Fastener Choice for Lazy Jack Install

[Clark]

I'll be installing Lazy Jacks soon and am not sure what type of fasteners to use for the mast and boom hardware. I think ~3/16 is the right size. I've narrowed it down to aluminum rivets or stainless screws. I'd love to do stainless rivets but don't want the hassle and expense of pneumatic tools. What are the recommendations of this august group?

 

[fastscot]

SS Screws

I just installed a SailCradle on my 23'. Rivets came with it, but I decided to use screws. Screws can be removed when necessary without drilling them out and loosing half of the metal inside the boom/mast. Since this is the first time I have installed one of these and I am doing it with the mast down, I wanted to make sure I get it right and can make adjustments if necessary. I vote SS screws. The size of course varies with the fastner size, mast/boom size, etc. CVP

 

[Moody Buccaneer]

Screw it

Drill and tap the holes for 10-24 screws. Use Lanacote or Tef-Gel on the threads to prevent the SS screws from mating permanently to the aluminum. If you want to get fancy, insulate the back of any hardware (eye straps, etc.) with liquid rubber or a gasket made of electrical tape. The install will always look clean and you won't end up with the chalky mess that attacks un-insulated fittings.

 

[capt'n jack]

lazy jack

I like to know how it works out for you, I've been thinking about a lazy jack for my 30' bristol.........ps what is a ss screw ?sincerely, capt'n jack

 

[Paul I aboard "One Slip"]

I did something similar very recently

I just went through this a few weeks ago. Unless you can tap a minimum of three threads within the thickness of the material I would go with rivets. Take a look at your boom....how is it put together from the factory? Rivets I'll bet. And I'll bet all the hardware already mounted on the boom is stainless. The rivets might be aluminum or stainless. And I'll bet further that the factory made no attempt made to isolate the two metals. I think the corrosion issue might be a bigger issue in salt as opposed to fresh water.You might have a better shot using screws on the mast because it is thicker. WWW.Rigright.com might tell you thickness of the mast and boom.The common rivet size is 3/16" by the legnth needed. Don't go too much longer than needed of they wont snug down enough. Finding stainless rivets might prove difficult too though West Marine has them (at nearly a buck each!).And you don't need pnuematic tools to install stainless rivets. I installed about two dozen 3/16" x 1/4" of them or so a few weeks ago in my boom. I used a manual rivet gun from Home depot. No problem at all. Just more force required than for the aluminum ones.

 

[Jack2438]

I would also appreiciate a reveiw

If I remember correctly your installing it on a Catalina 27, which is the model I have. The main being only 150 square foot, it has never been that much of a problem for me. Of coarse, I didn't think I needed an autopilot too but I couldn't have been more wrong. Let me know how it works out for you, thanks, Jack

 

[fastscot]

SS = Stainless Steel

Sorry about that. SS = stainless steel PS I use Lanocote.CVP

 

[Moody Buccaneer]

Like I said ... screw it

The boom on any boat big enough to make lazy jacks a consideration will have enough meat to hold threads for 10-24 screws. 3 threads of 10-24 is only 1/8".True, many boats have rivets holding the mast and boom fittings on. Also true that little or no effort is made to insulate the dissimilar metals. It's a cost thing. Rivets and not insulating the parts saves money.I've made $100's doing repairs on rigs built like that. Once the corrosion gets to the rivets and fittings the holes are oversize, can't be re-riveted with the same size and the section is not thick enough to use threaded fasteners. The proper solution is to pull the mast, weld up the holes and start over ... with threaded fasteners and proper insulation.But what the heck ... if the manufacturer did it with rivets and no insulation it must be right ... right? Hell, at one time is was common practice to use sheet metal screws on masts and booms ... that wasn't real smart either. But it was fast and cheap ...

 

[Clark]

Hmm . . so far the preference is for SS screws

Which I can do "if" the sections are thick enough. It's good to know that a decent rivet tool can handle a few SS rivets which I'd like to have as a good alternate. Any thoughts on how to insulate SS rivets? Coat w/ Tef before installation?BTW, my boat is a Hunter 280 with an 11' boom and fat roach main. I'll be taking measurements today and will start a project for posting on this site.

 

[captain don]

yeah, lanocote

Yeah, self tapping stainless screws, assuming you have aluminum spars. Tef-Gel is best, lanacote is worthy too to prevent dissimilar metal corrosion.

 

[Clark]

Just finished with my measurements . .

and the mast is 1/8"; too thin for screws IMHO. Or, would self tapping screws have enough bite? Otherwise, I guess if I do this I'll need to use SS rivets (?) Also, it looks as though I'll need to mount the cheek blocks 2-3' above the spreaders since they are only 12' above the boom which is actually 12' long.

