| increasing rightingmoment #24251 09/16/03 11:01 AM 09/16/03 11:01 AM |
Joined: Sep 2001 Posts: 267 Switzerland alutz OP
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Posts: 267 Switzerland | Hi I'm thinking of increasing the rightingmoment of my ventilo F18HT for open class racing. I'm aming at a rightingmoment/sailarea between the f18 and the tornado. I'm looking for confirmation that I'm on the right track! So please feel free to post your opinions!Wouter gave me some good hints and help to start with. I'm using his formula to calculate the rightingmoment(RM) for my ventilo: boatwidth=2.5m boatweight=130kg creweight=125kg sailarea=20m^2 RM=boatweight * (boatwidth / 2) + (crewweight * (boatwidth + 1m)) RM=600 kg m I calculated the RM for several boat's: Ventilo F18HT=600 Ventilo F18HT with 0.5m wings=668.75 Ventilo F18HT 2.7m width=640 Ventilo F18HT 2.8m width=660 Ventilo F18HT 2.9m width=679 F18=684 Tornado=740 BIM F20=785 After that I put the RM in relation to the sailarea, (without calculating the height of the centre of effort CE) rightingmoment/sailarea= Ventilo F18HT=30 Ventilo F18HT with 0.5m wings=33.44 Ventilo F18HT 2.7m width=32 Ventilo F18HT 2.8m width=33 Ventilo F18HT 2.9m width=34 F18=32 Tornado=34 BIM F20=35 considering that my ventilo dosn't have a jib and a much higher sailplan, I'm thinking of increasing the width to 2.9mtr witch leads me to a relation (rightingmoment/sailarea) of 34, the same as the tornado. In this way, I guess because of the lower sailplan from the tornado, there should be still enough heeling force to sail the boat on one hull. thanks for every post to the subject! greetings from switzerland Andi Ventilo IF20 with wings (not my boat)
Last edited by alutz; 09/16/03 11:40 AM.
| | | new carbon beams
[Re: BRoberts]
#24257 09/17/03 03:23 AM 09/17/03 03:23 AM |
Joined: Sep 2001 Posts: 267 Switzerland alutz OP
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Posts: 267 Switzerland | Thank you Bill for your response!
I was not sure, how far I should increase the boat width. My current beams are made of carbon pre-preg, are 2.5m wide and have diameter of 16cm, they come with no dolphin striker and are incredibel stiff. I will build the new beams with carbon and a vacuumpump, by my own. I have never done that bevor. As much as I know is, that the strenght of pre-preg is higher than standard carbon laminate. Now that I'm not a engineer and I can't calculate the forces and the strenght on the new beam. I thought that applying so many layers of carbon, until I achieve a wall thickness of 115% to the old carbon pre-preg beam. In this way, there should be some reserve of stability.
Also the local supplier of carbon fibres, told me, that when I feel, that the new beams are not stiff enough, it is easy to apply some more carbon layers later, to increase the stiffness.
I'm thinking of mixing carbon-braids, the first layer standard carbon crosswoven, the inner layers undirectional and the outer layers crosswoven again.
What do you think? Will this work?
thanks again for your post! greetings from switzerland Andi
Last edited by alutz; 09/17/03 08:03 AM.
| | | Be careful
[Re: alutz]
#24258 09/17/03 04:24 AM 09/17/03 04:24 AM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe | Be careful when making assumptions.
If you are increasing the righting moment with 15 % than the beam will be under 52 % higher loads (if my memory serves me right)
I can do the construction calculations for you; please take a look at them before you make-up your mind.
IF the free beam is to weak or to felxible than fitting a dolphinstriker will be a good alternative. These things make alot of difference.
WOuter
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
| | | Re: new carbon beams
[Re: alutz]
#24262 09/17/03 09:05 AM 09/17/03 09:05 AM |
Joined: Aug 2003 Posts: 284 S. Florida BRoberts
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Posts: 284 S. Florida | Hi Andi, If all the geometry of the boat/rig remained the same as a standard boat and somehow, magic, you increased the righting moment 15%, all loads in the system would go up by 15%. This not to say that all loads go up by the same number of Kgs, but all loads go up by the same percentage. For example, the axial load coming down the mast is a much greater force than the sail force, but if the sail force goes up by 15%, so does the mast axial load, compression, coming down the mast. In your situation you have it better than that. The increased sail force is due to increased righting moment. The majority of that increase in righting moment is in the trapeze wire which intersects the mast at the most shallow angle of any wire connected to the mast. Therefore the increase in mast axial load and main beam bending load will be less than a 15% increase. Other loads that add to the total mast axial load are windward shroud tension, which could go down, forestay tension and mainsail leech tension, mainsheet tension. In a simplified analysis we could say that if the horrizontal sail force goes up by 15%, these other forces will also go up by 15% of their base value and we are on the safe side. As far as your main beam goes: Uniform composite parts, beams, loaded in bending fail on the compression side first. Therefore it is important to add material to the top of the beam, under the mast step, and tapered as the additional laminate flows away from the center of the beam. Axial strands of carbon is all you need. The base beam can handle any axial cracking loads. Good Sailing, Bill | | | Re: increasing rightingmoment
[Re: grob]
#24265 09/17/03 12:32 PM 09/17/03 12:32 PM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe |
No greg didn't tell the stresses to which a beam can be designed too.
But when doing the math you quickly realize that stresses are not the real concern. Stiffness is. You can easily make a beam strong enough; but it is far more difficult to get enough stiffness into it to make the platform go well in waves.
Wouter
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
| | | Re: increasing rightingmoment
[Re: grob]
#24267 09/17/03 03:39 PM 09/17/03 03:39 PM |
Joined: Jun 2001 Posts: 12,310 South Carolina Jake
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Posts: 12,310 South Carolina | If your boat is stretching and squirming as it goes through waves, it's absorbing energy and taking away from speed.
Jake Kohl | | | Re: increasing rightingmoment
[Re: grob]
#24268 09/19/03 09:40 AM 09/19/03 09:40 AM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe |
A quick reply as one can write a book about this subject alone.
But the following main points are important
Stiffness allows a craft to be driven harder in rough conditions. Compare this with a car with insufficiently inflated tires. Sure it can take a bend with high speed but the flexing of the tire will give is a wobbly fell while rounding the corner. It feels like your not totally in controll. SUch wobbling can quickly cause the car to break out uncontrollably where properly inflated tires may also let the car slide but than in a controllable sense. THe improved behavoiur of the craft allows the drive to push it harder. It also feel more confortable.
Stiffness (for some reason) allows a craft to punch through waves better and sustain higher speeds here. I compare it with two hammers of equal weight one of rubber the other of steel. While both land the same weight on the nail we all know that the steel hammer drives the nail more comfortably into the wood. I guess it is the same with catamarans.
Stiffness allows such elements as the leech of a mainsail to be better controlled allowing the craft to point higher and make it more responsive to alterations in trim.
One dlophin striker less design behaved as follows : When janking non the mainsheet the mastfoot would be pushed down and the stays would lengthen together taking up large quatities of the applied mainsheet. The leech tension didn't really change that much. When the mainsheet was released a little bit the springness of the beam and stays would keep the leech tensioned up where a stiffer design would quickly have lowered the leech tension. Leech tension is an import trim factor on mainsails.
Stuff like that make stiffness important.
Wouter
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
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