A model 49er?

philiprawson.rcsaili · November 27, 2004, 5:15am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Dick Lemke

Phillip -

just an observation - depending on circumstances, adding weight to your Tornado may increase chances of capsize, as you have just added to displacement, and if hulls aren’t buoyant enough to handle the extra weight, (and able to accelerate in the gusts) you may find the added weight more of a problem than a solution. All would depend on the starting design displacement of the boat, and how far off the designed waterlines the boat is floating.
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OK, That makes a lot of sense. My plan is to use about 2lb of movable ballast (the weight of the weightshift motor and battery) on the Tornado, replacing the 2lb of lead on the keels. The idea is to have more intelligent weight distribution.

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I am not directing the following at you - only making it as a general statement - “in making changes to a model, of a percent of weight, change of buoyancy location, increase/decrease of waterline or beam, and finding a negative reaction, it seems too easy to blame the boat - and not the modified design parameters.” I am sure you wouldn’t expect a plane to fly (or stunt) if you added more weight, so I would caution others to keep the “design specifications” in mind when someone modifies a design and the results aren’t as positive as expected.
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True…

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We seem ( in the multihull area, especially ) to quickly blame the design for capsize - and seldom take into account the experience of the skipper, the speed or strength of the winch/servo, the size of the sail area or the height of the rig… all we see is another multihull that capsized.
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Yesterday, as I rescued my capsized Tornado from the reeds yet again, this question entered my mind… I was trying to sail the boat in winds that were just too much for it. I’ve come to the conclusion that I definitely need a smaller rig for stronger winds.

Philip Rawson

www.flymodels.co.uk

philiprawson.rcsaili · November 27, 2004, 5:32am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Bill Korsgard

Philip,
Instead of trying to slide the ballast laterally on a track, why not have it be mounted on a swinging arm that would rotate across the transom as it went from beam to beam(or behind, if the rig had no backstay). This would have the added advantage of being able to have weight far enough aft to better resist pitching moment in a run. Maybe you wouldn’t need a kite after all [:D].
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I’m mulling that one over… I think the decision will be made when I draw out the hull to scale so that it’s possible to see the path of the arc and where the lead will be on each point of sailing. I don’t plan to have a backstay, but there are other problems…

Looking at the models on http://www.aquataurmodels.com/ which use weight shift, I see that to have the weight move to a point very low down in the hull on it’s centreline enables the boat to right itself in the event of a capsize. Whether I can do this with a swinging weight I don’t know yet…

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Then to take it to the next level, devise a electro-mechanical device that would automatically perform this function. Some sort of pendulum sensing heeling angle could send an appropriate signal to a dedicated (and very fast) servo. I’d have to talk to one of my engineer friends to get a clue as to how this could be made to work, but I’m sure it’s possible. I realize that an automatic device such as this is pretty much a sacrilege in model boating circles, but it may be necessary to reduce complexity for the skipper & provide the quick response to keep these thing upright.It also addresses the concern raised by Dick & others about the difficulty sensing subtle dynamics when not on board the boat.
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I’ve been thinking about an automatic weight shift system, but I’d rather not go down that route too far. Flying and boating for me is a challenge… make it too easy and I might as well be watching someone else doing it!

That said, as I only have 2 channel on my boats at present, when I fit weight shift to my Tornado it’s going to be controlled by a switch that’s moved by either the jib or main boom. This’ll send the weight to the opposite side of the boat to the boom. Of course the Tornado is wide enough not to capsize if the weight is on one side when there’s no pressure in the sails, so it should work. I’m trying to put off the purchase of a radio set with more channels, although it’s got to come sooner or later…

Philip Rawson

www.flymodels.co.uk

Dick_Lemke · November 27, 2004, 9:51am

Phillip - and others considering a self-righting system …

Back about 10 years or so, the Gougeon Brothers came up with a design for a 32 foot catamaran that could be self-righting. Kind of funky looking ( actually “ugly” to me) the boat used a combination of water ballast pumped to the floats, and a tilting mast.

It would seem that if one could tilt the mast (perhaps by endless shrouds and a drum winch) it would be possible to tilt a captive base mast far enough to allow the hulls to return to their regular sailing position. Positive floatation on masthead required to allow the boat to lay on it’s side, but not “turtle”. Using the winch to shorten the shroud in the water and lengthen the shroud in the air would gradually allow the hull in the air to fall back towards the water to it’s normal position (cat). Once the platform was floating correctly and stable, a reverse action would winch the mast back up to it’s normal vertical position.

I would think some of the mechanics for this might already be dealt with via Will Gorgen’s ideas about a canting mast, and incoorporating it into a cat design would be a do-able effort. One issue I would see needing consideration is the manner in which one would “lock” the shrouds to prevent wind forces from pulling on the winch and letting the mast fall off to leeward in heavy winds.

philiprawson.rcsaili · November 28, 2004, 9:29am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Dick Lemke

Phillip - and others considering a self-righting system …

I would think some of the mechanics for this might already be dealt with via Will Gorgen’s ideas about a canting mast, and incoorporating it into a cat design would be a do-able effort. One issue I would see needing consideration is the manner in which one would “lock” the shrouds to prevent wind forces from pulling on the winch and letting the mast fall off to leeward in heavy winds.
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Sounds like a job for some sort of ‘over-centre’ mechanism like that used in mechanical retracting undercarriage for planes. At the down position, the landing loads are taken by the retract unit rather than the servo operating it…

Philip Rawson

www.flymodels.co.uk

Matthew_Lingley · November 28, 2004, 4:30pm

But what about the weight penalties guys! Keep it simple, keep it light, that way the boat will more likely accelerate away the power in the gusts rather than dig in and flip!

Luff 'em & leave 'em.

mustang_1 · January 17, 2005, 4:03pm

Hi, im new to rc sailing (kind of) but i have been flying for about 4 years now. I have a pylon racer, glider, and aerobatic plane. My rc boat is a CR 914 which is leaking from god knows so it hasnt been sailed much. Also there is no place i know of to race it. As said getting into the hover is easy, but keeping it there is quite difficult. I think that sailing a 49er style boat would have to be easyer than that. The bigger problem which others have pointed out would be submarining. In my laser if i sail at right angle to the swells it too will bury its bow if it is not planing. To avoid this though i just sail at a slight angle to the waves and that keeps the bow dry. After it begins surfing its possible to head down and sail lower. Again fore and aft movement is general helpful. If that won’t work though i have found this website: http://www.microsail.com/s50photos.html which has a few different spinnkaer boats. There is also a movable ballest hydrafoil boat which looks interesting. The hydrafoil boat has flotation on the ends of the weights to help in lanuching.
Dan