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spinnaker #200591
01/16/10 10:03 AM
01/16/10 10:03 AM
Joined: Jan 2010
Posts: 1
B
buckwheat Offline OP
stranger
buckwheat  Offline OP
stranger
B
Joined: Jan 2010
Posts: 1
building a spinnaker for an 18 ft boat with a 30.5 ft carbon mast.....what would be the ideal dimensions, and how high to mount it above the hounds

-- Have You Seen This? --
Re: spinnaker [Re: buckwheat] #200627
01/16/10 11:11 PM
01/16/10 11:11 PM
Joined: Dec 2007
Posts: 1,430
california
F-18 5150 Offline
veteran
F-18 5150  Offline
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Joined: Dec 2007
Posts: 1,430
california
What is your beam? Sounds like a F-18 rig would work if your at 8.5 beam.


Richard Vilvens
Brand Ambassador
PSA Capricorn USA
R.Vilvens@yahoo.com
Fairfield, Ca
F-18 5150

http://www.capricornsailing.com/
Re: spinnaker [Re: buckwheat] #200635
01/17/10 05:33 AM
01/17/10 05:33 AM
Joined: Sep 2007
Posts: 571
Hamburg
Smiths_Cat Offline
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Smiths_Cat  Offline
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Joined: Sep 2007
Posts: 571
Hamburg
depending on the strength of the mast, so best is to contact the builder. Rule of thumb says from the length between hounds and top not more than one third.

Cheers,

Klaus

Re: spinnaker [Re: Smiths_Cat] #200636
01/17/10 06:23 AM
01/17/10 06:23 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
Carpal Tunnel
Wouter  Offline
Carpal Tunnel
Joined: Jun 2001
Posts: 9,582
North-West Europe

Quote

Rule of thumb says from the length between hounds and top not more than one third.



Actually that is not the rule of thumb at all, but an overly conservative rule initiate by Bill Roberts and followed by Bimare when they fit hooters rather then spinnakers.

All modern spinnaker boats have the spi hound at about 60% hounds-top distance. All alu masts should be able to withstand that when the spi area isn't significantly larger then 125% the mainsail area. With carbon masts it dependent on the lay-up and local reinforcements.

The dependence between flexing and spi hound higher is a very sensitive one (3rd power relationship) and going to 30% will see the flexing reduce by a factor of 8 where the stresses inside the mast will be lowered by a factor of 2. If you are unsure about your safety margin then go to ratio's of 50% or 40% but not 30%, the latter is really too small.

An example. The F16 use the unmodified lightweight aluminium mast of the Taipan 4.9 who developped their mast profile from the Alu masted A-cats of the 80's. The hounds on the Taipan are at 6000 mm from the mast based and the top is at 8500. We fitted all our spi hounds at 7500 mm or indeed (7500-6000)/(8500-6000) = 0.60 = 60%. The only mast that was broken under spinnaker sailing was in China where the owner fitted a F18 spinnaker with a higher mast hound then that and the mainsheet accidentially uncleated while they were 2-up beam reaching from the trapeze. The F18 hound fitting is about 8250 mm from the mast base or 750 mm (2.5 feet) higher then 60% rule.

Currently the new F16's are using higher stay hound hieghts of about 6100-6150 mm but this is unrelated to spinnakers. They do so to limit the (former) increased flexing of the mast top under the (much increased) square-top sails (40%) that the new F16's have over the old Taipans (20%). But even with this modifications the spi hound is still at (7500-6150)/(8500-6150)= 0.57 = 57%

The F16's founders chose the 60% rule after finding that the F18's, F20's and other modern purpose build spinnaker cats used the same rule. I think the only exceptions where the earlier F18HT designs (Bimare again). I've used this rule also on a Prindle 18 and never encountered problems there.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: spinnaker [Re: Wouter] #200670
01/17/10 05:44 PM
01/17/10 05:44 PM
Joined: Sep 2006
Posts: 586
Hobart, Tasmania, Oz.
Dazz Offline
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Dazz  Offline
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Joined: Sep 2006
Posts: 586
Hobart, Tasmania, Oz.
Translating Wouter into English...

Don't hoist the spi more than 60% above the hounds.

Don't ask me how I know......


