the IOM all have backstays. this allows the mast to bend and also support the mast on the downwind run. the mast on my first IOM was just a pine dowel will lots of bend to it. I used the shrouds and stay to keep the correct about of tension. and it worked fine , the newer aluminum mast are stiffer but they still bend. easily. does anybody know if wing are allowed on the IOM bulb and if so would they be measured strictly by wieght or by wetted surface area? i had this question asked of me and i could not give the proper answer. i think wings are allowed but the bulb cannot acceed 2.4 kg
anybody know the answer?
thanks in advance
p.s. still looking for plans for black majic nzl 32. if they are out there
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Dick Lemke
Hey Rob -
how soft or stiff are the IOM masts? Any measurements of bend at a specific weight/supported length?
am I correct in assuming pretty much all IOM’s use a backstay?
what is generally accepted luff curve for the “A” Rig IOM main?
Thanks
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
All the IOM’s use a backstay but I believe they’re optional equipment.
Most if not all IOMs use a aluminum mast. From there plenty of speculation on what mast is best. In the USA many use the T9 masts without pre-bend. One or two use them with pre-bend (which is a trial and error proposition as there’s a fine line between establishing bend). I have seen but don’t have the info you’re asking about.
Rob
Dick,
The IOM aluminum masts are comparatively soft to most all other rigs. If you tried your old 10# weight at the end, it would just crumble.
??? OK, just ran up to my shop and did a quick experiment that hopefully may help you out here. I took my CF mast from my US1M and an aluminum mast from my IOM and did the following. Note that my IOM mast is a 7/16? which is on the small side. Many IOMs use ?? . The IOM mast is also about 3? longer then my US1M mast, but at least you?ll get an idea here.
I laid each mast, one at a time, across the top of my small tabletop scale. The scale was at mid point of the length of the mast. The distance from the top of the scale, to the surface it is sitting on, in this case is a large jointer bed, is 1 ??. I set the scale to 0 and then pushed down both ends of the mast to the jointer bed and took down what the scale read. So it looks like this?
To put a 1 ?? bend in the CF mast takes 5 lb., 7 oz of force.
To put a 1 ?? bend in the aluminum mast takes 1 lb., 5 oz of force.
The IOM runs very little luff curve, probably less then most classes out there. I?m not sure if it?s in the rules or if it?s just a common practice that no one has ventured from, that?s something you might want to check out. This class generally sails with very flat sails compared to other also.
Added this. By the way I use a small amount of forward pre-bend in my mast. We sailed today in very light winds and in these conditions I keep the mast almost straight. The most I would bend my mast is maybe ?? to ?" before I feel that I?m not really using the mainsail with any efficiency at all. I use sa single set of shrouds (class restriction) and spreaders. I would say that my shrouds connect about 1 ?? aft of the mast. This somewhat helps in keeping a straighter mast
I have never seen an IOM without a backstay either, though on of our members lost his in the Nationals this year and said that the boat sailed great! Go figure. I?ve always told him that I think he sails with too much backstay anyway? (G)
Just another addition to anyone reading this. I remembered that I had a section of 6061 T6 ?? aluminum that I use for my Star. Same length as the 5/16" Bantock mast I tested. Same test and it took 2 lb., 14 oz to bend this mast 1 ??. Another thinner carbon mast came out at 4 lb., 9oz. For the fun of it I did the same for one of my laminated wood mast from a Soling and came out at 4 lb., 12 oz, but you must take into account that this is a shorter mast so I might assume that if it were as long as the others that it might be somewhere around 3 lb. Not bad for wood, and I make’m light! (G)
Dick, I would think that on a multi that you would want a lower aspect ratio mast. Not that I have experience, but it would seem to me that these boats might make a good amount of there own wind. I would just think that a high aspect might just make the boat that much more difficult to sail stability wise. Just a thought.
greg
is that a grooved mast?
i just run a pine dowel for a mast on my IOM. and it does not bend that easy. but when it does. it mach the main perfectly
cougar
No cougar, they are all round mast. The groovies are really flexible. Spaghetti!