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  #106  
Old 01-28-2017, 07:52 PM
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Doug Lord Doug Lord is offline
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Arrow cat

Quote:
Originally Posted by redreuben View Post
Dennis I agree also as I put in post #83 I'm thinking about boats like the Woods 6-8m cats where he uses a drop down floor, the nacelle would provide the footwell for the central cuddy.

Doug;
So the hydrofoil is an inverted "T" ?

What happens when that kicks up ?

Similar problem to inverted "T" rudders, when they kick up massive braking (and breaking) effect.

There is/was a design on the web somewhere where the horizontal foils pivot, but thats more complexity which is what we're avoiding right ?

By the way if anyone has a link to that design I'd still like to find it again !
========================

As far as I know that wasn't a kick-up foil. Interestingly, the boat had kick-up rudders with no foils! Think about that.......
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  #107  
Old 01-28-2017, 07:57 PM
redreuben redreuben is offline
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Supplementary questions.

Heavy objects like batteries, fuel, water, beer etc; Is it not better to have them in the hulls assuming even distribution than in a nacelle ?

What are the pluses and minuses ?

Load distribution, would a nacelle actually help with mast and forestay loads ? I just assumed they would as its a deeper structure ?
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  #108  
Old 01-28-2017, 08:05 PM
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nacelle

Definitely helps with the loads-that's why all the AC cats have them:




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  #109  
Old 01-28-2017, 08:10 PM
redreuben redreuben is offline
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What about where the weight goes ? Should a nacelle be light storage or heavy ?

The clear advantage is isolating dangerous storage like fuel and gas.
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  #110  
Old 01-28-2017, 08:13 PM
redreuben redreuben is offline
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Ok more questions, my interest is in cats in the 7-8m range.
Do you think there is a wet deck height where the effect of a nacelle is negligible and a height where it is going to be a major hindrance ?
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  #111  
Old 01-28-2017, 08:17 PM
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Quote:
Originally Posted by Stumble View Post
Brian,

Your design is interesting but the material choice is disasterous. UHWP has zero structural rigidity and deforms locally under even moderate loads. So much so that you can't use it for deck planking because it isn't self supporting over any distance. You could bend a 5' long UHMP board into a pretzel with your hands.
I think you are looking at this material a little differently than one should. Sure in long planks it is not rigid.
But in blocks etc it is a very incompressible, strong material, that has very good wear capabilities and can be self lubricating to a degree.

Here are a few quotes:
Quote:
UHMW is a thermoplastic that belongs to the polyolefin group of material. Molecular density characterizes polyethylene, with UHMW being the most dense with a molecular weight of 3.1 million or higher. UHMW is simple to machine. UHMW is light weight, has no moisture absorption, has high tensile and impact strength, is shatter resistant, is long wearing, abrasion and corrosion resistant, is self-lubricating, and has excellent chemical resistance. This makes it ideal for wear parts in machinery and equipment
Quote:
UHMW is easily machined into custom components. Though it is easily machined with standard metal working equipment, UHMW has a very high coefficient of thermal expansion making it difficult to hold close tolerance dimensions. Its main attributes are impact and abrasion resistance. Its self-lubrication properties and low cost makes UHMW a great choice for many demanding bearing and wear applications.
You can find many more positive attributes with an internet search.

Quote:
Originally Posted by Stumble View Post
The engineering is beyond me, but to get a reasonable projected area and decent aspect ratio you will need to go to a very thick fiberglass/core, plywood, or carbon/core. Again just guessing, but I would bet if you run the numbers that a solid carbon section is pretty price competitive when you take into account how much thinner it can be made.
I'm not sure of which item you are speaking of constructing here?