 

[Paul I aboard One Slip]

My final thoughts

In 1/8 inch of aluminum, a 10-24 screw will engage exactly 3 times. If the mast were steel instead of aluminum I might reconsider, but due to the poor threading characteristics of aluminum, I still have to recommend the rivets. The boom will be an even thinner extrusion. I just cant see going with screws there.I'm sure it depends on the specific screws used, but most self tappers I have seen are no better than regular screws when it comes to thread holding power. Some might even be worse. I think the main characteristic to look at is still the threads per inch.I stand by what I have already said regarding trying to insulate the metals. With all due respect to Moody Buccaneer's exploits, I am an engineer by trade and have a fair amount of design expertise. I have also done work on several booms, all of them over 20 year old (all in a fresh water environment). I have yet to see a corrosion problem between the anodized aluminum and the stainless hardware and/or fasteners that is anything worse than a slight discoloration. Nor have I seen any evidence of an attempt made by the factory to insulate the two. If one was to do a truly reliable job at insulating them, they would need to use some type of dielectric insert between the fastener and the spar. Brush on coatings would be very dicy. I do not think they would perform adequately considering the type of metal to metal contact that takes place with rivets or machine screws. If you do use some kind of brush on insulation method, it would be very interesting if you could measure continuity between the fasteners and the boom after you are finished. If there is a path for current flow between them, the insulation steps you took were in vain. In fact, they could conceivably make the problem worse by insulating some areas of contact and not insulating others. Any corrosion that does ensue will be concentrated in the areas that were not insulated. This could cause a problem instead of the insignificant amount of light discoloration surrounding the fastener.Lastly, consider mounting the lazy jack blocks so they hang 6-8 inches out on the spreaders instead of being on each side of the boom. It provides a bigger window to lower the sail into.Looking forward to your project post.

 

[Clark]

Paul, I would prefer to put the upper blocks . .

on the spreaders but the geometry seems off. The spreaders are 12' above the boom and the boom is 12' long. Now I know that the rear line will not need to go all the way to the tail of the boom but the angles look too shallow. Or are they? Most boats spreaders are a good bit higher in relation to the boom so that is an excellent choice for them. This Hunter (1996 280) is quite different.

 

[RichH]

Large pop rivets work well....

They match the materials requirements : aluminum touching aluminum and the are strong if sized correctly. I have a large sailplan (450 sq. ft. main) with lots of up and down possible movement of the boom, use 3/16" pop rivits (since 1999) anchoring small padeyes/blocks. I use nylon strretchy braided cord for the lazy jack system (actually similar to the EzJax system) with NO problems. Using stretchy nylon coriding allows for the 'adjustability' of the system with respect to varying boom height. Of course with an EzJax system when sailing the cording, etc. is stowed along the boom/mast so as not to interfere with the sail shape.

 

[Paul I aboard One Slip]

Oh... the old single spreader trick ha?

Clark,At first, I assumed you meant the lower spreaders are 12 feet from the boom. I was going to come back and say its the upper spreaders you should be attaching to anyway. But before I did, I went and took a look at a photo of your model boat. Which apparently, has just one set of spreaders.If it were me I'd go up and temporarily tie lines around the spreaders and make the 45 degree angle to the boom just to see if it works. You may be surprised. If you are not happy with the angle then you have no choise but to mast mount the blocks.Either way I'll be interested in how it turns out.Rich H: I agree on the 3/16" rivet size. That is all I've ever used. I also believe aluminum may be strong enough (it might even "flare" more once in the hole because the aluminum can be crimped easier. Where we disagree is the corrosion issue. You are correct that aluminum rivets touching an aluminum mast/boom will work out. The problem is that most of the padeyes, eye straps, and blocks we all end up using are stainless, with much more contact area than provided by the rivet itself. What to do?

 

[Paul I aboard One Slip]

One more thing...

I forgot to include this link....

 

[Paul I aboard One Slip]

One more, One more thing..

I just finished reading an article in the April 2006 issue of Sail magazine. It was an article on Spring commissioning and included info on doing refit work on spars. With respect to the corrosion issue, the article reinforces some of what I've been thinking right along, but also added a few pieces to the puzzle I did not know. According to Sail, galvanic corrosion of spar components because of contact with stainless hardware is indeed a significant problem. However the corrosion cannot take place unless there is moisture present. Fastening SS to aluminum and keeping it dry will not result in corrosion. I did not know this.All water is not the same when it comes to galvanic corrosion and saltwater is markedly worse. Hence the corosion problem is much more prevalent in salt as opposed to fresh water enviornments. I suspected this from what I read in forums like this one, and it explains why my own experience, all on the Great Lakes, show the corrosion problem to be a very minor one.The article does go on to recommend using Lanocote, Tef-gel, and Duralac for coating fasteners, and Sikaflex 291 or 3M 4200 sealant for larger areas under fittings such as cheek blocks. Do not use silicone that smells of vinegar. It contains an acid that acts as a catalyst to the corrosion process. It is highly recommended to bed all attachments to the mast The use of these sealants is predominately to seal water out, not to isolate the metals. It also tends to stop the threads on screws from siezing. Recommended fasteners are 1/4"-20 coarse thread screws, 304 grade stainless. According to the article, fine thread fasteners have less thread height and pull out easier.Aluminum rivits are also recommended for low strength applications. Tap out the mandrels after application if they are made of steel (many are, according to the article). Fill the holes with sealant to prevent water entry.