This is an old pic of a Cat I built a year ago as a speedsailer, with pivoting rigs. Over the past 6 months I have been working on this boat to convert it into a MultiONE class cat for course racing. I have had some interest from people who would like to have a go with this cat so I’m going to dust off the plug, make a few modifications (its just a little under 1m at the moment) and build a few boats. Would anyone be interested? I’m hoping to keep the price around ?250 for a complete boat ex sails and radio gear.
[:-bunny]Happy Easter[:-bunny] Matthew, I am keen to encourage you to retain the configuration of your cat for speed runs.
You wrote some time ago of an intention to participate in the <font color=“red”><font size=“2”>Weymouth Speed Week Regatta.</font id=“size2”></font id=“red”>
Whilst this may have been said in jest I would like to think that it may be possible to at least attend and set a benchmark for remote control craft with a sail area of less than one square metre. Let me know if that could be a possibility. Under the Speed Record heading I will be posting the results of my attempt to communicate with the <font size=“2”>Speed Record Council.</font id=“size2”>
Edited for crap spelling:
Do it NOW before it`s too late.
Here’s some spec’s LOA; 1m (after mod’s)Max beam; .57m Mast height; 1.1m Max hull beam; 70mm. Sail area 0.57sqm (triangle area) approx 0.8m (total area). Displacement 1.4kg. Another mod from that pic is that the new boats will not have a forward beam, as it causes too much of a trip if the lee bow goes down. Also the ‘lump’ right aft will dissapear to allow the boom to be lower.
Ian; I have found a great local spot for a speed trial, when the tide is at the right point we get practcally a speed ditch behind an oyster bank, now all I need is a steady force 5 to 6, rake the rigs right back, bit of lead right at the back of the windward hull (on a trap perhaps) and we shall be cooking! IF (big IF!) I can keep it upright I recon near 20 knots is possible…be fun trying anyway! BTW the original set up was too hard to steer in big winds, having a rudder might actually help speed!
Damn good looking boat, Dick. How much does it weigh? How do you control the squaretop(batten,gaff, other)? Will the rudder use a fixed, adjustable or no t-foil?
How does it sail?
Thanks
Haven’t weighed it yet. Still getting radio/sheeting lines correct. I have also been sharing (back and forth) plans/drawings and particulars on a powered ballast system that was designed by and is being developed by Jay Dee. [And yes, he is aware of my reservations of using a moveable ballast that cannot be seen from shore, felt through the seat of the pants, or replicated exact location on the next (successive) windward leg.] Unless he can address those concerns, I probably won’t use it - but our discussion will remain open as development continues. I have found him to be very open and receptive to an exchange of ideas regarding the proposed technology.
Square top is attached to a fixed distance (from mast) brass rod that swivels inside the tip of the mast.
Rudder currently is using a fixed (-2 degrees approx) T-foil, but since sail area is close to max - this will be light air rig. Between light air, and a 13 degree raked mast - not sure if T-foil rudder is also needed. Will wait and see. If not needed will replace with a standard profile rudder.
Also have a set of sail panels of smaller area but “pin head” profile main ready for tape-up.
Hope to hit water after Memorial Day weekend - barring any unforeseen plans by rest of family.
I haven’t been able to find a winch for a movable ballast system that is small enough for a multi one while also being fast enough-except for a Guyat 280 which is slightly heavy.Have you designed your boat so that when flying the main hull the ama has enough buoyancy for the boat weight + PBS? How much weight are you allowing for the ballast system?
My PBS for an F48 weighs 1.2 pounds with two Guyatts(fore and aft and side to side); the battery rides in the ballast cart using a flex cord like a telephone line to connect to the rest of the boat.
With the right radio positioning the PBS is simple as is re-positioning.
The thing is, you can SEE the effects of a PBS on any boat most of the time and radio settings are easy to get used to…
As I told Jay Dee - when (if ?) he can come up with a system where I can feel the hull getting light, so I can proactively move ballast in anticipation, I would consider it.
Reactive movement for shifting ballast, (as you have often said) is too little and usually too late. Especially in light weight, overpowered, high speed multihulls being watched at a distance!
Would rather watch and feather up in gusts, than use a moveable ballast as a “crutch” and wind up rowing/swimming - either due to inattention, slow winch, jammed sheets, bigger gust than expected - or a myriad of other “stupid moves” on my part !
In other words, I feel I will trust <u>my</u> ability to dump the boat, rather than an additional piece of hardware![:-dunce] At least for the immediate future.
Oh dear !!! Time to go back to the drawing board? An omen of things to come ? I hope not!
