boat designing help!! PLEASE!

the race is on june 21st, im planning on making one for next years race

yes i will be around for the newport race, im a big sailor and plan on doing it when im 18 with all crew 18

i got 5th in opti worlds and other top results

 

how will a outrigger make it faster?
thats just drag? the boats wont flip if u no wat your doing but they are very tippy

 

Build the main hull much narrower so it is more efficient and therefore faster. With this new hull type the outriggers will provide lateral stability when necessary since a human won't be able to balance such a narrow boat.

Boats like these have been known to be the fastest and easiest to propel at displacement speeds for hundreds of years. It's nothing new. Unfortunately the concept won't work for you since you require a monohull.

 

i understand now. makes sence

where can i get hydrodynamics soft ware and stuff like that?

 

wat do you think about a tornado sailbaot for a hull? i know its multi hull but it sails fast

 

Why not use just one of the hulls and make a small, skinnier outrigger - that way you'll get the wetted surface down (which is what you want).

 

that would proberly work

 

Now you're starting to think....

The Tornado is a good start but it isn't optimised for you're use. To start with a catamaran hull while very efficient will have little of no form stability, that's why we've all been telling you that you need an outrigger.

As DB mentioned the outrigger can be very small and in smooth water areas you can use your body weight to lift it out of the water (this is what Polynesians do).

What you basically want is a 4 man skull, reinforced to take waves over the bow and a small 2m long narrow outrigger shaped like a **** (pointed at both ends)

 

Not likely for an affordable price. Still very expensive, and numerics are a bit off of reality still.

Looking at the pictures you attached, and the quoted distance/speed for the course, these boats are mostly planing. So the notion of displacement hull design is probably not correct. That's why you see the fastest boats transitioning to flat surfaces aft.

Look up froude number and planing on the net, you will get an idea of planing vs. non-planing.

 

im sure its displace ment

a 25ft boat with 2 adults, cooler, gas and a old 5hp that proberly doesnt put out 5hp or a 6hp wouldnt plan

 

18+ knots for a boat that length is planing for sure.

 

My thoughts:
the pictures show what look like hulls with a twist to the bottom pretty far back. Go for a flat hull, maybe a bit of a V for directional stability, but a small fin in back might fix that, from about 50 to 60% aft. That will give you the best chance for planing. Note also that the less area the less resistance and the faster the boat when planing, BUT, you still need enough surface to get on a plane, especially with this small engine...
Then use the forward 40 to 50% to twist up to the nice sharp bows, so you can cut into the waves in the rougher weather. The idea is that in the rougher waves, you will not have the after flat part of the hull exposed where it will pound, so maybe the flat part can be more like 60% aft.
Next, don't put too much weight in the stern, for two reasons: 1) your boat might porpose, or at least have a harder time getting up on a plane, each time you loose it because of a large wave, etc. and 2) to not expose that flat part of the hull to waves. Traditionally the CG is aroud 60 to 65% aft.
Theoretically, you want your boat to trim at around 4 degrees when planing in smooth water, which usually means the flat part of the hull should parallel the water when at rest. Check out what some other designs that might come close to this design trim at to confirm is this is optimal.
And indeed, aerodynamics will play a really big role in these boats, so everything you can do to reduce and smoth the profile the better. Maybe the one best think will be somekind of bubble windscreen that helps streamline the air past the crew and engine. Or one for the crew, one for around the motor... Also, instead of squaring off the stern, maybe gently curve it down from the deck to the water...
This is all practical advices, the proof is in the pudding, or, someone will have to run a few samples through some velocity prediction programs... you dont want to have to pay for it.
This site suggest that for a 300 kilo (660lb) boat, you want your CG 2.5 meters (say 8.5 feet, which is probably further aft than I suggested above) from the stern, as narrow a water beam as possible (I used 2 feet), and a vee to the after hull of between 5 to 8 degrees. It says 4 HP is enough to get on a plane then...
http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html

 

I used to go this fast in my father-in-law's 22' Philippine banca fishing boat with an 8 HP engine and there's no way on earth that boat was planing. It was a full displacement hull with a half log for a keel/bottom and tapered rounded sections curving up like a banana all the way to the pointed ends. So yes, long skinny boats can and most certainly *DO* go 18 knots with low HP engines without planing.

Personally I believe a longer (say 32 feet = 4 sheets of plywood) double-ended hull with plumb ends, plumb sides, flat straight bottom, and a substantially narrower mid-section would be faster than these boats. It would also require outriggers for lateral stability, and the passengers would have to ride on the hull instead of in it, so it's a very different approach than these boats.

I agree with ber1023 that these boats are in displacement mode.

 

Alright, some extremes can give quick speeds in displacement regime- very narrow and long like a rowing shell. But at the Froude numbers that ber1023 is talking about, a planing hull will give better speed for the given horsepower.

The boats in the pics that ber1023 attached aren't rowing shell type of boats. The hull shapes are chined and planar aft.
Not looking to argue about planing or non-planing though. If you feel like providing consultation to him, have at it.

It seems that the boats have arrived at shapes that work for the conditions, through real-world "testing". Success would likely come from analyzing proven designs and looking for incremental improvement.

But you could strap an outboard bracket on a rowing shell and give it a go. Good luck!

 

I'd second that. Although, sometimes design improvements are a revolutionary leap, rather than evolutionary -like the flexible joint at the foot of the windsurfer's mast.

I found some rules dating back to 2001 here.