Goodwin Concave Bottom Hull Question

[Sunfish1909]

I am all cut out and have my sideboards bent and ready to assemble. I am going with the concave hull design.

 :-\When is the bottom hull skin glued to the underside? Can I transfer the template lines  to the plywood and glue it to the bottom of the hull and then proceed to build upon that? I have seen a flat bottom hull built over 6mil plastic, then the bottom skin was applied after the internals cured.  Should I build all the insides over 6 mil plastic over plywood that is tight to the bottom of the sideboard profile, sand it all equal and then glue the bottom skin on? It seems the bottom skin would help hold all the stringers up.

Which way is better / easier. Thanks

[Sunfish1909]

Me again..I just found a quote from Paul Goodwin from 2001 about his concave hull..............(this is in the "Collective Wisdom Archive)

building the hull from the bottom
skin up, that is my preferred method of construction. Ron Sherry
also starts with the bottom skin and works up. I don't recommend
it in my building instructions because I think it is harder for the
first time builder, but it saves time and provides a truer bottom
for the seasoned builder.


I think this is my answer. Still if anyone has any insight on this, please post your thoughts. I will check this post often.

[Ken Smith]

I've done it both ways.  The batch of boats built in the Pewaukee basement three years ago were done side boards first, then skins then bottom internals, etc.  With a curved bottom, this is easier, plus using a common jig to bend and assemble the side boards and structural bulkheads was possible.  Each week it was another's turn in the jig.

Once the sides are glued together with the structural bulkheads, the bottom goes on, and the rest is built into the boat.  Fitting the cockpit floor is a bit difficult, so remember to carefully mark it before you put the bottom on!  This method is easier, IMHO, for a concave bottom.  The alternative is to make a curved bench to match the bottom profile.

The bottom-up construction has some advantages for a flat bottom boat.  You lay out the hull shape on the bottom skin, build the listings and structural members on the bottom skin.  The cockpit floor is far easier to fit, make it oversize, and trim with a router and a formica edge-trim bit.  All the internals are done first, so teh side boards can be formed over teh internal structure without another jig.

Now two confessions:  I bought and used Paul's plans, but never followed his instructions.  Read them once or twice, but never studied them.  As I sit here, I am not sure exactly what Paul recommends.  He has built many boats more than I have, so trust his advice.  The Pwewaukee boats were built on a jig that slightly modified Paul's plans, making the fuselage a bit wider at the feet.  The side board profiles were also slightly different, using a template pulled from a Sherry hull.  I am very happy with mine...

[Sunfish1909]

..........side boards first, then skins, then bottom internals, etc.  With a curved bottom, this is easier, plus using a common jig to bend and assemble the side boards and structural bulkheads was possible. 

Once the sides are glued together with the structural bulkheads, the bottom goes on, and the rest is built into the boat.  Fitting the cockpit floor is a bit difficult, so remember to carefully mark it before you put the bottom on!  This method is easier, IMHO, for a concave bottom. 

   :)Very much appreciated info Ken. Thank you for the "ice-breaker" response to my dilema of how to proceed.   Pete

[Rick Lemberg]

We built 5 goodwin plans here at Wawasee 2years ago and the boats turned out great. Ken's right on making sure you pre mark your cockpit floor. so after you have the bottom on you can fit the cockpit floor in with not much cutting and fitting, if you forget to pre mark the next best thing is after the bottom of the boat is on you can make a pattern out of paper for the cockpit floor.  Rick lemberg DN4155

[cmgordon]

As a first time builder, who built the concave bottom ( and told later that it was too difficult), I found it easy. But I did it like this.

I put the plans on a table and covered the whole thing with a sheet of 6 Mil Poly. I could then jig up the whole thing off the plans. I DID NOT apply the bottom skin first nor flip the hull over. I needed to use the plan for correct placing of all listings and bulkheads without trying to transfer them after they were hidden. In all areas, mostly the front/mast area, I shimmed up wood strips up to the bottom of the sides with high quality wax paper on it. I could see the plans through everything and the glue wouldn't stick to the spacers. Because I had made screw down brackets to hold the shape and hold the clamps, I didn't worry about the sides raising. Removing and excess glue from the botom before applying the bottom skin was all I needed.

Had I covered the bottom first, I would have really had a tough time building the critical seat back area. Those who have built a lot of boats may do it differently. I can't see mself doing anything differently if I were to build another boat. At least in this area.

CMG

[Sunfish1909]

I am building the concave version too for a Super DN restoration. My table has the plan on it under 6 mil too. I used carbon paper and transfered all the listings to my sideboards as well as the side board profiles. I cut my sideboards out and re-sawed for the curve, bend. I also used the carbon paper (several sheets taped together) to trace slide all the floor plan listings to the inside bottom of my floor skins. I have built all my bulkheads and mast step and installled them flush, by sanding, to the top and bottom edges of the side boards. I will be gluing my bottom skin in soon and will have all my listings in carbon trace lines to glue the stringers to. I had to flip the hull a couple of times during sanding, but still pretty easy to do. Thanks Paul for some really well done plans to work from. I will be posting photos of the construction  on the J14 site. See ""Pete's Boat Restoration"" photo file on the J14 site. Pete