Fastening deck beam to frame

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sterbejj
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Fastening deck beam to frame

Postby sterbejj » Thu Feb 14, 2008 2:41 pm

The plan set for my project (a Glen-L 15) specifies that a deck beam be attached to the most forward hull frame using one screw and one carriage bolt at each end. Why the carriage bolt and not just screws? All other deck beams and frame parts are attached using screws and glue. Is there some structural reason for using a carriage bolt or would screws be suitable?

Casey Sterbenz

Mister McNulty
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Postby Mister McNulty » Thu Feb 14, 2008 3:15 pm

are you thinking that the one single carriage bolt is going to throw off your entire displacement? it is just my opinion that you should stick with the plans, after all they are tried and true plans.
It's not Murphy's Law, it's McNulty's Law

upspirate

Postby upspirate » Thu Feb 14, 2008 3:56 pm

my plans for the Pee-Wee call for assembling the frames with a bolt & screw too.This is common where the frames are lap-joined together(same as the lap joint at the deck beam)

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Stuart
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Postby Stuart » Thu Feb 14, 2008 4:35 pm

sterbejj - In the first place, a builder can deviate from the plans. In the second place, it is prudent not to deviate from the plans unless you not only think you know, but actually do know, the what and the why.

The carriage bolt is common to other Glen-L sail boat builds. The carriage bolt is much stronger than screws. In fact the carriage bolt is often reinforced against axial rotation using screws distant from the axis of the joint fulcrum produced by the carriage bolt.

You must agree, the carriage bolt forms a very strong frame structure whose strength could not be created using any other method. Glues like rigid structures and work well under most types of stress. Screws in the same way are great for certain types of stress. Consider all the glued joints and screwed joints you have seen broken and guess the direction of the force. Now, think if those joints had been through bolted with a good 1/2" carriage bolt, what kind of force would be needed to break that joint.

I suggest using the carriage bolt and not lag screws or some other self tapping fastener mainly because it is specific to that one frame and that should be indicative of some need for it to be there and not elsewhere. Other than the pressure of the water on the hull, what keeps the hull from spreading should several tons of wave inspire it to do so?

Stuart

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sterbejj
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Location: Crofton, MD

Postby sterbejj » Wed Feb 20, 2008 7:18 pm

Friends,

Much thanx for the inputs. I will be installing bolts along with screws to secure the deck beam to the frame per the drawings. When complete this will be the fourteenth hull I've built but is the first where I've seen this bolt-plus-screw arrangement, hence my query.

V/r,

Casey Sterbenz

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Postby FDMSIV » Thu Feb 21, 2008 10:56 am

If you use only glue and screws and you somehow manage to put the Glen-L 15 through such a maneuver that you break the joint, your chances of surviving to tell the story are quite slim.

I think quite a few of the Glen-L designs were created during a time when epoxies were not what they are today. I am not building a sailboat, but I have left out most of the carriage bolts, except in the keel to stem and keel to transom connections. The wood is going to break before the joint and in that case nothing will really help.

If you were building a larger sailboat that would have considerable loads on the deck I would say bolt it, but with a smaller boat I wouldn't bother.


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