Large scale RC boat design and build project - with questions

[CrunchyFrog]

Thanks for all the responses so far.

I mentioned Speed Dream, but my thoughts are more along the lines of Q. Without on-board passengers to worry about, a rotating collar is quite feasible. I'm looking into mercury switches to see if the cant control can be fully automated in a simple and elegant way.

Thanks for the other links. I have come across some of them but others are new. I'll check them out in detail.

I have some preliminary drawings. I will scan them and post them up for further comments.

 

[Doug Lord]

CF, I forgot to mention DSS-it's probably one of the most up-and-coming technologies for monohull keel boats and I think it could have an application on your boat unless you're shooting for a full flying foiler. I'm going to try to use it on my 15 foot Crossbow fl.
http://www.boatdesign.net/forums/sailboats/quant-28-foil-assist-keelboat-dss-38421.html

 

[CrunchyFrog]

DSS looks fascinating. I have read a bunch of your links and will read some more.

My first thought is that in RC use it wouldn't have to be dynamic. A fixed foil extending either side would do the same thing and offer little effect when not in use and above water on the windward side. Also an initial thought, but perhaps it could be placed somewhat forward of the longitudinal centre of balance. This to reduce the nosedive effect that RC boats tend to have while sailing in waves and stronger breeze.

 

[Doug Lord]

Hugh Welbourn, inventor of DSS tested the concept with fixed foils on one meter rc boats. With movable ballast, you may want to heel the boat in light air-with fixed foils you'd have the foil wetted surface when you don't want it......
Also, if the foil is too far forward, instead of lifting the whole boat it would tend to just lift the bow which would result in a pitch up and possible stall of the foil or at least "out-of-the-drag-bucket" operation. Unless you used a t-foil rudder but then you're adding more useless wetted surface in light air.
Lots of interelationships....
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I'm very impressed that you recognized the value of movable ballast right off the bat-good thinking!

 

[Doug Lord]

Here is "Fang" for those who don't know:
http://www.youtube.com/watch?v=uIPheVbG9LE

 

[CrunchyFrog]

I raced with a borrowed, untuned IOM against the Fang last year at the Great Ocean Race. I finished the race in 1 hour 11 min, I believe the Fang did it in 1 hour 2 min. It wasn't that much faster. From what I could tell it was about the same VMG upwind, while certainly being a little faster downwind.

From my recent experience building and sailing a small scale wing (radio ice boat), I'm not convinced a wing is the best way to go. It's certainly really cool! But I think to get the benefit of a wing, especially going downwind, you really need to be sailing on apparent wind. Which means you need some serious speed. I don't think any RC scale boat achieves that level of speed. Then you add the complexity and the unforgiving tendencies, and I'm not sold on wings for RC boats. But I also readily admit that I'm not an expert.

 

[Doug Lord]

If I were you I'd go with a Trapeze Power Ballast System because it's effective and very simple. I'd probably use a deep fixed keel with the least amount of ballast required to right the boat. I'd consider a spinnaker/Code Zero or screecher. And I'd definitely go with retractable DSS. I'd use a squaretop main and jib on a wing mast-not a wing rig. Now, thats if you're going up against "Fang"-if you were going up against a larger state of the art multihull, you'd need a monohull that flys most of the time. I think a big tri with the right foils would set a course record and also be much,much simpler and more reliable than any other boat. John Xmans 86" cat foiler would be fast but a souped up tri would be faster.
Once I get the Crossbow fl proto built I'd consider a race like this!

 

[CrunchyFrog]

Doug where did you source the mast section that is on the square-top main I see in your gallery?

 

[Doug Lord]

Doug where did you source the mast section that is on the square-top main I see in your gallery?

It's a Forte carbon spreader section made very thin(031")-only 10z for 8' and immensely strong. It was about $350 and I wound up extending it about 10". It can be made almost any lenth as I understand it.
It's the SP2115 section,laid up very thin: http://fortecarbon.com/marine/mast-section-diagrams/

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If you're interested in researching a carbon wing you might talk to Magnus Clarke whose boatdesign name is "High on Carbon"-check the membership list and PM or e-mail him. Not only is he an expert on C Class wings, he's Canadian as well! He's also and experienced rc sailor and designer. And a damn nice guy most of the time....

 

[CrunchyFrog]

Question for you marine architects out there.

When designing a hull shape for an RC boat (ie no passengers), why couldn't you use the same shape as a keel bulb? Let's assume that no form stability is required. And that the waterline would be such that half the bulb is submerged and half above water.

 

[Navygate]

No reason why not CF.

 

[Doug Lord]

Seems to me you have to consider that newer designed multi's like John Xmans boat are going to be possible challengers-if that is true then a mono will probably have to fly to have a chance. "Fang" ,in my opinion, is not representative of a state of the art multi. Johns boat is very close and he may have the windward foil pull down like the Bradfield and Ketterman boats do-virtually unlimited RM with the right design. His beam is a bit narrow for effective use of the Bradfield system though. We'll see.

Bradfields 18' Osprey with dual,independent wands:

click-

 

[Navygate]

CF,
A semi-submerged bulb hull.
Interesting.
I think the gains would be negligible.
Long and narrow with speed designed hulls would be advantageous but then you've got your different points of sail to contend with.
This is a complicated quest.
Perhaps prototypes are the easiest solution.

 

[Squidly-Diddly]

I think a small multi would be at risk of capsizing in the ocean, just do it is small size, then staying in "S2".

I think semi-submersible could be a winner, mostly because it should be much less effected by every tiny wavelet and keep the sails at the correct angle to the wind for greater % of time.....

and if successful: full sized manned semi-sub sailboats will become a fad in a couple years.


For any semi-sub, make sure any water breaking onto the hull is gravity channeled to the stern for 'thrust'.

 

[messabout]

If you could stay within sight of the fast cat with the IOM then you can beat him with a three meter boat. The three meter will have almost twice the potential speed as the one meter. It will be much more controllable, it will pitch less than the IOM or the cat. That will be a big plus factor in the long haul. The sails do not like pitching motions where the top of the mast is moving at high speed, in both directions. Under rigging the boat is worth consideration for several reasons. Control, consistency, and reliability is the bigger deal.

While I am fascinated with canting keels, foils, and other avante garde stuff, I do not think that such complexities are best advised for a long distance race. Build a long boat with a modest rig that concentrates on superior control in various wind and wave conditions. A modest rig implies that there can be fewer sail changes which is certainly a time/distance factor. The cat may be faster in short spurts but over a long course the big boat is more likely to win.