Some interesting information on the Nikita and Flyer A class designs:
http://www.boatdesign.net/forums/showthread.php?t=2924
Why does this shape lift instead of cause pitchpole?
Doug Lord
–High Technology Sailing/Racing
A couple of things - perhaps…
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Much “thinner” hulls along the entire length of the boat.
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A flat(er) hull section from just forward of the board back to the stern.
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Very thin top-sides/decks forward to shed water.
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if you look at the side views presented in one of the topic posts, you will notice that the boards are moved back and exist in the rear 1/3 of the hull length. This also means weight and skipper is back there as well - so with major volume back there, and very little (if any) weight forward of the main beam - all the drag/weight is toward the rear.
A simple measurment (unscientific) looks like the WaterRat is 8 inches long (displayed on screen), and the leading edge of the board is at about 3 inches from the stern, almost in the rear quarter of the boat!
- Finally, as hinted in several of the posts, the underwater sections below the static waterline are really pretty similar and of average volume. Compare that to the cross sections of the older Coyote or NACRA hulls, and it is easy to see that while wide bows “seem” to prevent pitchpoling, they also induce hobby-horsing. Once this happens you have the top of a 31 foot mast moving in a pretty big arc. With the finer bows, there is less up and down of the bow, thus less forward/rear swing of the top of the mast. Less movement at the top of the mast, less chance for the top of the sail to overpower the bows dowwind or broad reaching. Remember, seldom do boats (cats) pitchpole upwind ! So with rig and skipper so far to rear, there would be more leverage at the top of the mast required to move the bows down.
Picture the complete reverse - if mast and skipper were forward (in front of main beam) or even at a bow beam, don’t you think pitchpole would be easier and more evident?
An older U.K. cat design (Off shore - 30 feet I think) called “SHOTOVER” actually had the mast mounted on rear cross beam, with a very small footed main sail but an enormous jib/genoa. Just the opposite extreme of my example.
Dick
I think you’re on the right track. The bows on their own wouldnt make a huge difference. Its the buoyancy distribution, the wetted surface and the design of the hull in its entirety. When I was younger I worked for the company that designed the original “wave-piercer” Hoverspeed Great Britain, the 74 metre catamaran ferry. As these boats developed and became larger the bow shape changed quite a bit but the concept of the wavepiercer worked the same. Sure these were bigger boats (like 100 metres) but the concept was the same. Go through the waves, not over them.
Troy
Seems to me to apply this concept to models -if it is even possible-would require a movable ballast system capable of simulating a crews movement and then some because the model platform will be much more tender in pitch that the full size version…
Achieving the beam to length ratios used in these boats at a reasonable displacement/low wetted surface would be a hell of a challenge.
Doug Lord
–High Technology Sailing/Racing
Doug -
the real problem you face, is the design of the hulls needing to calculate and INCLUDE the weight/displacement of the all-up sailing equipment, not IN ADDITION TO !
You can take any cat - big or small, and if you add sufficient weight (ratio to scale), the boat will …
a) sit lower on it’s lines.
b) perform worse than if no additional weight was used.
c) be one more thing that needs to move - and sometimes - “move fast”!
If you take a look at a lot of the cat specs, and talk to their designers, you will find the boat is designed for a specific crew weight range. That is why you see so many models of cats from a specific manufacturer. One boat might be designed for single-handed sailing at a maximum of 175 lbs. - while another might offer skipper and crew at 250 lbs. while yet another might be designed to support a crew weight of 325 lb.s - or more !
Thus, if you take a Hobie 14 (as example) and drop a 260 lb. person on the boat, it sure as heck might be able to withstand pitchpole and sideways tipping more than a H-14 with a 150 lb. skipper - BUT - in the long run, if the skipper knows what he is doing, can sail the boat with good sail handling and depowering when called for, I would put my bet on the lighter weight boat.
My 18 Square was a Category 2 (heavy weight) at 335 lbs. plus my then sailing weight of 160-165 lbs. The ultralights at 265 lbs. with a 148 lb. skipper would leave me sitting in the water on the downwind legs. Upwind was a different story, as my weight and boat’s weight and using a trap wire would let me drive the boat deeper (and faster) than the light weight guys - who had to feather up in the puffs to keep boat level and moving.
