i tried useing the ballast below the deck and found that the benefits just were not worth it. it is simular to a canting keel. both are swinging the ballast from one side to the other. now i know form experince that the moving ballast does not work.( my own experience). keeping things below the deck would help with bouy rounding and starts. because you are concern with the hull. i was sure 9 inches would be enough, but a fixed fin. was just as fast. same design
cougar
long live the cup and cris dickson
Can you elaborate on why you found it didnt work?
Luff 'em & leave 'em.
If you think about it, matthew, what are you trying to accomplish with moving ballast inside the boat? You are trying to get righting moment with a smaller keel bulb. But look at how long the keels are on our boats and think about how little heel is needed to get the keel bulb mass as far outboard as the moving ballast inside the boat. you will see that you get a lot more bang for the buck from a keel bulb.
So if you take 2 lbs (about half) of the weight off the bulb of an IOM and put it below deck on a moving rack, you are only going to reduce the drag by a very small amount, but you will have lost a whole bunch of righting moment.
So you either need to add weight back into the bulb to get that righting moment back (which means your boat will be heavy) or you need to reduce the sail power (which means your boat will be slow).
Moving ballast (in the form of crew) works on full size boats because the keels are relatively short compared to the beam so the keel does not generate as much righting moment as the crew until the boat is heeled way over. And at the same time, the crew is already there so you might as well put them to work on the rail. but the geometry of our model boats make bulb keels much more effective than movable ballast under the deck…
- Will
Will Gorgen
lol
i see that i am not the only one that had this idea. and just like will said. some of the problem i had was the wieght was the motor and gears. and how slow the bulb moved from side to side. it was just simplier to put a 2.5 pond bulb on a 12 fin. i can rember what weight we came up to just to equalize what the rm was
but some how the number 7 rings a bell. maybe 7 pounds was the same as 2.5 on a fin
but dont take that number as gospel. we tried it for all of 6 months and it was just an experiment with a IOM hull
cougar
long live the cup and cris dickson
Why does the moveable ballast need to be beneath the deck? Can’t it be above deck, allowing a much greater moment arm?
With the ability to mold the lead ballast into whatever shape and size you require, isn’t it just as convenient to find a shape that will be easy to move from one side to the other above deck?
I can’t believe the increase in wind drag would overshadow the reduction in form drag from removing the long/deep/bulbous keel. With some carefully arranged ingenious mechanics, I think someone could come up with a suitable system for moveable ballast that wouldn’t interfere with the rigging and would still be fast enough to compensate for directional changes.
It’s got to be worth a try, at least.
“Its got to be worth a try at least.”
Well, go ahead and try. However, be aware that ballast at the deck level still won’t be as efficient as ballast at the end of a deep fin.
And expect that to carry a decent amount of sail area you won’t be able to eliminate the bulb entirely.
And to move your ballast you are going to have to design and build a ballast shifting system and carry its extra weight.
And to take full advantage of your ligheter weight, you’ll have to design a new hull since when you take away ballast from the bulb of a conventional boat, it will no longer be floating on its design waterline.
And finally, remember that out on the race course, you will have to constantly “tack” your ballast to match wind shifts. Get it wrong once, and the boat with a “conventional” bulb and keel will leave you in the dust.
None of the above means that building a shifting ballast can’t be done or that it can’t win races. It means that it will entail a lot of work with an uncertain result.
lol
guys, i have tried it, and i count not make it work. puting it undernaerth the deck was just what i did. and it was not because i thought of wind drag. I was thinking of crashes in the start line and the bouy marks. i am stating the the conventional IOM with the bulb at the bottom of the fin will always be better than a swinging boat with the same weight. i was had to carry a battery and a heavy motor, and then the ballast. it was just to much
that is why i stopped looking into it.
cougar long live the cup and cris dickson
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Roy Langbord
And finally, remember that out on the race course, you will have to constantly “tack” your ballast to match wind shifts. Get it wrong once, and the boat with a “conventional” bulb and keel will leave you in the dust.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
Well, since I’m planning on sailing twice as fast as anyone else with this type of boat, I should be able to recover from a bad tack. [8D]
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>
None of the above means that building a shifting ballast can’t be done or that it can’t win races. It means that it will entail a lot of work with an uncertain result.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
I’m not sure what you’re trying to say here. Of COURSE it will take some work. And of COURSE the outcome is uncertain. But isn’t that what this is all about? If nobody tried anything “uncertain,” then we’d still be living in caves and washing our clothes by beating them on rocks.
Nobody ever said innovation was “certain” or “simple.” But if the end result is worthwhile, then it’s worth doing.
Go ahead and give it a try Andrew.
