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Old 21-03-2008, 15:57   #16
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Ocean Cheetah

Guys

I looked at the Ocean Cheetah when it was 70+k and although the fitout was far from complete, it had a second hand rig and very serious crazing on the saloon roof, I was seriously tempted. It does have a couple of new Nanni Diesels in it and a mish mash of other inventory some fitted some not.

Time passed and I was waiting for some cash to appear (it's now here) and then I noticed it had dropped to 50k, having spoken to Bill he forwarded me a surveyors report and it didn't make pretty reading. Water in the laminate, which apparently has been there a long time. The surveyor even talked about scrapping the whole boat.

I took advice from my surveyor and he suggested that you could drill holes and hot vac it but as he said there would be no guarantees that you might not end up with delamination problems down the line and there would be a full paint job after the work. Sadly I have crossed this off my list. She weighs about 3.9tons according to a calculation done by John Shuttleworth (that was based on where she is currently sitting in relation to her waterline, guess she would have ended up at about 4.5tons finished.

The above not withstanding it is a very, very pretty boat and would have been perfect. For those of you who are interested there is only one other Cheetah in existance called Zendo. She is somewhere in Canada but who owns it I never could find out, although I have a couple of pics.

Yes the moulds are now in South Africa bought by a guy called Jannie Smutts, I have spoken to him about a price for a part completed boat, still waiting for a price after several months. In fact when I was considering building rather than buying I was looking for the moulds for this boat I found the guy (John I think) who sold them to the guy in SA about a month after they left the country.

Maybe if the price drops further on the Cheetah there is a bargain to be had if you are brave enough! Personally the surveyors report ran shivers down my spine, especially when you consider it was Bill's survey for insurance purposes.

Like the Poland idea, surely Latvia or Georgia would be even cheaper? Wasn't there a yard in Latvia building Farrier F41's?

Sadly part of my problem is the best value currently seems to be a in the US and not on my side of the pond! There was a very nice Catana 40 that just sold for 60k, but that was in Hawaii, nice place to start a cruise but a bit far to have it delivered.

Regards

Richard
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Old 21-03-2008, 16:05   #17
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[quote=Nordic cat;145291]
Definition: "Performance Index (0.5*(Lwl*SA/D)1/2) This index gives an estimate of the relative boat speed to wind speed on a reach, i.e., a figure of .8 says a boat will do 8 knots in a 10 knot wind."


Sorry for the unclear posting.

Displacement is in pounds, so tons x 2240

To write it more clearly:

PI = 0.5 x SQRT( Lwl x SA/D)

Lwl in feet
SA in square feet
Displacement in pounds.

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Alan
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Old 23-03-2008, 05:38   #18
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Multihull Stability and Performance Numbers ~ By Dave Gerr
"For multihulls, there are four important indicators of performance and stability: the Bruce Number; the Real Performance Index; the Stability Number; and the Stability Factor..."

Goto: Stability is the Key
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Old 23-03-2008, 06:30   #19
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Question? How do you ascertain the CE for production multihulls? It's not a number that is often quoted. Maybe especially tough to find for older boat?

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Richard
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Old 23-03-2008, 07:14   #20
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If you can find a profile picture it could be determined fairly easily. The ad brouchers usually have a profile view. Just draw lines from each corner of the sail to bisect the oppossing side. this should be a close enough center of area for the sail. Do it for both sails then connect the two points with a line. Find the combined centre by proportioning a position along the line in proportion to the sail areas. For example if the main is 66% of the sail area then the point is 66% of the distance from the point on the jib towards the main.
Then scale a hieght from the water line

Mike
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Old 23-03-2008, 07:24   #21
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Thanks Mike!!!

Sounds relatively easy. Just a question of finding brochures if you are looking at older boats, or taking to the bosuns chair with a tape measure in your teeth on a windy dockside!

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Richard
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Old 23-03-2008, 12:20   #22
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Quote:
Originally Posted by GordMay View Post
Multihull Stability and Performance Numbers ~ By Dave Gerr
"For multihulls, there are four important indicators of performance and stability: the Bruce Number; the Real Performance Index; the Stability Number; and the Stability Factor..."

Goto: Stability is the Key

Thanks for the link Gord.

What we need to remember, is that despite all the fancy formulas (Formulae?), none of these "indicators" will tell you the whole truth. Most of them are purely relative indicators. They can only be used for comparing similar boats with similar rigs, to give you an idea of how one will perform relative to the other.

Different hull shapes will give different stabilities when heeled, different rigs, different ratios of sail area between main and jib, wingmasts, variances in wind resistance etc.. All these factors are often not taken into account.

So use these formulae for what they are designed for, as a relative yardstick only.

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Alan
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Old 24-03-2008, 02:30   #23
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Centre of Effort (CE) can be approximated by locating the geometric centre of each triangular sail, and connecting the two centres with a weighted (by each sails relative area) line.

Goto:
The Nature of Boats: Insights and Esoterica for the Nautically Obsessed
By Dave Gerr (page 300)
The Nature of Boats: Insights and ... - Google Book Search

Or:
Sailmaker's Apprentice: A Guide for the Self-reliant Sailor
By Emiliano Marino (page 34)
Sailmaker's Apprentice: A Guide for ... - Google Book Search

See also:
MULTIHULL STABILITY ~ by John Holtrop
... The purpose of this article is to introduce a technique for estimating the wind strength necessary to capsize a multihull, with respect to a specific vessels dimensions, weight, and sail plan. The final product of this exercise is a table, unique to your particular vessel and personal risk level, that contains the maximum wind velocity you can operate in with a reasonably high margin of safety. The table starts with light air conditions (full sails and a cruising spinnaker}, and ends under bare poles facing hurricane force winds ...
Articles/capsize velocitiiy.htm
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Old 24-03-2008, 05:02   #24
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Gord,

I don't think that picture re COE is actually correct. The COE of a sail depends on the draft or shape / trim of the sail. As the boat moves off the wind and the sails are move outboard away from the CL the COE move forward.

The concept that the COE is locating near the center is accurate, but the diagram is more a cartoon than an actual representation of the location of the force.

Correct me if I am wrong.
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Old 24-03-2008, 05:11   #25
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Quote:
Originally Posted by defjef View Post
... The COE of a sail depends on the draft or shape / trim of the sail. As the boat moves off the wind and the sails are move outboard away from the CL the COE move forward.
The concept that the COE is locating near the center is accurate, but the diagram is more a cartoon than an actual representation of the location of the force...
Im no expert; but Id agree that the Centre of Effort (CE) can only be approximated geometrically, as shown in the simple line dwg.

The previously linked texts give better descriptions.

The Nature of Boats: Insights and Esoterica for the Nautically Obsessed
By Dave Gerr (page 300)
The Nature of Boats: Insights and ... - Google Book Search

Or:
Sailmaker's Apprentice: A Guide for the Self-reliant Sailor
By Emiliano Marino (page 34)
Sailmaker's Apprentice: A Guide for ... - Google Book Search
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