Nauticraft

Archive for March, 2012

Pedal Drive Unit: Quadritwist Belt Drive

Friday, March 23rd, 2012

We are asked from time to time by prospective new customers just what our drive units are like and what is meant by the term “Quadritwist”.

As far as what our drive units are like, the first impression on seeing one in a Nauticraft boat is that it “belongs there”.  This visual impression comes from the drive unit housing being made from the same material as the boat – a white plastic with black specks (we had the black specks incorporated into the material a few years ago).

On our original drive unit (which we now also call our “inboard unit”) the driving belt twists four times going through its path, from the pedaling sprocket to the driven sprocket, over the idlers, and then back around to the start – hence the term “Quadritwist”.  We have a very positive regard for this system because it gives us the required directional change as well as the required speed increase (a 1:4 increase) with no energy robbing torsional or axial side effects; with this type of layout the twists of the belt are actually “natural” ones.

Looking further at the drive unit it is obvious that the pedal cranks come from the bicycle industry, and this is so, as we purchase these cranks as well as its axle assembly (known in the industry by the unlikely term “bottom bracket”) from a bicycle parts supply house.  The pedals also come from there and, because they are often used that way, are of the “barefoot” type (some sophisticated customers, familiar with upscale bicycling, sometimes change these pedals for their own particular choice).

An even closer inspection of the drive unit shows that the mechanical aspects (all of the moving parts) are located on the outside of the drive housing.  Our drive unit is designed this way because the mechanical parts (particularly the belt and sprockets – being of plastic materials) do not need oil or grease lubrication as do metal parts (the plastic materials also are not susceptible to water corrosion as are metals).  Also, because all mechanical assemblies need care and maintenance from time to time, it is far easier to service an assembly that is out in the open.  For instance, although it will serve for a long time, the drive belt can be changed for a new one without removing the drive unit from the boat – and without requiring any tools.

We designed this system ourselves (using the quadritwist philosophy originally proposed to us by Phil Thiel, a marine engineer from Seattle) and have been happily using it in our boats for over 15 years now, with only incidental changes.  We manufacture it right here in our own shop – from rotational molding the housing through all of the subsequent assembly steps.

Next time I’ll talk about the “swing down” drive unit used in our Sprite model – why it doesn’t use the quadritwist system, but how it is similar to it as well as how it is different.

Printable View

Pedaling the Potomac

Tuesday, March 20th, 2012

Escapade on the Potomac

I bought my Escapade in the spring of 2001 as a 50th birthday present to myself. I named my pedal boat RiverSong, and now—as my 12th boating season begins—I still love it as much as ever.

I lease a slip near the Pentagon from April through October and pedal the Potomac within view of the Washington Monument and Lincoln and Jefferson Memorials. I usually take my first ride of the year while the cherry trees are still in bloom and my last as flocks of geese are migrating south overhead. Sometimes I pedal past the Kennedy Center and ride as far as Georgetown.

Because I have a demanding job in DC, I don’t get out on the river every day, but I try to take at least one evening ride and one weekend ride each week. People are always commenting on my boat, and tourists ask where they can rent one.  The cleverest remark from a passerby was: “Oh, a two-stroke engine!”

Like most boaters, I appreciate the beauty of the water and sky at least as much as what’s on shore. The scenery is perpetually changing, as is the play of sunlight on water. Occasionally I have trailered my boat to state parks and enjoyed pedaling on gorgeous lakes. As my husband Don likes to say, “The purpose of a boat is to take all the water up there… and put it back there.”

Sometimes Don comes along for a ride, but usually our dog is my only passenger. Our cairn terrier Boscoe accompanied me to Michigan when I bought the boat to give it his “paw of approval.” Boscoe passed away six years ago, but our young dog Skruffy enjoys boating even more than Boscoe did. He thinks we own the Potomac.  

 

Trish

Alexandria, VA

Bottom

Nauticraft Corporation
5980 Grand Haven Road • Muskegon, MI 49441
(231) 798-8440 • Toll Free (888) 709-7097
inquiry@nauticraft.com