A question was thrown at me recently and I could not give or find an answer in either the discussion "search" or on either of the building sites. Consider the following.
A new EC12 is built using the lightest yet strongest materials available (including 18 pound ballast and foam core decking). The total weight of the boat with rig and batteries is close to 23 pounds. Yet when the completed boat is placed in the water tank and measured, it's minimum waterline length is way too short. Additional ballast is required to reach the minimum.
Now consider the weights of the various boats measured at the 2005 NCR's. They range from 22+ pounds to 25+ pounds. Finally, on Rick's building web site he mentions that lighter building methods are being used since the 2005 Nats.
Understanding that the heavier boats are probably nearing the 43" maximum, how in the world are the lighter boats meeting the 42" minimum?
Is it beam width? Is it the degree of trim (bow up or down)?
Any of you light boat builders want to give away a secret?
Thanks.
Skip Allen
Atlanta [:D]
Waterlines and Weight
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Waterlines and Weight
by skip241 » Mon Jun 15, 2009 2:11 pm
- skip241
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by Rick West » Tue Jun 16, 2009 9:18 am
Skip,
Understanding that I do not know the Physics or the Math for displacement calculations, I do know that weight over mass in the water will produce a waterline footprint.
The Class has never presented specifications for the waterline of the EC12; meaning trim, beam measurement and whatever else would fall into the issue. Those two would seem to be the biggies.
The data taken during 2005 with keel measurements was to identify that problem in the rules. Because we cannot control this anomaly after manufacture the keel specification is not enforceable except below the minimum. The weighing of the boat was to get data versus the measuring sheet to determine a base for weighing boats at sanctioned events rather than the tank measurements which has been a logistical pain for years.
The conclusion was there were some very minor differences produced by boats with varying beam measurements at the narrow and wide edge of the Rule. The major change to the waterline was positive trim in excess of one degree. These boats tend to exceed the waterline Rule while falling into the norm of the weight data. Fat keels and boats dragging a waterline near the transom are not competitive.
The CAC consensus was not to change the waterline Rule to a weight moment because the latter was not a finite number.
The lighter we build boats the lower we bring the righting moments of the mass. This is the positive reason for me to build lighter boats because more ballast is needed to make the 42 line and adding weight lower in the hull. In my mind with reasonable casual thought regardless of how light you build, the total boat ready for the water will all be so close to the same weight at 42 because of the balance of building technique and ballast needed.
Ergo, an EC12 meeting the liberal beam measurements that we have will weight xx.xx and be so close to all the other boats measured to not matter. Trim does matter to drag if the boat is sailing off its lines. My experiments have shown me that a level to minus degree boat trim with the sails under pressure handles better. Better handling translates to less drag in my limited mental processes. Hence, I build light with integrity in mind and ballast for trim and to hit around the 42.5 line. I multiple ballast because I do not know the tank or the measuring details at a major event.
So, when discussion talk about the total weight of the boats getting lighter, I say then you have more room in the Rules for ballast. It is one or the other. Right now it is near impossible to build a boat ready for the water with no ballast in her using the approved materials to less than 5 pounds. Just to throw it outif you can be at the 42 line with 18.5 pounds of ballast, you will be quicker that a boat with the same ballast at 43"...without consideration for heavy air.
...94![[8D]](./images/smilies/icon_cool.gif "Cool")
Understanding that I do not know the Physics or the Math for displacement calculations, I do know that weight over mass in the water will produce a waterline footprint.
The Class has never presented specifications for the waterline of the EC12; meaning trim, beam measurement and whatever else would fall into the issue. Those two would seem to be the biggies.
The data taken during 2005 with keel measurements was to identify that problem in the rules. Because we cannot control this anomaly after manufacture the keel specification is not enforceable except below the minimum. The weighing of the boat was to get data versus the measuring sheet to determine a base for weighing boats at sanctioned events rather than the tank measurements which has been a logistical pain for years.
The conclusion was there were some very minor differences produced by boats with varying beam measurements at the narrow and wide edge of the Rule. The major change to the waterline was positive trim in excess of one degree. These boats tend to exceed the waterline Rule while falling into the norm of the weight data. Fat keels and boats dragging a waterline near the transom are not competitive.
The CAC consensus was not to change the waterline Rule to a weight moment because the latter was not a finite number.
The lighter we build boats the lower we bring the righting moments of the mass. This is the positive reason for me to build lighter boats because more ballast is needed to make the 42 line and adding weight lower in the hull. In my mind with reasonable casual thought regardless of how light you build, the total boat ready for the water will all be so close to the same weight at 42 because of the balance of building technique and ballast needed.
Ergo, an EC12 meeting the liberal beam measurements that we have will weight xx.xx and be so close to all the other boats measured to not matter. Trim does matter to drag if the boat is sailing off its lines. My experiments have shown me that a level to minus degree boat trim with the sails under pressure handles better. Better handling translates to less drag in my limited mental processes. Hence, I build light with integrity in mind and ballast for trim and to hit around the 42.5 line. I multiple ballast because I do not know the tank or the measuring details at a major event.
So, when discussion talk about the total weight of the boats getting lighter, I say then you have more room in the Rules for ballast. It is one or the other. Right now it is near impossible to build a boat ready for the water with no ballast in her using the approved materials to less than 5 pounds. Just to throw it outif you can be at the 42 line with 18.5 pounds of ballast, you will be quicker that a boat with the same ballast at 43"...without consideration for heavy air.
