Duck Punt - with a twist

Some may remember last years boat build project, a 16ft skin-on-frame rowing boat (see here: http://www.boatdesign.net/forums/boat-design/beautiful-skeleton-37456-4.html) that I designed from scrath and built partly as an entrant in a race for boats powered by cordless tools.

This year I've decided to enter the "Cordless Canoe Challenge" run by Watercraft Magazine, again, but have opted to go for a lighter design. I discovered a simple little hull form from a thread on another forum, with some super videos of it sailing well with a tiny Optimist sail. (see here: http://www.keepturningleft.co.uk/category/duck-punt-films/). I drew up the plans for the West Mersea Duck Punt in CAD and then fed the lines into a couple of hull resistance programmes. Despite the simple flat bottomed hull form she's a surprisingly easy driven hull, much like a canoe, but with a bit more initial stability.

As someone who can never leave well alone, and also as someone with a general aversion to working with wood to a good standard, I decided to take the Duck Punt plans and tweak them to build a super-light hull for this competition. Budget was a consideration, and ruled out super high performance materials, so I decided to use some 10mm thick insulation foam that's intended for use with underfloor heating. It's a fairly low density extruded polystyrene foam and some experiments showed that it was just perfect for the core of a small, lightly loaded, composite boat. I've used the same type of foam to make aircraft parts in the past, in fact I helped a friend build a Rutan home-built that was entirely made from epoxy glass covered XPS foam, so I'm reasonably confident it'll work OK. It's main advantage is that it's dirt cheap when compared to "proper" core materials.

A day or two of work saw the plans converted into a build jig and this morning I went out and planked up the hull sides. Working with this foam is great, it's really easy to cut it to shape and fit it to the jig with tape. The jig is covered with parcel tape to stop anything sticking to it and I've used a 10mm x 12mm strip of softwood around the internal edge of the gunwale, both to ease alignment of the foam sheets and to give a hard edge to better resist knocks.

The foam is glued to the internal gunwale and to adjacent planks with PU adhesive, the foaming stuff, which seems to work pretty well. As soon as the glue on the side planks has cured I'll trim up the edges and fit the bottom planks. Then it'll be on to sanding a radius on the corners and laying up glass cloth and epoxy for the outer skin. When that's cured I'll lift the hull off the jig and glass up the inside.

One advantage of building a small boat this way is I get a fair bit of built in foam buoyancy, around 40 kg of it. As the hull will only weigh around 12 kg (I hope) it will effectively be an "unsinkable" boat. Mind you, the postman called mid-morning and reminded me that it was the centenary of the sinking of the Titanic, and they reckoned that was unsinkable, too............

 

Good on 'ya Jeremy!

Fortunately, we now understand the difference between positively buoyant and "unsinkable".

That only took 100 years!

Keep the pictures and learning experiences coming.

Best of luck.

-Tom

 

Cheers Tom.

I discovered something curious about this foam - it has a "grain". I've used loads of pink and blue XPS foam over the years, but I've never seen it with a noticeable grain before.

The really good news is that the grain is oriented like end-grain balsa, from face to face. My guess is that this is deliberate, as this foam is intended for use with underfloor heating, where it would be subject to high compressive loads. This makes is ideal as a core material, plus it's pretty light. The whole hull will use less than 3 kg of foam.

 

That is interesting as I've used it for years as well and never encountered a grain.

All the power to you!

-Tom

P.S. How are you cutting it? I usually run it through either the bandsaw or table saw.

 

I've attached a couple of photos that show the grain of this stuff. It's pretty hard to compress when you squeeze it face-to-face, yet quite soft if you squeeze it across the edges. Edge-on it feels like ordinary pink or blue XPS, face-to-face it feels much stiffer. I suspect the foam has been treated in some way (stretched?) to give it a higher compressive strength, which is what's needed for flooring insulation I guess. It also happens to make it ideal as a really cheap core material. I got it from an underfloor heating system supplier, but looking at the box it came in it looks like the stuff came from China.

I've been cutting it roughly to shape with a fine tooth Japanese pull saw, which has been pretty quick and easy, but when I trimmed up the edges of the side planks last night I discovered that a sharp scalpel worked really well. One down side of the grain is that, unlike ordinary XPS, the edges don't sand easily at all. It's like sanding the edges of end-grain balsa, in that fibres tend to pull out.

