Brian’s remark in another thread caught my interest, and I happen to have an excess amount of time on my hands today. So, using the formula that theoretical hull speed = 1.34 * Sqrt(waterline length), I looked at all the available Nonsuch manuals and came up with this table:
Nonsuch Model
LOA (ft.)
Waterline Length
Approx. Theoretical Hull Speed
Naiad 18
Nonsuch 22
22.00
20.50
6.07
Nonsuch 26
26.00
24.38
6.62
Nonsuch 260
26.00
24.00
6.56
Nonsuch 30
30.33
28.75
7.18
Nonsuch 324
30.33
28.75
7.18
Nonsuch 33
33.42
31.46
7.52
Nonsuch 354
35.33
33.46
7.75
Nonsuch 36
36.00
33.75
7.78
Under the right circumstances, our boats can exceed this theoretical limit.
With the help of fair winds, friendly currents, and following seas, the max my N26 has hit on my GPS was 7.8 knots speed over ground.
I just helped my friend Phil post his N36 on the INA Marketplace, and noticed that the information includes a photo of his knotmeter registering at 9.1 kts.
I’d be curious about other folks’ records for their boats, and the conditions under which they observed them.
Bob,
That is some nice data on hull speed.
Phil’s 36 on the left coast is nicely appointed and going for about the same as one here on the right coast. Well done Phil if I may by so bold.
Brian
Hull speed is actually a point on a power/resistance curve where it takes very large increases of power to produce any measurable increase in speed. Each hull design is going to have its own curve, though most are so similar that it’s possible to make an arbitrary hull speed formula. Some people say it’s the square root of the waterline length, some say 1.2 times and some say 1.34 times the square root. I suspect that none of them are wrong, but they apply to different hull shapes. 1.34 is what I usually see associated with sailboats and that makes sense because our hulls are as low-resistance as it is practical to make them.
But it’s not an absolute number, it is just the point where it starts to take much more force to gain any increase in speed, so it is possible to go past it, as Bob’s chart shows. I was a rower for many years and have rowed a number of different kinds of single and double rowing shells. And it is very obvious that the curve on such a fine hull form has a much more gentle dogleg in it than on a sailboat because even human muscle power can push a shell well past its hull speed if measured by the 1.34 formula. Two people in a 32’ double shell can go probably close to 11kts. I’ve done a 10K in around 30 minutes which I just computed is about 10.8kts, and the double was not my usual boat. And it could probably go even faster in a sprint.
So yeah, I think it would be cool to see if we could flesh out that chart with measured maximums for the various boat models.
Waves travel through the water at a speed directly related to their wave length. The waterline length of your boat generates a fixed wave length. The hull speed calculation gives the speed of that wave length. Any boat can exceed its hull speed but you start to climb your bow wave and your stern starts to drop into the trough causing much higher drag and under power huge increases in fuel consumption. Under sail we get free fuel so we don’t worry about that and if the wind will supply the power we can exceed our hull speed.
Then there is surfing on following seas……
My top speed (STW) was on a run in around twenty knots of wind and seas big enough to give me a boost. I may have hit ten when I wasn’t looking but I did see 9.9.
The theoretical hull speed is an approximation based on a displacement boat that sits in the water. Planing hulls (e.g., a Laser or a racing shell) that sit on the water can do a lot better.
Semi-displacement hulls have the potential to get out of the water and plane under the right condition. I suspect that, because of the design influence of Finns and Lasers, Nonsuches may have some element of that DNA.
Here’s a picture of my boat at a rare point where it was clean and shiny. I think it shows how the hull shape could give our boats a fighting chance of doing a bit better than the theoretical limit.
Laser does plane, but a racing shell is most definitely and 100% displacement. To Paul’s statement: it just generates such a small bow wave that it is easy for even human muscle to climb over it, or punch through it, however it actually goes I am not sure.
Also, some might find it entertaining to learn that my friend and I used to go up into the commercial harbor in Portland (OR) and surf big tug boat wakes when the wind was so bad that we were going to have a miserable row anyway. Nice thing about tug boat wakes is that they don’t break after just a few feet like ocean surf. You can ride them as long as the tug keeps going and you don’t dig in your bow and broach. Oh, to be young again…
Christian_Pastore
(Magic Time, NS22 electric, Fishing Bay Yacht Club, Deltaville, VA)
8
I have briefly hit 6.4 SOG in my 22. I have no way of measuring speed through the water but I assume it was less.
