Hobie 18 step assembly repair

I have a Hobie 18, year unknown but likely 80's . Donated to me due to mast step damage. It looks like the mast step was ripped out forcefully as would happen from dropping the mast.

I have a lot of engineering on the fly experience but not with a Hobie. The mast step on the cross member is brass with a ball shaped contact point for the base of the mast. This brass unit has 4 holes that used to have rivets going thru them. The cross member that the mast step was attached to has 5 holes in it. 4 small rivet holes and a large central hole for the shaft on the mast step.

All 5 holes on the cross member are eccentric. The large hole for the shaft is eccentric on the top and bottom of the cross member. The material the cross member is made out of appears to be a treated aluminum alloy.

The holes in the brass step appear intact as does the step itself.

All the components of the mast appear intact except for eccentric pin hole at the base that receives the step.

Debated aluminum vs composite for materials to fix problem and chose aluminum due to easier to work with and unknowns on the glass/aluminum bonding interface.

I have 1/8" thick piece of aluminum plate and will bend it to match the shape of the cross member on the top. Then another piece for the bottom.

The 4 eccentric rivet holes in the cross member will be fixed by placing 4 stainless washers of the correct size inside the cross member to receive the rivets. The position of the large central hole and the 4 new rivet holes will be transcribed to the new aluminum plate and drilled. The bottom aluminum plate will have the 1 hole for the shaft that goes thru the cross member and it will match the top aluminum "patch" plate.

The aluminum patches will be riveted to the cross member first. The neck assembly will then be riveted to the top aluminum patch and cross member with 4 new rivets. All rivets will be 3/16 or larger and stainless.

The curve of the top, aluminum patch, where the step sits, will have a flatter curve relative to the original cross member and will have to have custom shaping to seat the step fully.

All components will be sealed. Aluminum anodized.

What are the thoughts on this repair?

Thanks,

Airlenny1

The mast step is solid brass? The more knowledgeable here, may laugh at me but I don't think Hobie used Brass for much of anything. It is heavy. All the originals I have seen, are aluminum with a Nylon type "Half-Sphere" pivot/swivel. Weld and redrill holes in the cross bar?

We will probably do a variation on that and use backing washers underneath, top and bottom plates riveted and the 595 adhesive for the brass/aluminum interface plus the rivets. Then JB weld to fill the eccentric voids above the washers. Will use 0.130 6061 T0 to bend to shape and then harden to T6.

Thanks,

Mark

The metal hardware on the H18 is aluminum (cast or extruded) and stainless steel.

I did a similar repair to what you describe by adding a riveted reinforcement plate to the front crossbar. I actually put the plate on the inside of the crossbar so there was no issue with getting the mast step to seat properly. The plate was cut from a scrap piece of Hobie 14 mast, and the curve matched the curve of the 18 crossbar almost perfectly. In that case, the crossbar I was repairing had a hairline crack starting between the holes for the mast step so I wanted to reinforce it. If your crossbar isn’t cracked, I would probably skip the plate and just re-rivet the step back down, using 1/4 diameter rivets if necessary. Anyway, if you do plate it, put the plate inside and you will save yourself some hassles with fitment issues. I would also skip the bottom plate- probably overkill.

Here is a post I made a while back about mast step replacement you may also find useful.
https://www.hobie.com/forums/viewtopic.php?f=13&t=42441&p=175874&hilit=Crossbar#p175874

sm

Thanks for the response. Question: how did you get the plate inside? I do not seem to have an opening to get the plate inside the cross member.

Thanks,

Mark

You will have to remove at least one of the aluminum corner castings (end caps). Once the dolphin striker assembly has been removed, you can carefully tap out the corner casting.

sm

Depending on how wallowed out the rivet holes are, I'd either just re-rivet a new mast step, or use a thick backing washer or plate like srm described on the inside. The mast steps are drilled by hand I believe, and the holes don't always line up perfectly, which may be why you have elongated rivet holes... the step may have been replaced in the past.

Srm's solution with the backing plate is a smarter way to go than riveting a new plate on top, as drilling additional holes in the top of the crossbar for more rivets significantly weakens the crossbar in the most crucial location. As he mentioned, it would be best to remove an endcap and slide a plate inside the crossbar from one side.

I would definitely look closely for any cracks in the crossbar, as I can't really imagine the mast step "ripping" out of the crossbar without more significant damage... though perhaps someone had just overtensioned the tension rod and forced the mast step up over time? This was the case on my '78 H18, when I replaced my old style 2-rivet mast step with the newer, 4-rivet step. By the way, the crossbar is a 6061-T6 tempered & annodized aluminum. Can't be welded without affecting the tempered alloy (just as an FYI).

If the mast base is damaged, you can get a replacement casting from a Hobie dealer and re-rivet it back in place, but an elongated hole for the mast step pin shouldn't be anything to worry about, as long as the base and hinge are in good shape. The mast effectively just "sits" on the mast step, with the shrouds and forestay keeping a downforce to keep it in place.

_________________
Mike

'79 H18 standard 'Rocketman II' sail #14921 RIP
'78 H18 (unnamed) sail #14921
'08 H16 sail #114312
'97 H21SC sail #238

Thanks, everyone for the input. Will definitely put the advice to work.

Happy sailing,

Mark

I "updated" my old mast step.

https://drive.google.com/file/d/1rZx0zo ... sp=sharing

https://drive.google.com/file/d/1rZx0zo ... sp=sharing
what is that?

Looks like he’s pointing out that he added extra rivets to the (old style) mast step to help secure it to the crossbar. The tubes bolted through the step are likely supports for magnum wings that are used during trailering and removed when setting rigging the boat.

sm

Spot on. The mast base was a bit loose, so I drilled out the old rivets to find the holes had corroded a bit. I reattached the step with 2 new rivets and it felt snug. I wanted to upgrade to the 4 rivet design without spending more than $3, so I "upgraded" my old step by adding 2 more holes and 2 more rivets.

i see this. but what to those brackets go to? the struts?