Pylon Repair

I have a 1995 Hobie Cat 16 with badly worn pylons and elongated holes. I would like to stiffen the boat. After reading different fixes including the beer can or cutting board shims or epoxing the boat together. I am looking for some comment on this idea. I have the boat apart now and think I could build up the pylons to their original size with Marine Tex or Bondo. Since some of the fixes include using epoxy to hold the boat together I thought the Marine Tex might hold. There is quite a bit of wear , I measure a difference of 1/8 inch between the top and bottom of the pylon.. I was also thinking of making shims out of aluminum, but they would have to taper from 1/8 inch to 0. That’s why I thought I could build up the pylon with marine tex but I don’t know how long it would hold up. As for the elongated holes, I would drill out the ½ inch holes to ¾ inch. It would take ¾ inch to cover the enlongated holes in the pylon. The only other solution I can think of is the get the hole welded up and just redrill with ½ inch hole. Of course there is obvious heat problems with welding near the fiberglass.
Can anyone help?
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Brig Bill

_________________
Brig Bill

Hello Bill:

I had the same problem as you but my pylons were in very bad shape so it was not only a problem of boat stiffness but also of boat integrity so I did not have much choice but to rebuild the whole thing.

If your problem is not so severe I´m sure In thish forum there are a lot of people with huge experience that can give you good advice on how to solve it not so drastically as I had to.

For obvious reasons I did not want to remove the old pylons and putting new ones and I did not have the cash to buy new hulls so:

I tried solving the problem by reshaping the pylons with an epoxy paste called quick steel ( I live in Europe I do not know if this stuff is available in the states, I´m sure there are dozens of similar products over there) I went out sailing with 15kn winds and a few waves and after two hours you could already see new worn areas where the epoxy was.

After searching around in the forums ( with no reply!) and talking to some friends and the maintenance guy in my company (who is used to weld alu) I decided to try and solve the problem by welding new alu on the worn areas. A friend of mine had broken his HC16´s front beam some time ago so I had access to the broken parts and I made two sheets of alu to fit them inside the worn pylons. Then we welded the new alu to cover the worn areas and the elongated holes were the bolts go throughfrom the outside right over the new sheets of alu and then reshaped the whole thing.
To prevent heat from damaging the hulls´structure we put wet rags where the pylon meets the fiberglass.
In order to give the whole thing more stiffness and to prevent friction between different parts (very important) we finished the job with a variation of the beer can method, instead of beer can material we got large sheets of thin alu from a print shop (around here they call them lito-sheets).

I have just finished the job so I cannot add any after sailing comments, but if you want I can post them as soon as I go out a couple times.

I hope I helped

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1983 HC16

Antxvilla,
Thanks for the info. I think I am going to try something similar. Welding alu inside the pylon to cover the elongated holes and another piece on the outside for a shim and then grind it down to shape. I will post pictures, let me know how you make out.

Thanks Bill

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Brig Bill

So help me understand something here guys. How long have the 14/16 been around? Going on 40 years? And over a period of time, and depending on use, the pylon to casting loosens up? And the best fix we have to date is "fill it with epoxy" or use beer cans? Can we do better than that?

This AL on AL wear can be expected. What is the root cause? Does the bolt have any effect on the wear? I think to a certain extent it does. This, over time, becomes a pivot point, assuming originally you have a close to snug clearance fit between the pylon and the corner casting. There is initially a small clearance that progressively becomes enlarged due to fore/aft and side to side flextion. Theoretically this "enlargement" will occur above and below the pivot point (the bolt)?

Why not drill and tap a set of holes in the corner castings say in four places as far above and as far below the pivot point as possible and install an S/S allen head machine screw to "lock" the pylon within the casting? Over a period of time, they would become loose and need tightening. I suppose after a long period of time they may cause some serious wear on the pylon, but do epoxied, beer canned or new boats stay tight forever?

What do you engineering gurus think?

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hobiejohn at earthlink dot net
Fleet 297

OK, how about this?

Since you guys are going to fire up the welders, how about welding the pylon to the corner casting?

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hobiejohn at earthlink dot net
Fleet 297

There is a posting dated Aug 28,2003 and Matt Miller mentions Hobie France has a sleeve that fits inside a pylon extrusion they use for making two piece masts for Hobie 14’s. I can’t find any info about them but that is an idea. I was also thinking of a second ½ inch bolt at right angle to the original.

Bill

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Brig Bill

Bill,

I had Hobie Nick tell me that threading the already thin casting material was no good. Threads will strip too easily.

But, determined as I am, I'm thinking why not thread right through the casting and into the pylon as well. Also suggested by Banzilla was one additional through bolt above and below. Another idea drill and tap from the rear and again right into the pylon, one low and one high, as you have suggested, but I'm thinking 1/4-20 maximum size. It's worth a try (corner castings are easy enough to come by) trouble is we won't know of the success or failure until '07.

