Cal 40 v. Cal 39 Performance Comparison

Tried to send this twice with an embedded screen capture of the comparison chart. No se puede, according to the mail demon. So here is the site and you can perform your own comparisons. I just want to know what it really means. I've been comparing the Cal 28 to everything in site and was glad to see the hull speeds were not all that different from her larger sisters. From: Bruce Stirling [mailto:br… [at] stirlinglaw.com] Sent: Wednesday, November 21, 2007 8:09 AM To: CalBoats Subject: Cal 40 v. Cal 39 Performance Comparison I stumbled across this site in the wee hours. There was a recent discussion about the relative sailing characteristics of the Cal 40 and the Cal 39. Here is the online comparison result based on someone's web site. It is fun to compare all boats. Go to: http://www.image-ination.com/sailcalc.html and scroll down. You can compare almost any sailboat. So what do these figures mean in the real world? Robert Bruce Stirling, II, Esq. 602.254.6638 602.460.5631 [Cell] 602.258.0706 [Fax] br… [at] stirlinglaw.com http://www.stirlinglaw.com/lawyers http://rockypointweekly.com http://groups.yahoo.com/group/freecyclephoenix/ This message is protected by attorney/client privilege. This message is intended only or the use of the person or entity to which it is addressed. If the reader of this message is not the intended recipient, or the employee, or agent responsible for delivering the message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this message is strictly prohibited. If you received this communication in error, please notify us immediately by replying to the sender of this email or by telephone. If you believe it was sent to you in error, do not read it. Please reply to the sender that you received the message in error, then delete it.

Bruce, easy reference is HS = 1.33 times the square root of the waterline. Since it goes up as the sqrt for displacement hulls, the HS number does not rise quickly. For a CAL 25 is is just about 6 knots. Cheers Charlie From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Bruce Stirling Sent: Wednesday, November 21, 2007 10:24 AM To: CalBoats Subject: [Cal_Boats] Cal 40 v. Cal 39 Performance Comparison Tried to send this twice with an embedded screen capture of the comparison chart. No se puede, according to the mail demon. So here is the site and you can perform your own comparisons. I just want to know what it really means. I've been comparing the Cal 28 to everything in site and was glad to see the hull speeds were not all that different from her larger sisters. From: Bruce Stirling [mailto:br… [at] stirlinglaw.com] Sent: Wednesday, November 21, 2007 8:09 AM To: CalBoats Subject: Cal 40 v. Cal 39 Performance Comparison I stumbled across this site in the wee hours. There was a recent discussion about the relative sailing characteristics of the Cal 40 and the Cal 39. Here is the online comparison result based on someone's web site. It is fun to compare all boats. Go to: http://www.image-ination.com/sailcalc.html and scroll down. You can compare almost any sailboat. So what do these figures mean in the real world? Robert Bruce Stirling, II, Esq. 602.254.6638 602.460.5631 [Cell] 602.258.0706 [Fax] br… [at] stirlinglaw.com http://www.stirlinglaw.com/lawyers <http://www.stirlinglaw.com/lawyers> http://rockypointweekly.com <http://rockypointweekly.com/> http://groups.yahoo.com/group/freecyclephoenix/ <http://groups.yahoo.com/group/freecyclephoenix/> This message is protected by attorney/client privilege. This message is intended only or the use of the person or entity to which it is addressed. If the reader of this message is not the intended recipient, or the employee, or agent responsible for delivering the message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this message is strictly prohibited. If you received this communication in error, please notify us immediately by replying to the sender of this email or by telephone. If you believe it was sent to you in error, do not read it. Please reply to the sender that you received the message in error, then delete it.

There is some disagreement about this 1.33 * LWL^^.5 formula. Seems it is a reasonable rule of thumb, but that a given displacement hull form may vary from this to a considerable extent. Also, that the hull speed of a given hull may be different under sail as opposed to under engine power. If you have a more-or-less correctly propped boat, finding your acutal hull speed under power is pretty easy in flat water. The horsepower to speed-through-water curve makes a pretty sharp bend at the hull speed.

