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Old Oct 31, 2007, 01:21 PM
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Portland, OR
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Wildcat

I replaced the mast and booms and first cross piece with carbon tubes. That took a lot of weight off. I'm not using the supplied ballast and after adding three ounces of lead to the sail winch hull to even them out it weighs 2.8 lbs. I have had my wildcat on the water twice now.
First time was light winds and it was a slug, my Victoria was faster. The second time was fairly breezy. The cat moved quite fast and accelerated quickly. I got one hull briefly out of the water a few times . The back end does lift a little burrying the bow but it didn't seem to want to pitchpole. Tacking presented problems but can be done easily with practice. There is a sweet spot for approach to the wind that makes it kind of on or off. It also doesn't point very well making it a little tough to retrieve. With practice it gets better and I reccomend this boat as being a fun model sailboat. I will probably put better sails on it though.
MikeV
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Old Nov 06, 2007, 11:03 AM
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Portland, OR
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More wildcat

Had the cat out again yesterday. I took it to the Columbia river where the wind was blowing a steady 15mph or so. I normally find rc sailing to be quite relaxing but this was adrenaline pumping total excitement. The sails don't have much shape so I made some battens out of thin plastic. This seemed to help a little in the lighter winds but they fell off in the heavier winds. With a steady wind you could keep it on one hull longer, that will take lots of practice though. In the sweet spot the boat just skipped along like it was planing. I moved all moveable weight in the hulls towards the back of the boat. I could get it to pitch pole on a broad reach but if you let the sails out it would recover nicely it seems like you have ample warning a head of time. I was going to replace the sails but now it looks like I need an A rig and a b rig, no way I want better sails in heavy wind. I'm going to try my after market Victoria sails on it in the light wind to see how it does. This boat is quirky but interesting to me. Any comments or suggestions would be appreciated.
MikeV
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Old Nov 06, 2007, 11:51 AM
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Asturias, Spain
Joined Mar 2001
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Mike, no doubt Dick L will be posting some comments soon. He seems to have an awsome knack of homing in on posts about multi-hulls. Meanwhile, enjoy your sailing.
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Old Nov 06, 2007, 09:48 PM
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I'm not familiar with the design, does it have daggerboards? Do model cats do that?

My only advice will come from full size cat sailing.

In big breeze, you can't get battens that are too stiff. So that would mean on a model, much stiffer battens than you would expect will be FAST. I use up to 3/8'' fiberglass rod in my Hobie 16 which is by no means high performance. I think the Nacra 20 guys are using upwards of 5/8'' in the big stuff. Remember, as the apparent wind speed goes up (like multi's will make it do) the draft of the sails will get pushed back. That's really slow and REALLY draggy. Stiffer battens will keep the sails looking like they should.

Do you have pictures of the boat?
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Old Nov 07, 2007, 01:08 AM
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Here's a link

Victor Model Products make it. https://secure.victor-model.com/Prod...7780CAFC4002F2
I don't have any pictures of mine. I also spent many years sailing Hobies etc.
So I am sort of used to how they sail. I did think they pointed better than this one though. I will make some new battens tommorow.
MikeV
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Old Nov 07, 2007, 05:48 PM
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Quote:
Originally Posted by wamf
Any comments or suggestions would be appreciated.
MikeV
Hi Mike -

not sure what you are looking for as to comments or suggestions. There are few of these in any kind of competition (too small) and most seem to have been purchased for cabin/pool/small pond sailing. Of the two that I know about and am familiar with their modifications, it seems the owners have modifed the following:

1. Deeper boards and larger rudders for better pointing and more responsive steering in light winds.

2. One made his boards retractable so in heavier winds, he can reduce the amount of resistance, allowing the boat to "skid" sideways in gusts.

3. Better sails - or trimming them as flat as possible in heavy winds.

4. Carbon cross beams, mast and booms.

5. Use a very fast action servo, to handle both torque and speed. Most have gone to the Futaba drum winch, that will fit inside the hulls (tight) but at $150 or so from Tower Hobby (example) it is nearly the cost of the entire boat. Still, having a fast winch will allow sail trim to keep the boat on it's feet in heavy winds. If you go to a fast arm winch, you will probably wind up with the arm being above deck.

5. Add or modify a boom vang on the main so you can keep the boom flat, and leech (trailing edge) tight. Modify the outhaul on the boom ends to allow you to tighten the sails so they are flat and without much camber for strong winds. Combining a lot of outhaul, a lot of vang tension will help reduce the "power" in your sails and let you take advantage of the boats light weight and potential speed.