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hobiejohn at earthlink dot net
Fleet 297

John,

I'm not trying to hound you guys about this, but what would threading through the casting into the extrusion do? This material is even thinner than the casting. You will run into the same problem as threading into the casting. One thing we try to avoid, if we can, when designing machines is threading expensive parts. If the thread is ever compromised you will eventually end up having to replace the entire part or put a larger fastener in it's place.

To address welding of the casting to the pylons... I would not do it. The material the casting are made of will not respond well to welding.

I would invest my resources into the sleeve idea mentioned earlier. I would also look into drilling out the holes to the next diameter up if you do go with the sleeves.

Keep in mind when working with the pylons and castings, that the material is relatively thin.

Good luck!

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Nick

Current Boat
In the market
Previous boats owned
'74 Pearson 30
'84 H16
'82 H18 Magnum
St. Louis, MO

Nick,

How thick is the aluminum plate that the rudder gudgeon screws thread in to?

We can double the pylon thickness with the sleeve.

I can't figure out how to effectively swage nuts in to the sleeve or I'd say that would suffice.

What about rivets? You've got a cast mast base riveted to the crossbar extrusion. What is the difference in potential load at this point, or is it all compression load?

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hobiejohn at earthlink dot net
Fleet 297

Guys,
I think we will probably weld a piece of aluminum on the inside of each side of the pylons behind the elongated holes. Then we can weld up the holes and redrill them and use ½ inch bolts again. I would have to move up to a ¾ inch bolt to round out the elongated holes. I am still thinking about another through bolt at right angle the original.

I have not been able to get any information on the sleeves. The only reference was a posting by Matt Miller that said Hobie France used them for 2 piece masts. I am still not sure how we are going to build up the pylons to their original size
.
As for welding, I would glue the boat first, not quite so permanent.

It’s a long winter in New Jersey and I have plenty of time to think about it.
Bill

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Brig Bill

John,

I don't know how thick the rudder mount plate is. If I had to guess, I would say they are about 1/2 to 1/3 the thread length of the gudgeon screws. This could be way off, but for aluminum this is what I would design in. Stainless, I would go clsoer to 1/8" thick for this application.

As far a riviting the pylon to the casting. This would be fine as you are not relying on the thin walled aluminum to hold threads. The forces the rivits will see are basically the rotation of the pylon relative to the casting and the weight of the hull trying to pull out of the casting. The weight will not be a huge factor, but the rotation will fatige the rivits pretty quickly (especially aluminum rivits). Any load pushing the casting down onto the pylon will be taken up by the casting itself as the pylon rests against a step in the casting.

If anyone is going to do any welding on the pylons, make sure you get a good welder. The thin material is hard to weld without warping or overheating. It can be done, but make sure the guy knows what he his doing.

Another thing to think of is making your own sleeves using sheet aluminum and forming it to the pylons. You can do the same with some thin sheet UHMW.

If you have a picture of the area needing repair, I might be able to think of some other solutions.

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Nick

Current Boat
In the market
Previous boats owned
'74 Pearson 30
'84 H16
'82 H18 Magnum
St. Louis, MO

Nick,

If the gudgeon backing plate is more than 1/8", I'll eat my hat.

I'm doing SOMETHING different on the 16 for next season, so thanks for hanging with me on these rants.

What if I use S/S rivets? Is there a better choice of rivet material?

Does this lead us back to the same elongation of the holes over a period of time?

Would do you think about backing at the rivet locations (necessary?).

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hobiejohn at earthlink dot net
Fleet 297

John,

Not a problem.

I would use Monel rivits. The SS rivits will react with the aluminum over time and eventually the holes will open up. You can use rivit sheathes (the little plastic spacers that go over teh rivit before it is inserted into the hole) but i would worry about them being cut by the aluminum.

I really would concentrate on how to tighten the fit between the casting and the pylon. This will reduce the relative motion of the pylon in the casting which will reduce the amount of wear around the fastener. I can say I have seen 30 year old boats without any hole elongation. They have a very tight joint between the casting and the pylon. Almost too tight to assemble and disassemble.

You can always add material to the inside of the pylon to give the walls some more thickness. This will help spread out the load the through bolt sees and will reduce the hole elongation.

Please feel free to run any ideas by be.

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Nick

Current Boat
In the market
Previous boats owned
'74 Pearson 30
'84 H16
'82 H18 Magnum
St. Louis, MO

People the alum plate the gudgeons screw into at the transom are 1/4 inch thick, Im 100% sure of this as I had to fab and install new plates on my 1987H16.

I measured very well the sandwich construction in the transom...Its gelcoat/glass/plywood/alum and glass again on the inside...about 1 1/4 inch total thickness.

I used a 4" hole saw to make and opening on the inside of each hull, Bought a 2" wide X 1/4" alum flat bar, bits and taps and spent about two weeks total,. I didnt remove the old plates...just glassed the new ones in and used longer screws after opening the threads on the original plates for the new screws to pass through and reach the new plates....

lots of work but I restored all 6 original threads and added 2 more for the euro gudgeons....

John....eat ure hat!

munch, munch, blahhh!!! I need a beer and I don't drink

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hobiejohn at earthlink dot net
Fleet 297