Okay, there has been a lot of conjecture on some of the other forums about cats "planing" or not- Especially "round bilge" ones.

Now, I respect Bill R. BUT they have a TON of these "boats" here in Arkansas called "pontoon boats"- Most are "catamarans" (ie have two hulls) and most of their "hulls" are two, PERFECTLY round aluminum "tubes". And THEY "plane" no doubt about it (pull waterskiers and hit ~30+ mph)! And it doesn't take a 1000 HP motor for them to do so!! For their size they are quite "light" though- all aluminum and some plywood decking. Also, they have other, round bottom aluminum fishing boats w/ NO chines or sharp edges that plane as well here in the land of lakes and rednecks. Also, Bill pointed out you use "flat" rocks when you go to "skip" them on water- Well here in the land of hunting dogs and ATV's we "skip" round bullets off the water just for s*7ts and grins! SO, as far as I'm concerned it IS "possible" to plane on a perfectly round bottom hull shape- I don't know how efficient it is or practical, but I KNOW it's possible (Maybe this is like the bumble bees that supposedly- according to the engineers- are incapable of flight - But the joke is, Nobody told them!)-

Now, this got me thinking- How to "prove" whether or not a particular boat (catamaran) could plane? (And not using all that fancy "math" stuff Wouter and Bill use- I'm NOT up to that! (Here in Arky the definition of "using a calculator" means you take your shoes off! :-)

Well, what I decided is- Just use a powerboat (I happen to have one of those), a ski rope, and whatever boat you want to try to "prove" will or will NOT plane- DON'T put the sails up (You'll generate so much apparent wind and/or tear your sails up) and tow it behind the powerboat, recording the speed as you slowly accelerate- Have 2 persons on the boat being "tested"- one holding the tow rope- By my reasoning, just like waterskiing, you will KNOW you are "on plane" when the tension in the tow rope suddenly decreases-



Okay- What do the rest of you all think of my crazy "experiment"? OH yeah- If it "works" then a person could actually "test" several boats/types of boats and see which plane "easier" (ie at a lower towing speed). And since I even have about 6 different cats I could test several if I just had time and 2 other idiots to help me!



Kirt

(Wrapped in my Arky "fire suit"- Aluminum foil head to toe!)

Kirt

That has to rank as one of my all time favorite posts…LOL…Like yourself I have great respect for Bill Roberts…his expertise is undeniable…however you have brought up some very good questions with the pontoon boats.



However…my question is… are they really planning? Or are they just narrow and streamline enough to be forced through the water at what are normally considered planning speeds? Tornado’s can hit speeds of 30 mph in perfect conditions right? But are they planning? What about a torpedo? It is perfectly round in section and goes very fast but is it planning?



The bullet analogy falls through the cracks by virtue of the velocity involved ( interesting word picture though…LOL)



How much horsepower does a modern sailing rig generate? (I would love to hear the answer to that question) Is it on par with the outboard motors used to propel these pontoon boats? Or is the power to weight ratio grossly in favor of the powerboat?



To relate this to another type of sailing craft…sailboards…it is immediately apparent the minute you step on one in planning conditions if it has hard crisp rails or soft egg rails.

In fact if the board has too much rocker and soft rails it is almost impossible to get it to plane…even while all around it, designs with less rocker and harder rails, are planning instantaneously when sheeted in.



With that said, I would still love to hear how your experiment turns out…it may not prove the boats can plane but might prove very interesting as to how much resistance each of your designs exhibits when pulled behind your power boat…Maybe you could borrow a accurate heavy duty hanging scale and hook that up to the tow rope, giving you a way to quantitatively measure the differences…at least with relation to each other…



Your logic reminds me of what my 85-year-old High School chemistry teacher told our class. He said that most of the real break troughs in research were found by the new (fresh out of school) chemists. He attributed it to the fact that the more experienced chemists knew too many reasons why an idea wouldn’t work; therefore they never tried, and therefore never came up with a solution. Think about it!



Give it a go…can’t wait to hear the results.



Bob

Bob-

Good idea about the hanging scale and I just happen to have one that goes to 300 lbs. (the one I used to find out my Taipan platform is ~140 lbs.)- We usually use 'em to weigh our wild hogs, deer, etc. before we butcher 'em and eat 'em ('course I won't double the actual numbers like we usually do when tlaking to our hunting buds down here)-



Kirt

Kirt,

I've towed my fair share of cats when running regattas. If I was trying I'm fairly certain I could make them plane.

