Builder's Open - Any Thoughts?

rules ... clarification

Two questions came in offline ...

Q1 ... what about digging into the parts bin for fittings, blocks etc ... ?

I'd say, go for it ... can't see the need to have everything made from coat hangers and paper clips ... also, I'm sure having to fabricate your own bearings etc would put all but the most ardent builders

Q2 ... carbon rod / carbon tube ... ?

Yeah, either, whatever ... I just threw out the first example that came to mind ... there are no restricted materials

Regards, Trevor

ps ... this whole thing is still really really nascent ... pitch any questions either online or off ... and please chime in if you've got any opinions, yeah or nay ....

 

Sum rule

heres a wierd idea I had at work last night. What if you took a single number, or 'budget', say 2800 scm and subtracted ten square centimeters for each centimeter of length, beam, and draft. Whatever is left in the 'budget' is your allowed sail area.

To make the idea a little more interesting, I thought of introducing a very simple hadicap aspect to it. Multihulls would have their beam counted as one and a half times its actual number. Canting ballast boats woud have their drafts counted as double.

The idea is to have some diversity of design possibilities, so all the winning boats don't all start looking alike.

Bob

 

Following this with interest although I would be unable to attend myself. the sum rule seems to ensure that boats will look more similar rather than less. The "spirit" rule is genius. If somefolks can spend a fortune, great. Often though without strict design rules new and fabulous ideas are born and developed for very small outlay. Most importantly each gets to exercise the brain and have a little fun.

 

3R Class Rules

You guys might want to take a look at the 3R Class rules. Produces boats between 30 and 44"LOA
more or less. SA gets bigger the smaller the boat. Whats cool about this boat is that the upwind SA is less than most boats in this size range leaving physical room for a spinnaker-which is legal. The downside is that movable ballast is illegal like every other AMYA or International Class-VERY unfortunate for a new wanabe class. At any rate, perhaps these rules with legal movable ballast?
My YaBB 1 Gold - SP 1.4 - Draft 9 of the 3R Class Rules {final draft}
Address:http://www.cwcg.com/cgi/yabb14/YaBB.cgi?board=news;action=display;num=1073838321

 

This winter some minor changes may be made to this draft, to make measuring a boat easier.

If your interested in the 3R class, i posted some information on the building of my 3R here.
http://www.shermanyachts.com/informational/radical/

I'm currently working on her replacement.

 

You're absolutely right. I was just having a little fun. As previous posts have pointed out, the size itself my be a very effective design limit. I am afraid that the only boats that would stand a chance would be those with deep fixed keels, and moderate beam (25-35cm).

The reason for this would be the great reliance on pendular stability. As Mr. Lord has so aptly pointed out, once a canting keel swings outward, the boat's fore and aft stability quickly diminishes right at the time it is needed the most, causing the boat to pitch forward. If the boat broaches or rounds up, the canted ballast could end up on the wrong side.

Meanwhile, back on the pond, the fixed keel will continue to sail on. It will pitch forward too, but the huge size of its keel fin, along with a rudder, a healthy proportion of that, will, for the most part, keep it boat on track.

I can imagine what I have in mind might look bizzare. At least compared to most RC sail boats I have seen. It would have its beam somewhat foreward and it would have a relatively wide stem post which will be part of a wide keel that tapers as it goes astern.

The sail would be a boomed lateen with a 127 cm yard and a 89.5 cm boom, giving it 4000 cm of sail area. The idea would be to avoid, as much as possible, the forward pitch caused by gusts.

The major governing factor here is how deep to make the keel fin. Only the person familiar with the pond its going to sail on knows that.

It's no fun when some one spends a Winter building a 30cm deep boat only to find out it has to sail on a 20 cm deep pond.

I think Tmark needs to be more forward about this. If the course had a minimum depth requirement, everyone would know how deep to make their keels.

One of the problems with no rules or specitications is that it gives the home team an overwelming advantage. Particularily if they get to set the course.

So, perhaps only the original three rules should be kept. But with minimum course specifications added.

Bob

 

couse depth

Thanks Bob ... truth is I could care less about having a home-team advantage. I'm figuring I'm against some tough competition and will enjoy the process, the dialogue, and seeing who and what shows up as much as the event itself ...

I do NOT think course depth should limit what gets built, ... ergo the post a while back (Sept 15th, I think) suggesting 1m min course depth and an independent race commitee (perhaps agreed upon by first ten registered builders.)

A bit back, I also suggested the dinghy docks at RCYC ... Magnus may yeah or nay that idea as he knows the weed and water conditions better than me at that time of year (perhaps the docks in the lagoon behind the junior club may suit) ...

In any event, anyone with an idea is welcome to pitch a course and location and we'll toss it in the mix ... RCYC () aside, I've got a soft spot for Meaford Harbour and the sailors up there ...

General Question ... would it benefit those interested if I were to throw up a web-page with rules, dates etc. clearly posted? It's not a particularly huge effort, but with 3 kids, a mortgage and blah blah blah I've got to measure where the time goes ... if determined useful, no problem ... otherwise, I'd let it go until the project picks up steam ...

