Kids Pirogue

[beekeeper]

Andy started this build.
"J D I am always curious, Still on a search for a lighter weight boat that younger kids can make. Is this the 5mm plywood with exterior glue? do you think it would be strong enough built uncle johns style, ie with gusseted ribs and plywood butt joints with scabs over the joints. trying to cut down on build time and epoxy exposure."

I decided to build this boat to answer that question and some other thoughts I've had. I can answer most of this question now and have not finished building . Gusseted ribs, exterior wood glue. and plywood butt joints work just fine without any epoxy exposure for a UJ "style" pirogue.
The 5mm luan is rated for exterior use. I think it will require some extra steps/support for use in the floor.
Should have made better picture of ribs. Simply put side piece on top of floor rib and used two pieces of 5mm ply attached (glued and fasteners} on each side. I trimmed them flush with router but hand saw or belt sander would have worked. My attempt to make the arrow head shaped stem pieces failed so I went with how I usually do them. This would be easier for young builders if they are doing the cutting.

---

 

[oldbuffpilot]

Thanks J D ! Hearing this from someone else(more knowledgeable in the style) helps me. I gave up on the Arrow head shaped stem after the first one. I found that some 10 year old can learn how to set up the saw to duplicate the stem angle THEN I plug in the saw a cut it for them. John has a pasel of grand kids, (our Great grandkids) all outdoor types I can't wait!! In a few weeks I be back to clear up how to easily handle flair and chine angles.
Thanks

Andy

 

[beekeeper]

Lets talk rocker, flare (angle of the sides), cutting an arch in the sides and stem angles.
I first assembled the boat 11" tall sides, sides angled (flared) 15 deg. (per plans), and the stems angled forward at 30 deg. Plans call for 45 but I don't like that look and you loose some bottom length. A not too precise measurement indicated about 3" of rocker.

Thinking the 45 deg. angle might reduce it I cut stems to 45 and cut the sides to fit. It did reduce the rocker but only about 1/4". It also reduced the floor length 3" to 4".

Changed back to the 30 deg. stems. I then cut the bottom edge /chine line of the sides with an arch. It is 1.75" high at mid ship. This reduced the rocker to aprox. 1.5" to 1.75". Side width was reduced to 9.25" mid ship. They are 11" at the stems.

This started as a 12' boat, For a 14' I would do 12" sides and start with at least 2" cut out for the arch.

 

[beekeeper]

After installing the gunnels I turned the boat bottom side up and installed the chine logs. They will eliminate the need for epoxy/fiberglass. One might considering using 3M5200 marine glue if building for other folks kids. It is rated for use below the waterline. Gluing/nailing the floor to the ribs and chine log will make the joint strong enough.
The logs can be as simple as a batten strip with 90 deg, shoulders. I chose to make these by cutting a 1/2" X 1.5" strip off a 2" X 4'. I then ripped it down the middle with a 15 deg. (same angle as the ribs) cut. This gave me 2 logs 1/2" X 5/8".
The widest side faces the sides of the boat with the pointed edge up. All this does is reduces the sanding/planning needed to level them with the bottom. If you chose to use the 90 deg. batten there would be even more material to remove. The log's edges will be level/flat at midship but will change as the sides become more vertical at the stems.

I start by leveling the chine logs with the hand plane. 40 grit sandpaper attached to a board longer than the width of the floor the used to dress them to a precise fit. A belt sander will work but I can't get as tight of joint with it because it tends to round over the edges and no relationship to the other side.

 

[beekeeper]

Clamped the plywood for the floor in position and traced around the chine logs. Cut out the bottom with 1/4" overhang and then glued it in place.

The router with trim bit was used to cut the excess over hang.

Finished fitting the bottom flush with a hand plane and belt sander, also rounded the floor and chine logs at the stems.

 

[beekeeper]

It is a boat, meaning it will float.

 

[jdupre']

Yep, looks like a boat. Should make a nice craft for a kid.

 

[oldsparkey]

Sure loooks like a boat. I would say it's a boat in the raw since the finishing coat is not on it ....yet.

 

[oldbuffpilot]

Thanks JD,
This helps a lot. Today I was settled on a boat (design) and ready to write it down, it was straight sides (no curve) for simplicity. Then I woke up a while ago thinking about your sanding stick for chine logs and got out of bed to look it up and found your post. Don't know how I missed it. I was thinking how more flare would be good and easy for older kids or even adults to build. I opened the computer and complete with pictures was my future boat that was keeping me awake! You and Joey have been very helpful..
Back to bed,
Andy

 

[beekeeper]

The boat does need some finishing work to elevate it above the "raw" condition it is in. That will have to wait until some more construction work can make it into a more practical boat.

