DN NA Class

Progressing with my build and ran into some issues:

Halyard catch position- When the sail is hoist to the highest position as dictated by the balls on the halyard, should there be any space between the halyard shackle and the sheave on the mast top or should the shackle be snug against it? When raising the sail to the highest position should the shackle be in the innermost (mast side)or outermost (leech side) headboard hole for purposes of positioning the catch?

Stud Plate/Fuselage Plate Installation Sequence- Which should be installed first, stud plates on the plank or the plates on the fuselage? I’m using double stud plates and the tolerance with the fuselage plate holes is tight, making alignment critical. I can drill the nut clearance holes in the hull and then position the fuselage plates by placing them on the stud plates previously installed on the plank. Alternatively I can install the fuselage plates and then use them to position the stud plates on the plank. Both sequences seem to offer the same alignment challenges but I wonder if I’m overlooking something obvious to more experienced builders. Also, I'm assuming that the "flange" on the stud plates should be positioned pointing out towards the ends of the plank so as to prevent wear and tear on the plank when it flexes against the fuselage plates. Correct?

Bob Stay Post Height and Bracket Position- the post I have protrudes about  4 ½ “ (standard Sarns dimensions)  from the socket. I think the rules say the post must be a minimum of 3”. Is the longer post a problem? I know it is a stronger arrangement but I’m wondering about clearance. This is going on a Goodwin hull, which has a clearance of 1” above the rules’ datum line. I also realize the clearance is affected by plank deflection, which at this point is largely unknown. Is there enough play in the cable adjuster to accommodate a smaller post if I cut the post down after installing the bracket?

Sail Outhaul Bracket- I’m stumped on where exactly to install this. I’m going under the idea that I should raise the sail in the mast and boom, install the tack bracket in the appropriate position on the boom and then stretch the sail to the end of the boom. After that, I’m not sure how to proceed. How tight should I stretch the sail and where should the clew grommet be relation to the keeper pin in the outhaul bracket?

If you’ve made it this far thanks for bearing with me and, as always, any and all thoughts are appreciated.

You certainly should leave enough room between the shackle and sheave so that you're not pulling the shackle tight against the sheave in order to get the top ball out of the catch.

What kind of mast do you have? 
If it's bendy, then something to consider is that you'll likely want to drop the sail down a few inches much (most?) of the time.

I don't have double studs, but I'll give it a shot.

Are the holes in both plates round?  On the single-stud system, one side is slightly oval to allow some tolerance.
When the plank flexes, the studs move inwards a bit, so you want to have the "no load" location near the outside of the oval to allow that motion to occur.

I have a jig for drilling the holes for both sides of the system, but before that, I always mounted the hull-hardware first, then used that to determine where the plank-hardware went.  It's a PIA to try and mark the location of the stud-plates then remove the hull so you can drill the holes and mark them.

It's also possible to set the hull plates 16" apart and do the same thing on the plank (that's essentially what my jig helps with).

I'll be interested to hear what other builders have to say on this topic...  :-[

I've always just used the standard Sarns parts "out of the box"...

No clearance problems on flat and Goodwin-style hulls that I've ever seen.

Most people these days use some kind of threaded outhaul adjuster with a slug/car that rides in the bolt-rope tunnel in the boom.  That makes adjusting the outhaul tension easy.  With a multi-hole plate it can be a challenge to pull the sail taught and then insert the pin.  It also assumes the tunnel is strong enough to hold the leech loads.

What kind of boom do you have?  Wood?  with and aluminum tube?

If you need an outhaul bracket to transfer the loads from the sail to the boom itself (or for some other reason), I'd use the procedure you describe.  Make sure the forward-most hole in the bracket is at the lowest-tension setting you would ever want, and that the aft hole allows you to pull the foot very tight.

    If you set it up so you have another 1/2-3/4" of threads left when the cable is tight using a standard length bobstay post, you can shorten the post to min. legal and still be able to tighten the cable. I have a flat bottomed boat and it works fine for me so I'm sure a curved bottom would be the same.

I just set up a spare boom on the cheap. 

For the outhaul, put a bracket, made from aluminum angle or flat stock, with a 5/16+ hole .  Mount it so that the hole part stands vertical and the hole is just above the top of the boom. on the outboard side. 

Then get a stainless threaded hook or eye bolt from your local hardware store in 5/16, plus a wing nut.  Open the eye so it can easily engage the grommet on the luff of your sail.

When the sail is up and the boom is on, just engage the hook and tighten the wing nut to adjust.

Being a bit a. retentive, I put a lock nut on the end of the eye bolt or use a nylock wing nut so it all stays on when the boom is off.


A bit more elegant is to use a car in the sail track that is threaded, and have a bolt with a knob that goes into the car.  The bracket as described above is mounted so the bolt is in the sail track, and the adjustment is by twisting the bolt to pull the sail track back.  This is cleaner, nothing sticks behind the boom, but it requires special hardware and room for a shackle to tie the car to the sail.  It won't work if your boom is just long enough for your sail or was built for the many-hole end bracket.

Thanks for all the input and new ideas.

My boom is wooden with a CPVC track and completely buried in the wood so it should be strong. I've got the many hole bracket so I'm going to install that and see how it goes.

The double stud fuselage plates are perfectly round and have almost no tolerance so alignment is critical. After reading the good advice here, I think I will install the fuselage plates first, dab a bit of epoxy on the plank plates, line everything up and then bolt in place after the epoxy cures.

Bobstay will stay long for now unless my gross tonnage overwhelms the plank.

Stay tuned, building fans! More exciting questions on the way...

You may find it helpful to tie a loop of thin rope (~3/16") through your sail's clew-grommet so you have something to pull the foot tight with while you're pushing the pin into the desired hole.

