, makes for a good quick jigless build. The downside of jigless construction is lack of accuracy. On non planing hulls it is accurate enough.


When designing Marissa, I attempted to build jigless and maintain the accuracy of a jig built boat. By using the boats structure as a jig you save the cost of cutting and purchasing disposable materials. The self draining cockpit sole set on a couple boards on a pair of saw horses became the jig base.


To get the performance that I wanted necessitated keeping the hull light. To achieve a desired strength you can go with a thin skin with lots of internal structure or have a thicker skin and less internal support. The latter method will be heavier. 


The advantage of using the cockpit as the base, means that the boat cannot be out of square as both sides are identical, we proved this later when the cockpit was removed to finish the inside bottom, putting it back in the boat we deliberately put the port half in the starboard side and starboard into port, it made no difference (that had never happened to me before).  While 9 mm ply can be a bit wavy, when the frames fit into their slots in the cockpit and the bottom stringers fit into the frame slots they straighten and true each up. 


I would not attempt to build a Marissa upright because you would never be able to get all of those pieces to fit without trimming after the fact, losing the methods main advantage.


We design our boats to a resolution of one thousand of an inch which is also the resolution our CNC machine is set to. Do we get parts cut to within .001" (.025mm)? No, there is backlash and bit deflection to account for, but we get close. For example when we cut solid wood we cut the part .01" oversize and cut it again to size. This trim cut has very little bit loading, making a more accurate part.


Our full size templates are printed from the same files that we use to toolpath our CNC files from. On larger boats like Marissa they are printed on mylar, while expensive, it is dimensionally stable and will not expand and contract with changes in humidity. Therefore a home builder can build just as fine a boat as the kit builder if he or she is a good and careful craft person and has a longer attention span.



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