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Old 02-20-2006, 09:17 PM   #1
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Foam Marsh Boat Construction Part 1

In summer of 2005 I was thinking about a KARA, but these surfboard boats just looked too tempting to try and build. However, I did not like the square styles that everyone has been constructing. I really liked those duck canoes that used to be made in MN – Hoegren, Hoefgren? So here is the “Monitor” with a cockpit with rounded ends. The rounded ends just seem to make it a little more “classy” looking. Structurally they also more easily transfer stress around the boat hull better than square corners.

This boat hides very well in our grass up here in AK. It actually does too well, because I couldn’t see the ducks until they were right on me. I had never shot from a layout position before and was not able to mount the gun in time to connect with a bird. It was really fun to have them in my face though. It holds 300 pounds very well, but I have never tried to sink it by filling it with water. It paddles best with a long double bladed paddle while you are sitting on the floor in a kayak seat or on a MoMarsh Invisa lounge chair. You could use a bird and buck folding chair but they are made with outdoor patio chair foam and let water in so they won’t float. The Invisa lounge is made with the same foam as PFD cushions and can be used as one even though they have yet to be given Coast Guard ratings.

The following is the basic “how to” of building this boat. I have not inserted all the knowledge I have gained from reading the many books (Devlin, Kulczycki, and Schade to start) on boat building. There are a lot of technical gaps for the novice to fill in, but with the great online sources at RAKA, WEST System Epoxy, Glen-L, and other places this is not a major issue for anyone that is “handy.”

I started with three pieces of 4 foot by 8 foot by 2 inch EPS foam (blue is all there is in AK). The third piece was cut in two and glued to each end of the 8 foot pieces using staggered butt joints and polyurethane glue, making a 12 foot double layered “hull.” I do not have a flat garage floor so there were some problems with small gaps between the layers of foam. I filled with expanding foam as best as I could, but gaps remain in some areas between the two layers.

The first photo group shows the lay out of the curves and bends. I used a length of ash scrap as a batten. I stuck 16 penny nails into the foam to hold the batten against. The nail head keeps the batten from jumping up when being adjusted or drawn against. I used construction paper to draw the end curve on for transferring to the cockpit floor piece later.

The upper left photo in photo group 2 shows the bow or stern measurements from the center line. The lower left photo in group 2 shows the measurements from the center line for the layout of the rounded cockpit. The final curves did not come out to these dimensions because I figured out that these measurements made a cockpit much longer than what I wanted – 7 feet. Upper right photo in group 2 shows the bottom of the cockpit after being cut out of ¼ inch ACX plywood. It is 30 inches wide. The lower right photo in group 2 shows the piece that will be bent around the end of the floor. They are 9 inches wide. I used a ¼ inch up spiral bit in the router and free handed the cuts along marks about 1 inch apart. I recommend using a traditional router bit or clear out the shop to use the table saw for cross cutting grooves in an 8 foot long board one inch at a time. What I found out later is that my ash batten bent much better than the ¼ ACX even with the grooves. I recommend using the same material for the batten as for the cockpit. The two end pieces are a full 8 feet each and were about 2 and a half inches short of making a full enclosure of the 7 foot cockpit floor piece.

The upper left photo in group 3 shows the rounded ends stitched to the floor piece with zip ties. I love zip ties. I will never stitch another boat with wire. I you leave them in. No welders. No battery charges. No propane torches. Did I mention that I love zip ties? The lower right photo shows my zip tie assistant. I could not have bent the side pieces and held them in place for stitching without her. Upper right photo in group 3 shows the cockpit with the inner floor seams filleted and taped with 8 inch glass. Prior to glassing, I filled the grooves with epoxy thickened with a 50/50 mix of wood flour and fumed silica (cabosil). I also placed a second strip of glass tape up to the top edge of the cockpit. I used the shelf brackets to hold the cockpit as flat as possible on my shop table. (Table is 24” bi-fold doors on small horses.) I had to epoxy in small filler pieces between each end piece, and then epoxied on an over lapping piece to hold it all together. I could have just moved one end in 2 inches and made a shorter cockpit, but I wanted 7 feet not 6 feet 10 inches. Lower left photo in group 3 shows the cockpit after all the epoxy has cured.
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Old 02-20-2006, 09:20 PM   #2
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Foam Marsh Boat Construction Part 2

