Idea for Plank attachment plates for the hull & plank

[DN5135]

Has anybody tried to us fiberglass in place of stainless for these? I was thinking these would look cool and by bonding them to the hull they would be very strong as well. I have a bit of prepreg on my hands that I could bond to the birch ply bottom while curing. I was thinking of doing this prior to applying the west epoxy over the skin. I could also apply a layer of carbon.

On the planks, I was considering using filled west epoxy to bond some special cold headed studs I have from work. These are stainless and have a thin head about 1" in diameter. After they are epoxied in place, I was thinking of reinforcing them in place with a strips of the same prepreg. This would be bonded to the plank skin. My belief is this approach will be very strong and by not using fasteners in either the hull or plank, I should be avoiding stress concentrations that would be occurring at the point loads generated by the fasteners.

Another advantage of this approach is that the glass beams that would be created on the plank and hull would space the plank away from the hull so that as it flexes, the glass would take up the movement and prevent bending stresses in the hull. sides and bottom.

[Geoff Sobering]

I'd be hesitant to bond the plank attach hardware to the hull.  In my experience it's almost a consumable; I think I've replaced three sets of hull plates in the past seven years or so.  I'd be a little concerned that if you tightened the nuts down a little to much the flexing of the plank might crack the composite plate (or even the bottom of the hull where it's bonded).

OTOH, I also regularly replace the screws that hold the plates to the hull, so a bonded solution does have some appeal from that perspective.

Re: the hardware on the plank.  IMHO it's better to have the attachment between the plank and its hardware be the weak link.  You will rip the plank off your hull someday, and attachment systems that allow that to happen with the minimum damage to both the hull and plank are desirable (ex. see some of the bungee-cord systems).  If the hardware pulls off the plank then there's less damage to the bottom of the boat than if a stud arcs across the bottom skin gouging a long deep gash in the plywood and stringers.  If nothing in the attachment system gives way, then the next weakest link is the hull itself... (although you could mitigate that with plastic nuts that would probably strip before much damage was done).

I'll be interested to hear what others' opinions are about hull-plank attachment.  There seem to be a number of methods in common use (stud plates, double-studs, center point bolt with cleats, bungee and cleats, ...).

Cheers,

Geoff S.
US-5156

[Paul Goodwin - US 46]

I've used a lot of plank attachment systems over the years, and have settled on the stud attachment (per the class plans).  As Geoff points out, this system allows the plank to be ripped off the boat with only minor damage.  It may not look minor when it happens to your pristine boat (chunks of plywood and cockpit structure ripped out of the boat, broken screws, etc), but it can be repaired easily overnight in a motel room, you might even be able to put it back together in between races

When I put the plates on the hull and plank I do a few things to make life easier:
1) Wax the screws.  I put the screws in a little paper cup, throw in a little dab of paste floor wax, and hit it with a heat gun.  When the wax melts, shake the cup up, and dump the screws on a paper towel to remove the excess wax.  When you put the plates on, predrill the screw holes and coat them with epoxy (pipe cleaners work great for this).  The wax will allow you to get the screws out later.  (By the way, I do this with all screws on the hull.)

2) Geoff mentions having to replace the screws regularly.  I have found that stud plate screws loosen for one main reason - as the plank flexes the distance between the studs changes.  If your both of your hull plates have holes, then when the plank flexes something has to give, and it's going to be the screws.  The hull plate on one side should have holes, the plate on the other side should have slots - if you don't have slots on one side take a file and (very) carefully turn the holes into slots.  The slots don't have to be very long, maybe 1/8" or so.  Try leaving the nuts off, weight the boat to flex the plank way down, and look to make sure the stud doesn't bottom out on either side of the slot.

3) Now that you have plates with slots, you can lock the plates down solid so they don't move around.  A method that works for me is to brush a thin layer of epoxy on the plank and hull, and screw the plates into the wet eopxy.  A small bead of epoxy will form around the outside edges of the plates and lock them into position.  In order for the plates to move, they have to shear off this epoxy bead.  Now you can just look at the the epoxy bead when you take your boat apart to tell if the plates have moved.  This also takes the shear load off the screws.

4) Don't tighten the nuts all the way.  As the plank flexes, the stud angle changes and if the nuts are tight they will flex the hull plates and tear things up.  I tighten mine down and then back them off about 1/2 turn.

[Geoff Sobering]

3) Now that you have plates with slots, you can lock the plates down solid so they don't move around.  A method that works for me is to brush a thin layer of epoxy on the plank and hull, and screw the plates into the wet eopxy.

As always, good system.
Do you do anything like wax the hardware to allow it to be more easily removed?

Cheers,

Geoff S.

[Ken Smith]

I agree with Paul.  I still need to re-do screws.  Runner-ice chunk (that is it, I swear) collisions load the plates in shear.  The counter sunk screws tend to get lifted, bent, and occasionally broken. 

There is a very neat system developed by some of the guys in Maine, and if I can ever get a few pictures I will try.  They take a ball-head mill and mill (or mold) a half-sphere indent in the hull bottom and in the plank.  Two are on each side.  Then four 3/4 inch plastic balls (hardware supply house) sit on the plank and engage the hull.  The hull almost snaps in, I am told.  The whole thing is held together with 3/8 nylon bolts, one per side. 

