Keep in mind in comparing the proposed boat to an existing boat that you can figure that for the same sail area you can have 40% less ballast in the new boat. More power less weight.
Doug Lord
–High Technology Sailing/Racing
errmmm, dunno cougar, the boat was second hand to me. It was supplied by sailsect as a kit but I dont think they make them anymore, best thing to do is email him via his site (lost the adress, it my be on the links page)…
Luff 'em & leave 'em.
doug
i dont want to start anything here. but a purposed boat and a old boat. i dont get it. you ever heard of a yardstick to compare by. what you are saying is your opion. i could easy say that my new class will destory the IOM, just beacuse of your reasoning. but i dont say that. untill i know , i dont make any suggestion to saying 40% or 50 % differnence. i have been defending you, but you are making it hard on some of us. do you have any proof that 40 % is accurate?
cougar
Cougar, Doug meant 40%less displacement for the same sail area. Not performance. A ligher boat will almost always be quicker than a heavier boat withthe same sa, thats the main reason multis are so damn quick…
Luff 'em & leave 'em.
wis ,
what i was saying is that you need a something to measure agianst. to say what is better. doug is saying that canting keels will improve your boat performance by 40%. but that 40% is purposed. i agree with the satement that less wieght and more sail , will make the boat go faster. but is has not been proven in the rc community. at least not to my knowledge. we have to watch what we say here. because alot of people are mad at each other. and i for one do not want to get into the middle of it. I ma staring a new class and would like help. ckeck out the luna rosa site. and you will see what i meen
cougar
Cougar…[:-banghead]
[:-banghead]
Doug said 40% less weight with the ballast!!!not 40% more perfomance…[:-banghead]
Wis
if it isn’t broken, don’t fix it!
Cougar, Wis and Matt are 100% right! My statement reflected the PHYSICS of utilizing a canting keel as compared to a fixed keel. Theoretically, you could keep the ballast the same and drastically increase sail area. But generally, it seems better when comparing two boats of the same length to reduce displacement by the largest amount possible on the canting keel boat with generally the same sail area. On full size boats the ballast reduction between a fixed keel boat of the same length and a canting keel boat is on the order of 50%. In the model, I made some allowance for the mechanism of the canting keel boat though the available ballast reduction is still substantial.
These are general terms based on an assumption that the fixed keel boat has the maximum ideal sail area for it’s length.
Ballast reduction on a canting keel boat is possible because of the fact that it can develop so much more righting moment than can the fixed keel boat while maintaining a fixed angle of heel.
Performance ,one way or the other, was NOT mentioned —only the physics of a canting keel design.
Doug Lord
–High Technology Sailing/Racing
Just thinking out loud…
I was thinking maybe instead of having a canting keel you could have a canting mast, and the hull could be shaped sortof like a sausage so that when it heels to extreem angles, it doesn’t drag the deck. The mast could be attatched, by about the midway up point, to another mast which pivots to a steeper angle than the taller mast. The heel of the tall one could be drawn slightly to windward that way so that the effective boyancy would be farther to leeward. The advantage would be you wouldn’t have to make a fancy hull fitting for a swinging keel. it could have two angled dagger boards each side for lateral plane.
John, your idea of the hull addresses the problem of getting the keel out at least 55 degrees to the vertical but I dont understand the second mast concept.If you use a canting mast set up like Will has proposed and Hal Robinson has built you might have a problem getting that much mast movement.
If you use twin daggerboards you’d still have to tie the rudder into the mast to keep it vertical and I would assume you’d want to be able to retract one or both boards.
Doug Lord
–High Technology Sailing/Racing
Basically I was thinking that if you just swing the mast port and starboard from a fixed point on the deck, instead of the bottom of the boat, the mast ends up on the lee side when heeled, and some pretty steep heeling would be going on from the perspective of the hull, not the rig. In essence, you might get a little effective form stability if the mast wasn’t down to leeward like that when heeled. Wouldn’t make a whole lot of difference in a narrow hull I suppose.
On the other hand, stepping the mast in a triangular trunk would probably work better, with the heel on the bottom. The trunk would however probably ship some water, which wouldn’t be that big a deal.
It could have two spars sticking up and out either side of the mast with small blocks and tackles going down to a winch to lift the mast to port or starboard. I like this Idea mainly because it could be made by the average person.
Wish I could think of a way to balance the load so the winch that hauls the mast wouldn’t have to work so hard.
I’ve always tried to imagine instead of hauling it to windward, just use a standard servo to drop the mast to leeward, and hold it there, and then tack the boat. Voila! you’ve got the mast on the widward side. Probelm is, you need the mast to stay virticle in light air. Hey, how about an elastic!Hmmmmmmmmm…
(I should shut up and actually try this instead of speculating)
John, how would you solve the rudder problem?
Doug Lord
–High Technology Sailing/Racing
I’ve been working on the canting mast design a bit for my US1M.
There are two advantages of having the mast canting be deck mounted instead of keel mounted. The first is that you can have a fairly well sealed deck so you don’t have the extra weight of two water tight bulkheads on either side of the mast. The second is that the servo that drives the mast (which is a pretty heavy servo) can be lower in the boat which will allow its mass to help the righting moment slightly.
I also designed the mast canting mechanism + bulkhead + servo as a “plug in” module. I plan to instal a rack on either gunwale to allow me to adjust the fore and aft position of the mast by moving the bulkhead fore and aft in the boat. This is easier to do with a sealed deck and only a small slot for the mast rotation cup than it would be with a full width “V” bulkhead. I think that the mast position is going to end up a bit aft of a “normal” position since the canting rig will not build up as much weather helm because of the lower amount of heel. We will have to wait and see on that one… But having the ability to move the mast around in the boat is going to be important in the initial tuning of the boat.
