DN NA Class

Guests & Members Post & Read => Building, Maintaining and Repairing => Topic started by: Rob Evans on February 05, 2016, 11:31:22 AM

Title: Plank to hull attachment
Post by: Rob Evans on February 05, 2016, 11:31:22 AM
I have reviewed what has been written on this subject but would like to re-open.  I recently got a plank that has just two 8mm holes, 16" apart - no stud plates.  I have the standard 4 hole, 10 screw hull plates mounted on my hull.  It would be great to glue the hull plates in place and have: 8mm nylon bolts be the 'breaking' point.  In the event of a 'separation' It would be so much easier to reassemble on the ice with no damage to the hull or the plank.  Has this been done?  Thoughts? Certainly pre-mature separation would be a bad thing.  :-\

Title: Re: Plank to hull attachment
Post by: JOHN BUSHEY on February 05, 2016, 11:51:12 AM
I'd be concerned about using plastic bolts.  While they would shear off without damage to your hull or plates like you hope, they could too easily shear off in normal sailing.   There is a lot of leverage from forces applied out at the end of a plank and the force at the stud/bolt would be very high.   I think having a plastic nut is the best compromise, allowing the stainless stud to react shear while sailing, and allow the nut to strip out in extreme cases, if you get my meaning.

Title: Re: Plank to hull attachment
Post by: Ken Smith on February 07, 2016, 08:15:28 AM
I agree. I've sailed on many systems stronger than plastic bolts and experienced premature failures too many times. At least I think they were premature- the hull didn't break but no one else came apart. I include premature failures of "standard" system you describe. Stud stub weld fatigue was early for sure. Popped screw heads likely premature. Lost screws from hull plate also, due to screws working away the Sitka in the hull bottom. 

My system now is 3/8 bolt up through plank to standard hull plates. Failure would be by pulling screws out of the hull. The plastic nuts I expect to see no load if I hit something with one end of the plank or dropped one runner in a hole.

Ken Smith

Title: Re: Plank to hull attachment
Post by: Rob Evans on February 11, 2016, 02:06:16 PM
Sounds good Ken.  I will go with your system.  Thanks!

Title: Re: Plank to hull attachment
Post by: DN 805 on February 11, 2016, 02:33:59 PM
Have to weigh in on this

It is essential to not overtighten the nuts.   After you have the nuts tight, then back off one full turn.  As the runner plank flexes, the studs necessarily must move athwartships.         One of the hull plates has oval holes to accommodate the movement of the studs.   But if the nuts are tight, the studs cannot move and will break away.

Title: Re: Plank to hull attachment
Post by: KB [us5219] on February 15, 2016, 06:52:30 AM
I have seen a few boats out there "rubber banded" with innertube rubber straps...  And what US 805 says is very important: to back of the plank bolts to make sure you allow a slight bit of movement - especially on the side with the elongated hole.
I chose to go with the conventional modern Sarns set up, though there is a weld-failure history associated with them (I have had two fail in 10 years of use)  one took me out of a central region regatta.  I believe, but am not certain that they addressed the issue by using thicker plates, but US 216 and I have taken failed ones, or ones assumed to be about to fail, removed the stud from the plate, then put a hex-bolt through the plate, and rounded off the hex head somewhat to allow it to pull away easier in case of an impact.  We grind a slight hollow in the plank to accommodate the head of the bolt.  when being re-assembled, the bolt head is lightly greased, and then bedded in thickened epoxy, which keeps the bolt from turning, but the grease insures the epoxy doesn't bond enough that it affects the smaller screws hold and should allow the plate to pull out if necessary.