A couple or three questions on mast construction

[DNewbie]

I've recently built a mast according to the Goodwin plans on the IDNIYRA site. I want to put some extra reinforcing around the area where the boom jaws hit and I'm not sure how much area should be reinforced. I've got a sail and can see where the highest point of reinforcing should be but I'm not sure about the lowest. I don't yet have a halyard so I don't know how low a halyard can adjust the sail. Is there a standard amount of adjustment? I didn't see anything in the rules.

Also, the yearbook plans, which briefly describe Goodwin's mast plan, calls for two tows of CF top & bottom. I've got the mast wrapped in 6 ounce FG. Is the CF neccessary? When the plan says "tow" is it referring to a standard size? My concept of a tow is a little hazy.

Lastly, Goodwin's plans call for a sail entry slot 10" from the base. This seems a little tight for raising the sail. Any problems putting this higher as long as it's below the lowest position of the boom jaws as dictated by halyard adjustment? Any and all comments are welcome.

[Geoff Sobering]

Lastly, Goodwin's plans call for a sail entry slot 10" from the base. This seems a little tight for raising the sail. Any problems putting this higher as long as it's below the lowest position of the boom jaws as dictated by halyard adjustment? Any and all comments are welcome.

Depending on the mast's bend characteristics and how you tune the boat, it's not unusual to have the boom pulled down so far that the standard Sarns fitting for the block on the tiller post is too high.  Many sailors these days have switched to hardware that mounts the block just and inch or so above the deck.

I don't have a good photo of the feed on my Jeff Kent mast, but it appears to be about 10" from the bottom and even with the standard mainsheet block hardware, I sometimes pull the boom below it.

FWIW, it's not generally much of a problem, because the boom shouldn't be bearing on the mast much (at all) when you're sheeted in hard (the boom generally is pulling back to de-rotate the mast).

Cheers,

Geoff S. - US-5156

[DN 805]

Ideally the boom jaw will never touch the mast.   The jaw should have a very wide radius so that when the mast is rotated in the sailing position the jaw does not touch the mast.   Then position the tack fitting on the boom so that as the sail hangs at rest you can put your middle finger between the jaw and the mast (very scientific).   Make sure the mainsheet line as it passes up from the ratchet block on the tiller post to the forward boom block is running parallel to the back edge of the mast, i.e. the luff of the sail, so that when you trim you are tensioning the luff of the sail.  If you move the mast a significant range on the mast step, you may need to reposition the forward boom block to keep the mainsheet line parallel to the aft edge of the mast.   Then position the back boom blocks so the parts of the mainsheet line run parallel to each other and pulling back slightly.  As you fine tune the boat you will find the sweet spot for the blocks.  The goal is to have the back boom blocks nestle down between the back deck blocks when you're trimmed hard, this gets the back of the sail on the centerline of the boat and generates the best performance. 

It's a never ending process of "tweeking" the boat to get it perform to the ultimate.   When you get it zeroed in, it's a real blast.

DN 805

[Ken Smith]

Notes on the lay-up.

When Paul did those plans, Carbon Fiber was hard to find.  Gougeons sold carbon tows in a ribbon, and that was the easiest accessable source.  It was a heavy fiber.  Now Carbon can be found from many sources, including UScomposites.com and any experimental aircraft materials suppliers like Wicks, Aircraft Spruce, and many more.

To answer your question:  Pauls wood mast required carbon to be stiff enough and to be durable.  If you ended up with a thicker than planned mast, side to side, then you might get away without.  For a while.  Maybe.  The DN mast goes into bending and this is on purpose to work with the sail.  Full camber as cut with the leech tight and the mast straight, and very flat with the mast bent out.  Less drag and power for when your relative wind is mostly because of your excessive speed.  If the mast won't bend, you will never go as fast or point as high as the boat is otherwise capable.  You'll have great fun, go fast and thrill yourself... until you sail with a well tuned DN. 

If built well and properly tuned with uni-directional fibers on the side, as on Paul's plans, the mast will work well.  Unidirectional fiber 1 inch wide and with a heavy weight, or a lighter weight 2 inch, should work well.  Back in the wood mast day, we built them a bit light on reinforcement, bent the mast and then added more to get the desired deflection .. Remember, the three feet halfway between the base and the hound is the spot that sees the most stress. 

Look at collective wisdom (dnamerica.org and click on the archives) and you will find lots of info on mast deflection and how to do that... But if you sail it hard, it won't last long.  Hence the love of composite masts.  They work well and can last long.

Ken