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 Post subject: Excess flex in my 17
PostPosted: Tue Jul 20, 2010 9:30 pm 
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I would appreciate general advice -

I have been renovating my '92 H17 for some time. I'm at the point where I need to address the amount of flex occurring when I lift one bow before the other bow rises. I know it is excessive because I can feel the front beam moving relative to the hull. I have removed one of the stainless rod-nuts and found that it had a slight (0.5mm) bend in it. I believe by re-fitting with an epoxy cushion I can get a better interface and re-gain some stiffness, but I suspect there is more to the problem. I should add that the dolphin striker rattles, and that at present I have no trampoline. I'm thinking I may have to face up to pulling the beam off.
If I pull the boat apart, what am I likely to find at the castings? If I do have it apart, is it sensible to replace the parts anyway?

I have no experience with this and I would greatly appreciate some direction. Thanks in anticipation...


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 Post subject: Re: Excess flex in my 17
PostPosted: Tue Jul 20, 2010 9:41 pm 
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Joined: Sun Mar 16, 2008 10:46 pm
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No 17 technician but thought this thread was interesting: Check out the pics in the latter part of the thread.


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 Post subject: Re: Excess flex in my 17
PostPosted: Wed Jul 21, 2010 6:32 am 
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Location: Lake Champlain, Vermont
Seems these boats are loose compared to the others (16,18). I bedded my caps and beams and I bet it had little effect in tightening them- way too much stress out there. The tramp will tighten things up quite a bit. I wouldn't sweat it too much, its strong enough, just floppy.

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 Post subject: Re: Excess flex in my 17
PostPosted: Wed Jul 21, 2010 3:29 pm 
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Thanks for that, much of the mystery has gone. Happily I have none of the cracking shown in the pics JJ linked to.

I assume the cross beam fits snugly into the end cap, and the end cap is actually the casting I have seen reference to in other postings?

Is there an insert piece in the end of the beam to give it more substance? Or does it rely on "goodness of fit" and a good bed interface with the hull? I had guessed there might have been some locating pins to ensure alignment.

The new tramp is an after-market version and can be tensioned from midships as well as the stern, so I should be able to get some improvement there.

I'm still a little unsure about pulling the boat apart - if it ain't broke don't fix it - or take a precautionary approach and go in now whilst I have it in the workshop. I want to get the boat on the water before I am too much older...

Meantime, thanks very much for the help...

Cheers & good sailing


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 Post subject: Re: Excess flex in my 17
PostPosted: Thu Jul 22, 2010 4:54 am 
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Joined: Thu Sep 17, 2009 12:35 pm
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Location: Lake Champlain, Vermont
You could perform the pressure test and see if there are any leaks in that area (search hull leak test), that would give you that added reason to take it apart. I did, and as you mention, stuff happens to things that aint broken. A bolt seized and snapped off. But I need to check everything to feel comfortable and just cause I need to see whats going on. Yes, pin on the casting that sits in the hull and locates the casting. I reglassed that area and redrilled. Yes the cross beam fits nice into the casting. All is not super tight tolerance so hence the slop. Check the hobie parts list on the site and I think you'll see the parts broken out. I put it together by myself but two people would make it super simple. Go at it.

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 Post subject: Re: Excess flex in my 17
PostPosted: Thu Jul 22, 2010 9:28 am 
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Joined: Mon May 09, 2005 10:25 am
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Location: Jersey Shore
If the boat is getting sloppy, I would pull it apart and check the crossbar end fittings, they've probablay worked loose. If you catch it early enough, all you probably need to do is re-tighten the screws that secure the end caps. If you wait too long, you'll have to re-build the holes in the hulls that the caps engage into, or deal with more severe damage. In any case, I wouldn't ignore the problem.

Disassembling the Hobie 17 is proabably easier than any of the other fiberglass Hobies. Remove the tramp from the hull tracks, undo the four crossbar bolts, and rock the hulls outboard to pop them free from the crossbars. Its really a piece of cake and can be done singlehandedly although it's easier with a helper.

When you put the boat back together, be sure to use anti-seize compound on the crossbar bolts. You'll also want to go back and re-check the crossbar bolt tension periodically since they do tend to loosen up. A T-handle allen wrench is nice to have for this.

sm


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 Post subject: Re: Excess flex in my 17
PostPosted: Thu Jul 22, 2010 1:48 pm 
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Looks like I'll have to man-up and pull the boat apart, something I was dreading. Actually it does not look so daunting now with the extra info. I will have a look inside and see what needs to be done.

