What is the speed capability of a NE Dory?

Builder's Forum
1

I was doing some research/dreaming the other day about how I would like to use my Dory once it is complete. I found a chart listing the nautical miles from one harbor to another off the Washington coast.

It shows that form Cap Sante Marina on Anacortes to Friday Harbor on San Juan Island is 19.6 nautical miles. It states that at 7 knots you can make the crossing in a little under 2.5hr. So.....how fast will a Dory with a Lug sail go? I know it all depends on the wind and how good at sailing I am. And I will not even attempt something like this until I have lots of time sailing under my belt. But since I have never sat in a complete Dory yet, I don't have a clue what they are capable of.

2

   Building mine too.I'm  interered in the same question and would also like to inculed fixed seat rowing.I know lots of things factor into it but  I'm sure folks have kinda figured an average speed.for my shearwater 17 kayak i figure 5mph

 

3

Mike,

The rough formula for calculating the maximum speed, in knots, of a displacement hull is 1.34 x the square root of the waterline length in feet. I'm not sure of the waterline length fo a NE Dory, but as an example, if it were 16 feet:

1.34 x 4 = 5.35 knots or 6.17 mph.

Remember that this is an approximation. Many years ago, I owned a Cape Dory Typhoon and using that formula, her maximum hull speed should have been around 5 knots. That was pretty much what she did under ideal conditions.

https://www.easycalculation.com/physics/classical-physics/hull-speed-calculator.php

Cheers,

Dick

4

Nice formula, but I don't know the waterline length either. Maybe someone from CLC could help?

   

5

   

Greg27 Howdy! How far along in your build are you? I will be putting the final coat of paint on the outside later today.

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6

That hull speed formula is actually a rough approximation of the size of the standing wave created by a boat as it pushes through water. Once the wave reaches a certain size the boat cannot push through it. That's the theory.

In reality, the size of the wave is controlled by much more than the boat's waterline length. Specifically, the boat's shape has a much greater effect. A displacement boat with a fine hull shape will easily outrun a full one, even with identical waterline lengths. A boat with greater wetted area can be left behind by one with less wetted area. So it's not just size that matters.

The other thing to keep in mind is that with a small unballasted boat, the waterline length is constantly changing as the boat heels, rides over waves, the crew changes position, etc. So at best, it's a very rough approximation, not worth using to plan a trip.

I'd suggest that you use the hull speed as a very rough guide, get familiar with your boat and learn how fast it really goes in various conditions, then plan your trip.

One way to find out how your boat performs is to find a windless day and row your dory. Try to compare the effort of moving the oars with the effort of picking up various weights. That will let you know approximately how much force it takes to move your boat at a specific speed.

When planning your trips, don't forget the tides and currents. All the hull speed in the world does you no good at all if the tide is running 1/2 a knot faster.

Have fun,

Laszlo

7

Mike,

As I said in my earlier post, the formula is an approximation and many factors affect a displacement hull's speed. It does, however, identfy an upper limit to that speed. To exceed that speed, a hull needs have a planing or semi-planing form. As Lazlo pointed out, the overall hull shape affects the power necessary to reach hull speed and on a sailing or rowing boat, that available power has real limits.

I think that if you used the length of the bottom panel on the NE Dory as the waterline length, you wouldn't be too far off on the speed you can expect the lug rig to deliver on a reach under ideal conditions --- probably somewhere between 4 and 5 knots. Of course, it is hard to go everywhere on a reach.

Cheers,

Dick

8

I am a life long sailor, having done a lot of racing in my younger years and more cruising lately.  I have never sailed a NE Dory but have sailed and raced a number of boats that size.  I beleive that the real answer to Mike's question has more to do with what average speed he can expect rather than maximum speed.  I have no doubt that in good wind a competently sailed NE Dory will get up there around the 6kt mark as suggested by hull speed.  In the real world, it is difficult to maintain high speeds in an unballasted boat like a NED for more than an hour or two.  Pushing a small unballasted boat hard is physically demanding.   Eventually fatigue sets in or you have to drink, eat and/or take a leak.  The result is that you end up sailing the boat a bit conservatively (reefed) on longer trips.  You also have to consider that you will not always (almost never?) have favorable conditions for the trip.  The winds may be light, you may have opposing current and/or you may have to beat to windward.  Sailing to windward, your velocity made good will only be about 70% of your speed through the water.

   On my 25' yawl with an autopilot, I could average 5kts all day long in good conditions.  In lighter winds I would be lucky to average 3.5 and in tough conditions maybe even less.  For a boat like a NE Dory, on a great day you may average 4kts for 20 miles.  For day dreaming purposes, you would better off planning on a 2.5-3.0 kt average.         

9

   

Mark N, thank you. That is very informative. So by your logic which sounds extremely reasonable. The 2.5 hour crossing for a 7 knot craft, would be more like 6 to 8 hours for my Dory. The good thing about this is there are several island between Anacortes and San Juan. I just looked at the map. There is upwards of 6 islands you would pass on the way? Lots of options!!

10

Here is some data from actual sailing on my Northeaster Dory for you to consider:

https://www.strava.com/activities/535069945/analysis

 https://www.strava.com/activities/617715158/analysis

 http://lakenorforkadventures.blogspot.com/2016/10/the-ruins-of-red-bank.html

If you run your cursor along the "Speed" graph of the Strava data logs, you can see where I was on the lake, my speed, and my heading. I've had my dory up to about 11 mph for brief periods, and I think it can average 7 mph in the right conditions on the right tack. But you are talking about going from point-to-point (perhaps on open water). In a steady, manageable breeze you can probably average 3-5 mph without risking too much. But if you have to beat straight upwind, you'll have to work very hard (and ship some water) to manage 3 mph. (Your boat speed might average 7 mph, but your progress upwind will be 3 mph).

