Builder's Open - Any Thoughts?

First Go

Good to hear from you Magnus ...I'm guessing you're the Magnus with a sailing pedigree that puts the rest of us to shame ... I'm also guessing the Fred you refer to is currently working on a high tech project hid in a shed on the Island ... perhaps I should rescind the open challenge, the rest of us are beat before we've even started ... damn!

First iteration attached ... flat bottomed sled, bulb hung deep, and perhaps a sliding fore/aft ballast to keep the nose up ... either that or a chute if I can figure out how ... any hints, Doug?





Regards, Trevor

 

I am not a model builder , are these to scale ,,,,,,,,,,,wieght also? longliner

 

first go

Trevor, great rendering; I think you might want to consider a MUCH narrower hull. Ask Magnus about it.
The simplest spinnaker I ever came up with was on a 36/600. It used a retracting bow pole(12") and an asymetric spinnaker-not a mast head spin! There is a "set angle" that is critical to make sure the spin lifts the bow instead of pushing it down. E-mail me at lorsail@webtv.net and I'll forward you my "standard" collection of responses to people about rc spins-lots of important info.
The 36/600 spin only worked on a boat that uses a main only rig-and thats a bit of a disadvantage in that particular class because under the rules it costs upwind SA. Anyway, the beauty of the system was that it used a "Hoyt jib boom" as a spinnaker "boom" so that the sheet could be tied into the mainsheet winch. You only need one guyatt winch to set/douse the sail-only one extra channel.You can gybe at will just as if the spin was a jib. So you could sail with three channels. A line from the boat thru a block on the spring loaded spinnaker pole allows the pole to retract and set with the sail-no extra channels. An asymetric has a big disadvantage when used on a model: it can't sail anywhere near as low as a symetrical spinnaker unless you rig up a "wagging " pole where the pole end goes out opposite to the boom. The spin on a small boat like this needs to pull down under raised "deck arches" made of carbon instead of in the hull. Makes the thing look like a dinghy and functions very well.
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You can do it but I don't recommend it! I suggest you build a very narrow deep keeled boat
to start off with.
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If you want to mess with movable ballast wait a while(to get some experience) then use an on-deck "rack" that moves fore and aft and side to side. Put 50% of the ballast plus the battery in the on-deck system and the rest in the fixed or 20° canting keel.You can make a simple 20°canting keel that requires no elaborate seal by making a "V" trunk integral to the hull and deck such that to install the keel you push it up from the bottom, put a pin in it(f&a) and then set it back dowm. It can then be hooked up to your side to side servo...(minimum 4 channels!)I can help with more detail later if you want.
Your best bet in my opinion is to go with a very narrow hull with a deep fixed keel with all the details right. You'd be surprised how many small important details are overlooked by some people. This first go you can get those sorted(and probably win) and then go on to more complex, faster boats. Good Luck!

 

Longliner

Rendered to scale 75cm loa, 21cm beam ... rendering foreshortened perhaps by the 'camera' angle ... designed light ... hydrostatics don't work because I've yet to render the transom which I've discovered FreeShip doesn't like ... that said, I've drawn it at 1.8kg to 2 kg which could be way optimistic ... an IOM is 4kg but from what I understand they could be built a lot lighter ... Trevor

 

I just like playing around with boats, and yes some happen to have wings.

Dont worry, I drew it up last night and my 75 cm boat will not use a wing, not yet anyways.

With a small boat, on a short course with gusts and shifts. I would opt for the lowest wetted surface area possible in whatever I built. Parasitic drag is big at scale. Being able to pick off shifts effortlessly and then ghosting downhill with a very light boat in the light stuff we usually get stuck sailing in works for me.

This is reflected in my latest one meter which is kind of like a USOM with a bigger IOM sail plan, and more keel depth. The hull, with electronics and deck weighs about 9 oz I think. All up weight is 6.1 pounds, almost everything in the keel.

It's simple, responsive and fast.

That having been said I did draw up a monohull canter as well last night, a scaled version of a 50 incher I've been working on for a bit. Might work using regular winches.

Like I said let me know when you have a rule together.

MC

 

In the mean time here's what I'm working on....

 

C-

Wow--don't forget to send them again. Fantastic!

