Sailing Dory Design Alterations

[Mike123]

I'm wondering why the sides on the swampscott dory differ (knuckle instead of straight) from the banks dory. What is the advantage?

The banks dory sides provided reserve stability, which I thought would be benificial to a dory modified for sailing.

[SeaB]

More initial stiffness when lightly loaded, probably better for carrying sail.

[Ian McColgin]

Actually the swampscott (and chamberlain gunning) dories have greater stability. I could walk Leeward's gunnel. Try that in a banks dory when it's light. Also I could stand on the garboard to induce a little heel - handy when hauling a long line over the oarlock.

The banks shape was made to be cheap and simple to build, as well as having fabulous seakeeping ability when burdened. A bit nasty when light, as any recreational banks dory rower will tell you after comparing the boat after 15 or 20 miles light versus ballested with an extra 200# or so. They also stack nicely.

The gunning and swamscott shapes row superbly whether light or burdened though they can't carry the ultimate load of a banks dory. They have the midships bearings (less deadrise in the garboard) to sail far better, though both are limited like the banks shape to a lack of bearing aft which lack of bouyancy there causes them to sink more rapidly into their own wake and pushing "hull speed" down.

[TerryLL]

Mike,
Welcome to the forum.
Yes, the flared sides of the Banks dories do provide some reserve stability, but the initial stability of these boats is very low. The result is a boat that heels quickly with very little wind pressure, even with a very small sail area. Not exactly what you want in a sailboat.

The Swampscott dories are wider and have more initial stability, so they stand up better to the wind pressure. Some very wide and flat Swampscotts, like the Mower X-Dory, the Alden Indian, the Town Class, the Sea Chanty, and the Crocker Compass are flat-out racing dories and are essentially round-sided hulls with very high initial stability.

[Lance F. Gunderson]

There is a good video on YouTube of a Swampscott Dory under sail on all points; careful observation will reveal her healing with stunning quickness, leaving about 3/16th" of freeboard. This is why sailing dories were eventually decked over....to give them a greater margin for error (see Tweedledum & Tweedledee in Gardener's Dory Book). Sailing dories are fun if you have smooth water and an agile crew, otherwise they are just about the most dangerous sailboat you can be in.

[rbgarr]

The Banks dory were intended to be built fast, cheap and tough... and nest on 'mothership' decks with the thwarts out. All that is easier with the straight sides. AFAIK the sail rigs they had were for downwind trips only.

[Charles Burgess]

Mike,
Welcome to the forum.
Yes, the flared sides of the Banks dories do provide some reserve stability, but the initial stability of these boats is very low. The result is a boat that heels quickly with very little wind pressure, even with a very small sail area. Not exactly what you want in a sailboat.

The Swampscott dories are wider and have more initial stability, so they stand up better to the wind pressure. Some very wide and flat Swampscotts, like the Mower X-Dory, the Alden Indian, the Town Class, the Sea Chanty, and the Crocker Compass are flat-out racing dories and are essentially round-sided hulls with very high initial stability.

The tippiness of a banks dory allows a low aspect rig/sail to spill excess wind in a sudden gust or squall...helping to prevent her from being knocked down. That is why the traditional riggs worked so well.

Even with the Swampscott and other similar dories the low aspect riggs perform closer to their design parameters than they do with high aspect riggs.

If you put a high aspect rigg and sail (or simply too much sail on a low aspect rigg) on any dory you are asking for trouble...or excitement.