Cheers all, Trevor Paetkau

 

750mm RC Yacht

There was a 750mm model yacht class started in Sydney in '86, of which I was a founding member. Our rules essentially limited ony the LOA (750mm excluding rudder) and the bulb weight (1.5kg). Multihulls were not allowed, mainly because at this scale we believed that most of our time would be spent rescuing them, which would lead to frustrating racing. We were limited to two channel radio, to keep costs down.

The boats evolved over the years so that in the end the rigs were over 1500mm high (some were 1800mm). The keels were up to 750mm deep.

We used rudder foils to prevent nose diving. As far as I know, this was the first such use of rudder foils on a monohull. The foils were sometimes linked to the sheeting system so that the (negative) angle of incidence increased as the sheet was eased.

We sailed these boats for about 10 years, but no-one is sailing them in Australia now as far as I know. There is quite a comprehensive web site about these boats at http://members.optusnet.com.au/mal.smith1/750.html

Mal.

 

Sorry, Tmark. Didn't mean to dis you. I must have missed the post where the 1m course depth was mentioned.

Instead of going through the trouble of making a web page, why not just refresh everyones memories, now and then, on what has already been decided. That way dolts such as myself can do a better job staying with the program. Here is what I think I know now:

1.) Owner built'
2.) owner designed,
3.) owner sailed,
4.) 75 cm length limit,
5.) a minimum course depth of 100cm, and
6.) course route to be decided by committy of first ten builders.

Am I correct?

 

Sharpii,
Wow, so far your boat sounds awsome! Since I'm most decidedly not a yacht designer and have no experience with model boats (although I have built fighting robots) please forgive me if this is a dumb question.

Would it be feasible and or effective to attempt to emulate the efficiencies of a windsurfer here? Or would the problem be the difficulty of creating tiny people in the shop form raw materials? But seriously? If you can make an RC helicopter and use a four channel radio as a collective maybe you could achieve something like that?

 

Thanks for the compliment, yotphix.

If you are refering to canting the rig to windward instead of the keel, yes, I have thought about it. I thought of a bipod mast that looks something like a large letter 'A'. The yard would hang from th apex and the boom pivot point would slide along the bar at the bottom. To make this work, I would need two additional channels (for a total of four). One for the hailyard, which would have to be eased, and one to haul the pivot point from one end of the arm to the other. I haven't done enough math to see if I would get enough cant to make all this worth while.

Meanwhile, it has occured to me that there is no reason why a multihull can't have a deep bulb keel as well. It could recover better from knock downs and should balance better than a pointy bow mono when hard pressed. The greater initial stability should give it more 'power' in blowing conditions. I thought of trying to get it to plane. It would, however, due to excessive wetted area, be a dead duck in near calms. But who wants a boat that always wins anyway. I think one that sometimes wins is far more fun.

Bob

 

In this thread, http://boatdesign.net/forums/showthread.php?t=13807
T-foil rudders are the talk for cats. Might be worth checking out. Dont know if I could make them work well on such a small scale tho'.
I have thought about a bulb keel on a cat also, but I think if your going to do that, might as well build a tri.

 

Wing Mast - Drawings

I spent the evening trying to engineer a wing mast based on my understanding Tom Speers articles. (It seemed easier to get my head around than what to do the platform it will drive.) I've thrown up the images to see if it engenders any discussion.

One member has already suggested being leary about wing-masts on a model. I have to agree that there seems to be a lot of weight in the mast itself; add in the bearings and there's even more mass above the WL.



In any event, here are the sketches at the moment ... they're based on an Eppler 377 profile. As a complete novice, I've yet to spend enough time on the learning curve to even know what Reynold Numbers and Polar Curves mean ... so don't ask!


Regards, Trevor

 

bulbs/foils

Robbe introduced a cat called the "Top Cat" years ago that had a keel which could be fixed or hinged. I didn't really get the hinged part-supposedly to make it easier to fly a hull or something. I did the preliminary design work on a one meter cat with a center nacelle to house all the radio gear. It used a canting keel(Guyatt winch) hinged on a fore and aft carbon tube. Lateral resistance was developed by retractable wings on the keel bulb. It would have used a relatively small servo to move the keel fore and aft as well. Still would like to build it someday.
In my opinion, using t-foils on a monohull that HEELS is probably a mistake since there is likely to be cross coupling upwind. However, if you have a movable ballast system and can sail the boat mostly level it's a different story since the t-foil will do the same thing it does on an I14. For small multihulls you either have to have a movable ballast system or full lifting hydrofoils or both. They are simply too hard to control otherwise. A retractable set of foils is relatively simple, light, less expensive and much faster than movable ballast. If you use a Bradfield type set up for the foils a small multi can be practical with virtually no chance of pitchpole or capsize since the foils develop all the righting moment .But the Bradfield system does not lend itself to the high pointing ability of a model monofoiler but is far easier to sail and so fast in anything over 5 knots of wind that it really doesn't matter.(yet)
In considering any type of movable ballast on a model it's really a better bet to make sure the weight(incl. battery) or at least part of the weight moves fore and aft as well as side to side...

 

So for a race like this, just for fun, should we forget movable ballast? It seems too complicated for a race of this magnitude, or lack thereof.

Also, we need a date. I dont even know if I can make it till we have a date set in stone.

Doug cant go, hes too far ahead of the curve already.
I'm kidding Doug, I think it would be great to sail next to ya! Although a foiling tri would be hard to beat!