Trimaran motorboat / stabilized monohull

[Dick Culkins]

Hi Eric
Thank you for replying so quickly and for the offer of help. I will not be able to start construction until January for a May launch so Ill have 4 monthsfor construction with one helper. I allready have a 50 HP outboard and I need to use the boat to transport 4 crew so Im thinking of buiilding an 8 meter verstion of the proto. I have built two 10 meter ultralight plywood sailboats with very similar scantlings to yours so Im very comfortable with this construction method and the amount of time required to complete. This gives me enough tmie to build a scale model do some testing, study, and round up the materials.
If I could get a lines drawing of the 10 Meter Im confident that I will be able to scale it down to eight Meters with the help of some Naval acritect friends here in Newport. I would like to compensate you for this information how ever Im whats know as a Yankie so Im very thifty.
Thanks again.

 

[Eric DEBORDE]

10m drawings

Dick, look in "Private Messages"
U

 

[Eric DEBORDE]

New design

12m by 3.5m / 300gk for the hull / 30 hp outboard / transport 8 boys / 5l per hour & 14/15 knots.

 

[Eric DEBORDE]

Video of the 1/12th model

http://www.youtube.com/watch?v=odIiwTBwsd4

 

[Guest625101138]

Nice work Eric.

How about some close up photos of the model? Some siting in water shot low down.

Also if you can find the right conditions I would like to see some video of it powering down waves a little longer than the hull length.

By the way I have found my flat bottom V14 hull to be very efficient. The flat sections at the bow give it lift and improve pitch damping. It is a simpler hull form than you have so would be easier to make.

Rick W

 

[Eric DEBORDE]

Thank's Rick

My favorit spot is 25 Nautics away and my country is verry windy (20/25kt) so I am scared about flat surfaces !

 

[Alik]

Cool looking boat, I like it.
Needs more open deck space, maybe a flybridge?

 

[u4ea32]

Looks beautiful!

It still exhibits the "flop roll" at 45 degrees to the seas -- as the boat turned in the video, just for a second.

There is a reason for this that goes beyond ama location. In control system theory, your "flop roll" is referred to as "roll coupling." The problem is that the very long vaka (main hull) has tremendous longitudinal stabilty, and the configuration of small amas (the outer hulls) has little lateral stability. Therefore, when the boat wants to pitch, its easier to dissipate the energy by rolling than by pitching.

The US Navy is seeing the same roll coupling in its large Littoral ship with similar configuration.

The way to solve this problem is through active controls. Like the stabilizers needed for non-planing powerboats. However, you could go with something very efficient.

Consider experimenting with Moth foils mounted on your amas.

This is a long video, but you can see clearly the wand mechanism on the bow that adjusts the angle of attack of the main foil. The angle of attack of the aft foil is done by the skipper twisting the tiller extension.
http://www.youtube.com/watch?v=QMsM4TG2ce4

 

[philSweet]

The way to solve this problem is through active controls.

Which strategy do you think would work better- to actively dampen pitch, or actively dampen roll?

 

[Guest625101138]

My favorit spot is 25 Nautics away and my country is verry windy (20/25kt) so I am scared about flat surfaces !

Eric
On such a slender hull the flat surface is not going to cause pounding. I also believe you will find a flat entry improves control in a following sea. In its present form I expect your boat will have a tendency for the bow to dive very deep into the back of a wave unless speed is eased right back.

Rick W

 

[u4ea32]

Which strategy do you think would work better- to actively dampen pitch, or actively dampen roll?

Roll dampening.

This is a real problem with these designs, but to get that efficiency, its probably worth the extra system.

The smallest Naiad stabilizer system appears to be less than $15000 USD, but then you'd need to also run a small generator, like a Honda 2K.

But the moth foils are a small fraction of that cost, and no power needed.

 

[Eric DEBORDE]

Roll dampening and dihedral

The simplest thing would be to have 10 to 15 deg of dihedral angle like on planes with 2 to 2.5 deg incidence on wings for a lift of 150kg @ 16 knots. (total 300kg for both foils)

I have experimented this on my proto and it worked very well. The foils have to be just on front of center of gravity.

 

[RossCromie]

Active Foils

Built a foil and control system about 4 years ago. I cannot tell you how it went because its never been in the water at speed. The project did however help me learn about microcontroller interfacing to gyro chips. This system was for stability only and implemented using a large R/C model servo and balanced T-foil, so very low power consumption. One day I may develop it further, but for now my interests are simple sail rigs and hull construction methods/materials.
Further boat stuff www.islandelectronics.com.au/boat.htm

Cheers,

Ross

 

[BMcF]

The stabilized foil-assisted monohull shown earlier in this thread (repeated pic below which shows only the hull 3D model without foils)) is actively stabilized in pitch, roll, yaw and flying height. All four of those degrees of freedom had to be actively controlled to make the design perform..but that said, the resultant seakeeping and stability in rough seas was nothing short of astonishing....and having been involved in the building and testing of so many advanced craft over the last 25 years, I'm not given to throwing out superlatives on a whim.

 

[Eric DEBORDE]

news

The boat is a bit heavier than expected : 400kg insted of 300 planed.
I catch a Suzuki 50 hp 4 strocks.
In the water in 3/4 weeks !!

more pics on http://www.5iles.blogspot.com/