How we designed and built a folding dinghy for under £350

 A dinghy provides an sizable quantity of amusing to a cruising excursion, but on a small boat there's usually the trouble of wherein to stow it. 2 stroke vs 4 stroke

hold it on davits and it gets within the way in tight manoeuvring and it is able to block the view astern; storing it on deck is often a nuisance.

Our first yacht became a 2d-hand Moody 31, which came with a neat Avon inflatable and outboard. We could stow it beneath and inflate it speedy, however we hated the gymnastics worried in mounting the outboard and didn’t like wearing petrol.

As we labored out our style of sailing we realised that we not often really needed the motor. In a non violent anchorage it became most popular to row quietly, and our dinghy rowed as badly as maximum inflatables.

The a great deal-cherished Moody became our weekend and holiday home for eight years and that was the dinghy we had.

Gordon retired in 2010 and we had our Sirius 310 deck saloon boat built. Alison was nevertheless working, so we stored Alshira at the builder’s base in north Germany through one summer time and got to know her.

Alison loved being able to see out as she navigated, and a trudge homeward down the Kiel Canal in pouring rain confirmed the benefit of the inner guidance position.

We preferred being capable of make the longer passages with both people interior, warm and dry.

The 360° vision changed into important. And that created a hassle for dinghy stowage on deck.

There had been first rate industrial folding dinghy designs and nesting tenders available on the market, such as the Banana Boat and the Porta Boat, but the versions suitable for 2 adults stow at full length (over 2.5m), so would should be lashed to the stanchions blockading our view. we've a self-tacking jib, and so can't carry some thing like a Nestaway at the foredeck.

We were also at the restriction of our boating finances.

but there was a easy solution which appealed to us. in view that we had extensive experience of making plywood kayaks, why didn’t we make a plywood folding dinghy, tailored for storage in the technical room?

We handiest once in a while have traffic and one cabin on the Moody had constantly been ‘the shed’. On our new boat we opted to have handiest one cabin. as well as giving us a much large cabin and heads compartment, we now had a technical room under the raised saloon.

properly, it became out to be now not quite that easy…

a way to design a folding dinghy

before slicing wooden we wanted an exact layout, however it changed into Alison’s concept to make a version which helped us recognize a number of crucial features of the concept.

1. each aspect panel is joined to its backside panel all along the chine. whilst the boat is folded up, the side panel lies flat on pinnacle of the lowest panel, that can handiest show up if the adjacent curved edges are precisely the identical shape.

2. this primary point dictates that after the dinghy is spread out the lowest panel will bend up at the bow and stern creating rocker, or curvature, on the underside of the boat.

3. the amount of rocker relies upon on how a great deal the perimeters lean out.

4. The gunwale isn't a easy curve way to the quantity of rocker and the specific angles of the panels while the boat is unfolded.

a way to make your very own oars

Our oar shafts are not the same old circular pass-phase – an elliptical form saves weight and is simply as robust in the direction of pulling.

A long time in the past we decided that it's miles better to apply a steel rowlock than a timber thole pin. We use a peg through the shaft and a cushion of rope to prevent the oar from sliding via the rowlock.

The blades of the oars had been made via laminating three layers of 3.8mm marine ply pressured right into a dish shape with the aid of an meeting of clamps. The blade is glued into a slot within the shaft.

First strive at constructing a folding dinghy

The technical room on Alshira is 1.8m long and so we reckoned that the dinghy must not exceed 1.4m.

that might still give us a usable smooth.

looking around for ideas, we had been inspired with the Flapdoodle design. It was too huge for us however gave us valuable ideas.

We commenced constructing in the cold iciness of 2010 – too cold to apply the storage for production, so the spare bedroom became the varnishing station and the living room was the boatyard.

The simple shape of that first strive turned into a success, and we have saved it through successive builds:

The boat had a single chine. each aspect could be folded inwards on top of the bottom board.

The slim principal strip furnished the room for the 2 halves of the boat to fold collectively to give a bundle that might be carried below the arm.

We reduce the panels for the hull in 6mm ply and stitched them together with nylon fishing line.

The joints have been sealed with plastic-covered cloth, held tightly to the panels through screwing strips of 6mm ply over their edges.

The fabric included the bow and stern, with 6mm ply panels slotted in in the back of them.

The seats have been 10mm ply for electricity. 2 stroke vs 4 stroke

The woodwork seemed accurate and the boat become amazingly sturdy.

but the power got here on the charge of weight – much of the hull became a double thickness of 6mm ply – and even worse, it leaked. We ought to by no means get the ends of the boat completely watertight. So ultimately we gave up and started once more. 

A Mark II folding dinghy

It became critical to get the load down, so we switched to 4mm ply and screws were banned. We needed to make all of the additives lock together. What accompanied is diplomatically known as a steep learning curve, however we did get some of it proper.

This layout used a transverse beam. To stop it leaping out of its mount we clearly pinned it with a chunk of 6mm dowel – a treenail, or trennel – which worked perfectly. Dowel is susceptible when bent however strongly resists shearing.

in this boat we glued water resistant cloth to the aspect and backside panels and continued the material round the bows and stern.

however again, it didn’t paintings. The material geared up the folded boat flawlessly, however it was saggy when the boat turned into unfolded and so was vulnerable to abrasion.

The nylon stitching additionally rubbed towards the cloth when the joints have been folded and spread out. And there was nonetheless the trouble of leaking on the ends of the chines which we ought to in no way resolve.

but we now had a light-weight dinghy that could deliver the 2 of us. It was a chunk cosy, looked ludicrously small, however was similar in length to our authentic two-person Avon inflatable.

but actually we may want to improve the design so it didn’t leak…?

1/3 time fortunate!

