[Public-List] Mast beam

[Mike Lehman]

Glenn

You may not like the appearance of the aluminum sister plates...but they 
have never failed. We have had boats racing in 50 knot winds with large 
waves and driving hard without a beam failure once the beams have been 
properly reinforced.

On all of the boats the bulkheads support the beam and the deck, the 
vertical oak pieces along the bulkheads are stiffeners that prevent the 
bulkheads from buckling under high loads. The main problem is the beam is 
not well supported under the aft end and the mast sits on the aft side of 
the beam which causes the beam to twist back. The solution to this is to add 
knees to the existing oak supports to prevent the twisting.

On the liner boats the problem is a bit different. I you carefully inspect 
the bottom of the bulkhead you will see that is rests on the floor liner and 
there is not adequate support under the floor. This is the problem that 
George mentioned in an earlier post on this subject. Adding extra support 
under the floor to transfer the load to the hull solves this.

One main problem with ALL the boats is the bolts that Whitby used are 1/4" 
threaded all the way to the head of the bolt. These bolts were used on the 
chainplates and the main beam. When these old bolts are removed they are 
often bent, especially the main beam bolts. They should ALL be replaced with 
5/16" shoulder bolts. The increase in strength is almost 3x because of the 
increase in diameter and especially because of the shoulder.

I don't think push the sag out of a beam in the liner boats, but you can 
stop its progress.



~~~_/)_/)~~ Mike Lehman ~~_/)~~~


-----Original Message----- 
From: Glennb
Sent: Thursday, May 30, 2013 11:18 PM
To: fongemie at gmail.com ; Alberg 30 Public List -- open to all
Subject: Re: [Public-List] Mast beam

Jeff,

My boat, Dolce is a pre-liner boat, built in 1968.  when I bought the boat 
the mast support beam was partially delaminated on one side - several 
laminates, varing lengths up to 1/3 length of the beam were separated.    I 
sailed the boat for two seasons this way then replaced the beam spring time 
of my third year when the delamination became worse.  I mention this because 
the beam was serviceable even when partially delaminated.

Rather than put in the aluminum plates described on the alberg30 site, I 
opted to saw a bigger one piece  4x6 beam out of purple heart.  This 
required a 4 x 12 beam to start with, as the crown of the beam extends the 
height of the beam vertically something over 9" top to bottom.  I 
reinstalled the sawn and shaped beam by glassing in the ends and thru 
bolting to the  plywood bulkhead.  Same method as the original.  I went 
oversize on the beam because I wanted a stout, permanent ocean service fix. 
Probably overkill now, but I never need worry about mast compression!! 
purple heart varnishes up nicely and is good structural-load bearing 
material.

The biggest problem I found is that the forward edge of the cabin top curves 
downward and forward at the upper forward corner of the beam, hence I found 
I had to round and shape the forward corners of the beam and forward edge to 
get a tight fit up against the cabin top.

Where it did not fit snugly, I injected a bunch of 5200 to fill the gap and 
act as a load bearing surface between the beam and the roof top.  This seems 
to have worked well as I have no compression on the door frame etc.

Had I to do it over now, I wouldnt hesitate to cut laminate strips out of 
oak or some other nice hardwood and epoxy a beam together as you are 
thinking about doing.  sawing a whole one piece beam also works well but 
uses more material.  (I never have liked the idea of bolting up aluminim 
plates over damaged/delaminated structural beams. The damaged beams will 
only continue to delaminate and fail behind the aluminum- eventually 
becoming nothing but a loose pile of laminate material wedged together by 
some metal.  Just doesnt seem like a seamanlike fix + wood compression beams 
look great when varnished.)

If you really wanted to reinforce the load bearing beams, you could put in 
beefier vertical posts, maybe knees up against the  beam, bolted and glued 
to the bulkhead.  this would certainly carry the load better. You wold 
probably need to install loading pads on the hull, to receive the bigger 
beams, as you wouldn't want small hard spots on the hull to receive the 
additional  downward compression loads larger beams would deliver.  However 
I've found the alberg cabin top and bulkhead is extremely robust and strong 
to begin with, so perhaps the extra vertical supports are overkill.  On the 
other hand Yves Galinas, of Jean du Sud fame recommends making up a 
removable vertical mast support beam to wedge in place under the mast when 
sailing in heavy weather.  So your call depending on what kind of sailing 
you might eventually decide to do.

The most work went into picking away at the original fiberglass beam ends 
and shaping the beam to fit back into the space.  The project is definitely 
doable.  But worth the extra effort when done right!

Good luck,

Glenn
Dolce 318

Sent from my iPad

On May 30, 2013, at 2:24 PM, Jeffrey <fongemie at gmail.com> wrote:

> Hi everyone,
>
> I'm diverting the conversation here talking about a pre-liner boat (sorry)
> but I also need to do something with my boat's mast beam.
>
> https://plus.google.com/photos/115571802364472829939/albums/5182769471833731569
>
> I keep thinking that I want to rip it out and laminate a new one to the
> same curve. One thing I'm a little unclear on is exactly how the beam
> transfers the load onto the hull. If you look at the my images in the 
> link,
> the fiberglass tabbing to the cabin side can't do much, or the bulkhead
> that it is bolted to. Seems the support posts must be doing all the work,
> but they don't even sit squarely under the beam. What the heck holds up my
> mast?
>
> Jeff Fongemie
> #116 Seagrass
>
> http://picasaweb.google.com/fongemie
>
>
>
>
>
>
>
>
> On Thu, May 30, 2013 at 4:57 PM, Kris Coward <kris at melon.org> wrote:
>
>>
>> I also get a bit of a dip on 583, but it's enough to cause slight
>> problems with the doors. I've been tempted to address mine by either
>> re-hanging the hanging locker/vee berth door a smidge lower, or sanding
>> off the top 1/8" or so, but I already confound that door with the filler
>> cushions always in place in the vee, so that fix is quite far down my
>> to-do list.
>>
>> -Kris
>>
>> On Thu, May 30, 2013 at 04:44:54PM -0400, David Gilbert wrote:
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