Cheers, and thanks again


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 Post subject: Re: Excess flex in my 17
PostPosted: Mon Jul 26, 2010 9:30 am 
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Location: Jersey Shore
Just as a follow up, I ended up pulling my boat apart this weekend to check the condition of the crossbar end castings. My boat's an '07. It hasn't seen a ton of use, but I still hadn't had it apart since it was new, so I wanted to see if things had loosend up. Sure enough, all or almost all of the screws that hold the casting in place were loosened to some degree. Most probably only a 1/4 to 1/2 a turn, but over time, they will just continue to loosen letting the casting wear on the hull and the boat will continue to get sloppier and sloppier. So IMO, it's definitely a good idea to check these screws if your boat seems loose.

I may pull the boat apart again at the end of the season and install lock washers under all the screws to help keep them tight. Not sure why Hobie doesn't do this in the first place, but I think it should help.

sm


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 Post subject: Re: Excess flex in my 17
PostPosted: Tue Jul 27, 2010 9:01 pm 
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More thanks!
I will be pulling apart in a few days. Mine is a '92, and it looks like it has had little use, but I'm betting it is loose in there. If I can tighten up the screws and get a reasonable result I will leave it at that for the moment - I want to get on the water. However if it does not look so good I will do the epoxy seating job as described elsewhere in this forum. I was even dreaming of canting the hulls 3-4 degrees like the Nacra F18. Has anyone tried that or have a view on it?


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 Post subject: Re: Excess flex in my 17
PostPosted: Tue Jul 27, 2010 9:43 pm 
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Location: Detroit, MI
gmhendo wrote:
I was even dreaming of canting the hulls 3-4 degrees like the Nacra F18. Has anyone tried that or have a view on it?


What would be the point? So the foils point straight down when you're going upwind with the weather hull just out of the water? That's not going to give you any significant performance advantage.

Not to mention it would be very un-class legal.


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 Post subject: Re: Excess flex in my 17
PostPosted: Wed Jul 28, 2010 4:22 am 
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Canting the hulls seems to be gaining some acceptance. The Nacra F18 has cant, as do some new (but not all) A class cats. The idea is not new, and was applied to a NZ design cat many years ago. See
www.coolmobility.com.au/Yacht/LightBrigade.pdf and "find" Sundancer. There is a good drawing of Sundancer. If anyone has time, the pdf is a pretty good read too.

If the best sailing angle for a cat has the windward hull just out of the water, and the best hydrodynamic profile for the hull is in a vertical (relative to the water) position then a canted hull has some logic to it. I suppose that assumes the designer intended the hull to be vertical in the water. Suppose then that the gain amounted to a mere 1% speed increase. In a 100 minute race that would put a canted hull one minute earlier across the line than other wise. I would even settle for one half of one percent.

If I was racing in the US, or anywhere there is a fleet of 17's I would be staying class legal, no problem. Sadly for me the nearest H17 is over 1,000 miles away. My emphasis is on good fast sailing, aided where I can by affordable (to me) technology or innovation. I don't mean to appear disrespectful to one-design.


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 Post subject: Re: Excess flex in my 17
PostPosted: Wed Jul 28, 2010 4:59 am 
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Joined: Thu Sep 17, 2009 12:35 pm
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Location: Lake Champlain, Vermont
I hear ya, but you by yourself won't notice that half a percent speed difference for a ton of work. How bout get an updated sail? My 17 smokes (well, is faster) than my 18 with its new pentex main. I was surprised.

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 Post subject: Re: Excess flex in my 17
PostPosted: Wed Jul 28, 2010 3:46 pm 
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Joined: Sat Nov 07, 2009 10:52 pm
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"How about get an updated sail?"

Yes that would be nice, not an inexpensive option, but it is on the list. Doubtless it would give a better than one percent increase in speed too. It is about incremental speed really, a point here, a point there and after a few things you have a boat that can prevail over the others when sailed to a similar standard.

BTW in my last post I should also have mentioned "Sundreamer".


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 Post subject: Re: Excess flex in my 17
PostPosted: Thu Jul 29, 2010 11:37 am 
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Joined: Mon Sep 20, 2004 12:36 pm
Posts: 758
Location: Tri-Cities, WA
If you want to improve your performance by 10% or more, then do the following: Tune your rudders and exercise better rudder control (find the sweet spot for the course, the sail set - then hold the course); get new sails and learn how to shape the sail with the down haul & out haul (if you have one); use your traveler (it should only be centered when going to the wind); AND get out on the water - practice, practice, practice. :wink:


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 Post subject: Re: Excess flex in my 17
PostPosted: Thu Jul 29, 2010 3:53 pm 
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Joined: Sat Nov 07, 2009 10:52 pm
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Can't argue with that fastcat. I'll forget the cant and get sailing. Interesting that the rudders are high on the list. Mine are in bits right now but have all the new parts ready to assemble and fit to the boat.


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