[Public-List] Lag bolts

[GLENN P]

Great discussion. Probably the bent bolts were caused by the hole not being drilled true, e.g. completely perpendicular to the centerline of the boat. I screwed up a bit when boring the bottom of one hole on my beam replacement and have now one bent bolt - slightly offset at the lower 1/3rd.. The bigger issue is the head and nut don,t seat true... nuisance and aggravation!! 


still not in favor of lag bolts into the beam. They are prime rot pockets when the mast step leaks, and almost never used in quality shipbuilding to fasten structure together. planks to frames, plywood screws, cattle gates on the farm, absolutely yes. Structure, hardly ever, and these places always are the failure points when the boat gets old. better to through bolt, at least to a backing plate under the liner/cabin top, or through the beam itself. oh well, just my soapbox... 


a side note I dont think anyone has mentioned yet, the mast step in preliner boats is held in place with like 6 flat head machine screws screwed into the fiberglass cabin top. On Dolce, all but 2 screws were stripped out and had no real holding power in the FG- except a prior owner bedded them with 5200. I ended up thru bolting all thru the cabin top with SS fender washers, and aforementioned SS backing plates. Very happy with the result. Secure as the toe rail, No movement from the mast step what so ever, and probably I dont now even need the two large through bolts. In fact, now, I think I would dispense with the bolts all together - except hundreds of boats have done very well with them in place! 


I wish we knew definitively why Whitby put the two bolts into the beam in the first place... do they exist on liner boats with Aluminum structure??? Seems to be a weird thing, and deep mystery why they are needed. 


thanks 
Glenn 
Dolce 318 

----- Original Message -----
From: "Robert Kirk" <isobar at verizon.net> 
To: public-list at lists.alberg30.org 
Sent: Monday, October 28, 2013 6:05:04 PM 
Subject: Re: [Public-List] Lag bolts 

Each 3/8 lag screw, 2 inches into the wood, will take about a ton of 
pull-out apiece. Much more than you'd expect to need for a compression 
loaded mast step. Shear load should be relatively small but not zero. 
(I'm not sure how to interpret the bend John Boor reported in his 1/4 X 
6 bolts where they 'exited the bulkhead' since bulkheads are verticals. 
I assume bending stress but not shear. I found lots of bent bolts in 
Isobar along the hull-deck joint. 

On 10/28/13, Greg Bover<[1]gregbover at cbfisk.com> wrote: 

According to my tattered copy of Wood as an Engineering Material, the 
graph 
of the holding power of a lag screw in a hardwood like oak begins to 
level 
off once the length reaches seven times the root diameter, i.e., the 
diameter as measured between the threads. For a 5/16 bolt that is 7/32 
x 7 
or about an inch and a half. 
Greg Bover 
A-30 #114 
LINNET 
Gloucester 
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