Tiny Tug

The Little Tug

The first iteration of this design looked like this,

It was obvious to me that there was too little bearing aft to make this a successful little tug. Working from the original concept I redrew the lines to give the boat more bearing aft, to place the center of the deeper box keel under the steering position and give a little more room for the propulsion system.

The original lines lines looked like this,

The redrawn lines like this,

As you can see the stern is wider as is the box keel, there is more bulk in the box keel closer to the fore and aft centre of the boat giving more space for the propulsion system.

We discussed the propulsion system here  and here . The little tug with the propulsion system fitted looks like this,

The two wheels at the helm station control the direction of travel, the smaller wheel controls the forward and aft motion of the Kitchen rudder clamshells given reverse, neutral and forward and the larger wheel moves the rudder arm from port to starboard. Here is the rudder layout.

You can see from this drawing that the bulk of the box keel falls right under the helmsman, the towing point and the motor.

Here's the tug in profile and plan. I'm pretty happy with it.

In the Kitchen

In the Kitchen

Rather than go one at great length about how the Kitchen rudder actually works you can actually see the operation of it here and here.

Why I am so enamored of the Kitchen rudder? Because it gives you twin engine manoeuverability with a single engine, watch here. The vessel you see in the video is single engine and the inner wheel in the wheel house controls the angle of the Kitchen rudder and the outer wheel is the helm or steering wheel. You can only get that sort of manoeuverability normally in a twin screw vessel with opposed outward turning wheels.

For that reason the Kitchen rudder eminently suited to our small tug not only can you run the engine a constant level of revolutions but you can vary the speed, stop within a boat length and quickly manoeuver to avoid girding or girting. (depending upon where you are in the world)

The controls for the Kitchen rudder could be hydraulic, Bowden or Morse cable or line on a drum. For one of my designs, much larger that the little tug, I designed an hydraulic system. However for the little tug a simple drum and rope system is more than adequate.

More on the little tug to come.

Conceptually speaking

Concepts

You are not going to find the ideal boat.
You are not even going to have it if you design it from scratch.
-Carl Lane

This is boat from the board of Tad Roberts, it was built by Barrett Faneuf, it's beautiful.

Years ago hundreds of these little launches plyed the waters of the BC coast, they were the main means of transportation mainly because there were no roads.

The reason I put this up is because in 2012 I saw a version puttering around Ladysmith harbour(it was nowhere near as good looking). So at that time  I thought that as a concept a low powered 15' plywood launch would be a great starting point.

So I drew these lines,

With that as a starting point I created the basic launch

Then added to that basic launch to make a yard boat,

Then modified the lines to produce a tug with a deeper body to allow for a heavier engine and scantlings and a horizontal prop  shaft.

The tug has a covered after deck and protection for the operator.

And then I thought what about a steam launch at which point I realized that a plywood boat would not be appropriate so I modified the lines yet again still keeping the original concept.

All that from a simple concept drawn from seeing a small launch puttering about.

CONCEPTS!

The concepts the thing

Practice safe design: Use a concept.

Petrula Vrontikis

So what was the concept for Kuai Lei? What I wanted was a small boat capable of carrying me around the Gulf Islands and possibly doing an overnight. As I mentioned last time it all started with this.

If you compare the sweep of the sheer in the above picture and the sheer of Kuai Lei here you'll see that they're almost the same. Further inspiration came from Jonque de Plaisance. The JRA magazine which featured Kuai Lei erroneously said that the sheer came from Jonque de Plaisance when in fact it came from this old picture.

With the sheer determined then came the question of square or round boat. The Jonques are round but I'm a fan of Phil Bolger so square was it.

Next question - how big? She need to be trailerable so nothing much over twenty feet. In fact she's twenty feet LOA but only 12 feet on the waterline not including the deadwood. From the stern post to the leading edge of the daggerboard she's 15 feet.

I wanted a small cabin long enough to sleep in with sitting head room and a large cockpit so essentially she was to be divided into two spaces.

So we had a concept, now came the work of actually designing the boat.

First came the lines.

Then once that was done it was on to what cabin height, what sail configuration. Should the masts be canted forwards as on most junks, can we cant the mast forward even if we wanted to? All design questions that need to be answered.

First and foremost form must match function. Lets look at cabin height. I'm 5'6 and a half (I used to be 5'7” but you shrink with age), the height of the sheer at midships is just short of three feet so another three feet on top of that would give me standing headroom but the boat would look clunky and boxy. At most another foot would be suitable. But taking that height out to the gunwale would also produce a boxy look.

Here is the main bulkhead as drawn and as built,

The left side is as drawn, the right side as built (the builder always knows better than the designer). The height to the top of the hatch is just over 4 feet which means that you cannot have sitting headroom except at the centre line. Them's the breaks.

To see what I mean by boxy, here's the bow of the boat as designed,

And here it is with the cabin taken to the gunwale without any slope.

Ugly ain't it?

We'll explore this concept thing some more next time.