Tonight I was setting my sheeting lengths and for the first time in my life, I had my boat do a pitchpole right off the boat stand (2 saw horses) ! [:-ashamed]
Now I do have to admit that the sheets were locked in place, and we are expecting severe weather tonight, so winds were definitely brisk - and very shifty! Regardless, I was just introduced into multihull pitchpoles - but luckily I didn’t have to swim/row to retrieve![:D]
I did have the maximum sail area up, but I can see that the fat-head type of sail just has too much power and too high up. I may have to drop back to a “pin-head” main, in order to keep the center of effort much lower - especially if this is indicative of on-the-water issues.
Also - to be honest, there was no counter-acting resistance to the pitchpole, since the boat simply pivoted around the front cross bar. No floats or main hull resistance forward, so - being an optimist - I am hoping not to recreate on first sail! [:-dunce]
Anyway - am am not quite ready to lean towards Peter’s comments on fat-head sails, but certainly took a step in that direction tonite. Will really have to wait and see how water resistance forward, and t-foil rudder to the rear impact this issue.
More updates as they happen. Will be interesting to see how the sail design plays out. [:-graduate]
Dick
A bit of a learning curve. I certainly hope that the boat wasn’t damaged by this mishap.
Nice to see that I have almost got a supporter to the “fat- head” sails point of mine. I find it truly amazing that there are people on this forum who say that they have experience sailing r/c multihull’s but argue that fat-head sails have a lower centre of effort than a pinhead.
The fat-head sails have there place, but that place is certainly not 7 feet in the air above a 48" long multihull in reasonably breezes.
From experience hull shape will help a little, and so will having a T-foil rudder, but the “person on the sticks” has the most control as to whether the boat stays upright or not.
Anyway will be nice to hear how the boat performs on the water.
No damage ! It was resting on cross beams between two saw horses, when wind changed directions. The boat simply rotated around the front cross beam as it’s pivot point. Pitchpole stopped when mast tip met the ground. [:D]
I believe resistance to pitching would be greatly improved once on the water, so hasten to add this might “NOT” be normal. I went back out after posting and watched closely. Here is a bit of “land” experience and observations…
The center of balance of the main hull (with floats, sails, etc. is slightly behind the front cross beam. This leaves a good deal of hulls forward of point of rotation. This length/weigh of extended bows also adds to pitching moment when not supported by water.
As wind gusts, the rear hulls tend to lift.
Even though the mast is raked back about 13 degrees, as the sterns lift, the mast goes vertical. All is still fine and bows are now down nearly the same 13 degrees.
A little more wind velocity moves the mast past vertical (more forward with negative mast rake) and this is point where there is no return. Pitchpole results from here.
Very little pressure applied to sterns kept hulls down. Pressure was very light, and would be difficult to measure without some good scientific equipment. I also placed pressure under the main hull bow, and there also, very little pressure was required to resist the tendency to go “bows down”.
Winds were about 12 mph (but with stronger gusts to 20 mph +) so I would conclude I might easily have been out of the max sail area range - and a “B” rig might have been more prudent. But heck - who ever heard of multihull guys being “prudent”?
What proved interesting in observed pitchpoles, was the tendency that even with the wind slightly to the sides and from the rear, the hulls seems to go straight forward, without tendency to twist one way or the other onto what I would call the leeward float! Again, this may change when on the water, as the bow of the main hull is longer (sticks out forward) than the floats. This would mean the main hull bow would begin picking up buoyancy before either of the floats begin to head down. Good or bad? Won’t know til on the water. Hopefully, with large (tall) bow on main hull and supported at the other end with a T-foil on rudder, there would be enough resistance to make repetition more difficult on water. Of course, sooner or later the wind will be strong enough to do that, and that is the wind speed I need to find![:-graduate]
Peter - I do agree that if one adds sail area to the top of the mainsail, the center of effort simply has to go up higher. Not sure of any textbook theory that would disagree with that so not sure where the idea of lower center of effort would come from. The higher up the mast with pressure, the longer the lever action, and the less pressure required to move that lever. Since this is/was designed as the maximum “A” rig, it is intended for light air, with as much sail area as possible up high to catch what little breeze there might be.
A fathead sail will only have the Center of effort of the sail higher than a pinhead sail if you hold both the sail area AND LUFF LENGTH constant. Most classes have a maximum sail area and a maximum luff length restriction. But if you were to design a fathead sail with the same sail area and hold some other parameter constant (like for example the boom length), then you would end up with a shorter luff and a lower CE.
