Hobie Cat Forums

It is currently Wed Jul 23, 2014 10:00 pm

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: Mon Jul 23, 2012 1:04 pm 
Offline
Site Rank - Deck Hand

Joined: Sun May 22, 2011 1:01 pm
Posts: 12
I don't own a TI yet - I am still researching. I used to own a Hobie 16 in the 1970s in Tennessee, and the first time I capsized on Percy Priest Lake, the masthead stuck in the muddy lake bottom..... it took a while to get it unstuck.

After that, I rigged a long righting line under the tramp. It was a continuous piece of 3/8" line that ran from the back of each rear support, around the front supports (with a few feet of slack), plus a long piece of heavy bungee running back from the center of the front span to keep the line tight when not in use.

When you flipped, you just crawled up on the closest hull, reached for the line and leaned way back, and back she would come, eventually... depending on wind direction and speed.

Has anyone made such a system for a TI? Has anyone made a mast float so the boat won't go completely inverted?

Is either available from Hobie? I don't recall seeing one in the catalogs or in any photos.

BTW: the line did double duty as a safety line for the crew when out on the trapeze - you would just squat and reach down with the rear hand and there it was. I added a row of figure eight knots so it would be non-slip. The first time I pitch poled, my sister flew way out into space and clear around the fore stay. The new safety line prevented that from happening again.

Thanks.

John Davies
Spokane WA USA


Top
 Profile  
 
PostPosted: Mon Jul 23, 2012 8:41 pm 
Offline
Site Rank - Old Salt

Joined: Sat Nov 05, 2011 1:58 am
Posts: 1428
Location: Forster, NSW, Australia
I don't think the incidence of Hobie Islands capsizing is high enough to bother with masthead floats. Unlike a cat, a trimaran is more forgiving, as the leeward hull is way less than a third of the wetted area, so it is far less likely to "trip over its feet" like a cat. The extra drag of a submerged ama is going to slow the vessel down and transmit a strong early warning to the skipper well before the point of no return is reached.

Interestingly, I have not heard on a single capsize of an Island that wasn't wearing tramps at the time (although I am happy to be corrected on this).

Rigging lines to assist with righting seem to be a simple back-up though, even if the prospect of needing them s slim.

_________________
Tony Stott
2012 Tandem Island "SIC EM"
www.scenefromabove.com.au


Top
 Profile  
 
PostPosted: Tue Jul 24, 2012 10:06 am 
Offline
Site Rank - Deck Hand

Joined: Sun May 22, 2011 1:01 pm
Posts: 12
tonystott wrote:
I don't think the incidence of Hobie Islands capsizing is high enough to bother with masthead floats.

Thanks for your comments.

Would a small mast float keep the TI on its side? It seems as if the boat would float that way pretty easily (compared to a cat) due to the small amount of floatation of the submerged ama, and the low wind resistance of the ama that is stuck up in the air. It should be much easier to get the boat back up if it wasn't truly inverted.

Though I suppose the wind on the tramps would push it on over.....? I guess this is another reason for having a mesh tramp that doesn't act as a sail.

I know the event is relatively rare, but I like to explore the options while at home rather than while floating upside down in the water.

John Davies
Spokane WA USA


Top
 Profile  
 
PostPosted: Tue Jul 24, 2012 12:18 pm 
Offline
Site Rank - Deck Hand

Joined: Tue Jul 10, 2012 10:22 am
Posts: 22
I might be way, way off, but here's my take on it:

The aka is 13'4" (160") long and I am guessing an average of about 4" wide and deep (taking the rake into account). So that's 2560 cubic inches, which is 213.33 cubic feet of water displaced by an ama. The bouyant force of a floating object is F=(Vw), Force equals Volume of water times specific weight of seawater. The specific weight of seawater is 64 lbs per cubic foot, so: 213.33 x 64 = 13,651.2. That means it takes 13,651.2 lbs of constant force to fully submerge an aka in sea water (a bit less in freshwater).

I would think that if a TI went turtle, the best thing to do would be (1) try to reach underneath and furl the sail, then (2) retract one or both akas and then (3) roll it back over. Then extend the akas and go back to sailing!


Top
 Profile  
 
PostPosted: Tue Jul 24, 2012 12:49 pm 
Offline
Site Rank - Old Salt

Joined: Tue May 18, 2010 2:31 pm
Posts: 2654
Location: Kailua 96734
A mast float is not practical for the TI. There is no reliable way to mount it on the current furling mast. Plus, the mast bends like crazy.

If you did graft one on, it would likely interfere with furling operations or increase drag on the sail, robbing it of performance. That would be an unacceptable tradeoff for most owners.

Better to focus on practical recovery techniques, and practice them on your boat, after you buy it.


Top
 Profile  
 
PostPosted: Sat Aug 11, 2012 12:19 pm 
Offline
Site Rank - Deck Hand

Joined: Fri Aug 03, 2012 6:53 pm
Posts: 6
jerinaldi wrote:
I might be way, way off, but here's my take on it:

The aka is 13'4" (160") long and I am guessing an average of about 4" wide and deep (taking the rake into account). So that's 2560 cubic inches, which is 213.33 cubic feet of water displaced by an ama.


I'm afraid you've only divided by 12; you need to divide by 12^3...
2560/1728 ci/cf = 1.48 cf. 1.48 cf * 62.4 lb/cf = 94.2 lb. I think the 4" depth is a little conservative so the actual buoyancy is probably a bit higher.

If you ever see your amas in a substantial wind, you'll wonder how much more wind before it fully submerges. At that point, there's so much drag from the amas and required rudder (which is near it's limit) that it's silly not reef.

Even if you push to amas buoyancy limit, the amas is being pushed through water, as opposed the the windward cat hull that is being pulled through air.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: Exabot [Bot] and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group