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PostPosted: Sun Jun 06, 2004 9:11 pm 
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Location: West Texas
I need to replace my mast base and a piece of the gooseneck on my boom. Therefore I'll have to drill out & replace some rivets.
A) I couldn't find any Stainless rivets and
B) All the rivet guns I can find say "not recommended for stainless rivets"

Therefore I purchased some aluminum rivets on the assumption that I don't think any of these rivets will be taking much shear load.

Comments / suggestions? Thanks in advance! :)


Last edited by JaimeZXv.2 on Wed Jun 09, 2004 10:08 am, edited 1 time in total.

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PostPosted: Wed Jun 09, 2004 8:21 am 
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Location: Underwater in Mid-Michigan
From what I understand, the aluminum rivets will have issues and not last long. Something about an "electrolysis" issue.

A new mast base from Hobie will come with stainless steel rivets. You'll also need a pro rivet gun or be prepared to throw out your regular gun after a couple (hopefully) pops.

Look around, they ARE available and you'll probably need to use it again sometime in the future.

Fair Winds,
Nick

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1978 H16 "Burt The Cat"


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 Post subject: Rivets
PostPosted: Mon Jun 14, 2004 2:59 pm 
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Shear strength is exactly why stainless rivets are used. The Aluminum is very weak in comparison.

Most hand rivet tools will pull stainless rivets... they just won't last long and are harder to squeeze.

P.S. stepping the mast is when the largest loads are on the base rivets.

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Hobie Cat USA


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PostPosted: Tue Jun 15, 2004 12:32 am 
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Location: Norway
MONTAL / Mondal rivits, can be used on aluminium and steel without corrosion and are stronger than aluminium rivits. You can fill old holes with aluminium rivits but I really would not use them for anything load bearing.

Also when replacing fittings try to insulate them by using sealant/gaffer tape on to the mast, so there is no direct contact between a stainless steel fitting and an aluminium mast (add salt water and you have an electro potential... or a battery, which will lead to the mast workiing as a sacraficial anode for the stainless steel... ie BAD).


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PostPosted: Tue Jun 15, 2004 3:49 pm 
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Location: West Texas
Thanks for the replies, guys. I finally found a rivet gun that'll do SS rivets, although it doesn't say *3/16"* rivets, but the fella that sold it to me says he has one and uses 3/16" SS rivets with it all the time, so I guess it should be okay.

Item: I got a new jib halyard cleat to replace a cracked one from Murray's. It came with its own SS rivets and rivet sheaths but I'm concerned that if I wrap tape around the sheaths they'll be too fat to fit in the holes. I can see the using SS rivets for the jib halyard cleat since it'll definately be under load the whole time the jib is up and under tension.

What I'm not getting is why the rivets in the mast base would be under shear. The base slides inside the mast only to a certain point before a little ridge stops it. If you rivet it in this position the weight of the mast & sail plus any other downward tension all sits on the ridge in the mast base, not on the rivet shafts, which would therefore not be under shear at all. What am I missing here?

Also:

I'm pretty much positive that the jib end where it connects to the gooseneck wouldn't have hardly any shear on those rivets since there isn't much pressure on the gooseneck. Frankly I'm surprised the pin that goes into the end of the boom broke - the downhaul pulls on the bottom of the sail, not on the boom. I feel comfortable using aluminum rivets here to prevent dissimilar metal corrosion, unless someone presents me with a convincing argument to the contrary.

Thanks in advance for your further comments, most of you are far more experienced than I when it comes to this boat.

Warm regards,

Jim


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PostPosted: Tue Jun 15, 2004 11:29 pm 
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Location: Norway
Wee bit confused, but will press on... the goose neck is normally the boom fitting to the mast for the main sail (not the jib). If it's this then EEEEEEEEEEEEEEEEEEEEEEEEEeekkkkk :shock: don't even think of using Al rivits. Think when you let the sail out on a run or a reach. The sail is basically supported at three points: the head at the top of the mast, the clew at the outboard end of the boom and the tack at the boom mast fitting. All three of these places take 'huge' loadings as the force is transfered from the sail into the boat structure.