The 5mm floor is too thin and flexible to be serviceable. Normally the solution would to cover it with fiberglass and epoxy. That is not an option because oldbuffpilot did not want to expose children to the epoxy. The simplest solution for someone starting a similar boat would be to use thicker wood for the bottom. That is what I would have done but the question was "will 5mm luan without fiberglass be strong enough for a UJ pirogue style design?"

Right now it is not strong enough for anything but very delicate usage. Can it be made strong enough for practical use? These are some possible solutions and thoughts. Please add any other ideas or comments you might have.
1. Add more ribs/floor braces. Neg. = more clutter to the floor.
2. Add two bottom runners/keel strips to the length of the boat.
3. Install another layer of 5mm to the floor, at least between the ribs. Neg.= More weight, hard to fit in place.
4. Tear the existing bottom off and install a stronger one. Neg.= Not easy to do, time consuming
5. Install another 5mm bottom on top of the existing one. This would be a total of 10mm ply in the floor. Neg. = Weight but it might be the easiest, fastest and most likely to succeed solution.
6. Poor Man's Fiberglass the bottom. I have some 9 oz. canvas and a gallon of glue. Not sure if this will be ridged enough but sometimes "you have to go to know."

 

[oldbuffpilot]

Thanks for doing the testing, it's been a big help and very informative. It will be a while before I can give it a try for experience. We need to finish up the current boat. I suspect your documentation will help a lot of people, and more kids will get the chance to be outside in their own boat. That's a real plus for all of us.

 

[ulav8r]

I would be tempted to try ribs on the inside of the bottom. Run them between the frames, one down the center and one or two on either side parallel to the center rib. Maybe 5/16" thick for the center rib and 1/4" for the others. 3/4" or 1" wide of cedar, cypress, or yellow pine.

 

[beekeeper]

I had not considered running the braces down the center. That would be structurally similar to using the keel strips.
The 5mm luan is not very stiff and I don't think it offers much puncture resistance. Right now my two best choices seem to be either continue to experiment and try "poor man's fiberglass" or pass the boat to someone who wants to epoxy/fiberglass the bottom.

 

[ulav8r]

Reinforcement on the interior will add more stiffness than the same on the exterior as water, rock, or logs pushing against the bottom will be trying to stretch the interior and most reinforcement materials are stronger in tension than compression.

Fiberglass on the inside would provide the most strength against punctures. I don't know which would add the most stiffness but if you glue in runners and it is not stiff enough you can add another layer on top to double the thickness of the runners. Putting on them on the inside will leave a slick bottom that will be harder to hang up on submerged whatever.

 

[beekeeper]

I understand your point about putting the fiberglass on the inside . It would offer more resistance for stresses coming from below. Fiberglass would have been the proper method for building with this thin of plywood. It is basically a skin on frame boat. The 5mm luan is the skin. Adding more framing would tighten i.e. stiffen the floor. Inside it would add weight and clutter, outside, weight and resistance. I doubt if it would erase all the puncture concerns.
The more I build and experiment the more I realize "There are reasons they are built the way they are."
No mater how I choose to make it a serviceable boat it would have been best if done correctly from the start. The criteria was for a simple design and building methods kids could do with no epoxy exposure. I think using thicker plywood in the floor would meet those needs very well.

 

[oldsparkey]

All of my boats , especially the ones made from 1/8th inch wood were glassed inside and outside to help strengthen the wood. Also as additional protection from abrasion caused by the scuffling of the feet when inside the boat.

 

[ulav8r]

Thicker plywood would work. Also, the ribs I first suggested if wider or more of them would add more strength and weight.

An experiment you might try would be fiberglass cloth adhered with Titebond III instead of epoxy. Maybe a 4 inch wide strip of plywood and fiberglass to compare to a 4 inch strip of plywood only.

The ribs or fiberglass might save this experimental boat for further testing before having kids build another boat. Another thing to check is the weight of rib material versus plywood. Cut another piece of 5mm plywood and compare the weight to the same volume of of rib material. It it were a 4 inch strip the same length as the test with fiberglass and Titebond, then you could do a direct comparison of the bending of the different methods. If you want to add plywood to the existing boat I would try a panel that was 2-3 inches narrower than the front and rear frames. That would leave a 1 to 1 1/2 gap between the panel and the chines at those frames.

 

[jdupre']

Idea. Cut a piece of 5 mm luan to the exact shape of the front walking area of the boat's floor. When fitted, cut out square or round "lightening" holes in it and then glue it down........ a bit less weight and a bunch more strength.

 

[beekeeper]

I'm still trying to decide which solution to use for the bottom.s issues, but I did weigh the boat today. It weighed 26.1 lbs.

 

[jdupre']

26.1 lbs is great. BUT, a light boat where your foot goes through the bottom is not great. 5lbs of reinforcement is a small price to pay for more durability.