My F16-class pontoon design (comments/suggestions?)

[Guest625101138]

Attached picture is my ultimate reverse bow. The boat is doing around 6kts. It is pre-GODZILLA days when I was trying all sorts of hull forms.

The nose is 100mm below the surface and there is no hint of a bow wave. Taught me that it pays to look aft when you are considering wave energy.

Michlet supported the fact that it was a dog after the event despite no bow wave.

Rick W

[kerinin]

Rick:
I had been ignoring the GODZILLA portion of the docs - I guess I'll have to take a look so I can understand the process.

A quick googling didn't turn up anything for 'Ward Optimum Symmetrical Ship' - do you have a link? That sounds interesting.


Bad Dog:
Thanks for the pointers on V-hulls, I think it makes a little more sense now. I'll have to chew on that for a while - it explains some questions I had watching some A-cats in action which seemed to be practically flying out of the water.

[kerinin]

Michlet supported the fact that it was a dog after the event despite no bow wave.

Was that due to the reduced aspect ratio of the hull?

[Guest625101138]

Originally Posted by kerinin

.......
A quick googling didn't turn up anything for 'Ward Optimum Symmetrical Ship' - do you have a link? That sounds interesting.

....

Here is a reference to the original paper:
http://www.dtic.mil/srch/doc?collection=t3&id=AD0623551


This is a reference to earlier work of Ward and others:
http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf

Leo posted a .mlt file of the Ward OSS on the thread I previously referenced. The hull has virtually no wave drag at the design speed but it is not the lowest drag hull. The main interest is how a couple of bumps can eliminate waves.


On the topic of the orange boat - it was too short for the target speed. Things I found out once I started using GODZILLA.

Rick W

[Ad Hoc]

"...Leo advises that there are two lowest drag hulls but I have never seen this. .."

This doesn't sound like a very quantitative approach or explanation, yet you claim the program is perfect and better than tank testing...!

A "technical" statement like that requires validation.

[Ad Hoc]

"...Here is a reference to the original paper:
http://www.dtic.mil/srch/doc?collection=t3&id=AD0623551.."
This is dated 1965.
So when the authors make a statement thus "..demonstrate a decided advantage of such direct wave survey methods over the classical Froude method of determining the wave resistance.."..if it is so much better and more accurate, why has this "new" method not been adopted world wide by test tanks and taught at Uni's?..been over 40 years! Doesn't sound like validation to me....unless you can show otherwise with other references of this "new" method that is so much better?

[Guest625101138]

Originally Posted by kerinin

....
A quick googling didn't turn up anything for 'Ward Optimum Symmetrical Ship' - do you have a link? That sounds interesting.


...

I dug out the Ward OSS file from Leo's original post to save you hunting around for it. See the attached.

Rick W

[Ad Hoc]

"...Michlet supported the fact that it was a dog after the event despite no bow wave..."

Kerinin

There is always a "bow wave" from a body moving through a fluid, and wash. Just because one cannot see it, does not mean it is not there. Any simple study of Lord Kelvin about a single pressure point moving in a fluid in a straight line will tell you that.
What has emerged in recent years with regards to wash is the qualitative documentation of solitary waves first discovered by Russel in 1838! As the name implies, consists of a single elevation of the water level above the original undisturbed water level.

[waynemarlow]

Originally Posted by CTMD

I'm assuming thats on the dwl. How much reserve bouyancy do you have?



Quick Weight estimate.
Item. Weight LCG LMMT
Hulls 40kg 2.2 88
Mast 16kg 2.5 40
front beam 5kg 2.5 12.5
back beam 5kg 0.5 2.5
steering assembly 10kg 0.2 2
prod, kite, etc 5kg 4 20
sails 10kg 2 20
boards 4kg 1.8 7.2
misc (tramp etc) 9 1.8 16.2
Total 104 2.0m 208

your LCG 2.77

required crew location 3.27m fwd of transom.

The above numbers are very rough. but if you hash them out in more detail you'll be able to calculate the required LCG. For your initial calcs set your crew's front foot on the front beam (so crew's LCG is say 300mm behind beam and skippers is a further 600 behind that)

The above weighs are quite a bit out individually but never the less the class weight is 104 kgs. Hulls are now less than 26 kgs, masts about 12, beams about 7 front and 5 rear. Its surprising how all the other little bits add up. Check on the Catsailor F16 forum where this has been discussed regularly.

First thing to consider when designing a F16 is which is it going to be, a single hander or a dual hander. We have worked out that a boat can't be both. My Stealth is a great single hander but a much slower dual, the Viper is over weight by about 30kgs but is volumous to say the least and is doing well as a dual hander. The loss of one sail is enough to accentuate the higher volume and hence extra drag to such an extent that in my belief the boats have to be designed primarily for one purpose or the other.

I love the LR2 design but sadly I think it won't succeed in the F16 world and its not the eliptical design, its the bow design. We have a 3.5m prodder holding down a 17.5msq very very flat spinnaker ( almost a screacher ), the upward forced are enormous. Those designs which have diagonal wire braces mounted from the front stays are now breaking 4mm D12 ( which is stronger than 4mm wire ) due to poor triangulation angles ( we are limited to max luff length and height ), the only way to get better angulation is to move the bottom of the stay foward to the bow area, now if that stay is now in the water it will have a lot of drag. Perhaps a modified nose section would be enough to get these angles better. This upward pull is great until it starts to go wrong. If the bow does go down the speeds are enough to trip the boat really quickly, those without T foils seem to be planning on the hull one minute and the next the bow just dissappears and over you go. All recent design such as the Falcon and Viper have large volume well ahead of the beam and with each new generation of boat that volume is getting further foward.

As to the veed hull laying on its side to get a better planning aspect, yes the stronger the wind and faster we go ( we are regularly now up around 20knots with the spinnaker ) the recommendation is to fly the hull higher to get a more flat section in the water, last years WC winner was the best at this and left everyone in his wake, it takes balls to do it but it does work in rougher water.

Crew weight is more than what you think, very few crew with sailing gear and harnesses etc are going to be less than 8okgs per person, more like 90 - 100, the buyers of these boats are typically not in the flush of youth and tend to have a little added girth.

There is mixed feelings about the worth of T foils on the rear, they do work extremely well and should be considered in any design.

The F16's are little hotrods, they are not subtle like the A's but boy are they fun and you can wheel them up and down the beach on your own. Any more questions fire away.