C2 AUS 222 by Goodall design
"Darph Bobo"
Re: spinnaker [Re: Dazz] #200671
01/17/10 05:50 PM
01/17/10 05:50 PM
Joined: Nov 2003
Posts: 749
Santa Cruz, CA
SurfCityRacing Offline
old hand
SurfCityRacing  Offline
old hand
Joined: Nov 2003
Posts: 749
Santa Cruz, CA
Originally Posted by Dazz
Translating Wouter into English...

Don't hoist the spi more than 60% above the hounds.

Don't ask me how I know......


That's the general rule that I used to in development of my Hobie 18 and Getaway spin kits. No problems reported.

j

Re: spinnaker [Re: SurfCityRacing] #200690
01/18/10 09:22 AM
01/18/10 09:22 AM
Joined: Jun 2006
Posts: 431
Netherlands
DennisMe Offline
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DennisMe  Offline
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Joined: Jun 2006
Posts: 431
Netherlands
You know what gets me;
All the third order relationships and such aside. What really drives the message home is "Don't ask me how I know..."

Re: spinnaker [Re: DennisMe] #200691
01/18/10 10:28 AM
01/18/10 10:28 AM
Joined: Dec 2001
Posts: 5,590
Naples, FL
waterbug_wpb Offline
Carpal Tunnel
waterbug_wpb  Offline
Carpal Tunnel
Joined: Dec 2001
Posts: 5,590
Naples, FL
speaking of masts and spinnakers, anyone got the scoop on what happened to that Viper (I think it was the Viper) mast Friday at Tradewinds?

We went past them and the mast was in three pieces. Obviously they were on the spin reach, but I don't think they said anything happened with the mainsheet or anything obvious like that.

Sad, because they were doing pretty well...


Jay

Re: spinnaker [Re: waterbug_wpb] #200695
01/18/10 10:54 AM
01/18/10 10:54 AM
Joined: Jan 2008
Posts: 3,655
Portland, Maine
T
ThunderMuffin Offline
Carpal Tunnel
ThunderMuffin  Offline
Carpal Tunnel
T
Joined: Jan 2008
Posts: 3,655
Portland, Maine
I didn't see it - but I was right there when it happened.

I came around the A mark and they were right in front of us and they were having some issues with their spin set. The skipper was driving pretty high while still trapped out past the A mark (no offset mark so you didn't have to reach anywhere). There was some "elevated voice levels" on the boat for a moment and I didn't want to get stuck there as I had Mark Smith coming up quick behind me so I ducked below them and set.

About 30 seconds after we set and started trucking - I hear a *crrrrrrrrreeeeeeeeeeeeeaaaaaaaakkkkkk BANG* and Bailey turns around and notes that the viper had lost its mast.

I know its not much to add....

Re: spinnaker [Re: ThunderMuffin] #200702
01/18/10 12:36 PM
01/18/10 12:36 PM
Joined: Dec 2007
Posts: 1,430
california
F-18 5150 Offline
veteran
F-18 5150  Offline
veteran
Joined: Dec 2007
Posts: 1,430
california
I hope that wasn't Karl's new boat.


Richard Vilvens
Brand Ambassador
PSA Capricorn USA
R.Vilvens@yahoo.com
Fairfield, Ca
F-18 5150

http://www.capricornsailing.com/
Re: spinnaker [Re: F-18 5150] #200723
01/18/10 04:03 PM
01/18/10 04:03 PM
Joined: Dec 2001
Posts: 5,590
Naples, FL
waterbug_wpb Offline
Carpal Tunnel
waterbug_wpb  Offline
Carpal Tunnel
Joined: Dec 2001
Posts: 5,590
Naples, FL
Squidpig is doing just fine...


Jay

Re: spinnaker [Re: waterbug_wpb] #200739
01/18/10 08:38 PM
01/18/10 08:38 PM
Joined: Mar 2009
Posts: 901
Solomon's Island, MD
S
samc99us Offline
old hand
samc99us  Offline
old hand
S
Joined: Mar 2009
Posts: 901
Solomon's Island, MD
I believe the two day old viper blew up one of the diamond wire fittings....not good on a new boat. This is second hand on the boat age, but I saw the damage and it was a viper (not the viper with the mast in two pieces).


F18 Infusion

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