 

Cats are ok, right? One cat hull, worked on it some last night. I havent ran it through Mitchlet yet, new computer and I cant remember how I had it all set up on the old one.
With all the Spi. talk, I want to be able to keep up. Square top main, blade jib if any, and IF I can figure out how(small scale), I'm thinking NACA 0009 all the way around. We havent talked about course layout so I'm not sure.
For construction, just balsa striped with epoxy coating.
I know its only for one hull with no appendages yet, but here is what Delft says;

General
Start speed : 1.00 [kn]
End speed : 15.00 [kn]
Speed step : 1.00 [kn]
Water density : 3994.700 [lbs/ft3]
Water viscosity : 1254.6217*10-6 [ft2/s]

Hull
Length on waterline : 2.114 [ft]
Beam on waterline : 0.247 [ft]
Draft hull : 0.080 [ft]
Total draft : 0.250 [ft]
Wetted surface area : 1.33 [ft2]
Waterplane area : 0.40 [ft2]
Displacement : 0.085 [ft3]
Longitudinal center of buoyancy : 9.939 [%]
Prismatic coefficient : 0.6552

Keel
Average chordlength : 0.000 [ft]
Wetted area : 0.00 [ft2]

Rudder
Average chordlength : 0.00 [ft]
Wetted area : 0.00 [ft2]



Calculated variables
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Cwp = 0.7661
Cm = 3.1057
Am = 0.06 [ft2]
Lwl/Bwl = 8.559
Bwl/Tc = 3.087
Lwl/Displ^3 = 4.808
Tc/T = 0.320
Aw/Displ^0.67 = 2.069

Lwl/Bwl is outside valid domain [2.76 - 5.00]
LCB is outside valid domain [-6.00 - 0.00]
Cp is outside valid domain [0.52 - 0.60]

Comments welcome!!

 

Cats etc.

Figgy, I noticed you said LCB 9.9%? Is that right? Most hulls are in the vicinity of 50-60% aft of the bow/ waterline intersection. Larsson and Eliasson and some model boat designers get more specific -like around 53.6 % for lowest resistance.
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As I mentioned earlier multihulls under 48" LOA are EXTREMELY difficult to sail in wind over about 5mph. So I'd suggest the boat I did for Trevor but perhaps with your skills you could go with the narrow hull plus a combination of simple 20° canting keel and movable ballast right off the bat. In essence, you'd have a low wetted surface "monomaran". The negative is that it's more complex and a bit more costly requiring 3-4channels and PRACTICE to learn to use the movable ballast properly. The positives are: you can roll tack, heel the boat to weather downwind , steer with the movable ballast w/o using the rudder , heel the boat to leeward in light air, it's very fast , infinitely easier to sail than a multi in this size range-and self righting-which you'll appreciate on a cold day. And this is an area of model yacht design only a few people have started to explore like myself, Wind Warrior in NZ and Aquataur in the UK. So if you guys come up with rules that allow ,say, 4 channels and movable ballast, you'll have a lot of room for development of fast, unique, miniature dinghies that are a blast to sail .

 

Yeah, I guess it is. Its not quite what I intended tho'. My thinking behind it was to be able to keep up on the downhill runs, without having to tack. What I mean is, to be able to have alot of reserve buoyancy so as to not pitchpole. Was I going in the right direction, or am I totally off?
I do like your idea and think I'll run with it, less problems.
Thanks! -Figgy

 

Rules ... 2nd Iteration

Alright then ... thanks and regards to those who posted their opinions online and off ... here goes:

BUILDER'S OPEN

- Owner designed
- Owner built
- Owner sailed
- 75cm loa

Rules apply to hull, appendages, rig and sails (carbon rod is fine, a pre-formed carbon mast from a 3rd party vendor is not). Remember the intended spirit: reward what's in your head, not your mailbox.

Let's just say a minimum course depth of 1 metre.
Course determined by an independent race committee.

Why no channel or electronics restrictions?
- ummm ... ummmm ... I guess I'm thinking a 75cm boat is self-limiting. That, and I like the idea of being foolish enough to cram as much technology as possible into the envelope (perhaps not me, and perhaps not the first time out, but who knows ... )
- We know a computer can outplay a human chess-master, but can a robot outsail a human? (refer to Marshmat's earlier posted Sailbot link). This won't be the project that finds out, but we should all be curious.

Why no predetermined course?
- ummm ... because ... because it's one rule too many ... let's design boats that sail at all points ... home field advantage can be ameliorated by selection of an independent race committee.

Q's
Owner Sailed: I for one would like to see one of Doug's boats show up. Likewise, Crag may yet come 'round and adapt one of his S70s. I imagine there are builders around the country and around the globe who might wish to build but can't attend. Any thoughts on proxy drivers for those who can't make the trip?

Regards, Trevor

 

Figgy,

why the V bottom?

 

It got a little bit more crease than I would like, but its not intended to be a v hull. Kinda looks it though.

 

Figgy,

You’re using freeship correct? If the lowest two control points on a control curve have the same z value, then you are guaranteed to have a first order smooth (rounded) bottom.

 

Here's a weird thought ...

Rather than limit length, limit weight.

Somewhere between 5 and 10 pounds ... anything else goes (within the other rules re: owner built etc.)

But the limit lower than a One Metre can be built to (and still sail well) and that effectively limits length also (if you choose to haul lead around).