Thread: Periwinkle

Mike,

The matter of hull-form in the forrard sections is one which I have been pondering for a very, very long time. I have to admit that I'm still working largely according to gut-feeling, but I hope that those feelings are being shaped by some analytical thought!

I try to keep the bow half-angle (at the waterline) down to less than 19.5 degrees, that being the angle of wave probogation in water (I think!). My belief is that under 19.5 degrees gives you a good chance of getting a nice, curling bow-wave, and over 19.5 degrees gives you a good chance of ending up with what Phil Bolger onece described as, "...an untidy jumble of water...". Now, there are plenty of exceptionally good designs which produce the 'untidy jumble of water', and yet are very good, seaworthy, and in many case, fast boats (Some 12 metres, Cook's Endeavour, many Dutch vessels, ten million Optimists etc etc - the list is enormous).

I don't follow the 19.5 degree half-angle religiously, but I do feel that for an open boat working in a steep chop, it produces a dryer boat. When the fine entry lines are combined with the spray-deflecting characteristics of a lapstrake (clinker) hull, I believe you end up with half-a-chance of staying dry. In addition, I like the (relatively) soft and loping sort of ride that is produced. The danger is that the fine entry is, by definition, lacking in buoyancy, so that particular element of the design must be combined with other parts of the overall hull shape. The most obvious way to approach the problem is to include substantial fare and/or flam in the bow sections above the waterline, thereby ensuring adequate reserve buoyancy. All of these elements tend to result in reverse curves in at least some of the forrard sections, and very often in the forrard waterlines at about the level of the DWL.

All of the above strikes me as a huge over-simplification, but I'm short of time at the minute, and I'm probably not a good essay writer.

As for the cut-away bow in profile, it comes from two differing design aspects. One is that wide panels of sheet material must (within reason) be of a developable shape in order to lay fair. In a glued-lapstrake boat (and all sorts of other construction methods) the wider the planks, the more dificult it is to achieve fair lines running up to a steep stem (take a look at a Swampscott Dory for clues). I deliberately walked a fine line between wide planks (for less intimidating construction for the amateur builder) on the one hand, and a fine entry on the other. I'm pleased to say that Periwinkle and Phoenix III have both turned out well in that regard.

The second aspect of the cut-away bow shape is that of behaviour when running down the face of a wave at high speed. I use substantial rocker in all of my designs (there are other reasons for that as well, but I haven't got time to discuss them in print right now). One of the reasons I use such rocker is to reduce the likelyhood of broaching, and to make downwind steering more predictable and pleasurable. Have a look at the profile and sections of an Australian Surfboat (the rowing sort) and then meditate on the matter.

This has been a much too brief and broad-brush answer to your questions, but it is the best I can do right now. I hope it helps a bit If you look at some of the photos of Phoenix III and Periwinkle on my website you may get some clues - there are too many to include here.

Ross Lillistone www.baysidewoodenboats.com.au

Originally Posted by RossL

All of the above strikes me as a huge over-simplification

Ross simple is good

I deliberately walked a fine line between wide planks (for less intimidating construction for the amateur builder) on the one hand, and a fine entry on the other. I'm pleased to say that Periwinkle and Phoenix III have both turned out well in that regard.

Yes both are easy on the eye. I was wondering about the wide plank thing, interesting you have put ease of construction ahead of aesthetics. I can see how this aspect is important as it is a common theme here and other forums that is us amateurs looking for designs that offer relatively easy construction. Boatmik makes the point often regarding the advantges of square boats.

The second aspect of the cut-away bow shape is that of behaviour when running down the face of a wave at high speed. I use substantial rocker in all of my designs (there are other reasons for that as well, but I haven't got time to discuss them in print right now). One of the reasons I use such rocker is to reduce the likelyhood of broaching, and to make downwind steering more predictable and pleasurable. Have a look at the profile and sections of an Australian Surfboat (the rowing sort) and then meditate on the matter.

Ross Lillistone www.baysidewoodenboats.com.au

Thanks Ross, do you have a recommendation for some reading on the principles of small boat design that is basic enough to follow. In other words won't baffle a novice with too much science.

Regards
Mike

Mike,

Sorry for the delay in replying - beyond my control, I'm afraid, due to commitments elsewhere.

The matter of plank width is a difficult one for which to find a perfect solution. I would love to design all of my boats with nine or ten planks per side, but having just completed the heat-gunning, scraping, and sanding of the internal plank laps on the prototype Periwinkle, I'm very glad indeed that she only has five planks per side!

Now it seems to me that whenever a culture has had access to wide plank stock, they have modified their designs to take advantage of the plank width. For example, the Scandanavian (small) open boat designs seem to have used only three or four planks per side, and the American dories (particularly the Swampscotts and related types) show just what an exceptionally beautiful shape can be produced from three planks per side. Other examples are some of the beautiful shapes from China, the Middle East, and our neighbours to the north and north-west.

