Hobie Cat Forums

It is currently Mon Sep 22, 2014 7:56 pm

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 9 posts ] 
Author Message
PostPosted: Mon Apr 30, 2012 9:15 am 
Offline
Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 2570
Location: Jersey Shore
I figured I'd share my recent experience with replacing the mast step on my H18. This post kind of a follow up to this thread..

http://www.hobiecat.com/forums/viewtopic.php?f=13&t=42206

This weekend I planned on re-riveting my mast step. I had re-riveted it at the beginning of last season, but it loosened up again over the year (it had a considerable amount of fore & aft wiggle). When I removed the step, I found that the front crossbar had developed a crack between the dolphin striker post hole and one of the rivet holes. This old crossbar had been converted from a two rivet mast step to a four rivet step by a previous owner. It had some extra rivet holes drilled during the conversion. Also, some of the rivet holes as well as the top dolphin striker post hole were elongated.

Image

Since I had acquired a spare crossbar last year, this wasn't a major catastrophe, but still a bit of a bummer and more work than I had planned on doing. My spare crossbar also had the old-style two rivet mast step installed. I drilled out and removed the rivets so I could install my four rivet step. Aside from being faded, the spare crossbar is in much better shape and doesn't look like it's seen much use.

Image

I decided to try bedding the mast step to the crossbar using Marine Tex. With the mast step just sitting on the crossbar, there is about a 1/16" gap between the step casting and the crossbar extrusion. My hope is that by bedding the crossbar, this will both reduce the amount of wobble that can occur and also reduce the chance for point loading. Hopefully this will keep the rivets from loosening and prevent crossbar cracking (I have now had three front crossbars crack at the mast step over the years).

It's important to note that the aft rivet hole in the four rivet mast step is not in the same location as the aft hole in the two rivet step - it's 1/4" farther back. This presents a bit of a problem because if you just drill a new hole in the crossbar (as the previous owner of my old crossbar did), the new hole will be very close to the existing hole and the crossbar is likely to crack through. I decided to instead drill a new hole in the mast step so that it would align with the existing hole in the crossbar (the fewer holes in the crossbar, the better IMO). This isn't hard to do as long as you measure carefully and use a center punch so your drill doesn't wander.

Image

I decided to use aluminum rivet washers inside the crossbar on the back side of the rivets. The washers should help to spread the load at the crossbar holes and also provide a buffer to minimize direct contact of the stainless rivet with the aluminum crossbar.

Figuring out how to hold the aluminum washers inside the crossbar took a little thought, but wasn't too difficult. I placed a small dab of 5 minute epoxy on the washer and then used a bent piece of clothes hanger wire to insert the washer through the bottom dolphin striker post hole and press the washer against the desired rivet hole. Once the washers were in place, I flipped the crossbar over, double checked their locations, and let the epoxy cure. Once the epoxy fully cured, I placed the mast step on the crossbar and verified that the rivets could be installed (and ran my 3/16" drill through the holes which were a little tight).

Image
Image

Before applying Marine Tex to the crossbar, I marked and masked off the mast step contact area on the front crossbar in order to keep things clean. I then waxed the front crossbar. The wax will act as a release agent for the M-Tex in the event that I ever need to remove the mast step in the future.

Image

I mixed up the M-Tex and applied a thin coating to both the crossbar and the mast step casting. I used grey M-Tex because it supposedly has higher compressive strength than the white.

Image
Image

I placed the mast step onto the crossbar, inserted all four rivets, and pulled each rivet about half way to seat the mast step and squish out excess M-tex. Then I pulled off the masking tape and cleaned up any smears. Last, I gave the rivets their final pull until they popped and let the M-tex cure.

Image

Right now the M-tex is cured rock hard and the step seems good and solid. Only time will tell if it stays that way. The next step is to re-install the dolphin striker bar. Then I have to remove the broken crossbar and install this one.

sm


Top
 Profile  
 
PostPosted: Mon Apr 30, 2012 9:32 am 
Offline
Site Rank - Old Salt

Joined: Sat Jul 25, 2009 11:19 pm
Posts: 354
Location: San Diego
Thanks for sharing this. I will add Aluminum washers like you did.

_________________
ALLEY CAT 1984 RED LINE HOBIE 18 MAGNUM
Sail # 10505 or 277
Image Image


Top
 Profile  
 
PostPosted: Mon Apr 30, 2012 1:48 pm 
Offline
Site Rank - Captain

Joined: Wed Jun 30, 2010 2:24 pm
Posts: 112
Location: Todd Mission, Texas
You might want to drill a 16 mast bearing and put it in between the ball and the step.

