More about Flint

I've recently received an email from a fellow who is interested in putting a sailing rig on Flint and I thought that my reply may be of interest to others. Here it is (with some illustrations added) -

Dear Martin,

Thanks a lot for your email, and please accept my sincere apologies for the late reply. For some reason or other, I forgot to highlight your email for a response, and I've only just re-discovered it!

Flint was designed as a rowing boat capable of taking a very small outboard motor i.e. the hull is optimised to be easily driven at displacement speeds. One of the primary requirements was for her to cut through a short, steep chop with minimum pounding.



Eddie Guy's Flint, built to replace a flat-bottomed boat which pounded too much, and was difficult to keep on course

 She was actually designed for an experienced waterman who lives on one of the Moreton Bay Islands, who had been having lots of trouble with an existing long, narrow rowing boat which had a flat bottom.The existing boat pounded badly and was difficult to keep on course when rowing in a crosswind.

It is common for passengers to sit too far aft in small boats, particularly when using an outboard, so I deliberately desinged Flint with quite wide sections aft, but only above the waterline. Therefore, when trimmed properly she is effectively a double-ender, but if someone moves too far aft, the wide sections pick up buoyancy quickly.


Note the wide aft sections on Bill Bronaugh's Flint

  As a rowing boat she has proved to be very successful indeed. One builder has taken his Flint on a number of  coastal cruising trips of several days duration, entering and leaving his home port on the Gold Coast through the surf. In addition, he uses her occasionally with a "crab claw" rig made from polytarp, without any form of centreboard or leeboard. Despite this lack of conventional lateral plane, she sails quite effectively, so I'm assuming that the very sharp forward sections provide reasonable lateral resistance - particularly in a chop.


Alec Morgan's polytarp Crab Claw rig - it works very well!

 Under power, Flint is extremely efficient. On the day we tested the one I built for a customer, we achieved a GPS-measured speed of 6.1 knots with two adult men and two teenage girls aboard (probably an overload) using a 2 horsepower Yamaha two-stroke at just over half throttle. Steve Dorrington, in New Zealand, has got his Flint to 6.3 knots with a 2.5hp British Seagull, which is amazing when you consider the gear ratio and propeller design of such a motor. 


Steve Dorrington doing 6.3 knots on 2.5 Seagull horsepower!

 


6.1 knots with a 2hp Yamaha, and a heavy load

 But to get back to the hull design -  When looking at the lines, I noticed that the wider sections above the waterline aft had produced quite a reasonable sailing hull, and a year or two after the boat was first built, I caved-in to pressure from a number of people, and I designed two sailing rigs - a gaff-headed knockabout (sloop) rig, and a gaff-headed cat rig. I normally use free-standing rigs, but in this case I decided to use stays in order to keep the diameter, length, and weight of the mast as low as possible, and more importantly, so that I could step the mast on top of the existing buoyancy tanks without cutting holes. If I had designed the boat with a sailing rig from the outset, I may have arranged things differently, but this set-up is quite simple (stays and shrouds can be made from Dyneema or Spectra if you like) and allows for the use of very simple, un-tapered spars.

Similarly, the sails have been located so that the daggerboard case can be positioned in front of the main rowing thwart. This means that retro-fitting an existing boat only requires the cutting of a slot in the bottom of the boat, without chopping into other parts of the structure.


I haven't had any reports regarding the sailing performance of this rig, because to my knowledge, none have been tested. However, my feeling is that the boat would sail very well indeed.


As for your question about a simple lugsail option, I am very keen to have a look at the figures, but I suspect that it may be necessary to cut a hole in the buoyancy tank to instal a mast step and partner. I've got a lot on at the moment, but I'll try to get something done as soon as I can. Please give me a nudge if you don't hear from me in a reasonable time!


I hope this helps a bit,


Ross Lillistone