6. Consider that "B" Rig and smaller sail area for really heavy winds if you decide you want to sail it in winds stronger than it was intended or designed. I would hazard a guess that the probable top wind speed for the stock boat would be somewhere in the 5 - 8 mph range.

All things considered, I still wouldn't recommend - or build - a multihull under 1 meter in length - and preferably at 1.2 meters (48 inches) since they are much easier to control, and are a bit more predictable in heavy winds. Just a lot more forgiving (though they will still flip if overpowered).

My $ 0.02 worth. Enjoy !
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Old Nov 07, 2007, 11:13 PM
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Dick has an extremely good point with making the sails as flat as possible in bigger breeze. Efficiency goes through the roof when you make the draft that small, especially with medium small AOA.

Also, from that pic it looks as if the mast is an almost round section. If it is, in bigger breeze the top probably 4-5 inches of sail aren't doing anything because the flow around them is too turbulent for any degree of efficiency. All they're doing is making more heeling moment, so a big performance jump in stronger winds would be making a fat head main that's about 4'' shorter.

Deeper, narrower boards will be more efficient and you'll point better.

Please notice that the word efficient is used a lot in this post. It's not by accident. Cat's don't rely on sheer power nearly as much as mono's (though they can afford to since they're so stable). They normally rely on the ultra high efficiency of their platforms and sailplans. For that reason, if ever you find something that will be made much more efficient, even if it means a loss of power, it's probably worth it.

For instance a wing mast is often worth its weight in gold on a cat. Same with high aspect blades.

Your boats hull shape really reminds me of a Teeny Tornado. If that's what it's modeled after (I'm nearly sure it is from the boards) then it won't have much of a problem with bow digging except when power reaching in big waves. It will have the problems you describe (pointing, tacking, ect.) until you put blades on it that look a bit more like this

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Old Nov 08, 2007, 01:49 AM
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Quote:
Originally Posted by ballywho
Dick has an extremely good point with making the sails as flat as possible in bigger breeze. Efficiency goes through the roof when you make the draft that small, especially with medium small AOA.

Also, from that pic it looks as if the mast is an almost round section. If it is, in bigger breeze the top probably 4-5 inches of sail aren't doing anything because the flow around them is too turbulent for any degree of efficiency. All they're doing is making more heeling moment, so a big performance jump in stronger winds would be making a fat head main that's about 4'' shorter.

Deeper, narrower boards will be more efficient and you'll point better.

Please notice that the word efficient is used a lot in this post. It's not by accident. Cat's don't rely on sheer power nearly as much as mono's (though they can afford to since they're so stable). They normally rely on the ultra high efficiency of their platforms and sailplans. For that reason, if ever you find something that will be made much more efficient, even if it means a loss of power, it's probably worth it.

For instance a wing mast is often worth its weight in gold on a cat. Same with high aspect blades.

Your boats hull shape really reminds me of a Teeny Tornado. If that's what it's modeled after (I'm nearly sure it is from the boards) then it won't have much of a problem with bow digging except when power reaching in big waves. It will have the problems you describe (pointing, tacking, ect.) until you put blades on it that look a bit more like this

The mast is round but tapered I'm using a carbon kite tube. It's good to see a picture of what the boards should look like. I was invisioning fat and deep.
The hulls are a semi flat bottom U shape most of the way which seems to let it slide across the surface like it is planing. Can someone briefly describe how deeper narrow boards help with pointing and are there any draw backs?Also, should they be more forward or more back from where they are now if they are narrower? I bought it just to have something different than a mono but would be happy if it did point better. I might have to buy another one to do it to because what's there now is epoxied in. It's faster with loose sails I think Dick meant to tighten to decrease the chance of being over powered in a strong wind.
Thanks
MikeV
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Old Nov 08, 2007, 05:10 PM
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Light wind - no waves = flat sail for acceleration and speed
Medium winds - small waves = fuller sail for power to punch through waves.
Strong winds - waves = flat sail for acceleration and speed. You really don't need the power if wind is string.

These are rule-of-thumb for multihulls. Obviously changing conditions and how the boat sails, accelerates, handles waves, and course type will all influence final tuning. Above is just a place to start with the tuning.