_________________
Jeff
1986 Hobie 18 #13031


Top
 Profile  
 
PostPosted: Mon Apr 30, 2012 5:34 pm 
Offline
Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 2570
Location: Jersey Shore
presto13031 wrote:
You might want to drill a 16 mast bearing and put it in between the ball and the step.


I don't have a 16 mast chip handy, but there is a nylon washer in there, you just can't see it in the picture.

sm


Top
 Profile  
 
PostPosted: Mon Apr 30, 2012 7:52 pm 
Offline
Site Rank - Old Salt

Joined: Mon Dec 31, 2007 6:06 pm
Posts: 610
Location: SE PA/ Chesapeak Bay
SRM,

Pert' slick .... I like ...

Do you think you need to run alittle more Dolphin Striker Tension if the frontcrossbars keep cracking??? Or do you think the boat is faster w/ slightly lowwer dolphin striker tension ... more flexiblity maybe??? Shallow water river steam boats are faster when they are "slighty" flexible. (There are ol' stories of riverboat Captains actually cutting out ribs before a "big" race ...)

You going to "Gunpowder" ... if so which boat will you be bringing??? the H18 or the H17 ???

_________________
HarryMurphey
H-18 mag/ #9458
Fleet 54 Div 11


Top
 Profile  
 
PostPosted: Tue May 01, 2012 5:27 am 
Offline
Site Rank - Captain

Joined: Wed Jun 30, 2010 2:24 pm
Posts: 112
Location: Todd Mission, Texas
srm wrote:
presto13031 wrote:
You might want to drill a 16 mast bearing and put it in between the ball and the step.


I don't have a 16 mast chip handy, but there is a nylon washer in there, you just can't see it in the picture.

sm

gotcha. I was about to comment that you put it on backwards, but Hobie did that, by putting the beam on "backwards".

_________________
Jeff
1986 Hobie 18 #13031


Top
 Profile  
 
PostPosted: Tue May 01, 2012 6:56 am 
Offline
Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 2570
Location: Jersey Shore
I think there are probably several factors which have caused the crossbars to crack. The first one we broke (over 15 years ago) was probably at least partially the result of not keeping the striker tight enough. The top of the crosssbar cracked all the way around the mast step. Since then, I'd say I've always tried to make sure the striker is kept good and tight. The other two have cracked along the centerline of the crossbar and I think that was caused by a number of issues.

First, there are several holes all placed along the centerline of the front crossbar (top and bottom dolphin striker post holes, two mast step rivet holes, and at least one furler cleat rivet hole). This excess of holes is a problem. On my most recent broken crossbar, the previous owner added even more holes to the centerline when they converted from a 2-rivet step to a 4-rivet step. That's a lot of material missing from the middle of the crossbar - not good.

I think another issue is with the mast step rivets loosening up. When the rivets become loose, the step can move up & down as well as forward & back. The dolphin striker effectively loosens, the crossbar flexes more, and the mast step may end up point loading the crossbar - none of this is good.

Galvanic corrosion between the stainless rivets and the aluminum crossbar is also a factor and virtually impossible to avoid in costal locations - certainly unavoidable for a beach boat.

The last issue is that all of my "replacement" crossbars have been bought used. They're old, have likely sat out in the weather for years un-maintained by the previous owners, etc., so if I get 5 to 10 years out of them, I guess I'm doing OK. I'll just keep buying used ones for spares as they come along.

I think as long as the mast step is firmly mounted to the front crossbar (no fore / aft wiggle) it's probably OK. If it starts to loosen up, it needs to be re-riveted ASAP. I also now make it a point to throughly rinse off the front crossbar with fresh water whenever possible after sailing in salt water.

sm


Top
 Profile  
 
PostPosted: Fri May 04, 2012 2:54 pm 
Offline
Site Rank - Admiral

Joined: Sun Jul 25, 2004 4:46 pm
Posts: 159
Location: Bakersfield, CA
Awesome stuff SM! I'm going to do this to mine as well based on your info. Can you tell me what size the rivets are for the mast step? Washer size too if you know it!

Thanks,

Tom
1988 H18M


Top
 Profile  
 
PostPosted: Sat May 05, 2012 5:17 am 
Offline
Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 2570
Location: Jersey Shore
thundley wrote:
Can you tell me what size the rivets are for the mast step? Washer size too if you know it!


I used 3/16" diameter x 3/4" long stainless steel pop rivets and aluminum rivet washers (zinc plated steel may be an even better choice for the washers since it will be harder than aluminum washers and won't corrode the crossbar). Check out Mcmaster-Carr (http://www.mcmaster.com).

I also used the Pittsburgh 17-1/2" Heavy Duty Riveter from Harbor Freight. It's only $20, and it beats the crap out of hardware store hand riveters. Also has a lifetime guarantee.
Image

sm


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: No registered users 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