Tag Archives: design

Image

Sketch-a-day

image

Another dynamic pose. Gotta work on those facial expressions though, can’t have him looking like he is squeezing out a painful turd all the time.

time taken: 15mins

Advertisements

Junk Rig

I know, I know! It’s been almost three weeks since I posted anything. Ithere have been many things happening, but nothing much to do with drawing or with my boat so I thought I would spare you the drivel. I am editing my book. 100,000 words to edit, am about halfway through and needing (so far) to completely rewrite about 3-4000 of them. The rest are looking pretty well chosen (thank goodness!).

In boat news I got my copy of Hasler and McLeod’s Practical Junk Rig. Basically THE definitive tome on all things to do with Chinese style rigs. They are notoriously easy to sail, cheap to make and require minimum of stresses on both the hull and the sail. Perfect, no?

Thing is that my boat plans do not come with a junk option so I had to design one. It took all day and about eleven slightly different sails to arrive at the perfect configuration. I initially thought that you just plonk a siutable piece of cloth on a stick and call it a sail. Sadly it is about a hundred times more complicated and involves several things including your LWL, CLR, CE, rake and displacement (ballast in my case). You can see I am deliberately being cryptic.

Basically it is very important that the ‘average’ centre of pressure from the wind on the sail is more or less directly above the centre of lateral resistance of the hull. If not then your boat will not easily sail in a straight line, sacrificing speed and handling. If the point is too high above the boat then you will easily capsize, too low and you miss the swiftest winds. The height of your mast depends on the depth of your hull, so a little boat can’t have a tall mast because the mast will fall off and/or my boat will tip over in a gust. Finally the mast has to be the right proportions fore and aft of the mast to allow space for the rigging, and the right height above the boat to not hit you or trail in the water.

Anyway brace the contents of your various sphincters for the finished article!

 

image

I know…amazing…

Anyway, the important thing is I have plenty of sail (15 sq ft) and my CE is above my CLR, and my mast is a decent 19/20 ft. It should go like a scolded cat even in light breeze but I will have to reef early or risk taking a dip.

I was tempted by many things, extra masts, funky sail shapes, but I am going to keep it simple, this time.

You all knew

The boat I designed doesn’t outright suck! Yay!
I spoke to the people on boatdesign.net and the comments were mainly about details. So I was very pleased that my little piece of egestion would go somewhere.
Of course there is a however. It was a half decent boat, however only really useful for lakes or protected waters. This was due to several of the design aspects including it’s long straight hull. I designed it like this because I can’t get my head around how to design curves that curve in two planes. I want to sail in the sea, and my boat would not have been able to cope with probably even average sized waves, or have been able to ride surf onto a beach.

Luckily for me a very helpful chap who runs the website tacking-outrigger.com pointed me towards a few excellent designs. I had lots of fun designing some (awful) boats, and I feel that thinking about all of the various aspects of design will undoubtably help me when it comes to the build. However I will leave the design in this instance to the pros.

In the end I chose this design: Salmo 19 by Andrzej Książyk. Here are some photos of it in action. Click for higher resolution.

image

image

 

As the name suggests it is 19′ long, weighs 185 kg and is a tacking outrigger. That means no shunting and no worrying about having to reverse the rig.

I will be making a few modifications. Firstly and most importantly for me I will be adding a ‘sacrificial’ keel to the underside so I can hit rocks and drag it up the beaches without too much worry.
Secondly I will be using a junk rig instead of the Gunter shown in the photos.
Thirdly I will be increasing the potential displacement of the outrigger by making it a bit taller. The benefits will be that I can carry more weight, and the crossbeams will be horizontal so I can attach a nice wide platform for chilling out.

Those are the ‘simple’ modifications and the ones that are guaranteed to happen.

After that I am considering raising the deck so it is more of a ‘sit on’ boat rather than a ‘sit in’ boat. This will give me more storage and less time bailing water. Plus then I can have ‘scuppers’ and a ‘poop deck’!

Finally I really do not like the idea of a keel stepped mast because it necessitates a hole in the deck, so I will see if there is a way for me to attach the mast to the forward crossbeam. This will be the most dificult thing to accomplish properly so I will spend plenty of time getting it right.

I bought the plans yesterday, and I bought a book about designing junk rigs for a bit of light reading.

One step closer.

With trepedation….

…I quietly announce the ‘pretty much’ final design for my boat.