...94
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Rick West - Posts: 3204
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by skip241 » Tue Jun 16, 2009 1:29 pm
Rick, I think I understand what you are saying, but, in my simple mind, consider this.
With the exception of Charleston, most of the regatta's in the Dixie Cup and in certain Florida venues, the wind ranges from nothing to a gentle breeze. If you have two boats with the same waterline, but one of the boats is 1-2 pounds heavier, isn't it easier for the wind to push the lighter boat resulting in faster speeds?
Maybe we're getting too concerned with the weight thing.
(P.S.- I haven't smashed "Grape Surprise". Everything is working again including the radio.)
Skip [:D]
With the exception of Charleston, most of the regatta's in the Dixie Cup and in certain Florida venues, the wind ranges from nothing to a gentle breeze. If you have two boats with the same waterline, but one of the boats is 1-2 pounds heavier, isn't it easier for the wind to push the lighter boat resulting in faster speeds?
Maybe we're getting too concerned with the weight thing.
(P.S.- I haven't smashed "Grape Surprise". Everything is working again including the radio.)
Skip [:D]
- skip241
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- Location:
by geeks2you » Tue Jun 16, 2009 7:00 pm
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by skip241</i>
(P.S.- I haven't smashed "Grape Surprise". Everything is working again including the radio.)
Skip [:D]
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
Yay!!!!!
EDIT: I guess my new sails made all the difference at Elon
I ended up squeezing my beams on the bow stations narrower then before the redecking. My waterline was at ~42 1/4" rough measured and I know that I was able to take out weight from when I had originally bought <i>Spot</i>. Last time I weighed her she was just south of 23#, but since I have lightened the rig a rig a bit, but not enough to make too much of a difference. I am sitting just about neutral trim currently but have the ability to move my battery storage fore or aft depending on the water conditions. <i>Spot</i> does have a fat keel (Old Ozmun hull) but she is not dragging her fat ass in the water which it seems is a good thing. My beam stations are all narrow until you get to about 45" then they go mid measure then actually wide near the stern. When I asked around it seems that most of the Ozmuns had/have a fat stern though.
Eric Olson
Atlanta Model Yacht Club
AtlMYC.org
(P.S.- I haven't smashed "Grape Surprise". Everything is working again including the radio.)
Skip [:D]
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
Yay!!!!!
EDIT: I guess my new sails made all the difference at Elon
I ended up squeezing my beams on the bow stations narrower then before the redecking. My waterline was at ~42 1/4" rough measured and I know that I was able to take out weight from when I had originally bought <i>Spot</i>. Last time I weighed her she was just south of 23#, but since I have lightened the rig a rig a bit, but not enough to make too much of a difference. I am sitting just about neutral trim currently but have the ability to move my battery storage fore or aft depending on the water conditions. <i>Spot</i> does have a fat keel (Old Ozmun hull) but she is not dragging her fat ass in the water which it seems is a good thing. My beam stations are all narrow until you get to about 45" then they go mid measure then actually wide near the stern. When I asked around it seems that most of the Ozmuns had/have a fat stern though.
Eric Olson
Atlanta Model Yacht Club
AtlMYC.org
- geeks2you
- Posts: 61
- Joined: Sun Apr 19, 2009 1:37 pm
by Rick West » Wed Jun 17, 2009 10:47 am
Skip, I agree that lighter is faster in acceleration. That was the purpose of multiple ballasting. It is also evident when sail plan vectoring causes a light boat to inch forward in drifting conditions when the rig is vertical with no heel.
What I was saying and thinking is that two boats of the same trim and waterline (sitting in the water or tank) will be very close to the same weight; plus or minus the beam footprint. The latter being minor in most cases unless you built one boat to fractions of the narrow limit and another fractions of the wider limit. Build another boat for mid range and you would have boat choices for anticipated sailing condition. Only a few in the class do that, very very few.
Having spent 10 years racing on the East Coast and learning from all that rise above the radar on the circuit, I have come to believe much of this is micro knots with the exception of drag and the properties of balance in maneuvering. Most of the micro knots I have gained in building technique and thought is most often lost by actions of my right thumb.
I think Elon is unique to all other places where wind lanes often are only 18" wide even when overlapped with several boats. It would be hard to build a boat for this...maybe a mat for praying.
...94
What I was saying and thinking is that two boats of the same trim and waterline (sitting in the water or tank) will be very close to the same weight; plus or minus the beam footprint. The latter being minor in most cases unless you built one boat to fractions of the narrow limit and another fractions of the wider limit. Build another boat for mid range and you would have boat choices for anticipated sailing condition. Only a few in the class do that, very very few.
Having spent 10 years racing on the East Coast and learning from all that rise above the radar on the circuit, I have come to believe much of this is micro knots with the exception of drag and the properties of balance in maneuvering. Most of the micro knots I have gained in building technique and thought is most often lost by actions of my right thumb.
I think Elon is unique to all other places where wind lanes often are only 18" wide even when overlapped with several boats. It would be hard to build a boat for this...maybe a mat for praying.
...94
-
Rick West - Posts: 3204
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