The balls take all the load,  as most of the force pushes down on the hull.  In a plank-ripping event, the nylon screws break, and no damage anywhere.  Drive a screw driver into the top of the broken bolts and screw out the remains, add four new balls and two new bolts and you are back on the course.

Sounds great.  I hope some one who has tried it writes in the forum!

The Poles use a carbon composite bottom plate.  It screws to the hull for fore-aft plank location adjustment.  The plate has a molded in block fore and aft to constrain the plank.  In the center of the hull is a single 5/16 (7 mm) round head bolt through the hull and plank for side-to-side restraint.  The hull hole has a brass or plastic bushing as large as the bolt head.  In a plank-off, the bushing pulls out and the plank either trips (usually) out of the plate or the plate pulls the screws out of the hull.  On -ice fix:  Move the plank to a different position.  In hotel fix:   Epoxy a new bushing and patch the plate screw holes in the hull.

The  common thread is that when the plank comes off, there is a structural fuse.  Fix the fuse, not the whole hull.
Ken

[Ken Smith]

Mikey uses a composite plate .  The plank is attached and retained with hefty wire ties.  The nylon wire ties break in a plank-off.  I don't know the details.

[DN5135]

Ok, I get all the points, I just don't see where a little f/g in place of stainless is any different except when it rips off, it will go in a sheet. I was trying to avoid the screws tearing out of the hull and plank. I was intending on making the plank side attachment permanent and the hull side the part that tears away. Also, the plank side method would create a rail area on each side of the hull for the plank to rotate on as it flexes thus reducing the twisting stress on the hull. I also have had the hole one side slot the other concept and generally keep the nuts loose.

I guess the question is, will the glass to plywood bond be too strong? 

I already have 4 1-1/8" holes drilled through the cockpit floor on each side for multiple plank locations, another thing I considered was making snug fitting UHMW Polyethylene bushings with a light flange and spanner holes for each side. In this case, the bushing would pull through before anything breaks. It seems like all the forces during normal use would be torsional...ie tending to twist the plank during turns. Also, the plank is pushed into the hull therefore a strong bolted connection isn't really needed. I still need to build in some tol for the movement during plank bending with this. Hey...several months left to think this over !!


There are a lot of choices, I just don't like the looks of the stainless plate screwed to the hull and plank and the idea of it ripping apart and splintering the boat bottom isn't that pretty either.

[Bart POL221]

hello
I want to mount my plank to hull. And I'll be happy if I could do that without breaking the DN class rules.
Hull is fresh tuned by me to attachment metal plates/one bolt per side.
Plank is ready( incl. bearing plates from epoxy) to drill the holes.
I got stuck because I can't find dimmensions:(
photos:
- the hull     https://picasaweb.google.com/bartanonim/Warunki#5575826788998928338
- plates       https://picasaweb.google.com/bartanonim/Warunki#5575837650227484146
My questions to You:
1. 16" dimension for bolts, is this a rule or can be less (like about 1 inch per side) ?
2. I need starting dimension from front of the hull  to first plates hole. Majority has got 4 hole plates in hull.
I found different dimensions in DN sheet plans (102 3/4 inch in english plans but in polish translation is 246,4cm to 261,6cm)

thanks in advance 

[DN 805]

DN specification I.15 controls the runner plank mounting hardware
DN Specification F.1 controls the fore and aft location of the pivot axis of the side runners.     You must make sure that when you have mounted the runner plank to the fuselage that the pivot axis of the side runners complies with F.1. 

If you are meeting the requirements of I.15 and F.1, you will be OK.

I hope this will be a help to you
Jane Pegel. chairperson, IDNIYRA Technical Committee

[Bart POL221]

Thank U for Your qiuck answer and clarification about rules.
I know it could sound silly but I can't understand that part (block capitals):
I.15.b) the runner plank mounting system shall be located
in area does not exceed 30" IN THE FORE AND AFT DIMENSION.

The whole thing is that my fuselage is thin and dimension from DN plans (16") is too large for my hull.
Can I give plates more narrowly ? (about half inch per side)
and additional question:) I found on Sarn's site plates:
http://www.sarnshardware.com/store/products.php?pid=40&detail=true
should I have oval holes in both plates (both side or just one side like it's shown on picture)?

I'm doing side mountin system for the first time therefore I'm asking

best regards

[Bob Gray]

   There is no restriction on how far apart the plates can be, on one of my old boats I had to place them about 15 inches apart. 16 inches is kind of an unofficial standard, it makes it easier to swap planks around between boats.
                                                         Bob US 65

[Paul Goodwin - US 46]

Hello Bart,

I.15 -- Because the DN class does not control how the plank is attached, the design of the mounting is very different between many DNs.  This rule is to control the maximum size of the mounting hardware.  When the plank is mounted on the boat, the size of the mounting hardware must be no more than 30" fore and aft.

The 16" between plank mounting studs is not controlled by the DN class.  You can make this dimension anything you want.

The Sarn's plank mounting plates are very simple, and work very well.  The oval hole is only on one side.  This lets the stud on one side control the location of the plank, and the oval hole allows the stud to move when the plank flexes.

The distance for the plank mounting holes is based on the distance between the front and rear runner pivot bolts.  The DN class rules specify 97"-103" (246.4cm -261.6cm).  However, these are the maximum allowed positions.  You need to allow some reasonable tolerance for these positions on you hull.  The DN class plans show position for the holes which allows 1/4" for tolerance at each end (97.25" - 102.75").

Hope this helps...
Paul Goodwin