Post some photos!  ;D
(the "Additional Options..." link below the message window reveals options for doing that)

Cheers,

Geoff S. - US-5156

The basic idea with the hull plates and stud plates being screwed to the hull and plank is that the screws should pull out when in an accident so that the resulting damage to hull and runner plank is minimal.  If you epoxy the hardware in place, it won't break loose and the hull or plank will be damaged more severely.

In actual use, I've never been able to get the screws to pull out and when I hit holes in the ice the plank was broken.   

I'm sure others have had better results with the break away feature.

....DN 805

Jane's comments are spot on (as usual).  ;D

I was thinking that a couple of dabs of 5-minute epoxy or the like - just enough to hold the plates in place as the hull is (carefully) lifted off after squaring the plank to the hull.

Jane's comment about the attachment strength is particularly good.  Even since I saw the (extensive) hull-damage to a friend's boat caused by the hardware staying attached to the plank and ripping through the bottom of the hull when the hull-plates ripped during an "interaction" with a crack, I have been working to make the plate-to-plank attachment the "weak link" in my system.  Specifically, I use maximum length screws to attach the hull-plate and relatively short screws to attach the stud-plates to the plank (I think 3/4" flat-heads).  This worked well in my crash at the NAs last season when there was no damage to my hull or plank other than bent screws (and a sheared-off stud).

There were some good comments on this topic in a thread last fall: http://dnamerica.org/forum/index.php?topic=622.0

I'm now following Paul's suggesting of building up an epoxy ridge around the hull-plates to help take some shear forces off of the screws.  Time will tell if that is an improvement; so far I've only sailed the boat one day...  :-[

Cheers,

Geoff S.

Yes, good point about caution when attaching plank/fuselage hardware.
I was planning using only a couple of dabs of 5-minute epoxy, just enough to keep the plates in place while I screw them down.
The fuselage plates are attached using #6 3/4" screws. I think the plank plates are drilled for #10 screws. Any recommendation on the length? I was thinking the longer the better but now I'm not so sure.

I'll post some pics when I get this finished. For some reason I hate showing my work in progress.

I'll be interested to hear what others do, but this is my current system...  (YMMV, as they say)

A standard cockpit floor is about 3/4" thick (5/8" core/listings and 1/8" skins on the top and bottom).  I've been taking 1" flat-head screws (which end up with about 7/8" of threads) and grinding the tip off so they just barely avoid breaking the cockpit floor (sometimes not so barely...  :-[).  I usually "tap" the pilot-holes with an unmodified screw because the self-tapping action on the clipped screws isn't that great.

#6 screws seem awfully small-diameter to me.  I think I'm using #8s for both the hell and plank hardware (but they might be #10s - I'll try to remember to check next time I'm in the shop).

I'm not sure what length screw I use in the plank, but it is short - probably 3/4" flat-head (which has about 5/8" long threads).  There's lots of holding power in a solid-wood plank, esp. with Ash skins.  I've been using short screws for a couple of years now, which included the high-wind, super rough ice at the 2008 NAs on Lake Pepin.  So far I haven't had any problems; things mostly held together in my crash last season, so I'm getting increasingly confident with the system.

Cheers,

Geoff S.

You really don't want to go over board with the size and length of screws for plank or hull plates , there will be less damage  to wood if using smaller screw. I had a head on collision a while back where another boat out of control hooked runners going in opposite directions. Plank came off the boat with no damage to hull plates or plank , screws were sheared off stud plate. I originally put hull plank screws in with epoxy 10 years ago still holding, stud plates I just screw in . You need to check the screws from time to time to make sure they are still tight. I remember Bob cave taking his hull off the plank after a day or sailing on corn cob ice and his hull plate swung down attached with 1 remaining screw.

I've got seven screws per plate. The reason I used #6's is that is what fit flush in the countersink on the plate. I suppose a small amount of protusion would be OK so I'm going to replace with #8's. Seems like the trick is to find the sweet spot of holding enough but not too much...

I've used #8 flathead screws.    I think they were 3/4" so they wouldn't poke through the floor of the cockpit.     #6 sounds too small for me.     Must also add that the blocking under the floor where the plates are mounted is sitka spruce, which allows the screws to bite in.  The runner plank is solid and ash on the top, sitka spruce in the center.  The screws bite into the ash very nicely.

DN 805

I am more conceerrned about the comment that teh hull plate holes are all round.

When teh plank flexes, teh studs get closer together.  Measure the distance between them, thne stand on the plank and measure--and teh plank will bend more in a big breeze.  In my experience, the difference is on the order of 0.25 inches.

Whether bought or fabricated, my hull plates have oval holes on one side.  This is to accommodate the stud(s) moving when the plank flexes.  It only takes a few minutes with a rat-tail file to elongate teh holes toward the boat center, and some attention to make the holes round enough to really let the studs move.

Another thought to the "weakest link" is Nylock nuts.  No problems with the boat/plank coming apart when it shouldn't and has saved many hrs in overnight boatwork over the past few years when it needs to.

 Happy New Year, Chad

Canny observation, Ken and one I hadn't considered. Definitely going to get out the rattail and have at it, as needed.

Chad, when you say Nylocks, are you talking about an all-nylon nut with no metal? This sounds like a good idea especially since I will have the holding power of 4 nuts instead of 2.

yup,   I  use single studs  and it has been fine.  Buy a bunch since they will strip and wear out if you try and tighten them down or if you just get to sail alot!

Good Luck,  CA

The "holding power" of the nuts isn't really an issue.  Once the rig is up and tensioned, the nuts aren't doing anything (you could sail without them).  As Paul points out in the other thread, you actually want the nuts to be loose to allow the studs to move as the plank flexes.

Many people sail with plastic nuts exactly so they will be the weak link and allow the plank to pull away from the hull in a crash.