PS: Rake mast back for stronger winds and/or higher pointing. While much harder to tack, you can always sail with main only as a uni-rig.
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Old Nov 08, 2007, 05:23 PM
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German Mini40's Video

Note last few seconds of a large scale Hobie 16

Clicky
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Old Nov 08, 2007, 06:40 PM
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For the narrower boards:

Pros:

Faster
Higher pointing
Better tacking

Cons:

Will most certainly be harder to get in the "groove".

The narrower boards won't be as easy to use, and you'll have to keep the boat moving at all costs (you're now not relying on surface area, but the lift they create). The reason you'll be able to tack better is because the boat will have a more defined "pivot point" number one, and also it's less board to swing through the water.

Dick pointed out why flat sails are better for cats. Also what you have to remember is that because they have so little drag, attached flow over ALL the foils is what matters most. If you watch full sized high performance cats sail in light air (or look at the AC boats, they sail rediculously flat too) they're all sailing low and fast with flat sails. This keeps the boats moving, which makes the daggerboards more efficient, which makes for better pointing, which makes the sails more efficient (see a trend yet?).

Also just keep in mind that the A class cat is an extreme example. They are upwind and apparent wind machines. They never, ever, go DDW and they are PURE efficiency boats.
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Old Nov 09, 2007, 07:29 PM
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Thanks For the Explanations

One thing I seem to remember from my sailing days was that boats with tall skinny sails pointed better. Like The picture above illustrates. I think the wildcat could handle a little more sail area on the main. With the wild cat the jib stays full when pointing but the main flutters. The wild cat has a flat non panneled sail it seems that when I get it tight there is no shape and the boat really slows it does seem to point better but in light winds it barely moves.
MikeV
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Old Nov 11, 2007, 05:32 PM
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wamf, you're quite right that taller, skinnier sails will often point better. However, what they lack is the power (more often refered to as "oomph") that lower aspect sails will have.

An idea you might consider would be to (when you get comfortable sailing the boat as it is now) put a shorter boom on the boat, and move the area you just took out into the head of the sail.

That would give you more driving force for only slightly more heeling force since now you're getting effective lift off the top of the sail rather than just drag.

The rule that many, if not most, sailors forget is that sail area isn't neccesarily king. It's effective sail area while minimizing drag from the total package that's fast. Most people will say that the drag created by the sails is miniscule and negligible compared to the drag made by the hulls. You must realize that this is so far from the truth it hurts. For instance, in a 49er (Olympic skiff class) the sail plan (not rigging, not mast, not even including the spinnaker. just the main and jib) accounts for 30% of the total drag on the system. Another 10% comes from the mast/rigging, about 40% from the hull, 10% from the foils, and 10% from the windage of the crew.

Keep that in mind next time you're considering whether to go with mylar sails, or a wing section mast.

Efficiency is king...
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Old Nov 11, 2007, 10:30 PM
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This is my resurrected, Formula 48 (F-48) build that has resumed. Wife said finish it, or get it out of closet.

Will be hollow foam covered in epoxy/glass. Basic size: 1.2 meters long x 1.1 meters wide. (48 inches long x 42 inches wide) Yellow part of the measuring tape showing is at 1 meter for size reference. Target sailing weight is 1.36 kg (3 lbs.)

Had built laminated wood beams, but not sure I "liked" their look, so am building a set of foam beams with thin ply central spine and then see which I like best. Ones not selected will go for next boat.

More info at a couple of multihull forums at other sites:
RC Sailingnet
or
RC Universe (multihulls)
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Old Dec 30, 2007, 02:47 AM
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Portland, OR
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New main sail

I bought the flat panel Victoria sails from Mariner sails http://www.mariner-sails.com/partdetail.asp?id=25661. I used the main on the wildcat and the jib was used for the main on a Victor Blackhawk 24. The wildcat is faster in medium winds still easy to control in heavier winds 15mph or so but it does bury the down wind hull more on a reach.. Doesn't tack better though (wasn't expecting it to). The main is about an inch longer on the foot and 2 inches taller. It is more fun with this set up. I'm thinking about getting a main made that is basically a vic main but three inches taller with the vic jib which is smaller than the stock jib. Other than the first time I sailed the wildcat I haven't sailed my upgraded victoria. The wildcat is just way more exciting to sail if the wind is moderate to heavy. Now the Blackhawk which is also using a paradise keel is faster in light winds but spins into the wind if it is moderate to heavy. I don't have any specific questions but am interested in any input.
MikeV
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