On a reach the centre of effort of the sail is ~ 0.6 m aft of the mast, say the sail is ~14m^2 in a wind speed of 16 knots, with (dry) air density of 1.3 kg/m^3 this gives a force on the sail of: 328 kg ~ 1/3 metric tonne (in actual fact owing to the angle of the sail and forward speed this force will be slightly different to this, downhaul, main sheet tension and mast rotation ratchet up the forces). Taking a simplified case the lever arm acting on the goose neck is the force x distance at which the force is applied... which roughly is 200 kg of force ~440 lbs. This is napkin engineering, but it's trying to illustrate that a considerable percentage of the force is transfered to the boat through the goose neck fitting.

All boat specific rivits that I know of, in Europe are Montal rivits, which are okay between al and stainless steel fittings. Make sure you put gaffer tape or an insulating layer between the mast and the fitting before riviting.


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PostPosted: Wed Jun 16, 2004 3:12 am 
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Ps... those calcs are a wee bit flawed... but you can't go back and edit on this thing.

If you don't belive the goose neck takes force... disconnect the goose neck and try holding it :lol: very quickly you will realise that this is an :twisted: (evil) suggestion as it will be almost impossible to do anything until you have lowered the mainsail (in itself, not easy on a H16 in any kind of seaway). Please don't use al as it will end in tears and almost certainly at the worst possible time...


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PostPosted: Wed Jun 16, 2004 5:44 am 
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I see what you're saying (you're right, I meant the tack of the main, not the tack of the jib. Heheh) I also get the napkin engineering, but what I'm not getting is, if this is the case then how come after the pin broke we just tied the boom to the gooseneck and still sailed around for the whole morning with satisfactory results? If there was that much load on the gooseneck the (32 year old rope) should've snapped much faster than the gooseneck pin.

What do you think?


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PostPosted: Wed Jun 16, 2004 7:39 pm 
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I have never heard of MONTAL or MONDAL rivets, but I am familiar with MONEL rivets (page 18 in the Murray's catalog).
They are much stronger and harder to "pop" than stainless rivets.

From the web:

What is Monel and why does it cost so much?

Monel is a special metal formulation trademarked name of the Inco Corporation. Monel is rustproof and chemically resistant.

Monel Properties

Composition:

66.5% Nickel & Cobalt
1.2% Iron,
31.5% Copper
Carbon 0.3%
Silicone 0.5%

Resistant to:

Seawater
Salt
Sulfuric Acid
Hydrochloric Acid
Hydrofluoric Acid
Organic Acids
Alkaline and Chlorine cracking.

High temperature resistance: Greater than 1,500 degrees.

Monel staple wire costs over $9.00/LB even before making the wire into staples - that's why the staples made from Monel are so expensive.


Is Monel better than stainless steel?

Yes for most purposes. Monel is more expensive, but will not corrode or exhibit galvanic reactions as can stainless steel.


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PostPosted: Sat Jun 26, 2004 8:22 pm 
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Well, it was kind of tough for me to find monel rivets. I got a few SS rivets at West Marine and some aluminum rivets at Lowe's. Originally I was planning to use the few SS rivets I had on the boom after I replaced the gooseneck. While drilling out all the old rivets, however, I found that the old rivets were *all* aluminum. So in spite of all you guys' well-intentioned comments, I guess aluminum really is strong enough. Dunno. The old rivets were 32 years old and still holding strong. Anyway, I figured since I only had 4 SS rivets I'd use them on the boom because y'all said it was probably under more load. The middle rivet I could fit a SS one but on the sides my SS rivets were too long so I had to use AL ones there. Obviously the new halyard cleat I put on came with SS rivets so I used those.

Here are pics of the old & new mast bases. Forgot to get one of the boom.

Image

Image


I'll be sure to keep an eye on the new rivets to make sure nothing untoward is happening.

Now if I can just get this one-person mast stepping thing down. :)


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 Post subject: pop rivits HA!
PostPosted: Fri Aug 27, 2004 9:23 pm 
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Location: New Castle County Delaware, U.S.A
I recently replaced my mast base. In doing so called a hobie dealer to seek advice. It was suggested to me was: use stainless stel self-tapping screws slightly larger than the old rivits.

Worked like a charm !!
<---this dude was stoked!!

I didn't even get out the drill.
I used a Punch, anangle grinder w/ soft disk to remove the old rivits and, a scocket with a screwdriverlike handle.
Not a ratchet as to have a better feel of the screws as they were tapping it was also easier to back out the screw to allow AL shaveings out of the hole.
:idea: In hind sight, I think I willl pull them out and put lock tight on 'em. Just in case a sea monster decides to back out the scrwes while I'm not looking.

Its a little late for me but does any one see any discrepancies with sefl tappers?


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