I included my blog entry about my 3-day camping trip because (as the weather charts show) I had some very windy conditions. My trip took me on joyous reaches downwind during the first day, and then I faced steady headwinds on the second and third days. My little boat never let me down.

11

Mike,

Hate to rain on your parade, but I just checked today's tides and currents for the San Juans and there were 4 kt currents along your proposed route. They were at right angles to the route, too. Looks like you're only going to be getting anywhere at slack tide, so plan for a leisurely trip.

Laszlo

 

12

   Got the inside glassed and turning it over today to fill in the seams, took the week off work to make some progress on the build

13

Greg27

I did the same thing! Took a week off just to spend time working on my Dory. I might do it again come spring depending on how far along I get. I just pulled the tape off of the underside rails. Bottom of the boat is now fully painted. Once my wife gets up and I can get her help I will flip it over and start work on finishing out the inside. My goal is to have her rowboat ready by the end of February. Then get going on the Mast,boom,yard, rudder and centerboard. Ultimate goal is total completion by the end of April.

 

 

14

   I have been sailing my NE Dory for three summers.  The highest speed ever clocked, and that was intermittent bursts down waves while reaching in strong wind while singlehanded, so light (read, on the edge of control) was 8kts by gps. On that 5 nm crossing i averaged about 6.3 kts.  That is FLYING for the dory.  Regular sailing ona reach or downwind, figure you can average ~4kts speed over water.  Keep in mind that speed over ground can be very different!  Also, speed made good to windward is probably 3kts at best.  The boat does not tack very close to the wind and with a flat bottom and smallish daggerboard, sideslips considerably.  I have been out once with my kayak buddies who i know can average 4kts straight into a 12kt wind, and they left me in the dust going upwind. 

15

 I realized that the links I provided earlier don't work, but the graph here shows my speed during one sail on a fairly windy day. I averaged 5.3 mph with frequent bursts of speed during the gusts of 8-9 mph. My peak speed was over 10 mph. The boat feels very fast in such conditions . . . but I think I can get it going a little faster still. (The gusts were pretty brief on the day I recorded this data.)

   

16

   I had mine up to at least 75mph on I-95.

George K

17

I was looking through an older post I made about the Everglades challenge. CaptainSkully had posted this list of a potential route around the SanJuans.

Leg   From                To                 Distance (NM)

1      Chuckanut         Legoe Bay        12

2      Legoe Bay         Sucia                 9

3      Sucia                Stuart                12

4      Stuart                Friday Harbor     10

5      Friday Harbor     Anacortes           11

   6      Anacortes          Chuckanut          13

CaptainSkully if you happen to see this, have you made this loop yet? If so in what type of boat? I would love to hear all about it!!!

   

18

I just ran across this article that does more to explain the performance (and performance potential) of the Northeaster Dory than anything else I have read.

The Windsurf Loop  

If you question whether the performance of an old longboard windsurfer has anything to do with the Northeaster Dory, I invite you to think about the shape and length of the hull in the water. The dory's length at waterline is very similat to that of a longboard and its weight is not terribly different. My old Windsurfer weighed 35-40 pounds; the dory hull is about 100 pounds (but a little more when the sailing rig is added). I think the performance is also similar. The dory accelerates smoothly as wind increases. This past year I've topped out at about 10 mph as measured very accurately by gps. The boat felt on the edge of a full plane and I suspect it can be brought onto a plane safely. . . . If so, it will be a very fun ride while it lasts. 

19

   LoL

While it lasts indeed!

20

Hey guys,

Great discussion here.  Comparing a windsurfer to a NE Dory is extremely unfair.  The Dory acts much more like a displacement hull and the windsurfer creates a ton of lift, which reduces wetted surface area/drag.

Laszlo as usual, has the right of things.  The water between the San Juans is a washing machine.  The turbulence of the tides, eddies, etc. destroys steerage which is a function of laminar flow over the daggerboard and rudder.  Also, there is "canyon effect" which causes venturi nozzle consequences in some places and wind shadow, which is horizontally 10x the height of the island upwind from you.  There is very little sailing between the San Juans.  Now if you go South of them, then tack North, you might have a clear shot.

I have only skippered a flybridge power-cruiser (named Sea-Cup, owned by NautiGirl) to Roche Harbor.  It was a slow, expensive ride, using lots of fuel to navigate around things like Obstruction Island (aptly named) and steerage was mushy to say the least.

IMHO, a trip from Anacortes to Friday Harbor may very well take a long day only if you take the Southern route, below the islands, which eliminates most of the scenery.  Or, you can go between islands and take the scenic route, which would take more than ten hours under sail.

Please don't take any of this to say that it shouldn't be done/attempted.  A good VHF, dry suit, proper water-activated lights (use SOLAS wherever possible) and some camping gear on board would make this an epic trip (think GoPro and YouTube).  When I finish my Passagemaker, you will be able to find me on Sucia on any given Summer Sailstice.

BTW, here's a map I made years ago while living on Lummi Island.  A lot has changed since then.  For example, I now own a daysail charter company on St. Thomas in the USVI, where I may build a Passagemaker or Dudley Dix's Oppikat for my son.