Technique

Edit:19 juil. 2012, Cre:06 janv. 2008

My small boat - the 'mouse'

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See also a study for a one-sheet motor boat

Presentation

We can find on the Internet, as 'style exercises' more or less successful, a few boats designed with one ply sheet (2500 x 1220mm or 2440 x 1220 mm).

As similar exercise, result quality varies. Needing a minimum boat, I've find that the 'Mouse' was the most realistic and effective of these design. Moreover, it is a a boat moved by a paddle, so 'facing the road', that I largely prefer to rowing, where you frequently have to check behind you where are you going, and if you are going there straightfully....
This boat have been designed by Gavin Atkin, who also have made numerous other designs, foundable on the Internet.

It's dimensions are 2.5 m x 0.75 m, for a weight around 11kg. Ply is external okoume ply thickness 5 mm, 3 layers (in Europe 1/4 inch ply, say 6.35 mm simply don't exist, thickness is 5 mm).

This boat behave well, and it's loading capacity is surprisingly high considering it's size. She behave like a kayak, but with a much better lateral stability.
The direction stability is not that good, comparable to a mono-place kayak, and the skeg is compulsory.

I've built the open model, without any floatability box, so it is required to wear a PFD for your safety, especially in cold waters.Anyways, that's wood, so she floats, but without you.
This open version, in addition to weight gain, is very easily acceded by front, having the boat front led on the bank.

This boat, for calm water navigation or paddling training, is much easier and practical than a kayak.

Original site of the Mouse is in English, and dimensions in inches. Hopefully, author supplies plans in DXF format, so I have translated in SI units (and slightly adapted) the plans. You will find here below the photo story of the building..

This type of building is called 'Stitch and glue'. We temporary assemble the boat with copper wire and definitive assembly is done with epoxy putty and glass tape impregnated with epoxy.

Whole boat is impregnated with three coats of epoxy. If you wish to let the boat under the sun, you have to add polyurethane varnish or paint, because epoxy dislike sun.

And finally you will find the proof that a 'Mouse' can enter inside a car, and not only atop.

Navigation: Mouse M87 !

I'm telling you that she is more stable than a kayak !
Paddler position is too much backwards, it is needed to move the seat to front of 10 cm (4 "). Moreover, that adds directional stability.

Seat is required, because not only it is much more comfortable, but being in higher position paddling is easier, else the boat border is hindering. And that seat will have further use for the picnic!

Construction photos

Download photos (3.4 Mo)

Outlining detail (half sheet only)

OutliningOutlining detailsCutting sheets back-to-back

For outlining, it is needed to precise that the method (nail the lath at reference points) must be completed by complementary nails at the ends, because if not the extremity tend to be too straight and will give openings when assembling..

DrillingSewingSewing Detail
UnfoldingAssembly
FilletingFiberglass + resin
Fiber + resinResinFiber+ epoxy
Fiber+ resinRabotageplaning side of glass tape
Gluing the borderProw gluingPoop gluing
Poop gluingSkeg
Ply sewingMixing resinApplying resin with a small roll
The 'Scarf' of the poorSmoothing of the angle fillet with a film boxSmoothing of the fillet with polyethylene pad
And that enters in the car
Honestly, that is not much practical...

Plans

Plan, PDF format. Design (c) Gavin Atkin.

Advices

When outlining, maintain a curve on the end of your lath (by adding some nails). If not, you will have openings when assembling.

Cut longitudinally the sheet in two parts, to outline only half of the boat. You will cut simultaneously the two parts.

Chamfer (bevel) the border of your part before sewing them. Distance between your stitches must be between 200 to 250 mm. 3mm holes must be at least at 6mm from the thinnest part of the sheet, if not the ply will cut and wires go away when tightening.

Sewing was done with rigid copper wire of 1.5 mm2 area, plastic wire envelope is removed with a cutter.

It is better to remove the wires before complete curing of the resin, but wait there is some strength anyway, in order to not have your gluing open slowly (it occurred to me, so I had to sew again..).
On the centre part, it is very difficult to remove the wires, they broke. You can cut the end with a mini-grinder, Dremel style. The wires will remains definitively in place. One suggestion have been to plug a car battery to both ends of the untightened wire, and to remove it with pliers when it is still red. I have not yet tried...

Before setting glass tape on the external angles, round them carefully with a plane, do not only chamfer them, the glass fabric will not be able to follow the angles, and you will have openings very difficult to fill.

For fabric tapes, I've cut at 45° strips in ordinary fabric. This works, but is not very nice, because the fabric thread goes everywhere, and the finishing time will be more important. It is much better to buy specialised biaxial tape, it will simplify your work.

I've made my mixing by weight. It is preferable to buy material for volume mixing (with 'mustard' pumps), more easy and more precise. Also buy mixing sticks.

Do not made resin quantity exceeding 150 grams, you will be at risk to have the resin curing in the pot before having finished your work. This is even worse when adding fillers, because adding mixing time. This is due to the fact that curing is an exothermic reaction, and that the curing go much faster when warm. So your resin will be hard in the pot before having began to cure on the boat.
Anyway, you will not need more than this quantity for such a small boat.

