[Public-List] Cutlass Bearing Flange Alberg 30

Gordon Laco mainstay at csolve.net
Thu Jul 22 10:21:52 PDT 2010 

I guess this is one of those issues where one may concede that the treads of
a steel or bronze nut will be stronger than those cut in a material like
FRP... But effectively the FRP threads are 'strong enough'.

I reckon one must keep in mind the actual dynamics of the situation being
examined.  In the case of the cutlas bearing flange... No threads at all
would do fine if a way were devised to keep the shafts of the bolts in the
holes.   What those bolts do (mainly) is oppose any tendency of the assembly
to turn with the prop shaft.  Granted, to a certain extent they pull the
flange in, but really preventing it from turning is what they do; and really
the caulking does most of that work anyway...

Gord #426 Surprise


On 22/07/10 1:09 PM, "John Birch" <Sunstone at cogeco.ca> wrote:

> Hi Roger,
> 
> Seems a waste of effort to me, suggest you read my 9:52 AM post today if you
> have missed it.
> 
> Hey, the lag bolts method has worked for 40 or more years ....
> 
> Best
> 
> John
> 
> ----- Original Message -----
> From: "Roger L. Kingsland" <r.kingsland at ksba.com>
> To: "'Alberg 30 Public List -- open to all'"
> <public-list at lists.alberg30.org>
> Sent: Thursday, July 22, 2010 12:52 PM
> Subject: Re: [Public-List] Cutlass Bearing Flange Alberg 30
> 
> 
>> Albergers,
>> 
>> I am trying to wrap my head around the idea of tapping fiberglass thru
>> which
>> machine screw (or bolt threads) go.  I assume the "grip" on the screw
>> exerted by the FG threads would be less than the nut, say, for yucks, half
>> as much.  So first one must torque the screw head, say to 50 lbs, into the
>> threaded FG then put the washers and nut on the end and torque the head
>> and/or nut to 100 lbs.  I suppose it would be possible to 1st torque the
>> nut
>> to 50 lbs then tighten the head to 100 lbs.  This way, at least in theory,
>> the FG threads would be snug w/ the nut and the nut threads would take the
>> additional load that the FG couldn't.  If the head were restrained while
>> the
>> nut was tightened (more likely w/ a slot or Phillips head) then even a few
>> turns of the nut would likely strip the FG threads.
>> 
>> If the justification for tapping the FG is added strength, I would argue
>> that fasteners alone must be more than strong enough to handle the load,
>> making the FG threads unnecessary.  Plus another critical component of the
>> connection is properly distributing the load via a washer and/or backer
>> plate.  The tapped FG won't help in this regard.
>> 
>> I suppose better waterproofing could be a justification but this would
>> only
>> occur if the weaker FG threads are not damaged during the installation.
>> Plus I would not like to rely on simply a tight fit between screw and FG
>> that might degrade if rigging forces cause them to loosen.  I would be
>> more
>> comfortable with some kind of "squishy" stuff between the two materials w/
>> enough room to flex just a little; what about a slight bevel at the top of
>> the fiberglass hole with an appropriately sized "O" ring around the bolt
>> shaft that could seat inside the bevel when squished down by a washer or
>> the
>> base of a piece of hardware?  This might work for highly loaded hardware,
>> like cleats, that should bedded in epoxy to prevent any movement.  I found
>> some adhesive, double faced, squishy tape that I put under hatch hinges
>> and
>> stanchion bases in the hope that, when I tighten the fasteners, the
>> material
>> will expand and seal around the fastener shafts (keeping my fingers
>> crossed).
>> 
>> Food for thought for those like me who agonize over this kind of stuff.
>> Any
>> opinions?
>> 
>> Roger 148#
>> 
>> 
>> 
>> -----Original Message-----
>> From: public-list-bounces at lists.alberg30.org
>> [mailto:public-list-bounces at lists.alberg30.org] On Behalf Of Gordon Laco
>> Sent: Thursday, July 22, 2010 10:18 AM
>> To: Alberg 30 Public List -- open to all
>> Subject: Re: [Public-List] Cutlass Bearing Flange Alberg 30
>> Importance: High
>> 
>> Good points John - you are correct about SS underwater... Bronze can be
>> iffy
>> too if the alloy is not correct.
