Robin- The m-23 IS a pure displacement hull and would have a difficult time exceeding hull speed on flat water. A 25 or 30 knot wind and a spinnaker would push things past hull speed, but not by too much. Surfing is a different story; when surfing the boat is sailing on a concave surface, and going downhill at that. Neil Clark of Tucson did the Ensenada race in his 23 in a heavy-air year, and was surfing at 12 knots. He stuck the bow and broached several times and I assume they were hanging on by the skin of their teeth. One of the guys went below and he said that they stuck the bow one time and the boat stood on end and he could see solid water out of the windows on both sides. They thought they were headed for China! We were all pretty young then. By O'Day 17 you mean the Daysailer? A good Uffa Fox design and it definitely will plane, and plane decently. It's a planing dinghy, 6 feet shorter than the M-23, but about 1/8 the weight. A displacement/length ration of 150 or less is critical for planing. A flattish bottom is helpful but the critical thing is weight. -----Original Message----- From: Robbin Roddewig Sent: Friday, July 29, 2016 3:36 AM To: For and about Montgomery Sailboats Subject: Re: M_Boats: 1) BBQ 2) m23 speed I will add that at some point either Jerry or an article I was reading about the M boat hull shape points out that it is not a totally displacement hull. It has some characteristics of semi planing. Of course planing hulls like the Oday 17 are not held to hull speed. If you look at the back of the M boat hull you can see that it flattens out a bit which is similar to the Oday 17. Happy sailing! Robbin M-23 pinch me On 7/20/2016 1:11 PM, casioqv@usermail.com wrote:
I'll second that, theoretical hull speed is no hard upper limit, it's only the point where it starts to take a lot more sail energy to go faster due to the bow wave having a wavelength longer than the boat, and the stern falling down off the wave crest.
I've often sustained 8.5-9.5 knots per GPS surfing downwind in my Catalina 22 (6.0 knot hull speed) coming back downwind from Catalina Island on a windy afternoon. The C22 rudder isn't quite powerful enough to control the boat at those speeds, and it will broach easily.
This article by our list member Dr. Judy Blumhorst does a good job of explaining why this is possible: http://potter-yachters.org/manyways/hullspeed/
Tyler
----- Original Message ----- From: swwheatley@comcast.net To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Wednesday, July 20, 2016 9:38:21 AM Subject: Re: M_Boats: 1) BBQ 2) m23 speed
You guys are talking about theoretical hullspeed, which is more like a rule of thumb than a law of physics. Boats with displacement hulls can and do exceed their theoretical hullspeed all the time, including by heeling (which lengthens your LWL), or by surfing along the front of a wave (which turns your displacement hull into a planing hull, albeit briefly). For an M23, 6.5 kts heeled and 8 kts surfing are both very plausible.