Tolerances of mixing epoxy are thin. If your proportions are not correct, it may arrive that you resin will never cure. Don't compare with polyester, because with Epoxy, excess of hardener will definitively block the curing.
This is the reason why insufficient mixing may block the curing of your whole batch. It is preferable to have slightly resin excess than hardener excess. Be careful and precise. And mix well.
And mix again ! Some are suggesting to sing traditional songs, or recitate poems, to complete mixing. A minimum of 100 strokes, or better 200 strokes are to be considered.

In case of absence of curing after two weeks, a hot air gun may help to scrap the uncured resin (which is toxic, as we must remind).

First resin coats needs around 150 grams for a complete internal or external layer. Last layers will need around 70 grams (this is because the ply suck the resin).

Plane the border of glass tape after the first coat, after curing. Avoid sanding, this is being potentially toxic before one week curing.

I've used as filler ordinary flour for filleting. That works, but you need a lot of it (around same as resin). That is heavy and not easy to smooth. I think it is better to use wood flour. Some are using baby powder as filler.

For internal angles (around the internal part of the boat), it may be sufficient to use only filleting putty, without adding glass tape.

Though, a glass tape is needed on the middle joint, and the outside angles.

Tape weight : 300-320 g/m2, over that, it will be difficult to have the fabric follow the rounded angles, which are relatively small.
If you don't find the required width (75- 80 mm), you may have to buy larger tape and to cut it in two parts.

Glue is done by adding fillers to the resin, same as making putty for filleting.

Evidently, brushes, rolls and gloves are to be thrown after every use. Don't forget to remove the roll from it's support, if you don't want to extract it with brute force.

Estimated building time : 20 hours, set on one week ore more.
(note this is my first boat and experience with stitch and glue, so experienced users may expense lower time)

Required tools :

  • Electric saw (Manual saw is usable, but that's longer)
  • Plane with interchangeable blades
  • Strong pair of scissors (to cut glass tape)
  • Hammer, screwdriver, pliers, etc.
  • Wood rasp
  • Around twenty clenches to glue the boat sides (can be replaced by screw, which will be removed later)
  • A letter scales and dosing 'mustard' pumps
  • Small painting roll
  • Small and large cutter, with replacement blades
  • Blade scraper
  • Special soap to remove resin parts

To be thrown after use:

  • Small brushes 10-15 mm width : 2 to 3
  • Small rolls 50-60 mm width : 7 to 8
  • 20 vinyl glove pairs (so, 40 gloves...)
  • Mixing sticks
  • Throwable glasses (normal and small size)

Materials :

  • 1 sheet 122 x 250 cm of exterior ply thickness 5 mm
  • 3 laths 9 x 32 x 2400 mm
  • 1 lath 25 x 25 x 2000 mm
  • 1 to 1.5 kg of epoxy resin
  • 200 g wood flour
  • 14 m of biaxial fabric 300 g/m2 (add 6 m if you want to cover internal angles).

Option :

  • dual components polyurethane paint or varnish (special to coat over epoxy)

Your health and safety

1) Epoxy resin is toxic at skin contact while not polymerised. It creates skin allergies, sometimes lung allergies.

Base care :
  • Always wear gloves
  • Use throwable tools

2) Epoxy resin emits few solvents, but it is needed to vent your workshop.
3) Polymerised resin is chemically neutral, but it is toxic while liquid or not completely polymerised.

Complete polymerisation might need 3 to 5 days.
Base care :
  • You must not expose yourself to projections, especially while using brushes. If there is projections, use chemical protection mask for organic solvents (cartridges in active carbon). Note that the cartridges have a lifetime of 8 hours.
  • Never spray resin. Professionals who are doing that use closed overalls with respiratory systems. Moreover, it is needed to decontaminate the whole workshop.
  • You must not sand incompletely polymerised resin. It is very toxic for lungs. It means that practically, you have to wait nearly one week before sanding. So, how to do ? The only way i found is to use a cutter, a plane or a scraper for preparation. High risk to cut yourself, but that's largely preferable than destroying your lungs.
Special care : A coat of resin chemically adhere to the previous coat if set less than 24 hours after the previous coat. When polymerised, you must have a mechanical adherence between the coats, by sanding the previous coat. It means you have to do a new coat within 24 hours, or after 4 days waiting complete polymerisation. So, schedule your work very well before beginning resin work.
Before starting resin, drink something because after the start, you will not be able to do so without throwing your gloves in the bin.

Suppliers for resin and accessories

Progressive Epoxy PolymersInteresting informations about Epoxy chemicals
System threeThe Epoxy book is a must read
West systemRead the part about safety and toxicity
Mase epoxies 
Raka 

All epoxy resins are not of the same quality. I've use one I've found in do It yourself store, and aside the very long curing time, it is not waterproof in three coats... For a boat, this is a big problem !

Internet links

First, the mouse

Next, one-sheet boats

Wood-Epoxy building

http://www.bruceroberts.com/public/HTML/WOOD-EPOXY.htm

Stitch and glue building

(c) Pierre ROUZEAU 2003-2012

1rst time on line : July, 12, 2003
Last update : July, 18, 2012

(c) Pierre ROUZEAU
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