Upper left photo in group 4 shows the rough cut “surf board”. It is 42 inches wide by 12 feet long. I shaped the bottom edges to give it a little more roundness like the hull of the KARA. And then, much like the dudes that make real surf boards, I used a powered hand planer to shape the edges and bottom. A word of caution: I nearly ruined my tool doing this. The surfboard dudes said they used a “modified” planer, with no mention as to what the modifications were. My Bosch has an opening in the belt housing that let the little pieces of foam in which then melted and nearly turned the belt to goo. It did melt/bend the plastic belt housing to such a degree that it will no longer fit the tool. I would guess that the surfer dudes mods were a larger chip vacuum uptake and a sealed belt housing. The lower left photo in group 4 was supposed to be in the next grouping. I cut out a large dado for the front deck board thinking to keep it at the level of the foam. I used the power planer and ran into some more problems in that the planer is not made to cut a dado. I didn’t do this on the back deck. Lower right photo in group 4 shows the bottom layer of 10 oz glass on the boat. I filled all the little holes in the hull with thickened epoxy prior to glassing.

Upper left photo in group 5 shows the bow deck board with the 10 oz cloth over it. I set it in thickened epoxy. At this point I had forgotten that my cockpit was shorter than the layout lines on the hull, so the deck board does not extend all the way back to the end of the cockpit. The lower left photo in group 5 is the cockpit placed onto the surfboard deck and held down with any large heavy object at hand. Notice that the front of the cockpit does not meet the drawn curve on the deck. That curve was for a longer cockpit that I didn’t want once I started laying things out. The cockpit was set into a layer of gooey epoxy spread over its underside. I also wet out the glass covered deck where the cockpit would sit. Upper right photo in group 5 shows the cockpit with a fillet around its outer seam where it meets the deck and glass tape over the fillet. Lower right photo in group 5 shows the boat on edge getting the edge final shaped and glass taped. The 10 oz cloth did not bend nearly as well as lighter weight material even with some good edge relief on the top deck.

Upper left photo in group 6 shows the two keels in place. I made the keels out of scrap 9mm okoume plywood laminated together with epoxy. This step took some head scratching to accomplish. I used 4 inch long deck screws as barbed pins to hold the keels down to the hull. With the thickened epoxy you don’t have to get things really tight and firm with the clamping as long as things stay put for the entire cure time. Once the epoxy had cured, I removed the deck screws and then filled the holes with ash pins and epoxy. Should I have taped over the fillets? I will find out, but so far in the moving around in the shop and outside the keels don’t give much. I am worried that I will ram something some day and push a keel right into the foam through the 10 oz glass and epoxy. We will see. The other three photos show the gunnels I built up around the edge of the cockpit. I have lots of scrap 9mm okoume plywood from building the BB3 and need to use it up as much as I could. I cut six one inch wide strips and then used the table saw to cut relief grooves into 4 of them. The grooves are about a half inch apart and to the mid point of the middle layer of wood. I then filled the grooves with thickened epoxy prior to clamping them to the boat. I double layered the strips around the outer edge of the cockpit. Since I had the pieces of ¼ inch ACX covering the butt joints I had to taper fit short inner filler pieces to meet up with them and give the outer full strip something to fit against. The tapers were just eyeballed on the band saw and then filled with thickened epoxy as gap filler.

At this point I should have thought about the outer strip becoming a grassing rail. I could have made larger gaps in the outer strip and used that to stick grass in. Instead I used bungee cord held down by plastic cable straps. This is not nearly as cool as grassing rails would have been. However, the bungee cord makes for easier maintenance since water can get into the grassing rail gaps and cause some issues with the wood over a long time.

The gunnels are what give the ¼ ACX plywood cockpit its real strength. If this was not done then the sides of the cockpit would be really floppy and not strong enough to support the weight of the boat or a person bracing against it. The gunnels are also what allow me to use the ¼ inch plywood rather than the typical lumber that other folks have used on their foam boats.
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Old 02-20-2006, 09:21 PM   #3
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Foam Marsh Boat Construction Part 3

Here are the final photos before and after painting. Sorry for the fuzzy photos. I think there is something up with the light meter or auto focus on the camera. Prior to painting, the boat looked huge and ugly. After the first coat of FME went on, the boat started to look “sexy” and smaller. In the lower left photo in group 7 you can notice the buried front deck board and the raised rear deck board. The lower right photo in group 7 shows the raised rear deck board. I left it outside over night and there was heavy dew in the morning so it went back into the garage drying out for a few days before I could finish the paint.