Taking the extreme example of a triangle versus a rectangle. Suppose you had a triangle shaped sail with a 10 inch foot and 300 square inches of sail area. The luff lenght would then be 60 inches (1/26010=300). The Centroid of that sail (a good rough guess for the CE) would be 1/3 of the height up the sail or 20 inches high. Now lets look at the rectangle. for the same boom length (10 inches) and sail area (300 square inches) the rectangle would have a luff lenght of 30 inches (30*10=300). The centroid of the rectangle is 1/2 the height up the sail or 15 inches high which is LOWER than the triangular sail.
now of course, we all know that a fathead sail is not a rectangle, but it is in the DIRECTION of a rectangle… So if you hold the sail area and boom length constant, the fathead sail will have a shorter luff and a lower center of effort. Thus it will have less heeling moment.
Another advnatage of fathead sails is that the top of the sail tends to twist off easier than a pinhead sail. So when the sail twists, the fathead sail will tend to loose effective sail area and also shift the CE lower on the sail. The pinhead will do so as well, but not to the same degree. So the fathead sail which had a lower CE to start with will have an even lower CE once it twists…
Another advnatage of fathead sails is that the top of the sail tends to twist off easier than a pinhead sail. So when the sail twists, the fathead sail will tend to loose effective sail area and also shift the CE lower on the sail. The pinhead will do so as well, but not to the same degree. So the fathead sail which had a lower CE to start with will have an even lower CE once it twists…
Will
Will Gorgen
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I can agree with that - and almost to the point of maybe too much. As part of my testing last night, I did a few photos, and this one taken from the rear with winds of about 10 mph I reinstalled daggerboard to give the boat a heel angle which is probably more than expected (hoped). Regardless, with this being my first fat-head, I will probably need to experiment a bit. Maybe even add a twist limiter so it can’t go too far. But regardless - it’s easy to see in photo.
My experience with Fat Head sails comes from windsurfing. I have a full quiver of race sails from the mid 1990s when the Fat Head / Flat Head sails were all the rage. Those sails did not use any sort of gaff rig and relied on a balance mast bend (which was controlled by downhaul) and the luff curve cut into the sail to control the twist. If you wanted more twist, you would crank on the downhaul and the top of the sail would go absolutely limp. It was amazing how fast those sails were even when a big chunk of the sail area was sacrificed to twist.
The funny thing about those sails was that when you got them really limp in the upper leach, they would flap in the breeze as you were sailing. It was not really luffing because they were fully battened. The flapping sound was really loud (mylar was bad but kapton monofilm was the worst). It sounded like a buzz saw coming! But it was fast that way…
Will
I fully agree that your example would have a CE lower on the “fat-head” sail. The statement that had been made was when comparing sail heights that are the same. If luff length of both a pin head or a fat- head are the same, the comment was made that the fat-head will have a lower CE than a pin-head. I commented that this was crap, and I was told I was wrong.
Your example and Matts’ rough picture example proves that I’m right.
On the multihull’s that we sail over here there are boats with 2.1 metre mast heights, luff length on both sails regardless of pinhead or fathead is around 2 metres, foot length is around 450mm. Naturally there is a vast difference between headsail size, but that doesn’t really seem to make to much difference to the pointing ability and speed of the boats.
I will state again that when sail height is the same fathead sails have a much higher CE than pinhead. TRUE or FALSE?
Well yes, but then if you design a rig to take a fathead, you either go for a shorter mast and have the same SA as a pin top, or depower it like hell (add lots of twist) when the wind pipes up, as Will is saying. If you get it right it should be possible to carry the top rig in much higher windstrengths than you would with a pin top, as it will have a low c of e for starters, and depowering will lower it some more.
<font color=“red”>Edited by mod dan</font id=“red”>
The thing that you need to remember is to keep the balance right, so if you shorten the mast to carry a fat-head sail in higher winds, you then are carrying a larger headsail. Balance on a racing multihull is the most important thing. If you set up a set of sails so that you can say that you are carrying your number 1 longer than everybody else that’s just stupid.
We have found many times that in that wind strength where it’s a toss of the coin as to whether you change down or hang on, your better off changing down and staying in control. If you set up your sails properly you can change down the main only and keep the same headsail which is something that happens here very successfully.
I honestly believe that fathead sails work better as a number 2 main.
I have tried several combinations and I think that after 5 years of trail and error have hit on the right combination for all wind strengths.
Regardless of how well you can make sails, these are model boats the hardest thing to work out is just how much twist you will want to set into the sail for the next race. Setting up is obviously done on the land, you have no means of allowing more twist half way around the course.
So to this end comparing the set up of a r/c multihull to any other boat model or real is impossible.
It makes no difference if you have been sailing full size monohull’s, multihull’s or model monos for years, r/c multihull’s are a whole new breed and they require time to understand them.
The best monohull sailor in the world in my opinion would have a very hard time racing r/c multihull’s successsfully straight of the bat.