On the reaches, the heavier boat seems to stay stuck to the water much longer, but traping on either light or heavy, still involved the use of a trap wire and standing with at least one foot on the top of the rudder casting! And even then, you travelled the main out about 3/4 to 7/8 way, sheeted in block to block (8:1 ratio) and watched as the leeward bow “played” with wave tops. Imagine with the new design of being able to drive through the waves, splitting them without too much (but some) worry about the forward cross beam hitting the back of a wave.
I don’t think you can just “add” a moveable ballast system without designing the hulls to support the maximum weight of the system. If you tried, the boat would sit well below her designed static water lines - and “squatting” in the water isn’t fast! Also, the system needs to be removeable for light air. And - lastly, it is just one more thing to have to think about while sailing. Instead of concentrating on tactics, on position relative to competitors, and seeking lifts, avoiding headers, you would now need to be concerned you didn’t hit the wrong r/c switch and suddenly have your moveable ballast go to leeward.
I’m not saying your ballast ideas aren’t workable - in theory - but I would rather get a good boat, a good set of competitive sails, and learn to get maximum performance without the need for moving ballast, or a radio that “mixes” signals at nearly 1/4 the cost of entire boat.
Until two or more “moving ballasted” boats are on the water and racing other boats, the theory that it will help is just theory. Putting it into practicality, (easy-to-use and easy-to-dismantle) is a big question in my mind.
You’re right about having to design the boat for a movable ballast system; thats one of the points I 've tried to stress almost every time I mention the subject.And for sure you would want it to be easily removable.
My point was that trying to use the same beam to length ratio’s used on full size boats on models is difficult to say the least. And the beam to length ratio is integral to the whole wave piercer concept…
Doug Lord
–High Technology Sailing/Racing
This whole concept of movable ballast has some problems. When you consider that the boat needs to be built to suit the conditions i.e weather, waves etc. you need to look at an average for the area you are sailing in. If the boats is then designed to sit on it’s waterline in (let’s say) 8mph winds, when you remove the ballast for light conditions it will sit well above it’s design lines then alternatively in heavier conditions possibly more ballast is added so that the boat is then sitting well below it’s designed waterline.
I think in a perfect world were you have the same conditions day in and day out movable ballast systems probably work, but in the real world were weather conditions change from day to day even during races, it becauses more of a problem than an assest.
We have found that boats designed to sit in the water as against on it are quicker and easier to sail. For various reasons.
At least over here anyway.
Peter
Peter, in terms of a multi hull
what exactly do you mean by “in as opposed to on” the water?
How does that design philosophy translate into hull(not boat) beam to length ratio? Just curious…
Doug Lord
–High Technology Sailing/Racing
I think as far as beam to length ratio’s are concerned, tri’s in my opinion should be built to maximum beam, whereas cat’s should be no more than 3/4.
Personally I don’t feel that wave piercing hulls would be all that beneficial in the conditions we have over here. We sail on a lake that is not huge, and therefore the waves that build up aren’t that big(relating to scale). The other point to this is wave piercing hulls to my restricted knowledge of them is something that is used on cat’s and not tri’s, our club members sail tri’s for reasons mentioned in previous other posts on this forum.
The other thing that Doug questioned was the “on and in” comment. What that relates to is the hull shape. Deep V design against “dish” design.
Peter
Peter, I was referring to the beam to length ratio of the INDIVIDUAL HULLS not the whole boat. Mine range from 13.2/1 for an F48 cat hull or tri main hull to 18/1 for an ama measured at thewidest point which occurs approximately 1/2 way between the bottom and the deck.
UPDATE: Interesting info on the 1997 Waterat: B/L(deck) 11.9/1 ;B/L level waterline-14.55/1 .
And on the 2003 Morrelli and Melvin A-cat: B/L-deck-11.39/1 ; level waterline-13.78/1
So,interestingly,the new boat is proportionately wider than the older boat even though the new boat uses a reverse bow. The volume forward of the new boat is much lower than the volume forward on the older boat…
Doug Lord
–High Technology Sailing/Racing