Mastodon 21′ by Daniel Powell Conti

Everything was well and good with my previous final design, so as I mentioned before I was doing some 3D modelling to put up a picture for your entertainment. It was then that I realised a horrible design flaw.

It looked shit.

I am not going to spend thousands of pounds on a boat that doesn’t look awesome. I realised too late that my final design necessity was a cool looking boat. The problem was that the accomodation hull was too tall and fat. It looked like a supermodel and her retarded sister trussed together and passed off as a princess. To put it nicely.

So this is the newer, sleeker design. Hopefully it will actually look like one boat instead of two random ones bolted together. Click on the picture for higher resolution.

image

The vitalstastics

Lee hull (with the mast)
Waterline: 21′
Beam at waterline: 1′
Displacement: 68kg

Windward hull (accomodation)
Waterline: 21′
Beam at waterline: 2′
Displacement: 136kg

Centre to centre beam: 10′

Hull displacement: approx 204kg
Draft: 2″

This is a ‘weight to windward’ design of pacific proa, giving greater stability than a more conventional ‘flying’ design. I will talk a little about the important changes. The crossbeams, the hulls length, the mast step, and the accomodation.

I have four crossbeams instead of the more conventional two, generally something more often seen on catamaran. This may be a case of structural overbuilding but I want to feel safe in this thing. I feel that with a hull made of 4mm marine ply I could use a little extra support for the extremeties of the boat wich would otherwise stick 7′ free from any lateral support. The four beams will have strong internal support built into the bulkhead below as well as longitudinal support from one crossbeam to another. There are other advantages too. I am now able to build the rudders closer to the end of the hull, increasing their leverage. I will also be able to string trampoline mesh between the outer and inner crossbeams, doubling the available deck area.

I have increased the length of the hulls as well as making the ama and vaka (main and outrigger) the same length. This was after I saw a similar design called ‘Ping Pong’ by Terho Halme. It has equal length hulls and sails just fine. It solves several problems for me. The problem I was having with the ‘weight to windward’ design was not having enough space or displacement in the windward accomodation hull. Having a 21′ windward hull solves it nicely. I have not gone back on my ‘easy to build’ principle either. By sacrificing a bit of inside space the hull can be made to be 2′ high with an additional 1′ cabin top. This still leaves space for two to sleep, head to head instead of next to each other. The space will allow two to sit and face each other with space to cook or play chess inbetween when they are not sleeping. However generally, while sailing, two crew members would not be taking sleeping shifts at the same time. If moored or at anchor there is space on the 14 sq ft deck to pitch a tent.

I have chosen to step the mast to the crossbeams rather than into a hull. I want a mostly freestanding mast for ease of manufacture. As I said in a previous post, stepping the mast inside the hull raises problems that I can just avoid. Furthermore, having the mast on the crossbeams allows me to move it, repair it and generally be able to access any part of it without having to mess with an integral part of the boats structure. It also makes it easier to earth the mast incase of a thunder storm, I can just trail some copper wire in the sea.

The unloaded displacement is 204kg for 2″ draft. Day tripping with three or four people would be around the maximum displacement of 520kg which would give a draft of about 6″. Adequate for smooth seas.

The only real complexities are the angled, three chine hulls. I feel they are quite necessary to avoid slamming into waves at high speeds so they stay. Because the boat has no rocker so it is a manageable level of complexity.

I have a boat designed. It is simple yet elegant and will look sweet as when decked out in bright red paint. Now I just have to think of the…cost…
COST:
14 x (4mm x 1.2 x 2.4) marine ply = GBP 252
60kg epoxy = GBP 624
27m sq of CSM fibreglass 300gsm = GBP 24
40m sq of 300gsm woven glass fabric = GBP 52
Paint plus antifouling = GBP 100-200

total cost of hull = GBP 1052

Then all I have is estimates for the other costs.
Workshop and tool hire GBP 800 (?)
Aluminium poles GBP 80 (?)
Sail GBP 200 (?)
Rope GBP 100 (?)

Estimated bild time: 240 hours

Assuming my estimates are sound the minimum cost will be around GBP 2232. Knowing from the outset that there is a snowballs chance in hell of sticking to the minimum budget I am giving myself a budget of GBP 3000 to complete the project.

That seems like a lot of money so I thought of other stuff I could buy for three grand that would help me enjoy travelling around New Zealand.
An old car and 6 months of petrol and insurance.
An old monohull sailboat.
A 14′ racing catamaran.
A cheap Armani suit. (Wait, that wouldn’t help at all)

So to hell with common sense!