Building wide or narrow within the rules

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Building wide or narrow within the rules

Postby s vernon » Thu Jul 07, 2011 11:26 am

A narrow front end will allow the boat to sink more for a given boat weight.

It is logical that building the boat to be minimum width up forward (with diminshed buoyancy near the bow) might make it so the boat will dive more on heavy air runs.

Two boats raced at the Disney Nationals in 2009 at weights of about 22.3 pounds (less than 22 plbs 5 oz); Hickman hull HIC0569 and Brawner hull DBY0027. I assume they are both 95 standard hulls.

Edited after Carl and Bob's responses. I had hoped to draw out building experience info from people with regard to building wide or narrow boats with respect to boat weight at a 42 inch waterline, but that might not happen.

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Postby Carl » Thu Jul 07, 2011 9:04 pm

Scott,
The data on the boat weights at the 2006 Nationals may be very misleading.
A 1995 std hull can never meet the minimum water line below 23# and a few more ounces.
Note - (Nothing about a Dumas Hull)
Before 1995 they trim out in the 22# range.
I built up a 1977 hull and it trimmed out even lighter.

You should get a lot of comments on this subject.

A good start is better than a light boat.

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Postby greerdr » Sat Jul 09, 2011 5:12 pm

A narrow bow DOES seem to bury in 10-12 knots.

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Postby RMDJBD » Tue Jul 12, 2011 2:31 am

Scott
The Nat's in Disney were in 2005 not 2009.

The weight vs waterline vs beam has to many variables since before the new mold's came out in 2005. The mold's prior to 2005 were all over the place, some were full forward and some were skinny, I know since I have a 95 Hickman and a 95 Robin, the hull's are different.

The only way you can start collecting data is from the Hull's made out of the 2005 molds which are the same since they came off of the same master plug.

You also have more variables:
1) Hull, is it 1001 grams or 1060-1100 grams, Yes, this makes a difference, don't forget I build complete boats.
2) Deck, Wood or composit.
3) Rudder, does it float or not, does it fill up with water and go negitive bouncy.
4) Ballast, long pour, short pour, tall pour and placement. Is it 99.99% pure lead or tire weights or have Antimony and Tin in it, you can loose up to 30% by volume when using second pour lead (Tin/Antimony and or Tire weights).

How are you weighing the boat, with 350grams on deck, with rig ( A or B )or no weight or rig.

Like I said, you need to use numbers from hull's from the 2005 molds since they come out of the mold with the same underwater displacement numbers.

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Postby Rick West » Tue Jul 12, 2011 2:16 pm

There has been discussion on this before. It is one of those many searches for micro-knots. I personally like handling first.

I agree with Bob Dudinsky on the variables and there are others. Boats that are weighed and reported are not always ballasted the same. The amount of ballast in the boat, if one piece, is not known. (The first thing I do in building a NEW boat is to document the weight of the hull, deck, rudder and primary ballast. If multi ballasted, I weigh all the pieces after sawing and the same when adding pieces for trim. Know the weight of the rigs. The 2006 NCR was the only I have seen to weigh the rigs to use the proper pig on the boat in the tank.)

If you are looking for comparisons, it is very hard to do. Building multiple configured boats in a controlled experiment is outside financial reason. Even for the data in the manual Optimizing did not do this.

Regardless of building efforts, a boat with 2 degrees of bow up trim will have a longer waterline than the same boat trimmed to level in the same tank.

Lastly, lakeside event measuring is notoriously inaccurate from the start with no controlled standards for the measurement. If you will look at The Weight section on the Building Site, you will see a controlled process with a properly leveled table and tank and measurements all perfectly square. This tank easily measures to a 1/16th of an inch.

94 is trimmed to be level under power. As such, she has been illegal at the lake and forced to take out the 1-1/2 pound Big Foot to make the 43 waterline. At another she barely made 42 with Big Foot inside. I generally sail with BF, as she is better balanced. So, I am not big on tanking at the lake but live with it.

I have build narrow and wide. Each is for a water and wind condition. That is not good. A traveler needs to have a boat for all. Here is my opinion from experience on narrow beam up front: It exponentially increases the rate of bow down driven by the moments of the rig under pressure. I do not like big changes to varying wind conditions in competition.

If all these things are considered in building, tuning and trimming and she is sailing on her lines under power, she will be all she can be and love her.


...94 [8D]
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Postby greerdr » Wed Jul 13, 2011 6:02 pm

Well said Ric.
Think about where you are going to sail most often:I found a narrow forward section will bury (submarine) more often than others in a breeze. With skinny forward sections
I could point higher upwind but just one spin-out / submarine canceled all that out.
I think going for "middle" numbers on beam -from bow to stern- is the way to go.
It really seems our fleet has reached a point where a "microknot" here or there is not going to win.
Have a boat that does not fail during a race (my major problem with batteries,switch,xmtr,etc) and stay calm on your thumbs.
There is always a superior sailor on the pond next to you to help with tuning.
Fair winds and following seas-get her on the water-it is summertime!

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Postby s vernon » Fri Jul 15, 2011 8:18 am

Rick West wrote: Regardless of building efforts, a boat with 2 degrees of bow up trim will have a longer waterline than the same boat trimmed to level in the same tank.

In the thread Waterline and Weight Dave Brawner wrote: The two methods of getting a lighter boat down to the waterline is to ... have the boat a bit bow down.

I read Optimizing page 48 which has words similar to Daves.

My feeling is that Ricks and Daves statements are the opposite of each other, but I have found that words have a funny way of not meaning what I think they mean, so I am not going to bet on that.