For grassing it up I attached black ¼ inch bungee cord around the gunnel. You have to find a way to hold the bungee down about every 8 inches or you will spend all your time picking up the grass that falls out each time you go to put more in. You can build wooden hold downs or use zip tie cable mounts with an adhesive backing. Make sure you stick these to the epoxy surface and not the painted surface. You could use netting. You can even build a set of fold away doors. There are endless options all of which have been covered on this site at some prior time.

Problems Encountered During Construction

I ran into several minor issues while building this boat.
The first was not having a truly flat surface to build up the foam core of the hull on. No easy solution to that one for me.
Using polyurethane glue resulted in unexpected problems. I have used gorilla glue before and it was easy to deal with on wood. However, on foam it is the stronger material and when sanding it will remain behind and the foam will go much too easily. It is also hard to cut with a knife.
ACX plywood is made to be laid flat. It has enough crappy grain and gaps in it that you can never tell how it will bend until you bend it. Be prepared for kinks in the fair bends that you make. Building the bends to the amount of stress the plywood can take before breaking is a better plan than trying to make it fit a curve that it can’t. If you look closely at the third photo group you can see that there is about a ½ inch of the floor piece sticking out from under the side piece at the center of the bend. That is the difference between the plywood bending and the ash batten bending when the lines were drawn.
I have used WEST epoxy on two boats. I really like it and its predictability, and there is a local dealer in Anchorage that breaks down their bulk containers into gallon kits for retail sale. However, it is still costly. To save money I used RAKA epoxy on this boat. I saved about $80 on the amount of epoxy that I needed. However, I noticed that there are some major differences between the two materials. RAKA stays rubbery for a much longer time than WEST does. This lead to some schedule delays in getting the boat together. It was more than likely due to the lower ambient temperatures I am working with up here. RAKA is made in FL so they don’t have to deal with 60 degree days too often. My experience with WEST showed me that after about 4 to 6 hours I could come back and sand or continue some aspect of the project without worrying about affecting the previous work. With RAKA I was looking at 12 to 16 hours of cure time before I could come back and work on the boat. I also used WEST on this boat to build the gunnels. I only had enough RAKA to finish the buildup coats on the hull, so I used some left over WEST on the gunnels. It was the predictable 4 to 6 hour cure time and sped the construction process up by two days.
The edges of the foam that was power planed off on the under side of the hull had a tendency to “off gas” during glassing. It did it after wet out and during the next two coats of epoxy. Weather wise there were high and low pressure systems so I don’t know what was going on. Areas of the hull that had not been power planed didn’t off gas at all. My guess is it has something to do with the structure of the extruded foam. If air can get out, then water can get in. Something to keep my eye on as time goes by.


Epoxy and glass (RAKA and glass plus shipping to AK) $267
Foam $63
Paint (FME from Lock, Stock and Barrel plus shipping to AK [only half the paint was for this boat so it really should only be $72]) $125
Hardware and other misc. stuff $25
Plywood 4x8x1/4 ACX under layment $25
This does not include about $25 in materials left over from other projects.

So for about $500 I have a marsh boat. BTW the Sportsman’s Warehouse in AK sells 120 pound Stealth 2000’s for $899. My boat weighs 82 lbs. It is heavier than I expected, but not by much. It is much lighter than a built-to-plan KARA
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Old 02-20-2006, 11:37 PM   #4
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Excellent documentary on foam marsh boat construction!! I especially appreciate your candor in making known your "mistakes". A great help to all of us that are considering foam as a building medium.
I'm curious as to where the water line is with 300 lbs in it; how much freeboard left on the foam?
Good luck with your next boat project, the Maxi Hybrid. Hope that you'll offer a similiar documentary on that one.
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Old 02-20-2006, 11:57 PM   #5
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good job now ya got me wanting to build another one
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Old 02-21-2006, 10:50 AM   #6
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free board

With me sitting at the "back" of the cockpit the back deck is awash by about 1/2 inch. The bow was still on the water with about 2 inches of free board. It paddles well, but my stronger right side shows up with the strokes and I have to fight the slight shifts in line.
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Old 02-21-2006, 09:28 PM   #7
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Great Job!
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Old 02-21-2006, 11:38 PM   #8
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Otterbfishin said it right, Good job! thank you http://refugeforums.com/ubb/smile.gif
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Old 02-22-2006, 09:56 PM   #9
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nice boat ! would it have helped to have another layer of foam up around the cockpit
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