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 Post subject: Crossbar Damage
PostPosted: Sun Jul 09, 2017 7:29 pm 
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Site Rank - Deck Hand

Joined: Mon Jul 03, 2017 8:40 am
Posts: 12
Location: Amsterdam, NY
Just to be sure, there is no amount of riveted reinforcement plates, alumiweld, or epoxy that is going to make this safe? Or is there something besides replace the crossbar I can do? Unfortunately I didn't see it when I bought the boat.

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http://www.hovak.com/hostedmedia/crossbar3.jpg

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http://www.hovak.com/hostedmedia/crossbar2.jpg

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http://www.hovak.com/hostedmedia/crossbar.jpg

Thanks,
Jason


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 Post subject: Re: Crossbar Damage
PostPosted: Sun Jul 09, 2017 8:28 pm 
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Joined: Sun Feb 22, 2015 8:27 pm
Posts: 92
Location: Dunedin, FL
No, glue wont work. A big enough plate riveted over the location would help but be super ghetto. Just weld it, a decent shop can handle that even if they have to put a thin plate on. It's gonna affect the dolphin rod angle since the striker rod wouldnt go as far through the beam with the step sitting on a reinforcement plate but it should still be fine.

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'82 NACRA 18 Square
'85 Hobie 18 "Honey Badger Don't Care"
'86 Hobie 18 "The Rippin & The Tearin"


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 8:44 am 
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Joined: Mon Jul 03, 2017 8:40 am
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Location: Amsterdam, NY
Marine Tex the heck out of it and set my old 2 hole mast step in it with some extra holes and washers since the crossbar is pretty much a goner anyway?

Probably not the best plan.

See my previous post:
https://www.hobie.com/forums/viewtopic.php?f=13&t=60945


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 9:34 am 
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Joined: Mon May 09, 2005 10:25 am
Posts: 3228
Location: Jersey Shore
Do not use marinetex (other than to bed the step, not to repair a crack - it will do nothing).

This is pretty typical front crossbar damage. The crack will continue to propagate below the step holes if nothing is done. Most likely this is partially the result of a loose mast base (notice the dolphin striker hole is severely elongated).

I have an old crossbar that I repaired (although have not sailed yet). It had a small crack in the step area and some extra mast step holes in it ( the result of a 2 rivet to 4 rivet mast step conversion). I took it to a shop to have the extra holes and cracks welded. Then I took a piece of scrap H17 crossbar, cut it about 6"-8" long and cut it lengthwise into about a 3"-4" wide plate. The plate fit very nicely inside the H18 crossbar and closely matched the bend. I drilled a hole in the middle of the plate for the dolphin striker post and then mounted the plate inside the crossbar using four 3/16" diameter pop rivets at each of the corners. The repair is invisible with the exception of four rivet heads on the top of the crossbar and the crossbar is now double thickness at the step area. I would suggest doing something like this before sailing the boat and in the mean time, keep an eye on the crossbar and try to source a replacement. I would not sail it in it's current condition.

sm


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 10:01 am 
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Joined: Mon Jul 03, 2017 8:40 am
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Location: Amsterdam, NY
How did you get the patch in the crossbar?


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 10:41 am 
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Location: Jersey Shore
Removed the dolphin striker assembly and the corner castings to access the inside of the crossbar.

I drilled the striker post hole in the center of the backing plate ahead of time and then I believe I used a bolt and washers through that hole to clamp the backing plate up against the inside of the crossbar and then match drilled the holes for the rivets to hold the backing plate in place.

sm


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 11:45 am 
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Joined: Wed May 25, 2011 3:15 pm
Posts: 454
Location: Buffalo, NY
TAMUmpower wrote:
No, glue wont work. A big enough plate riveted over the location would help but be super ghetto. Just weld it, a decent shop can handle that even if they have to put a thin plate on. It's gonna affect the dolphin rod angle since the striker rod wouldnt go as far through the beam with the step sitting on a reinforcement plate but it should still be fine.