Quote:
Originally Posted by Stumble View Post
But instead of using a massive pin, just invest in a couple of ring bearings. They are far easier to fabricate the board to fit and they already exist in the marine industry (used for stockless rudders).
As I mention above I had hopes of utilizing a simple 'plain' bearing, ...but there may well be other candidates

Quote:
Originally Posted by Stumble View Post
As for the nacell. Meh, this seems like a lot of construction to avoid a daggerboard, would probably be at least as expensive and a lot heavier than just making the board stiff enough to handle th unsupported length.
As I said before the central nacelle was not going to be constructed simply to support this central board(s) idea, but rather as a backbone to the catamaran fore-to-aft rigidity, and as a potential wave splitter up front, and as possible even the longeron for the headsay (no forebeam) , ala Gunboat
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  #112  
Old 01-28-2017, 08:19 PM
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One large foil is more efficient than 2 smaller ones. This is an aerodynamic fact. Less tip losses. 2 regular daggers have 2 sets of tip loss. The center mounted version only has one tip loss which would offset the lack of endplate to some degree.
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  #113  
Old 01-28-2017, 08:57 PM
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Bridgedeck Centerboard

I know model testing and the results obtained from it are anathema to some around here but in some recent European RC multihull races a cat with a single bridgedeck foil and a single center foil on a square platform has beaten all "normal" cats and tri's........
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  #114  
Old 01-28-2017, 09:41 PM
UpOnStands UpOnStands is offline
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models are fine, of cruisers.
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  #115  
Old 01-28-2017, 10:00 PM
UpOnStands UpOnStands is offline
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Quote:
Originally Posted by valery gaulin View Post
Maybe the center board could be mounted between two large heavy duty swivel plate in the bridgedeck! This would be for sure really strong configuration. Here is a photo of the type of swivel plates I am talking about. I am sure they make them even bigger and in stainless steel or aluminum.
sorry but that type of bearing is designed to accept heavy vertical loads directly over the center of rotation. Look at the center of the bearing -- a simple mushroomed rivet holds everything together. bigger and heavier versions? sure but how much additional weight is acceptable to you?

I actually used such a bearing for my son's 180kg motorbike -- made it possible to drive the bike straight into a tight space and then spin it around by lifting under the motor. But, even slight off-center loads created large wobble as the bearing is just not designed to take off-axis loads.
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  #116  
Old 01-28-2017, 10:17 PM
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This 'central board' right under the CE of the sailing rig, and central to the center of the vessel, could make for a quicker tacking vessel, particularly those cruising types that usually keep both hulls in the water at all times.
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  #117  
Old 01-28-2017, 10:50 PM
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Quote:
Originally Posted by brian eiland View Post
This 'central board' right under the CE of the sailing rig, and central to the center of the vessel, could make for a quicker tacking vessel, particularly those cruising types that usually keep both hulls in the water at all times.
Another benefit. As Oldsailor said his tri tacked much better with the central fin compared to 2 outboard boards. Moving the CE of the board aft by pivoting it will also reduce the tendency to broach in a following sea.

There are many benefits to this idea.
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  #118  
Old 01-28-2017, 10:58 PM
UpOnStands UpOnStands is offline
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this suggests possible implementation
yellow is UHMW
4 cm dia hole thru the stub arm is not shown
Attached Thumbnails
Bridgedeck centreboard why don't they work???-support.jpg  Bridgedeck centreboard why don't they work???-bearing.jpg  Bridgedeck centreboard why don't they work???-board.jpg  

Bridgedeck centreboard why don't they work???-cover-thru-screw.jpg  
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  #119  
Old 01-29-2017, 12:46 AM
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brian eiland brian eiland is offline
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You are pretty handy with those computer generated illustrations. Wish I could do it,... just never took the time to learn this new technology
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  #120  
Old 01-29-2017, 01:10 AM
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brian eiland brian eiland is offline
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I was trying to look up 'surplus helicopter blades' but is was getting annoying. I know there have to be MANY out there, and likely in decent shape for our use,...just not certifiable for flying any more.

I saw this,..oops file size exceeded forum limits

How about this..
http://www.nwhelicopters.com/nwh/
(files with photos within are too large)

How about this...
images for helicopter blades shape
or this...
http://aviation.stackexchange.com/qu...her-propellers
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