Posts Tagged ‘question of the week’
Question Of The Week
SA’er ‘Allen’ asks the community to weigh in on his tacking calculations.
I have been trying to figure out not how long it takes to tack but rather how much time it costs to tack. My boat is probably not typical as it is old and wood and has a long fin keel with the rudder hung on the end of the keel. I know it takes about 15 seconds to tack but part of that time is spent going directly up wind, which is the direction I would really prefer to go so there has to be some benefit to that.
I took a GPS track of a tack from our last race in which we did a lot of tacks, mostly on wind shifts, but this particular tack was not on wind shifts so I had a constant bearing before and after the tack. I then calculated the speed at each second toward a point a long way away. I adjusted the location of that point until the average speed before the tack and well after the boat settled down after the tack was the same. Next I compared the average speed of the entire sample, which was 200 seconds, to the steady state speed.
The conclusion was that while it took about 15 seconds to tack and my speed dropped from 6 knots to below 4 at the worst point, my average speed to windward only went from 3.9 knots to 3.6 knots. The net loss was just under 5 seconds or 9 meters to windward. Clearly the loss of speed was compensated by the almost full 6 knots toward the far off point as I turned the boat before it slowed down.
Has anyone done or seen this kind of analysis? Does my technique seem correct? How much time do other boats lose when tacking?
For reference, my boat is 36 feet long, 12,000 lbs.
Follow the discussion or weigh in with your own ideas here.
August 11th, 2014 by admin
Let’s say that you want to build a boat (or more accurately, get a boat built) to a design/concept that you cannot find in normal sailboat production. What you want is off-the-charts enough that there’s nothing out there that’s even close to it. At this stage, you already understand that resale value of what you want will be close to zero…and you don’t care. You have some engineering background but you are no yacht designer, so it’s time to get help from a pro. But how?
How do you select a yacht designer?
How do you approach him? Do you just email? “Hi, I want you to design a boat for me, can we talk?”
How do you frame a contract/deal so all parties are happy? How do you define the “deliverables” (some sets of drawings could be considered “enough” for the designer, where you are expecting fully detailed construction drawings, etc.)
Are there “predefined/preformated contractual agreements for yacht design?
How do you manage the timeline? How do you know you are not getting ripped off?
If anyone could share their experience, it would be a big help. Without naming names, if you do not want to…
This is about EXPERIENCE. If you’ve never been through part or all of the process, go away.
August 5th, 2014 by admin