 

The turn left videos are nicely done. The boat is apparently a downwind sailor only. I see no board or rudder and the skipper seems to handle it just fine. The impression, from the videos, is that it could use a small skeg to make it a little less twisty.

It looks like a combination of O'Briens Six Hour Canoe and a Banks Dory. I like it. The videos show that the builder had some ingenuity and thrift because there is almost no store bought hardware in sight. Good on the builder and or designer or both. Simple is good!

 

I've been in touch with Dylan Winters, the chap that built the "keep turning left" Duck Punt. He reckons it sails OK upwind as long as it's sailed on its ear, so that the leeward chine digs in, which makes sense. The nice thing about it is that it is dead simple and only needs inches of water to sail in.

It might well sail better with chine runners, as used by Matt Layden on his shoal draft boats. Might be worth experimenting with them to see.

I've planked the bottom this morning and sanding the foam ready to apply the epoxy glass. I've also added a bit of carbon fibre up the stem to give it a bit of knock resistance.

 

I plan on building something similar with chine runners just to test the theory. There is a small lake that I take the dogs for a walk around in the mornings that would be just perfect to practice tight and close quarters sailing on. Not much room to tack up wind so it will be the perfect place to test it...and catch a few blue gills, perch and crappie too.

 

It'd be interesting to see how you get on. Dylan has posted a few videos on his web site (http://www.keepturningleft.co.uk/category/duck-punt-films/) that seem to show the Duck Punt sailing to windward fairly well. He's sailed it in some pretty restricted waterways, too, so my guess is that it goes well enough with just the sharp angle of the leeward chine digging in.

When it comes to fish, Dylan seems to have a similar plan, but intends filming them. He's now fitted a polycarbonate underwater window in the side of his punt so he can sail into shallow water and film the underwater wildlife swimming by...........

My Duck Punt is destined to have her first outing as a racing boat, competing in the Watercraft Magazine Cordless Canoe Challenge, a race for boats under 5 m LOA powered only by cordless power tools. Here's a link to a video of last year's event, a fairly typically British affair: http://www.watercraft-magazine.com/wc_Canoe.html

 

I've seen videos of that sort...pretty nifty.

 

Jeremy,

I too have used a small backsaw on thinner sheets (I'm usually working two inch / 50mm).

I read the rules, I hope you're chosen.

Wish I could enter!

 

I had a go last year, in the skin-on-frame rowing boat I built, using alloy tube and aircraft fabric, but the drive system was broken by a thoughtless visitor who powered it up with the prop resting on the ground while I was off having some lunch.

This year I'm going for a similar drive system, a big cordless drill driving a 13" home made prop at low rpm. Some of the entries last year were like Rick Willoughby's pedal powered boats, but the winner was a very light monohull, that was fairly small (maybe 12 ft LOA or so). The course is a dog leg out and back, with a sharp 180 deg turn at the furthest point, so a good turning radius is a needed, something one or two of the entries tended to have a bit of a problem with. I have a cunning plan to make the Duck Punt turn on a sixpence.

Once the competition is over I plan on trying some experiments sailing the boat, using a Magnus/Flettner rotor, powered by a small solar panel on the top plate. I've been fascinated by these for years and the thread we had here a while ago re-fired my imagination. All I need to do is find a way to mould an accurate cylinder for the rotor. I need something around a foot in diameter.

 

I think I saw that winning boat in the video.

Here is the doodle I tried to send you Jeremy.

Dashed line is on-foil waterline.

A foot operated air pump evacuates the pod once underway (but not necessarily making way) while a hand valve refloods it. It's about 60 litres in this drawing.

Articulating aft pod provides high angle directable thrust.

 

I like that idea, Tom!

Having seen the "flyak" video a while ago I had wondered whether or not it would be possible to get foil-borne on cordless tool power. There's little info on the continuous power output of cordless tools, I'm working on the basis that my 18 V Makita might put out about 300 to 400 W at the most, which might well be around the power that a fit paddler puts out. Might be enough to get a very light boat up on foils, with a bit of luck.

 

Jeremy, following this with much interest.