RMC - Righting Moment Corrected calculation

[Emerald]

Hi,

Does anyone have any idea how to calculate the RMC - righting moment corrected, which is the moment required to heel the boat one degree?


I am trying to find this for use in a formula for calculating forces/loads under different wind conditions. Here's the page where RMC is required:

http://www.wb-sails.fi/news/SailPowerCalc/SailPowerCalc.htm


BTW, there is reference to looking at your IMS certificate, which I doubt exists for a 1979 Independence 31. Anyone know anything about IMS also?


Thanks


-David
Independence 31
Emerald

 

[Seth]

Rmc

David,

You are right, I doubt there are any IMS certificates issued for the I/31 anywhere.
The best way I can think of is to google "IMS Rule" (which was developed by Jerome Milgram at MIT), or if that won't lead you to the actual RULE with all of the formulae, try "Americap"-this is derived from IMS, and may have it also. If all of that strikes out, the IOR rule also had a RM calculation-which may have been done slightly differently, but would be close enough. Let's see...You might also try MORC-this is another handicap rule (now almost extinct sadly, but there are pockets around the US) intended for boats up to 30' LOA-it also has a RM calculation. On of these should lead you to the formula to figure it out. I would do some research for you, but I am off to Paris for 5 days-I'll be out of pocket until late next week. Bud has an Americap cert-he may be able to help you...

Good luck!

S

 

[Guy Stevens]

Actual?

I have in the past used a measured number for this. It is pretty complex, but I will share the whole process with you.

It involves some fat friends, or on your boat some not too fat friend, a 6 pack of beer, string, a washer, a pencil, and a calculator.....

Call the fat friends, or not too fat friend over. While they are on the way, place the 6 pack of cold beer on a rail of the boat. Position the six pack at a distance that you have measured from the centerline of the boat.

Use the string the washer, a piece of paper to make a pendulum in the boat. When the fat friend goes for the beer, measure the heel, ask the friend what he weighs. A question such as; "Man what a lard butt, how much do you weigh?", won't get a good answer. More like; "You seem to have lost some weight, what are you at now?", will.

Of course, after drinking the entire six pack your math will have to wait till the following day, but hey what are friends for.

Guy

 

[Emerald]

Of course, very cool and makes sense, some basic physics and math - high school academia was worthwhile after all


I guess it's suicidal to do this with a spouse, regardless of her wieght, I can hear it now - I made the boat heel how much?!?, are you saying I'm....:eek:


-David
Independence 31
Emerald

 

[NateHanson]

Ferenc Mate has a description of this calculation in his book "Shipshape", one of my favorite boat-maintenance reads.

 

[footrope]

Guy,

I'm kind of ashamed about how hard I laughed at your post. I mean, it's the righting moment, a real serious subject. But, all that talk about a 6-pack inspired me :thinker: to go make myself a martini while I dried my tears.

Sigh. I should be working on the hatch lid.

 

[Emerald]

Hey, if you laughed that hard, it was all worth it. A good laugh is one of life's gifts, even if it is tied to a serious subject.

I've got to launch before I can implement the six pack test. Hoping next week. It will be interesting to see if the numbers make sense when I am done with the sixpack and run my calculations


-David
Independence 31
Emerald