With plywood being largely immune from problems of cross-grain weakness, it seems sensible to make planks as wide as possible, while still retaining a shape which will run into a head-sea as smoothly as is reasonable. I love sharpies, but pounding is a genuine problem in any situation where the boat is not heeling significantly, so as to present the angle between the bottom and the topsides to the waves as a "V". Another problem with sharpies is that the hull requires thicker planking, or more internal framing, because of the large panel areas which are curved in only one direction.

A lapstrake (clinker) hull can be designed in such a way as to produce a shapely, strong hull which requires only a few planks. The resulting hull can be stiffer, softer-riding, and drier (due to the spray-deflecting characteristics of the laps) than most other plywood construction methods. I have built and sailed everything from flat-bottomed skiffs to strip-diagonal hulls with the most voluptuous curves, and I have come down to choosing glued-lapstrake as being my favourite method of construction - but, I try to keep the plank numbers to the minimum. A close second on my list is a multi-chined hull built using the stitch-and-glue method.

As for a recommended book on design, I find it very difficult to think of one, single title. The books on Naval Architecture do not deal with the issues of importance to a small-craft designer (and I struggle with the mathematics). Every "How to Design a Small Boat"-type book I've ever read has left me dissatisfied, and unhappy. My most important teachers have spoken to me from books which are not "how-to-design" books as such, but which have furnished clues. If you ask me to name a single book which has been the most important, I'd say "The Commonsense of Yacht Design" by L. Francis Herreshoff (out of print to the best of my knowledge, but luckily I have a copy on my bookshelves). Other very important titles include "High Performance Sailing" by Frank Bethwaite; "Elements of Boat Strength" and "The Nature of Boats" by Dave Gerr; "Yacht Designing and Planning" and "American Small Sailing Craft" by Howard Chapelle; "The Dory Book" by John Gardner; "Small Boats", "The Folding Schooner", "Different Boats", "30-Odd Boats", "Boats with an Open Mind", "100 Small Boat Rigs" and "Schorpien" all by Phil Bolger; "Sail and Oar" by John Leather - the list just goes on and on.

I can't put my finger on a single title that says it all (not that I am qualified to judge anyway!). I've got around 1,500 books on my bookselves, and a lot of them have furnished clues. I tend to be obsessive, and my mind has mulled over matters concerning small boats for in excess of four decades. Most of what I know has entered my head through a process of mental-osmosis. I am not clever - I just learn from others - and I am grateful for the information which has been passed on. Despite that, you can't learn from reading alone - it is vital to sail/row/paddle/build as much as possible. I've built around fifty boats in the last eight years, and I feel that I've still only begun to scratch the surface when it comes to knowledge.

I'm sorry that I haven't been able to be more specific, but I'm afraid that I just don't know the correct answers......good talking points anyway.

Ross Lillistone www.baysidewoodenboats.com.au

Howdy Ross,

You are spot on about the mental osmosis. I'd read all the texts you mention and totally agree that they were the most important ones for my development too.

But the catharsis came for me when I was first employed at Duck Flat and pushing bits of timber through the saw to make kits for Kirby, Bolger, Kelsall, Oughtred, Devlin, Culler and many more. I think the construction side is the hardest bit to come to grips with ... and seeing how they all did it was really the rounding off of my education as a designer. Getting intimate with the way different designers approach things.

I would probably add another two books.that were really important. Ross overlooked "Skene's Elements of Yacht Design" ... which he has commented on before, so I know a well thumbed through copy is on his bookshelf. The old one and the new one are kinda like companion volumes almost, but either will do. And for those who are OK with arithmetic, a very useful update is "Principles of Yacht Design" by Eliasson and Larsson.

One of the most useful ideas in Skene's is learning the effects of scale. That you halve the size of a boat and it will have
A quarter of the sail area
An eighth of the displacement
A sixteenth of the stability.

These more technical books serve a different function from the others that Ross mentions though. They are more concerned with HOW rather than WHY. Though Skene's original book sorta covers both sides to some extent - a great achievement for one slim volume.

Bolger's books are absolutely pivotal, I think. Purely because the guy is SO HONEST about the process of design and both the positives and the shortcomings of his boats. It is like sitting beside him at the drafting table. Francis Herreshoff is the same.

Both great writers and both truly original thinkers.

In recent times too the OZ and NZ racing dinghies have changed shape a lot to gain more control. In the past there was a focus on planing area and having a "long run aft' and this has been well and truly ditched as it makes the boat slow in light winds and hard to control in waves - upwind and down.