Husar, Charlie [USA] wrote: > > Bruce, easy reference is HS = 1.33 times the square root of the > waterline. Since it goes up as the sqrt for displacement hulls, the > HS number does not rise quickly. For a CAL 25 is is just about 6 knots. > This is a subject that is of greater interest since I got a little GPS. The Cal 20 can do over her theoretical hull speed fairly easily. It calculates to just over 5.6 knots. On a good breezy day on a reach, I can maintain 5.8 to 6 regularly, higher in puffs. This is in an area without notable current so the GPS speed ought to be fairly accurate as through-the-water speed. That hull speed formula used to seem like one of those inexorable laws of nature that just WAS. It was a rule, something that you'd just have to live with unless you were surfing or otherwise planing. But the Cal 20 romps past it without surfing. So I sorta assume that it's a guideline, not a law or a rule. What's really interesting is that the Cal 20 is faster in similar conditions than my other boat with a foot longer on the waterline. That boat has a mechanical Sumlog that gives very optimistic speed reports--great for the owner's ego, but not for accuracy. The GPS tells me that she's going slower than the Cal 20 would likely go, or at least not a bit faster. Of course, the boats are about 140 miles apart and I can't race them--it would be fun--but you do get a sense for wind and waves and comparability. This experience confirms Charlie's comment that the square-root relationship makes the number change slowly, that a small waterline length change doesn't do a lot to hull speed. Chris Campbell

--- In Ca… [at] yahoogroups.com, Chris Campbell <clcampbell@...> wrote: > > Husar, Charlie [USA] wrote: > > > > Bruce, easy reference is HS = 1.33 times the square root of the > > waterline. Since it goes up as the sqrt for displacement hulls, the > > HS number does not rise quickly. For a CAL 25 is is just about 6 knots. > > Before making my Ebay purchase I'd never heard of hullspeed or the calculation used to figure it out. When we took possession in Oceanside and moved her to San Diego my brother first mentioned it to me. He calculated away as we headed south. I was impressed. My mind glosses over when I hear math formulas. My little brother, though, once tested as some kind of wizard in elementary school, and to confirm it, he came out number one on the Arizona Bar Exam in February 1979. I just use him as a great resource. But I was surprised to note the Cal 40's hullspeed was only about one mile per hour faster than the Cal 28. I assumed that if I ever found myself in a drag race with a Cal 40, that she would walk away from me a little bit faster than at just one mile per hour. I take it that's where all the other variables kick in. So how long would the Cal 40 remain in sight, more or less? So how come those damn catamarans on the Potomac in D.C. would blast past us in our Mobjacks like we were standing still? We were standing still, but for the current taking us to Ft. Belvoir. I guess that's the displacement hull v. lack thereof, or something like that.

Bruce Stirling wrote: > > > > So how come those damn catamarans on the Potomac in D.C. would blast > past us in our Mobjacks like we were standing still? We were standing > still, but for the current taking us to Ft. Belvoir. I guess that's > the displacement hull v. lack thereof, or something like that. > You've got it. Planing hulls are not limited by any theoretical hull speed. For displacement hulls, the limit is created as the hull tries to climb up onto plane, making a big bow wave that it can't overcome. Planing hulls are designed to be lighter (usually) and to have a shape that encourages getting up on top of that wave, as well as enough power to get there. I've read that even our sailboat hulls will try to plane if pulled with enough power but that when they do, their hull shape causes really unpleasant consequences--substantial misbehavior. Chris Campbell

Actually, I believe most sailing catamarans are non-planing designs. However, because of their high length to beam ratio, the usual hull speed formula for monohull displacement boats does not apply. Harleigh Ewell From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Chris Campbell Sent: Wednesday, November 21, 2007 4:11 PM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] Re: Cal 40 v. Cal 39 Performance Comparison Bruce Stirling wrote: So how come those damn catamarans on the Potomac in D.C. would blast past us in our Mobjacks like we were standing still? We were standing still, but for the current taking us to Ft. Belvoir. I guess that's the displacement hull v. lack thereof, or something like that. You've got it. Planing hulls are not limited by any theoretical hull speed. For displacement hulls, the limit is created as the hull tries to climb up onto plane, making a big bow wave that it can't overcome. Planing hulls are designed to be lighter (usually) and to have a shape that encourages getting up on top of that wave, as well as enough power to get there. I've read that even our sailboat hulls will try to plane if pulled with enough power but that when they do, their hull shape causes really unpleasant consequences--substantial misbehavior. Chris Campbell