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Old 06-12-2014, 16:30   #91
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Re: A Catamaran Question

Considering the drawbacks to foils in heavy seas, I think I'd rather explore parachute type sails for a combination of lift and speed, as long as the winds are cooperating.

As a former helmsman/planesman on fast attack subs, I'm very aware of the power a foil exerts on a vessel, especially near the surface. I was involved in extensive testing of bow planes vs sail planes and bow planes were far more effective in controlling depth near the surface - less susceptible to "sea suction" which pulls a sub upwards with the waves and causes it to broach. That's why 2nd flight 688s switched from sail to bow planes, as a result of our research in a simulator.

All this is to say, foils are far more stable/predictable when they're going through "smooth" water (I like 400' myself) and can really exert a great deal of force in unwanted directions in heavy sea states.
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Old 06-12-2014, 16:42   #92
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Re: A Catamaran Question

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Originally Posted by s/v Beth View Post
One of the main reasons stated that a hydrofoil cannot be used for a cruiser is that we cannot drive it. I predict that the evolution of autopilots will eventually overcome this, and allow for the safe passage of large foil boats in almost all types of weather while foiling. When they cannot foil, deep fins may keep them upright, as well as things like remote deployed drag cutes and masts that telescope back into itself, providing a much lower center of gravity.
Bottom line- if it was 100% safe we probably wouldn't be doing it anyway.
Let the flames begin....
You bring up a very good point.

They now have very cheap (just over $100) 3 axis gimbal systems for RC quadcopters that perfectly stabilize the camera and eliminate vibration. There's no reason why that very same controller board couldn't be used to control an active foil stabilization systems so the wife's bathwater doesn't spill in state 5 seas.

Not that I'm advocating taking a bath at that time, but the technology behind the capability interests me.

Along those lines, one must have a means to move the foils, either hydraulic or electric. In the same study where we experimented with depth control at various sea states, they also varied the simulated hydraulic power plant on us, with high pressure low volume, low pressure high volume, low pressure low volume, etc. The difference in planes response time and depth accuracy were pretty dramatic when hydraulic power was reduced, especially when pressure was reduced.

Now with recent advances with electronic power steering, one could probably build an adjustable foil system with off the shelf or junkyard EPS units from Saturns and other small cars.
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Old 06-12-2014, 17:01   #93
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Re: A Catamaran Question

I agree that the mechanics would be complex, but they build hydraulic flaps for airplanes with great reliability. I have watched how it feathers the ride. Seems like we could do this also. But we are getting ahead of ourselves. Just building a cruiser on stilts seems like the first step.
There has been at least one hydrofoil cruiser that I am aware of. Looked awful, and didn't seem to get much out of them.
http://www.amazon.com/Hydrofoil-Voya.../dp/1466350164
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Old 06-12-2014, 18:10   #94
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Re: A Catamaran Question

Guys, foils on a cruising multihull are not a new concept and in fact were proven on Williwaw, a 31 ft plywood trimaran back in the 1970s on a cruise from California to New Zealand and back. I saw it in Auckland while she was there. She was not just foil stabilized, she would get fully foil born on big fore and aft ladder foils which could be hinged up out of the water if i remember right. I believe there was also a race on San Francisco bay between Williwaw and Manureva the big French aluminum tri, i don't remember the outcome.


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Old 06-12-2014, 22:26   #95
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Re: A Catamaran Question

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Originally Posted by socaldmax View Post
Considering the drawbacks to foils in heavy seas, I think I'd rather explore parachute type sails for a combination of lift and speed, as long as the winds are cooperating.
you know Ive just been watching a video of IMPI doing just that:

http://youtu.be/bs3kpZpBaiw


Quote:
Originally Posted by socaldmax
As a former helmsman/planesman on fast attack subs, I'm very aware of the power a foil exerts on a vessel, especially near the surface. I was involved in extensive testing of bow planes vs sail planes and bow planes were far more effective in controlling depth near the surface - less susceptible to "sea suction" which pulls a sub upwards with the waves and causes it to broach. That's why 2nd flight 688s switched from sail to bow planes, as a result of our research in a simulator.
as you would know then
trimming a submarine is more easily accomplished when viewed as flying through water. Her depth keeping sustained by controlling ballast down to the cubic cm still needs to manage periscope tower heights and prevent them popping to high out of the water, best accomplished with the higher leverage from CG that bow planes exert in a deeper water environment.

Sail planes, which for those out of the vernacular are controllable planes placed on the boats sail or conning tower, and being higher up on the boat ride in the more turbulent sea water space near the surface, and greatly affected by sea state conditions which are from predictable in rough seas.

There are other important design parameters such as vulnerability to damage, containment of operating gear and noise, noise abatement.

Quote:
Originally Posted by socaldmax
All this is to say, foils are far more stable/predictable when they're going through "smooth" water (I like 400' myself) and can really exert a great deal of force in unwanted directions in heavy sea states.
and 'smooth water' is key here
we can make it work in flatter water, and all the successful examples of surface ships using foil technology pull us to this place, but it is in lumpy rough sea conditions that to me are a question.

But I guess in rough seas when we might be more interested in slowing the boat down perhaps we could partially retract them.

Im interested enough to keep thinking about this, its a common practice to manage a boats weight and stores to prevent going below the design water line (DWL) most sailors would be familiar with. What we are asking here is to jack the boat up and relieve some LWL thus reducing resistance and drag using a dynamic attained force.

That said, we dont want to lose LWL length which limits the type of hull shapes
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Old 06-12-2014, 22:40   #96
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Re: A Catamaran Question

In my 36' x 24' cat, when I get above 10, I'm psyched.
Above 12.5, the boards start humming and life is sweet!...(depending on sea state and heading)
Start hitting higher teens and I'm entirely thrilled, but also GRIPPED!
To think of sustaining 15+knots hour after hour, day after day would be exhausting.
If it was downwind and downsea ...MAYBE!
In reality though, on most passages I've done longer than 24 hours, I'm happy to average 8.



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Old 07-12-2014, 16:12   #97
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Re: A Catamaran Question

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Originally Posted by ZULU40 View Post
a video of IMPI...

http://youtu.be/bs3kpZpBaiw
Thanks...to ZULU and Impi! ...for a very pleasant flashback to our own ocean crossings.

We certainly agree with Impi's conclusions about the L440's 'blue water' suitability.

Now Impi...are we likely to see you in OZ anytime soon?
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Old 03-01-2015, 23:43   #98
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Re: A Catamaran question.

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There are slower

My question for "speed" was related to a my Gunboat experience, and whether or not it was possible to have a sub 40 footer that was a fast (15 knots) passage maker over a regularly traveled distance, for a reasonable purchase cost. (Used).

Physics and related costs for exotic materials, along with lack of comfort in a cruising vessel would appear to prohibit the higher speeds in a smaller Hull.

I considered buying a motor cruiser for the trips, but the cost of fuel made my knees shake and head spin. 130 miles at 30+ gallons an hour is the best part of $1500 each way. (European prices)

I just will set off a day earlier and enjoy the sail

P.S..... Sailing the Centaur around Southern Britain is so relaxing. It forces a person to enjoy the scenery... its going to be in view for a while.

Maybe this is what your looking for???

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