So those shapes are well worth observing. They guys who are doing big dinghy style racing yachts still haven't understood some of the subtleties and are totally focussed on planing area and stability, not realising yet that a few little tweaks that are almost unnoticeable will make their boats easier to handle and won't reduce the top speed by much at all, but will allow the boats to be driven much harder and make the boat much faster in the light stuff.

Some of the recent out and out offshore racers just launched are showing Chines aft - good work guys!. So maybe they are looking more at dinghy design - they just need to see what dinghy designers do with chine shapes.

Now if they can only ditch the engines they use to make those keels cant to the side!!! (how many mpg to Hobart? - it is cr@p and the authorities are in denial because of the bucks).

Interesting that some of these same features of modern dinghies are the centre of traditional boat design!!! Mostly to try to give the boat a balanced shape/volume however it is hitting the water at the time.

Best wishes
Michael Storer.

Thanks Gents,
I am now armed and probably will become more dangerous to the unsuspecting yacht designer well anyway hope to at least be able to pose the odd question that is backed by at least some reading.

Ross please keep us posted on your progress with Periwinkle.
BTW how do you stop your clients wanting to help. I think I would have to poke my nose in every five minutes if you where both designing and building for me.

Mike

Yep, I should have mentioned "Skene's Elements of Yacht Design", but not the Francis Kinney edition. I've got Edition 6 (Skene) and edition 8 (Kinney),but the Skene original is the only one I consider useful.

Other important reading matter which I left out of the last posting includes about eight volumes of the "Motor Boating's Ideal Series" containing hundreds of thousands of words from William and John Atkin, plus some from William Deed, Chester Nedwidek, Chas Mower, John Hacker and others. Not to forget Weston Farmer's wonderful book, "From My Old Boatshop", and T. Harrison Butler's "Cruising Yachts - Design and Performance". The list just goes on forever - but the important point is that there is a need for constant study of as much varied work as you can possibly get your hands on.

As for keeping clients out of the workshop - well, I'm a failure in that regard. The reason that we moved from Brisbane out to the relative isolation of Esk is that we were innundated with visitors in the Brisbane workshop and were loosing about 75% of the available working time to interruptions. I like talking to people about boats (and other things!) so I was my own worst enemy. In the end, the realities of needing to pay bills made me move to a less easily accessed location. It has worked, but the preceeding seven years of 14 hr/day, six-and-a-half days/week working had worn me down physically, and I ended up being slowed down by serious illness for quite some time. I'm kept working throughout, but it has taken me a long time to get back to something approaching my previous work levels.

Currently, I'm in the fortunate position of having clients who are happy to receive regular (i.e. nearly daily) up-dates via email and the website. The owner of Periwinkle has given me exceptional freedom to work at my own pace and to dictate elements of the design - he is a man of great intelligence and tolerance, and I am extremely grateful for the commision. You can't get much better than a design-and-build commision! I just hope that the quality of my work lives up to expectation.

Ross Lillistone www.baysidewoodenboats.com.au

You are a top chap Lillistone!

MIK

Mik,

I don't know whether you are pulling my leg or not , but I am grateful for your kind words.

The process of design has got me well and truely puzzled, and I find that the more I learn, the more I discover that I don't yet understand. While there is much to learn about how to make boats go fast and handle easily, there is even more work to be done in making boats SATISFYING. That satisfaction relates to a range of areas (building, maintenance, aesthetics, comfort, simplicity, cost, speed, durability, etc., etc.) but the most important thing is to use the boats as often as possible - something to which I need to pay more attention........

Ross Lillistone www.baysidewoodenboats.com.au

Nothing tricky there Ross! You are a good chap!

MIK

Thanks very much indeed, Mik. I'm very grateful for what you have said.

Ross

You know you're a designer, when you have the strong urge to go back and redraw all of your previous designs, incorporating what you now understand.

You trying to ruin my day, Paul!!!!

MIK

Originally Posted by PAR

You know you're a designer, when you have the strong urge to go back and redraw all of your previous designs, incorporating what you now understand.

Careful there Paul. By that criteria even I am a designer !

cheers
AJ

I converted all my hand work to digital format some years back. In the process I stumbled upon several of my older designs and couldn't help but notice how little I understood things at times. Many of these older plans sets where just scanned and dumped into a file, but quite a few were "touched up" and some received a lot of work.

This was to bring them up to speed, so to speak.

An example was my SwordFish design. This was a knock off of an old rule boat and it had several issues, some of which I dealt with, others, I'd get around to someday. I made the changes that we incorporated into the rig (it's on it's third version), attended the weather helm and moved some displacement aft. Now I'm pleased with the design and it'll be a more manageable craft, though likely not the thoroughbred it was when first launched (she was a screaming witch, but hard to control).

I tucked up the buttocks on a small pulling boat I did many years ago to make easier arm effort. Cooper 26 needed to have her longitudinal stringers moved out a couple of inches to clear the motor mounts on typical engine installations. The list goes on.