As far as the rudder goes, I am going to try sailing the boat with a fixed rudder to start with. The hull that I am using is not well suited for a canting rudder (the Cobra hull has a relatively flat section in the certer of the hull back where the rudder should go, so the canting rudder would tend to “hit” the bottom when it is turned from side to side). If I find that I reall yneed the canting rudder to keep the leeway down, I will add it later.
I have decided to try adding a spring to the mast canting system to “help” the servo move from side to side. The spring would be attached between the mast pivot and the sliding tube on the mast base. The spring would “pull” the slider up toward the pivot to help overcome the portion of the servo motion where the most torque is required. When the mast is centered, the spring would not add any extra torque either. I have added the spring to my calculation spreadsheet for the servo torque and it does seem to smooth out the biggest humps that the servo must overcome.
The biggest issue now is getting a servo that can rotate through 270 degrees. I talked with the guys at Radio South (they modify servos for 180 degree rotation) and they told me it was not possible with their modification system to do that. I may need to add either an external pot or find a multi turn pot that will replace the internal pot in the servo.
Anyone have any experience modifying servos like this? I hate electrical circitry stuff and am fairly hesitant to start clipping wires inside a fairly pricy servo without knowing what I am doing…
- Will
Will Gorgen
Will has drawn an excellent sketch of his canting mast mechanism and you can see it under:“RC Offshore Concept Boat” under “Technology”. It has potential to be used as a canting keel mechanism as well and may be particularly suited for the CK Trainer.
Will, could the design handle two pounds at 14" from the pivot point?
Doug Lord
–High Technology Sailing/Racing
Hey will, If your canting rig boat has wide flat sectons where the rudder goes could you not get away with twin rudders, the windward one could be worked to end up out of the water as the boat heels…
Luff 'em & leave 'em.
Hello Matthew,
THe US1M class rules specify that the rudder (singular) must be aft of the keel fin. Based on the singular usage of the term rudder, I believe twin rudders are illegal. However, I will ask the class secretary.
I race scows in my “spare time” and most scow classes have twin rudders and most of the time (at least upwind) the rudder is clear of the water. With twin rudders, you need to be very careful with the alignment of the two rudders so that they do not toe in or out. THis is very slow if they do. Given the general “sloppyiness” of the connections between horns and cranks with RC harware, I doubt you could control the toe well enough to use twin rudders. but it might be fun to try…
- Will
Will Gorgen
If one was to use the kinds of linkages and horns available for rc helicopters you could assure yourself of a slop free linkage.
I think allowing the rudder to heel with the boat is a mistake. And I think there are a couple of relatively simple solutions, one of whch is Matts ,the other could be mounting the rudder on a carbon tube that sticks thru the transom and is turned by the mast winch. The rules on transom rudders would have to be considered; I don’t think the losses due to the rudder not being under the boat would be significant ESPECIALLY if the transom could be exactly round for the 40 degrees each side of center and a rudder endplate be incorporated to tie into the hull in some way.
UPDATE: the rudder shown in Gregs picture would seem to invite huge tip losses and canted might still hit the boat; maybe with some refinement for those concerns something like it could work though not as effectively as a properly done transom hung rotating rudder in my opinion.
Doug Lord
–High Technology Sailing/Racing
Maybe you guys should all take a moment and come up for air?
I have read, and re-read this topic, and I still don’t see where any/all of you have even agreed on boat size as yet. Just a suggestion, that instead of worrying about canting masts, canting rudders, multiple rudders, etc. - if this really is supposed to “evolve” into a realistic “TRAINER” class, someone really ought to start putting together a resonable agenda on how to build this boat and eventually the class.
Why don’t those who are trying to make this a “real” on-the-water boat, start putting pen to paper and list the agreements you have so far for a “physical” description of the boat - unless you are planning on sending this one to Graham Bantock for design. Several suggestions have been made - but until all agree on length, beam, displacement, and sail area - it seems like still a “theory class”.
If you read between the topic lines, it appears the “trainer” might have turned into an F-100 - so maybe all ought to just embrace that class - and agree to something? How about some decisions? Without them, you will probably still be discussing this at the <u>END</u> of the 2004 sailing season.
Is it a trainer for canting keel as originally proposed? What is the objective for the class?
To whom should it appeal?
What are physical sizes?
What rules for development are going to remain open?
What rules will “close” off development and in which area?
What are cost limits - or expectations - before everyone “Thinks” they are building a $300 boat when in reality it will cost closer to $1,000?
Who is spearheading this class - or just a post with no expected conclusion?
Just a few things that are needed to get back on track and on topic !
it has slipped a bit, dont quite get how a canting mast got blagged into it but hey! Go back and read Dougs breif in his first post and up to the first bit about the tactic and start again folks…
Luff 'em & leave 'em.
I think this topic should be as wide open as possible within the length framework outlined in the first post. Canting mast ideas are off topic a bit except for the fact that the mechanism Will has designed may in fact be ideal for this boat–I’ve asked him some technical details about it a couple of posts ago as well as privately. When I know more I’ll post it.
I don’t think there is a great rush to come to definite decisions since I’d like to get the widest range of input possible.
But I agree that we don’t need to go on very long on subjects not directly related to a CK Trainer.
There is no chance of his boat evolving into an F100 because of the costs which would go thru the roof at that length due to canting keel mechanics requirements etc.
So if you have a suggestion to make there is still plenty of time to contibute; don’t hesitate to read the first post of this topic again as a sort of focus.
Thanks for everybodies input!
Doug Lord
–High Technology Sailing/Racing