Keep in mind that if you take all the ballast out of the keel, then the boat will be able to capsize. So you will need to be able to recover from a capsize situation. I would say that the capsize will not be a learing curve phenomenon, but will actually be a racing event. So don’t count on always being able to wade out there and right your boat. You need to design it so that it can automatically recover from a capsize.
A couple people have done this already. Take a look at the pictures of the APS1200 here: http://www.rcsailing.net/forum1/topic.asp?TOPIC_ID=866
The “skipper” on that boat acts both as the ballast as well as flotation to right the boat after a capsize.
I am contemplating doing something similar with an RC laser and then removing the keel ballast. I’ve been chatting a bit with Steve Lang and I think I have figured out a way to add the required modifications to the boat in such a way that I can easily convert it back to a class legal boat. I’m not sure how much quicker the boat will be, but it no doubt it will be fun to sail…
- Will
Will Gorgen
Andrew: What I’m trying to say is that what you are proposing is not guaranteed to be successful.
What I am also trying to say is that theory and talk is easy, success in the real world is hard.
What I am further trying to say is that to be successful in developing a moving ballast r/c boat you have to have the knowledge, background and experience to design a fast hull and a light weight, efficient canting system from scratch and you have to be able to master a totally new kind of r/c sailing.
Maybe what this whole subject needs is an “X” prize–that is a trophy or even a cash award put up by the proponents of moving ballast for r/c sailing for the first moving ballast r/c boat that beats a non-moving ballast r/c boat of equal size and sail area in say a best of seven race series.
Oh, and Andrew, while it is true that without trying “uncertain” things we’d still be beating our clothes on rocks, I think it took a couple of hundred years just to develop the gas/electric washer/dryer.[8D]
Andrew,
You should also be aware that moving ballast is illegal for almost every recognized racing class. The F100 monohull allows moving ballast and I think the F48 multihull may as well. but it sounds like you are talking about something completely different from either of those two boats…
So if you do this, keep in mind that it will only be for fun…
- Will
Edited out my stuttering…
Will Gorgen
But if Andrew is successful and he can demonstrate that a moving ballast system works and works well, then I don’t see any reason why we can’t have the rules changed and/or new classes formed to incorporate new technology. I believe that the AMYA only requires 20 boats to reconize a new class.
The other thing that is really important is to get started and try your ideas. Don’t believe that BS about your ideas having to be properly engineered. Build it first then we’ll let the engineers figure it out later. [;)][:)][:D]
Rcher,
You are right. you have to be willing to try things and tinker rather than trying to figure it all out before you start.
And any class rules can over-ride the RRS with respect to the movable ballast rule. But I would think you would want to get a boat working before you worry about writing up a bunch of rules about what it can look like…
As I indicated above, I am in the design phases of modifying an RC laser with moving ballast “skipper” instead of the ballast bulb keel. I’m planning on making the modifications fit within the existing deck plate such that by swapping out one removable piece of the boat, you can attach this system to any RC laser. Oh, and you would also swap the keel for a non-ballasted one as well.
If it works and works well, I may ask for permission from Steve Lang to sell this as an add-on kit for the existing RC laser. If it catches on, then maybe a spin-off class will form for this modification.
Or maybe only one will ever be built and I will sail it just for fun off the dock in front of my cabin on the lake…
- Will
Will Gorgen
Hi Will,
There actually exists a prototype for this laser, from a few years ago. I think Robbe manufacturered it. It was built at a scale slightly smaller than Jon’s Laser.
The example at Central Park sailed very well. It was manned by a rotating figurine with a lead head. The skipper, who was on an extended visit from Austria, called it “Leadhead.” The figurine was posed as though he were hiked out. There was a single pivot point and – speculation – an over-center spring loading mechanism, as in a landing gear retractor. As the boat came about, the mini-skipper would begin to rotate slowly, then swing quite suddenly to the other side of the cockpit.
As I remember, the boat had both movable and fixed ballast.
Doug Lord as done a lot with weight shifting technology. Probably he could suggest something a propos. Best, Michael
Just cause i havent seen it mentioned and it replies to the initial question , a designer once told me , when i was playing with an add on bulb and a new rudder on our keelboat , was something along the lines of " About 30 % of the drag is the leading edge , about 50 % the trailing edge , and the middle is really just fluff"
Basic but i kinda like it , ands it seems to fit in well with the mumms and ingelas ive sailed , they have a reasonably sharp leading edge to their bows at water entry lvl , and on trailing edges seem to have very gradual angles to kind of ease the water past , sounds kinda stupid , but from what lil ive seen really seems to work
But back to the question; What makes a sailboat go fast?
I think the water-line is one of the most important factors in winning.
The longer the boat, the faster she 'll go.
Example: a Marblehead beats an IOM.