Your explanation of hull speed, is exactly why, my latest obsession with Soave has been forward/aft trim. A slight bias of weight aft increases the percent of time the stern is experiencing excess drag. Not an issue, unless you are competing with other boats that are optimized for local conditions.
In the limited experience I’ve had racing Soave, it seems like over 10 knots of wind, we’re OK. I suspect a loaded Nonsuch rig has a “bow down” effect on forward/aft trim. Over 14 knots we become more competitive against the Catalina, Saber, Tartan, and Pearsons in the fleet. Forget about the J-boats and X-boats not much we can do against them, luckily they mostly sail in the spinnaker division. A reason not to explore spinnakers on Soave.
Thanks for presenting the topic so clearly.
Rob….
timcordes
(Tim Cordes - Nonsuch e26C #32 "ENCORE" - Ford Yacht Club, Grosse Ile, Michigan)
10
My 26c hit 6.85 knots when I was singlehanding with one reef tucked in on a beam reach in blustery winds off the north shore of Lake Erie near Colchester Reef.
Yea…. I second the thought… Oh, to be young again !
I like that you make a distinction between planing and surfing.
I wonder what top sustained speeds folks have experienced in their Nonsuch boats. Over say 10 minutes ( several surfing cycles).
Maybe a knot or two over hull speed ?
NS233
(Bob Neches, Me Gusta, Nonsuch e26U #233)
16
As a moderator , my reaction is less infuriation and more along the lines of, neat idea, now why didn’t I think of that?
If the conversation goes way off into this, we’d simply fork those posts off into a new topic. Ditto for any posts discussing whether or not “infuriation” is a real word.
Veering back onto topic, what strikes me about so many of those videos is that it doesn’t look like the boat’s working particularly hard or moving at all uncomfortably. Nice boats we got here.
Mark Powers just sent me a spreadsheet with a LOT more calculations on the boats, along with comparable figures for other common makes. I’m trying to get him to post it with some background on how it came together.
It is comfortable Bob, and yes we have amazing boats. Singlehanding in that weather was just another day at the office.
I know Mark has done a bunch of research on this. It will be interesting to see what he has.
FWIW, when I was building I seem to remember the formula for hull speed as being 1.1- to 1.4 X the square root of the waterline with the 1.1 to 1.4 part determined by a combination of design factors, mainly prismatic coefficient.
Those are all “rules of thumb” and each has its die-hard advocate. If you tracked them down I suspect you’d find that trawler designers adhere more to the 1.1x, sailboat designers adhere more to the 1.34x, superyacht designers adhere more to the 1.2x, rowing shell designers don’t bother because there isn’t such a determinate point on the power/speed curve for such a long, narrow boat.
NS233
(Bob Neches, Me Gusta, Nonsuch e26U #233)
19
Haven’t gotten @RMP (aka Mark Powers) to post his spreadsheet in this thread, but I took the liberty of updating the INA website miscellaneous boat information page ( International Nonsuch Association - Misc. Boat Data ) so that it now includes the data I posted earlier and a link to the spreadsheet from Mark.
Here it is. Didn’t realize you were waiting on me. Sorry.
It came together by me spending a bunch of time collecting numbers from the manuals and inputting the data in to sail calculators like Tom Dove. I came across some discrepancies in the numbers so some of the calculations might need revision. I also keep thinking about the format. I think a different layout might be easier to view. 1.34 times the square root of the waterline is the formula used for hull speed in the calculation sheet. It made sense with boat designs from the 1950s and earlier but as boat shapes have morphed into flatter bottoms and wider sterns 1.4 is often used. I have a theory that with the big sail keeping a nice airfoil shape place right at the bow that in stronger winds the stern of the Nonsuch starts to lift so are not climbing out of such a deep hole and this allows our boats to exceed theoretical hull speed down wind even when we are not surfing. La Reina (26C) has exceeded 8 knots through the water without sliding down waves. Highest speed was 9 knots but that was wave assisted. I could go even faster if I changes the calibration on the knot meter .Beam reaching 7.5 is about the max.
Sorry, can’t find the paper clip to attach the spread sheet.
, my reaction is less infuriation and more along the lines of, neat idea, now why didn’t I think of that?
.Beam reaching 7.5 is about the max.