In 2012, Alison retired and we set off on the primary of our 4-plus month summer season trips, which gave us time to assume.

For ease of rowing, and further security, it might be excellent to have a bigger boat, round 2.5m long.

For stowage that would require a brand new layout allowing the boat to split into halves.

We had by no means solved the problem of creating the folding joints watertight, so the solution became to avoid this hassle altogether. We determined to make the cloth into a pores and skin that could sit down across the plywood hull, using beneficiant darts within the cloth to get appropriate overlaps. That manner we would just be gluing flat portions of cloth together, and this is reliably finished with the endorsed -component glues.

building was behind schedule even as we moved house, escaping from London to the East Coast. We constructed a workshop in the garden, however the first matters we constructed there had been lawn gates, bookcases and then a rigid dinghy and a new kayak to apply on the river across our lane.

the new folding dinghy turned into designed again first as a paper version, then, since the hull has a easy shape, an Excel spreadsheet was used to test the draught (and as a result the freeboard).

We additionally calculated the location of the centre of buoyancy with extraordinary loads, due to the fact in a light-weight dinghy the team must be able to sit so that the boat is balanced. The best solution is to use a longitudinal seat and feature two units of rowlocks. With  people in the boat, the forward rowlocks are used and with one or 3 people the aft set is used.

planning completed, it was time to start constructing. The hull panels have been reduce in three.8mm 3-ply marine plywood bought on line from Robbins wood of Bristol.

The hinge joints were made through sewing the forums together the usage of Ultima Seastrike fishing line with a 100lb breaking energy. the road passes through holes 2mm in diameter, 5mm in from the rims of the panels and spaced 25mm apart alongside the rims.

One thread follows a zigzag along the holes, and a second thread paperwork the crosses by zigzagging in the opposite course. We gave the wood multiple coats of polyurethane before sewing the panels together, so that the polyurethane ought to seal the edges of the holes (outdoors grade polyurethane from a DIY store is enough for the process).

The dinghy breaks in half at about the midpoint. because the joint does now not ought to be watertight, we truly slot the back half of between plywood sleeves attached to the inside and outside of the front 1/2 of the boat. four small, fundamental toggle latches acquired on-line from RS additives at ease the two halves collectively. 

To maintain the edges of the dinghy out, and also to assist assist the seat, we have a bulkhead throughout the center of the boat. We repair it in location with a system used at some point of the boat: at the aspect panels we glue portions of 10mm square-segment softwood leaving a gap into which the bulkhead slides. anywhere we have glued components together, we've got also drilled via them and stuck in a few 6mm dowel, to similarly support the joint without greater weight. The bulkhead is held in vicinity on every aspect of the boat by way of passing a 6mm dowel pin via it and the rectangular-segment wooden. those pins have never broken in use. 

to maximise useable space in the dinghy, the bow is squared off. A plywood vertical panel is glued to the relevant plate at the lowest of the boat, sandwiched between square-sectioned wooden. The front fringe of this plate has square-section timber glued to both aspects, down which the bow plate can slide into role. The vertical partly supports the foredeck, which locks directly to the bow plate and the sides of the boat. by the point the deck has been pulled downwards with the aid of toggle clips, the the front of the boat is becoming rigid. The equal device is used on the stern.The longitudinal seat is made in two portions. The ends are slotted to connect to the two verticals at each cease of the boat. The centre of the seat sits on the transverse bulkhead and additionally on  extra vertical ply portions, which sit on the primary plate at the lowest of the boat, close to its middle. those verticals are right where the vital board bends maximum whilst the boat is spread out, and so can not be glued into role. There has to be a few flexibility for the motion, even though it is only a few millimetres, for instance by using using square-section wooden to lure the vertical in a groove.

pores and skin and skeg

subsequent changed into the water-resistant pores and skin for the boat. We used 560g/m² p.c covered polyester from Attwoolls manufacturing, glued with Polymarine % two-component adhesive. Our sheet was 1.5m huge, enough to cover the lowest of the boat in a single piece with some get dressed-making darts. it may be cut the usage of home scissors, and without difficulty and reliably glued the usage of the 2-part glue.

All the edges of the pores and skin are folded over and glued, to offer a double thickness for resistance to ripping, and a cord runs around the boat, inside the fold, to forestall the edges from stretching.

on the bows we overlap the skin directly to the foredeck and slide the plywood structure into it. That overlap further strengthens the bow shape. similarly on the stern a flap within the skin overlaps the stern deck and is tied down the use of the wire.

On each aspect of the boat there are two short lengths of heavy responsibility Velcro, 50mm huge, to stop the skin from sagging.

The skeg is integrated inside the skin. In go-phase it has a T-form with the top part of the T secured to the skin by using glued strips of the plastic sheet. For strength, the skeg is made from 10mm marine ply. The material is powerful enough to keep the skeg in place. In truth we've had no tears everywhere inside the pores and skin in three years of use.

In use on a cruise

The folded hull stows in home made baggage in the technical room on our Sirius 310. each bag is light enough to be easily lifted out and carried to the foredeck in which the plywood structure is assembled. A spare halyard lifts it so that we are able to slide the pores and skin on, the dinghy is then diminished on the halyard into the water, and towed round to the stern for easy access. assembly takes ten mins.

The dinghy has now been used on journeys to Denmark, Norway and the west coast of Scotland with minimal put on and tear. glaringly we take care while touchdown on a pebble seashore, but the dinghy is effortlessly carried up the beach by one man or woman at each end. It rows effortlessly and is strong – an adult can stand at one facet with out capsizing it – and it tows luckily. 

The emphasis with this boat is its practicality and we don’t pretend that it’s lovely. but regardless of the lengthy genesis, its production and use have given masses of a laugh. 2 stroke vs 4 stroke