Thankyou CT,

Enormously influential books for me. Perhaps I am still trying to come to grips with some of them.

One of the important things was they gave a particular geeky kid something to chomp down on where he could actually see results rather than seeing marks out of a hundred – one of life’s unfortunate abstractions.

Did you ever try the Gentry Bathtub experiment?

It is pretty compelling how the “Karman Vortex Street” we see curling off the edges of a paddle or oar suddenly disappears as the angle of attack allows attached flow. And if using a real oar, paddle or ruler alongside an actual boat there is suddenly a strong force perpendicular to the flow that has to be restrained at the moment the vortices stop being generated. Blame Wallis Lake at Forster and family holidays!

Karman Vortex Street of a stalled foil

And the classic bathtub experiment is recommended to readers. I’ve stolen the graphics from North Sails.
https://www.northsails.com/sailing/en/art-science-sails/gentry

I totally agree with all your comments. Each writer had weaknesses, but at the same time they wrote lucidly between the stumbles that we all make. I used to get infuriated by some of Bethwaite’s graphs for example.

I have been looking for the Peter Mander book for years. I remember seeing something you wrote some time ago on Sailing Anarchy that retriggered another search. Just checked Abebooks again – nothing!

For those who don’t know, Chris wrote the exquisite “Sailcraft Blog” an elaborately and meticulously researched history of Sailing Dinghy Performance. I’ve spent more hours there than I am happy to admit to. Also a great place for follow on research or confirmation (or dismissal) of my own (and other’s) thinking.

https://sailcraftblog.wordpress.com/

This is all a long way of agreeing with your choice of great books. Twiname changed my life, and that of my brother. Gordon is brilliant. Frank was a fascinating man, a thorough gentleman in an old manner (and I mean that in the best way) but while he was very bright and innovative he missed out on a couple of the vital aspects of being the scientist he wanted to be. That sounds more negative than it’s meant to be – his brilliance and experience meant that he was accelerated in life and therefore missed out on some other aspects. His work on the unsteadiness of wind in itself was a relevation; it’s something that the “natural” sailors picked up early, some of the rest of us learn later, and most never learn. Gentry annoyed me for years because I don’t think he mentioned that circulation was more of a mathematical construct, not something you could see – it was obvious we couldn’t see it, but the clash between reality and theory was frustrating for a teen.

One other fantastic book is “Give a Man a Boat” by Peter Mander, 1956 Olympic medallist in Sharpies and 18 Foot Skiff champ. He won the Games in a boat he and his crew made, from cutting old church beams into planks down to recutting sails just before the Games. If you ever get to Armidale I’ll lend you one of my copies.

A nice page of outriggers too.

http://outriggersailingcanoes.blogspot.com/

You can probably use the standard PDR rudder directly. Don’t forget the bolt through the tiller/rudder box juncture!

MIK

Thanks a lot, this was very interesting! I had been wondering why the dagger board and rudder of the oz racer were so “enormous”. I am dreaming of building a GIS, but have neither the time nor the building space at the moment. So I bought myself a very cheap O’Day daysailerII (17′). The rudder of the DSII is probably even a bit smaller than the oz pdr rudder. Now that you have cleared up this mystery for me, I’ll probably just go an build something similar to the oz racer rudder for my dsii (it has got only the original fibreglass “slabs” for centreboard and rudder, horrible).
A great thanks for your beautiful designs and all the knowledge you are sharing so generously! As you mentioned above; the internet at its best.

best regards,
Viktor

In a way the PDR/OzRacer line is not like other sailing scows. With regular sailing scows you can heel them to reduce wetted area in light winds and upwind. But the PDR, because of its sides being straight will dig in the corners of the bow and stern transoms if you heel too much.

The scow Moths in Oz died off because they were outperformed by narrower skiff moths.

The thing that the PDR points out to me most strongly is
1/ That you can’t beat stability if you want to get performance out of a small package.

2/ Aft rocker shape is what is responsible for the bows of sailboats raising out of the water at speed. Good when going downwind in waves. The PDR overdoes it a bit – but it does improve the safe handling of the boat. In my designs I’ve started putting just a shade more rocker in the backs of the boats if rough water handling is a priority. I think that is at least part of the reason multihulls tend to concentrate rocker in the backs of the boats – it means you can push the boat harder and faster without the nose going in.

3/ A frivolous attitude to designing and building leads to many fruits!

As far as expanding the length of box boats more and more …
… in a way I don’t think it makes a lot of sense. There starts to be so much materials and effort put into a bigger boat that the pressure to build something nice looking starts to be strong too.

MIK

A pleasure! It is one of the great things about the net. Finding worthwhile stuff to share!

Best wishes
MIK

Even more so, how do you think that a properly scaled up (not just stretched) box boat up to the size range of the GIS would stack up, other than the obvious of not handling chop nearly as well as the GIS. Are we just holding on to the romantic notion of a pointy boat? I know that Oz had it’s share of scows. Why did they die off?