I think the only real question is at what speed.



I expect that will vary and be related to basic things like suface area, angle of attack (which will create the dynamic lift) and total weight.

The only real way to find out is to conduct your experiment.



Making a boat plane when being driven by the wind may be quite fifferent (than when towed) because the forward thrust is not in line with the drag (changing angle of attack) as it would be when being towed. Having said that what could be learned by your experiment may bring us closer to plaing when driven by the wind.

For example, it may assist in quantifying the problem to aid in say the design of a spnnaker/hull combination that gives just the right amount of lift and forward drive. Possibly the right balance could have you planing downwind at least.

In my ignorant state, I feel sure it is possible



Regards,

Phill

have a read of Bethwaites book.. He has a reasonably detailed account of his experimental test design..



An actual data base on real boats would be interesting..

Stewart-

Yeah, I have Frank's book as well and that was in the back of my mind when I thought of this "experiment"- He details many such endeavors in his book-

And I agree with you Phill on both issues- Not exactly the same (obviously) but "real numbers" would give us a place to start at least and also agree on the planing downwind issue. Apparently, according to Bill R., it's the projected areas of the spi in the horizontal direction that determine forward drive, and the vertical direction that determine "lift"- It may be that the REAL "key" to getting downwind fast (er) on boats such as ours (at least in decent wind and "flat" water) is to have a spi w/ MOSTLY vertical lift and just enough drive to cancel out the "drag" (ie keep the sail filled or maybe a little more- probably is a necessity) and rely on the main to now (continue to?) produce most of the "drive" and utilize the fact the boat is actually "planing" to provide the higher boat speed-

I even thought a spi w/ 2 "panels" (at least) and "slots" or "tubes" even, would be interesting to try- (sort of like some of the kites/parachutes being used) and allow more lift or at least the ability to alter lift vs drive more perhaps- Possibly what we need is a spi w/ tack and head adjustable together- As move tack forward head moves down (more vertical projection- more lift- to "get on plane"?) then can bring tack back and head moves up- more horizontal projection- more drive, more speed- may need way to allow/force spi to become "flatter" as well as speed increases- Heck, at this rate we may need fully battened "spinnakers" to keep them from collapsing as we blast along downwind! Then, if we can only carry that speed as we carve it upwind we could plane upwind under "spi"............ Ooops, guess I got carried away...

Gotta go back in the trailer house now and chase the hunting dogs out of the bed- Time for them to get up and ketch a 'possum for breakfast-



Kirt from Arkansas

Kirt,

I know the speed of a skiff under kite is related to the length of the luff..

So increase pole length should be the first place to play with..

Stewart-

True, but the F 16HP rules limit pole length-- Say, you probably know- what are the lengths of the 18 skiff masts and prods by the way?

Thanks!



Kirt

The F16HP already features are rather long pole. It sticks out about 1 mtr in front of the boat, this is equal to some 3,5 mtr. in front of the mast.



I think the 49-er skiff pole sticks out as much too. They will

surely be very close.



The hound on the F16 is only just lower than that of the 49=er, so if their spi's lift than our can so too. Weight of both boats is about the same too.



Stewart ? Are the 459-ers the fastest skiffs after the 18's ?



Wouter

interestingly my last post disappeared..



To answer the questions to the best of my ability..



The 49er is just faster than the 16teen and 14 less than 2%.. Though the 14 is a tad quicker downhill.. With the 49er a tad better uphill. guess waterline length comes into the equation..



But remember the 49er is designed for short shrp tacking duels.. The longer the prod the slower the tack..



Prod lengths..

the I14 (4.3 meters) has a 2.7 meter prod from the stem with the mast back 1.9 meters from the stem.. or 4.6 meters from the sheer mast step.



The 18teen has a restricted rig these days.. the big stick is limited to 10.5 meters with a prod of 3.8 meters (12.5 ft).. but that depends on where your talking league or PG rules..



12s are wild.. their big sticks are 10 meters or so long and I have heard tales (may or may not be true) that some prods have gone out to 12 foot.. 12s suggest they take 14s downhill.. overall they are a lot slower than an I14..