DN NA Class

I’m building a wood mast using the yearbook plans and Paul Goodwin’s article titled “A Wood Mast Made Easy”. I currently have both halves of the mast constructed and am ready to glue them together. I have a couple or three questions about details that I’m hoping some of you knowledgeable builders can answer. I’ve never built a hollow mast w/internal halyard before so I’m a little fuzzy on the details.

The yearbook plans call for a fixed sheave on the top of the mast. From the pictures this appears to be a sheave cut in half and then, I guess, screwed/glued to the wall of the mast and then packed out with epoxy/microballoon mix. Is this correct? The sheave looks to be about 2 ½ inches in the plans. Does the size matter? I’m guessing bigger is better up to a point. How about material? Does this need to be marine grade or can it be something from a HW store?

Goodwin’s article suggests using an external hound for ease of construction but the yearbook plans indicate an internal hound. I would prefer an internal hound for looks and an all around cleaner mast. The yearbook plans suggest two layers of FG tape under and over the flanges of the internal hound but I’m having a hard time imagining the sequence of steps that would allow me to get tape over both flanges at the same time that I’m gluing the mast halves together. Anyone ever tried this? If so, can you describe how this is accomplished?

Last question is about the luff tube. Both plans call for aluminum tubing, with Goodwin’s article stating that the aluminum tube is necessary for mast stiffness. However some posts in the Collected Wisdom advise that aluminum is not a good choice due to thermal instability. Suggested alternatives are PVC or fiberglass tubing. Will either of these be rigid enough? I would like to use FG tubing for superior bonding but I can’t find a source in the NYC area. Anyone know of a source for this?

Thanks for reading this long post and any advice you can send my way!

 I have external hounds available. Much easier to install just add a little blocking for screws.As far as a sheive, I use patio door rollers you can get at Home Dump or your local hardware store. You could install it after the mast is glued together.I built the Goodwin design several years ago and used aluminum tubes. Problem with the aluminum is it shrinks in cold so mast will curve back abit. also not easiest to cut slot in. You might want to use pvc or the fiberglass tubes that you can get from Ron Sherry.Ive used pvc in a number of composit masts work just fine dont add as much stiffness as fiberglass or aluminum  but you can add glass or carbon to outside of mast later,you need to sand the pvc with course paper to get good adhesion with the epoxy. The pvc is cheap and you can get at hardware store. The inside diameter id larger than fiberglass tubes so sail goes up easy. The fiberglass tubes are smaller diameter and will cost more. If you are worried about stiffness, dont.Since Paul wrote that article the rules have changed and  you could add carbon or glass on exterior to get stiffness you want.We used to try to get proper stiffness with internal layup and I think the carbon wasnt allowed on exterior,I may be wrong but now you can build a mast out of any material as long as it meets overall dimensions and balance specs.
If you need a external hound or have any question feel free to give me a call.

Bob Rast
DN1313
414-791-3056
Robertrast@aol.com

I have a tag on question...If you can now build a flexible wood mast and use carbon & glass to strengthen/stiffen as needed, for the home builder, is there any advantage to the composite mast if the wood one is easier to build?  It would seem like allowing the glass and carbon on the outside would fix the durability issues of the past as well as the stiffness predictability issues.

I've built wooden DN masts of strip and Goodwin design, and remember the painful rules migration path, from wood, (but not veneer), to ok some fiberglass, to glass, to what we have today.  None of the masts I built exist today, except the surviving halves of one cut up as trophy stock.

If memory serves, the year Jeff Kent won the worlds on Lake Geneva, (in the wood mast days) about half the gold fleet suffered at least one DNF due to mast failure in one day.

Wood spars have a high mortality rate, Competing a DN actively with a wood mast is a two spars a year program, the composite spars have a much much lower failure rate, I understand the Jeff Kent, CSI spars have a mortality rate near 0.  From a total cost of ownership viewpoint, that's ton's cheaper than wood if you sail. 

In the roughly ten years since we began allowing fiberglass/composite spars, I've lost only one composite spar, due entirely to personal greed for speed on the racecourse, that is, I suspect there isn't a DN mast that I couldn't have pulled down on that leg of the course.

Then there's that speed thing... tuning a wood mast is a lengthy process, and it's always done post production, putting the glass/carbon (don't be sanding carbon) on is fast, sanding it back until it's happy isn't.   The composites by almost all makers have standardized deflection characteristics that are substantially defined in the layup process.

To Bob's construction tips, the patio door rollers work great for a sheive, and pvc is just fine for a luff tube, (aluminum luff tubes/wood spars together make a large and pretty good thermostat, aluminum and carbon fiber combine to make a pretty good battery).

Following a few seasons of a mast experimental policy, careful study led sailors to the conclusion that the failure of masts that had wood in the side walls, even when supplemented with carbon and/or fiberglass, was attributed to failure of the wood component.  Therefore the members approved an amendment to the specifications so that wood is no longer a required element in a mast.  The result has been fewer failures (by a factor of many-fold), and boats the are easier to sail, more responsive, and faster.

If buying a new composite mast is beyond one's budget, then look for a good used mast.  Ones become available at very reasonable prices.   It's well worth it.

...DN 805