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Postby Rick West » Fri Jul 15, 2011 12:50 pm

Bill Cullen and I have spent many hours testing in a finely calibrated tank. A bow up trim in the tank barely moves the waterline at the bow to the aft. However, the waterline moves greatly aft at the stern measurement point; exponentially to trim up. That is an increase in the waterline. It is not my opinion.

I do recognize the reference to excellent builders and the documentation done in the 90's. Larry Robinson made the sails used by 11 time National Champion Kelly Martin. Kelly's boat was trimmed and tuned to the research and his history in full scale sailing. Kelly trimmed for a level boat if not a bit down in the bow.

Bill and I noted this and checked it out. I have been sailing to this trim since. About a half degree in the tank levels her out with wind pressure (generally). This does not make her faster but when the seas are up she is digging through the impacts. There is sailing history for this and all of this has been open source.

Two degrees bow up was the standard when I arrived. So was a deeper cut of sails on a straight mast. It produced many champions. Today, if you will study the boats and rigs of good sailors directly from behind, you will see flatter sails, tighter main leeches and more narrow slots. This tuning is in general and not for all conditions but the trend is there. I also do not see the trim up as there used to be. This is better seen in photos of boats that are digging in and driving. There are some great photos of starts at the 2007 and 2009 NCRs of the boats that hit the line powered up...bow down and main footed slightly. It is a beautiful thing.

Boat performance is good. You need a base. Placing well is in the person.

We need a volunteer photographer for the 2011 NCR...serious. It is the best show of the year.

...94 [8D]
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Postby rayhall » Fri Jul 15, 2011 3:01 pm

Not to change the topic, I'm coming to the Nats and will happy to take pics, just bought a new Nikon D5100 with a couple of lens....
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Postby Rick West » Sat Jul 16, 2011 11:33 am

Thanks, Skip. Will you be sailing?

...94 [8D]
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Postby rayhall » Sat Jul 16, 2011 10:57 pm

I don't think so, Bill Ewing and I will drive down togeather. I just would get in everyones' way, probably next year....
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Postby pgfaini » Sun Jul 17, 2011 11:44 am

Are Dumas hulls noticeably wider? My #614 weighs 24lb-14.5oz with batteries. Adding the 12oz pig, this comes to a total of 25lb 10.5oz. To get a 42.5" waterline.



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Postby s vernon » Mon Jul 18, 2011 11:04 am

The only info I have is from Reichard on this discussion group and from Optimizing page 22. The first info is from a thread with the word relic in it.

This is last paragraph of Reichard's post. To sum it up, strip the old boats down to the bare hull. Remove all excess weight, striving for the minimum 2.2 lbs. (or as close as you can). Build a light deck and pour the ballast to the maximum waterline. Don't discount all of the older girls yet as some may have plenty of whoop-ass left in them.

I added up the weights that Reicard listed and guessed at others for Rick Gerry's Dumas.
Known
Hull slightly more than 2.5 lbs
Deck 8.5 oz
Lead ballast 17 lbs

Guesses
Rudder 3 oz
Electronics 1 #
Rig 13 oz
Misc glue and parts 1 lb

Total of 23 lbs on a 43 inch waterline. That should be a conservatively high estimate.

There is a Dumas listed in Optimizing and it is built as a light air flyer. YRN 919 is definitely 42 inches or more for it to be listed in the book. The weight of boat per page 22 is 20.64 lbs without the rig.

The weight of these boats is crazy maybe impossible to understand. I just bought a 95 standard boat from 2004 and it is built max rules wide all the way. It weighs 25.2 pounds ready to race (on a digital bathroom scale (that I believe is very accurate) sitting very level with Krylon painted bottom on a barely 42 inch waterline. Should be a fun project trying to get it to settle down into the water better. Keel width is the standard just slightly over 2.1 inches and that wide spot is hard to find, with the rest of the keel being narrower.

The funny thing to me is that when I sailed this boat it felt corky and I thought it might be underweight.


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Postby Bob Wells » Tue Jul 19, 2011 3:19 am

Scott, the Dumas hulls that I've seen had skinny keels that accept less ballast and present less frontal area for the water to flow around. It has been a while for me, but they accelerate better than a conventional 12 in the light air. That is the good news. They were hopeless in heavy air, and I think it would take a skilled builder-skipper to do well in medium air. When it gets to medium air you are at a disadvantage to the conventional 12s.

My broad thoughts to rebuilding a Dumas:
-Max beam to get as much lead as you can into this tender hull.
-Go with multiple ballast and be stern down in heavy wind. I wouldn't be bow down in this tender boat even in light air. Experiment to determine how much stern down?
-You need a rig that depowers well in medium - heavy wind conditions. That means a round mast to flatten the main, and not a stiff teardrop. I would include a 1" long main traveller on a Dumas in particular as part of the depower arsenal, but would want one on any 12 that I sail for this purpose.

A good Dumas rebuild has the potential to be a fleet irritant in light air and hang-in in medium air, but it takes a good build and skilled tuning. The heavy hull layup includes lots of gelcoat on the ones that I've known, so sand it like fairing compound for a sweet smooth hull. The only component heavier than the hull is that deck, I trust that you'll trash it.

Bob
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ps: I inherited a new Dumas kit in the 90s, but alas never got around to building it. While I thought it would be interesting to try the above just to see what it would do in the 12 fleet, that is a lot of work for limited performance. Mine is now an EC-11.9, but not destined to be an EC12[:)].
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