Welding the crossbar won't work. The crossbars are made from 6061-T6 aluminum, which is a tempered (heat treated) aluminum. Welding on it compromises the heat treatment in the area of the weld, and the aluminum will likely crack again right along the weld. Standard 6061 aluminum has a yield strength of 8,000 psi and tensile strength of 18,000 psi, while T6 aluminum has a yield strength of 35,000 psi and tensile strength of 42,000 psi. If it's cracking, it's either been stressed close to 42,000 psi, or frequently stressed/fatigued at >17,500 psi. If you weld on it, you reduce the strength of the welded aluminum to as low as 11,000 psi. No epoxy is going to build that kind of strength back. The only means of repairing the crossbar are a mechanical means, like srm suggested, with a riveted reinforcement plate, or to weld and then heat treat the entire crossbar, which involves putting the crossbar in an "annealing" oven and heating the aluminum to about 775 degrees for several hours, and then going through a slow, controlled cool down to relieve the built in stress from welding. (https://en.wikipedia.org/wiki/6061_aluminium_alloy)

Note that mechanically joining two plates together is a very imperfect means of transferring stress. In the days of riveted ships, a single row of rivets was expected to transfer just 21% of the stress on the adjoined plates, while even a quadruple row of rivets was only good for 67% of the stress. This is why riveted ships had such thick hulls, the steel was greatly oversized to account for the imperfect method of joining plates. I'd honestly be weary of the riveted doubler plate approach to repair a cracked crossbar, as four rivets aren't a very seamless means of transferring stress from the doubler plate to the crossbar.

As I mentioned in the posts about the mast step, the forward crossbar right under the mast step is the point that is under the most load/force on the entire boat. If you increase the tension in the tension rod, you can relieve some of the stress on the crossbar (that is the purpose of the tension rod, to help share the load of the crossbar), but you'll never relieve enough stress to be able to sail safely with cracks in the crossbar. I'd look for a replacement. Hobie does sell them for $572, currently. There are also a handful of ebay users that collect spare parts like crossbars and tend to sell them for around $300-$400.

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'79 H18 standard 'Rocketman II' sail #14921


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 1:40 pm 
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Joined: Sun Feb 22, 2015 8:27 pm
Posts: 92
Location: Dunedin, FL
The pos parts boat I just picked up had welding on the front beam and the mast in various places. It's a very old boat and the repairs are not new for sure. Seems like the welds held up in this boats case. I mean I'd take a welded patch over 2 pieces of metal that aren't attached due to a crack lol. Ideal fixes don't always come into play on old boats like ours. Just gotta do what you gotta do to keep it sailing.

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Matt
'82 NACRA 18 Square
'85 Hobie 18 "Honey Badger Don't Care"
'86 Hobie 18 "The Rippin & The Tearin"


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 2:48 pm 
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Joined: Mon May 09, 2005 10:25 am
Posts: 3228
Location: Jersey Shore
Personally, I think if the beam is welded, and then the area reinforced with a riveted backing plate inside and a 4-rivet mast step is installed in place of the 2- rivet step, you would likely be OK for a while. During that time, you can search out a decent used crossbar.

sm


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 Post subject: Re: Crossbar Damage
PostPosted: Mon Jul 10, 2017 6:19 pm 
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Joined: Wed May 25, 2011 3:15 pm
Posts: 454
Location: Buffalo, NY
TAMUmpower wrote:
The pos parts boat I just picked up had welding on the front beam and the mast in various places. It's a very old boat and the repairs are not new for sure. Seems like the welds held up in this boats case. I mean I'd take a welded patch over 2 pieces of metal that aren't attached due to a crack lol. Ideal fixes don't always come into play on old boats like ours. Just gotta do what you gotta do to keep it sailing.

srm wrote:
Personally, I think if the beam is welded, and then the area reinforced with a riveted backing plate inside and a 4-rivet mast step is installed in place of the 2- rivet step, you would likely be OK for a while. During that time, you can search out a decent used crossbar.

Fair points. Haven't tried it myself, I just know what I've been told and what the material specs are. That is encouraging that welded crossbars and masts have been done before and lasted. Not sure I'd trust it for long, but it is better than nothing!


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 Post subject: Re: Crossbar Damage
PostPosted: Wed Jul 12, 2017 8:09 am 
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Joined: Mon Jul 03, 2017 8:40 am
Posts: 12
Location: Amsterdam, NY
It was definitely due to the rivets being loose, the rear one was pulled through. I'm gonna keep an eye out for a donor boat, possibly try the weld/plate idea.


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 Post subject: Re: Crossbar Damage
PostPosted: Wed Jul 12, 2017 7:55 pm 
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Joined: Sun Jul 06, 2008 8:21 am
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Location: St. Helena, CA
I probably have one for $100 but I'm on the other coast.
If you are serious about replacing I will check with FedEx for a rate, send me a PM with your shipping address if interested.

As is I would only sail your current setup in a warm lake, not far from shore, in light breezes.

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