>> 
>> When my cutlass bearing came off I found that one of the bolts had
>> corroded
>> to the consistency of a biscuit.  It was just crumbly powder under a head
>> that look fine.  I was able to get the stump out by clipping vice grips on
>> it and gently turning it out.
>> 
>> 
>> Gord #426 Surprise
>> 
>> 
>> On 22/07/10 9:52 AM, "John Birch" <Sunstone at cogeco.ca> wrote:
>> 
>>> Hi Peter,
>>> 
>>> They are lag bolts, tapped into the glass. There are no inserts.
>>> 
>>> Periodically, all bronze bolts underwater should be removed and
>>> inspected - perhaps once a decade or so. You should never use SS Bolts
>>> (deprived of oxygen, they become active and move the wrong way on the
>> periodic table.
>>> 
>>> Buying silicon or manganese bronze marine bolts is hard to do, go to a
>>> reputable supplier - in the Toronto area go to Pacific Fasteners on
>>> Chauncey Drive off Islington to make sure you are getting the right
>>> bronze or monell fastners.
>>> 
>>> There are some instances where drilling and tapping machine screws
>>> into fiberglass is helpful to ensure a stronger attachment. One
>>> example I've done is the traveler track, another are the winches, all
>>> followed with as wide a washer or plate as can be fitted below and
>>> then lock washers, thread Locktight and then a nut. It makes for a
>>> particularly strong attachment that means the whole glassed area would
>>> have to break off - and I cant imagine the load necessary to cause such a
>> failure.
>>> 
>>> The cutlass bearing attachment is threaded on to the bronze shaft
>>> tube, which is bedded throughout its internal length in the hull with
>>> Dolfinite from the factory, or some other adhesive caulk if
>>> retrofitted, then the bearing housing turned onto the threads on the
>>> tube and then the housing is bolted into place. I suspect the cutlass
>>> housing would do just fine without the bolts, but why test the theory.
>>> Ensure the lag bolts are going into solid glass and not into resin
>>> starved glass and insert them with lots of caulking on the threads.
>>> 
>>> Water migration into the glass will over time degrade the glass. If
>>> your holes are degraded, suggest adding a fresh low viscosity epoxy
>>> resin to re-wet the glass fibers after ensuring is all dried out.
>>> 
>>> Those lag bolts were cut with a tap to create the threads into the glass.
>>> You cant just drill a hole and use self tapping lag bolts or you'll
>>> crack the glass. The holes have to be threaded with a tap set first.
>>> 
>>> Caulking is critical to prevent water seepage into the holes, which
>>> will eventually break down the resin/glass bond in the area if allowed
>>> to seep in.
>>> 
>>> Hope this is a help
>>> 
>>> Best
>>> 
>>> John
>>> 
>>> ----- Original Message -----
>>> From: "Jeffrey" <fongemie at gmail.com>
>>> To: "Alberg 30 Public List -- open to all"
>>> <public-list at lists.alberg30.org>
>>> Sent: Thursday, July 22, 2010 8:53 AM
>>> Subject: Re: [Public-List] Cutlass Bearing Flange Alberg 30
>>> 
>>> 
>>>> They screw into the fiberglass. Not sure if there are any inserts or
>>>> nuts imbedded in the fiberglass or not. I couldn't tell for sure when
>>>> I had mine off this spring. it looked to be just fiberglass.
>>>> 
>>>> -jeff
>>>> 
>>>> Jeff Fongemie
>>>> #116 Seagrass
>>>> 
>>>> http://picasaweb.google.com/fongemie
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Thu, Jul 22, 2010 at 8:30 AM, Peter Milley <milleype at kingston.net>
>>>> wrote:
>>>>> 
>>>>> 
>>>>> Do the two bolts behind the propeller on the Al 30, holding the
>>>>> cutlass bearing flange to the hull just screw into the fiberglass or
>>>>> are there nuts behind them on the inside of the hull?
>>>>> 
>>>>> Peter Milley
>>>>> 
>>>>> _______________________________________________
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>>>>> 
>>>> 
>>>> 
>>>> 
>>>> --
>>>> Jeffrey Fongemie
>>>> _______________________________________________
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>>>> 
>>> 
>>> 
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>> 
>> 
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> 
> 
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