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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Boat Buying By The Numbers
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Thread: Boat Buying By The Numbers Reply to Thread
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Topic Review (Newest First)
07-11-2013 11:12 AM
ctl411
Re: Boat Buying By The Numbers

Also check to make sure your sail areas are measured the same. Sometimes on cutters or ketches they don't list the stay sail or mizzen area. A place to check sail area is Sailrite web site they have a database of boats and you can also put in your own.
07-11-2013 10:18 AM
JulieMor
Re: Boat Buying By The Numbers

Quote:
Originally Posted by ctl411 View Post
Your numbers look high on these, you may have the math wrong???
You're probably right.

When I built the spreadsheet, I compared the numbers the spreadsheet was generating (based on formulas taken from Brewer's primer) to the numbers GoSail was generating and they were right there. So I thought they were good. Yesterday my SO found a post on a naval architect's forum that had motion comfort calculated for about 500-600 boats. Their numbers were much lower than what GoSail or I had.

I rechecked the formulas.

I used CR=Displacement in pounds/.65 x (.7 LWL + .3 LOA) x B1.333.

The NA forum used MCR = Disp / (2/3*((7/10 * LWL)+(1/3 *LOA))*Beam4/3 )

They are almost identical except Brewer calls it Comfort Ratio (CR) and the NA called it Motion Comfort (MCR).

I'll recheck the math Excel is doing. Maybe GoSail did the same thing I did and that's why the similar numbers. But I'm deferring to the NA for his numbers being correct.

Update: I forgot a pair of parenthesis in the Excel formula.
07-10-2013 01:30 PM
JulieMor
Re: Boat Buying By The Numbers

Well, the CR on this boat is 59 (according to GoSail) so she should be very comfortable!


And if sailing her doesn't kill us, we'll end up in great shape.
07-10-2013 01:08 PM
ctl411
Re: Boat Buying By The Numbers

Bob,Mule sail and we tend to forget the discussions we lose lol. Or give up on when you get bored (more likely the case).

James + 1. I've sold and bought a boat in less time.
But I've owned a few and know how bad it sucks to be without a boat.
07-10-2013 12:51 PM
jameswilson29
Re: Boat Buying By The Numbers

Quote:
Originally Posted by JulieMor View Post
...This may mean missing the perfect boat, but if that's your goal, you could be looking for years and visiting all parts of the globe...
I thought you were doing that already...
07-10-2013 12:50 PM
bobperry
Re: Boat Buying By The Numbers

ctl:
Can't say I can recall the "mule discussion".

I'm not saying Cp's are "stupid". I'm just saying a clear understanding of their merits and limitations is necessary if you are going to use it as a referance number. And it is a very hard number to find on many designs. Then, for most cruisers it may not even be relevant.

I'll talk Cp's all night long if you like. I'm easily entertained.
07-10-2013 12:46 PM
ctl411
Re: Boat Buying By The Numbers

Bob kind of a joke but she did say she likes numbers. I would also place her above typical. The typical owner doesn't even adjust jib leads lol. But from our Mule discussion I know the rules.
Stupid Stupid Stupid Cp.
Terry.
07-10-2013 12:16 PM
bobperry
Re: Boat Buying By The Numbers

ctl:
How are you going to use Cp to buy a boat?
Or, was that a joke that flew over my flat head?
I think you would be very hard pressed to even find accurate Cp's for used boats.
Not sure the typical boat buyer understand Cp enough to get much information from it.
07-10-2013 12:10 PM
MikeOReilly
Re: Boat Buying By The Numbers

Quote:
Originally Posted by ctl411 View Post
You will notice a difference in motion. Yes Ted did say it was a tongue in cheek formula but he as so said it is valide if used to compare similar size boats. Two 37 foot boats, a 37c vs. a 37.5 legend my wife noticed the difference at the dock. You could really tell the different motion out sailing. Don't discount comfort for a cruiser. I all you are going to do is day sail or race beer cans races then hop off for the night by all means buy a light quick motion boat. But if you plan to be on it for longer, a comfortable boat becomes higher priority. I'm not saying a full keel tank but really think about how YOU will use YOUR boat.
Speaking from one who has a full keel tank with a motion comfort rating of 45, I can assure you the numbers do mean something. Our previous boat was rated a very comfortable 30, and our current boat's motion is noticeably more "comfortable" when the seas get choppy and the winds pipe up.
07-10-2013 11:53 AM
ctl411
Re: Boat Buying By The Numbers

You will notice a difference in motion. Yes Ted did say it was a tongue in cheek formula but he as so said it is valide if used to compare similar size boats. Two 37 foot boats, a 37c vs. a 37.5 legend my wife noticed the difference at the dock. You could really tell the different motion out sailing. Don't discount comfort for a cruiser. I all you are going to do is day sail or race beer cans races then hop off for the night by all means buy a light quick motion boat. But if you plan to be on it for longer, a comfortable boat becomes higher priority. I'm not saying a full keel tank but really think about how YOU will use YOUR boat.
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