Large scale RC boat design and build project - with questions

Discussion in 'Sailboats' started by CrunchyFrog, Apr 22, 2014.

  1. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    If you can build a big monohull, why not build a big cat or tri? Keep in mind John Xman has said he is going to be there in 2015 with a very advanced foiling 86" cat. Even if it doesn't foil it will be much,much faster than "Fang".
    Also, keep in mind that the round the world race was won by a big tri using foil assist the whole trip. I'd think a bit about the likelyhood of some potential competitors with much advanced design over "Fang".....
  2. Navygate

    Navygate Previous Member

    They have R/C round the world races!?!?!
  3. CrunchyFrog
    Joined: Apr 2014
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    CrunchyFrog Junior Member

    I have to admit, all this talk of foiling multihulls has me thinking.

    In the meantime, here's my very quick thumbnail sketch.


    From what I understand of shapes, this would have the lowest possible wetted surface for a given amount of buoyancy and also the lowest possible drag.

    Clearly there is ZERO form stability. But since the keel cants, it can do 100% of the job of keeping the boat upright. The keel will not just cant but rotate on an external collar. The intention is to get the bulb out of the water, just above the surface. This is where it will have the greatest righting moment, while also minimizing wetted surface/drag.

    Instead of creating different size rigs, which is how conventional RC boats deal with different wind strengths, I would have a removable bulb, with 3 or 4 bulbs weights available.

    The twin cannards are Schock 40 style, rotating in opposite direction for steering.

    Ok what do you guys think? Have at it!
  4. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready


    Well, there's a problem with the old adage about semicircular hulls being the fastest especially where a foiler is concerned. The Moth class proved that beyond a shadow of a doubt. While the semicircular hull has the lowest wetted surface, a skinny hull with the same displacement has the lowest resistance.
    See the hull section sketches below. The higher length to beam ratio hull is faster than the semicircular hull because it has less wavemaking resistance from zero to foiling takeoff in the Moth class. You'll notice that all fast Moths have a squarish underwater midship section and a fairly high(for a monohull) Length to Beam ratio of around 11/1. In other words, L/B ratio trumps wetted surface in a foiler.
    I'm completely convinced that if you're going to race a state of the art multihull you'd better have a state of the art monofoiler! As I think I mentioned before, the Moth beats every multihull around a course and even has a higher top end speed than the Flying Phantom foiler(so far).
    The problem is that a monohull foiler must have an exceptionally quick movable ballast system and a 180+ degree canting keel is just not fast enough-especially when it's at near max cant. You'll note that in its last 20 or so degrees of movement the canting keel hardly moves the weight in and out at all, whereas a Trapeze Power Ballast System has just as much weight travel at the end as it does in the middle and can be a lot faster since the weight would only move up a 30 degree or so grade at worst case. But, to be self-righting you would need buoyancy at the end of the racks coupled with a small amount of lead in a fixed keel. But the numbers work out-I've done in several times.(See the sketch below ,done by NFlutter, of my 60' monofoiler concept)
    Even with the little bit of lead in the fixed keel the boat will still be a handfull:
    it's the rc helicopter of rc sailboats-extremely difficult to learn how to sail-at least my 36" version was. A larger monofoiler would be a lot easier to handle but would still take lots of practice -and probably some electronics-to get the most out of it. You might be able to devise an electronic system to keep the boat at a 20-30 degree angle of heel to weather, but I imagine that will take a computer guru. You might be able to learn to do it by hand(radio).
    One of the great unsung advantages of a monofoiler is Veal Heel-that is heeling the boat to weather up to 30 degrees when on the foils going upwind.
    The boat can gain about 40% of its righting moment by learning/designing the boat to sail this way. Thats 40% of righting moment it doesn't have when its level!
    Some of this stuff may be hard to understand but believe me it is real and has tremendous potential. Good Luck!
    If I can help just ask......
    The following two links might give you a grounding in the theory of how a foiling keelboat is possible:

    My 60' monofoiler concept:
    My 30' foiling keelboat:

    Attached Files:

  5. Navygate

    Navygate Previous Member

    I love it.
    Foil potential is huge.
    Electronic levelling from the R/C world that we spoke of on the phone is huge too.
    I can dig out the link if you like on RCGROUP.
    If you can get that bulb three or four diameters deep you almost eliminate your surface wave.
    The mast could then become another vertical foil/canard.
    OR, two masts could balance your current canards!
    Roll stabilizing could be incorporated into them as well thereby reducing angle of attacks and drag.
    I love this all!

  6. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    CF, check this out:
    I just read their rules for a proposed "giant" rc multihull class and am not impressed: they limit beam to square when the fastest multihulls are oversquare and they limit rig height to boat length. They also prohibit movable ballast from extending outside the beam of the boat. Very, very shortsighted to have such arbitrary and speed restricting rules!
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