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Spinnaker modifications to A-cat #232837
05/26/11 11:18 AM
05/26/11 11:18 AM
Joined: May 2011
Posts: 36
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ileestma Offline OP
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ileestma  Offline OP
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I am planning on making some pretty large modifications to my Bimare A-cat by adding a f18 spinnaker, which will be flattened slightly by my sailmaker.

I am going to run an additional carbon fiber crossmember between the hulls forward of the mast, through which the bowsprit will run, the inboard end of the pole will be secured to the forward existing crossbeam via carbon fabricated bracket, or aluminum, thereby allowing the bowsprit to be self supporting absent the mast, and also adding lateral support to the hulls.

I plan on using a flattened f18 chute, which will likely require a new tang be installed roughly five feet below the top of the mast.

My question is, how can i strengthen the mast to support the huge increase in load, especially considering the fact the mast rotates? If it were stationary, i would simply move the diamond stay spreaders aft and tension to force a bend in the mast (causing the energy to travel down the tube instead of across it, which would ultimately snap it)

But since it rotates, i am a bit perplexed. Could i, assuming the chute pulls sideways across the mast, just install perhaps a longer spreader, keep it centered and increase the tension on the diamond stays?

Finally, any thoughts on the sufficiency of the side stays ability to support the rig?

I weigh 225 lbs, and the hulls are carbon/kevlar.


Thanks.


By the way, this has been done a few times before, one with rigid support of the bowsprit, another with just cable between the bows and mast. The latter scares me....

http://www.youtube.com/watch?v=Lvdnrt39b8U

http://www.youtube.com/watch?v=U_dBbk6iCjk

-- Have You Seen This? --
Re: Spinnaker modifications to A-cat [Re: ileestma] #232840
05/26/11 12:29 PM
05/26/11 12:29 PM
Joined: Oct 2002
Posts: 606
Maryland
Kris Hathaway Offline
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Kris Hathaway  Offline
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Watching the videos, I am amazed by how much traveler is off of center. The main typically aids as a "backstay" for beach cats with a chute. Accordingly, be sure to have a fair amount of mainsheet tension and a nearly centered traveler. Of course, release the downhaul also or you'll encourage the mast section above the hounds to bend forward, not desirable.



Kris Hathaway
Re: Spinnaker modifications to A-cat [Re: Kris Hathaway] #232842
05/26/11 12:59 PM
05/26/11 12:59 PM
Joined: Dec 2003
Posts: 109
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Kaos Offline
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Kaos  Offline
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Originally Posted by Kris Hathaway
Watching the videos, I am amazed by how much traveler is off of center. The main typically aids as a "backstay" for beach cats with a chute. Accordingly, be sure to have a fair amount of mainsheet tension and a nearly centered traveler. Of course, release the downhaul also or you'll encourage the mast section above the hounds to bend forward, not desirable.



I agree, the main is very much a support for the mast. Letting out the main in a puff can break the mast, depower the chute first. I would also consider adding a wire/line to the top of the mast at the shrouds and stern quarter. That would help keep up with the rotation.

Re: Spinnaker modifications to A-cat [Re: Kaos] #232860
05/27/11 06:21 AM
05/27/11 06:21 AM
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waynemarlow Offline
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Have you thought that perhaps you maybe over doing it on the F18 size spinny ? the A class do not have much foward volume and I would suspect that the bouancy will not cope with such a large sail up front. Even if you do go out on the wire the hull will submerge over its length and be consequently slower than just the original A.

Its a real buzz flying the spinny but I'm not sure it will work unless you really back off on sail size and have a fairly full sail to allow you to go much deeper. Even a F16 sail will be a handful unless you expect to sail in very light winds.

Re: Spinnaker modifications to A-cat [Re: waynemarlow] #232861
05/27/11 06:52 AM
05/27/11 06:52 AM
Joined: Jul 2001
Posts: 2,844
42.904444 N; 88.008586 W
Todd_Sails Offline
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42.904444 N; 88.008586 W
Originally Posted by waynemarlow
Have you thought that perhaps you maybe over doing it on the F18 size spinny ? the A class do not have much foward volume and I would suspect that the bouancy will not cope with such a large sail up front. Even if you do go out on the wire the hull will submerge over its length and be consequently slower than just the original A.

Its a real buzz flying the spinny but I'm not sure it will work unless you really back off on sail size and have a fairly full sail to allow you to go much deeper. Even a F16 sail will be a handful unless you expect to sail in very light winds.


Good morning,

+1 on his post


F-18 Infusion
#626- SOLD it!

'Long Live the Legend of Chris Kyle'
Re: Spinnaker modifications to A-cat [Re: Todd_Sails] #232871
05/27/11 09:08 AM
05/27/11 09:08 AM
Joined: Jul 2007
Posts: 976
France
pepin Offline
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pepin  Offline
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France
A spi will actually lift the front, not burry it. What's pushing the bows down is the pressure on the main, not the spi.

So the bigger the better!

Re: Spinnaker modifications to A-cat [Re: pepin] #232904
05/28/11 06:12 AM
05/28/11 06:12 AM
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waynemarlow Offline
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Totally agree when its all going to plan, as those from our club with the 21sq metre kite on their Hobie 16's will testify, but its when it all goes a little bit wrong,the boats with that little bit of extra volume up front such as most F16's seem to now have, seem to survive. I'm not sure the A would.

Mind you the guy from Sweden with the modded Marstrom seems to have a ball. I guess there is only one way of finding out, give it a go.

Re: Spinnaker modifications to A-cat [Re: waynemarlow] #232912
05/28/11 09:54 PM
05/28/11 09:54 PM
Joined: May 2011
Posts: 36
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ileestma Offline OP
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ileestma  Offline OP
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Yes, there is alot of concern about the bows burying. I have recently put a masthead assym. on an e-scow class monohull (they're a blast to race)

While the "squirrely/nosedive" factor is certainly going to be less on a monohull (and a scow at that) It seems to me that the determining factor on whether those bows will go down or up is the nature of the puff and boatspeed when it hits. If the boat's already flying, the puff will lift, if the boat is dead, the level of inertia is higher, and the rig will, in effect, out run the boat, and drive the bows down.

That being said, i am heavily leaning toward throwing a curved foil system on it, with it being adjustable from 0 degree to 5+ degree lift. This should help greatly in keeping the bows up and out of trouble, but i doubt even that will solve the problem if going slow, i am suddenly hit by a gust.

Also, i am going to make a point of flattening out the F18 chute pretty dramatically, so i can basically always sail downwind with my apparent wind at the beam, this should lessen the down force on the hulls at least somewhat.

Finally, i am using an 05 Bimare cat, which is more voluminous up front than many.

Thoughts? - My real concern here is snapping the stick....

Re: Spinnaker modifications to A-cat [Re: ileestma] #232921
05/29/11 06:53 AM
05/29/11 06:53 AM
Joined: Sep 2005
Posts: 893
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waynemarlow Offline
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The smaller the length up from the hounds and a longer spinny pole maybe an answer, certainly I have run a F16 chute from a Saarberg mast without problem but think small as I can promise you even the 17 metre F16 spinny is enough.

The " Shadow " catamaran has a really small spinny ( and keeps a reasonable handicap rating ) and yet is not much slower than a F16, as most men would acknowledge, its not the size of the hammer, just the way you use it.


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