Select to expand quote<div>After 7 years on carbon booms with loads less breakages decided to give an aluminium boom a go..after reading all blurb sounded like the 2014 North Silver line was as good as any...At first thought boom was fantastic...lighter than Carbons and very stiff for aluminium... however first time out on combination of said boom and a 100% carbon tushingham (460) I managed to break the mast...first gybe..seemed very little force on mast at time and never use this mast on rough water...(Mast is 3 years old with perhaps 25 usages;little to no wear) At first thought it just coincidence..fragile mast etc etc but then examined clamp/mast connection (Mast broke immediately under boom;exactly in line with base of boom clamp) Putting it simply the mast just does not go fully home into boom cup;it leaves probably a 5mm gap between mast and front of clamp;to me it looks as though any sideways force on mast would be onto a single point at the base of the hinge;other side seems fine..there is a rubber block.. Spoke with retailer and distributor...both sort of blamed mast...100% masts break; and distributor implied the North mast would fit better.. (are modern SDM`s now narrower ???)If this is the case surely boom should come with a warning...not compatible with any mast over 42 mm (a guess) at boom cut out... All my SDM`s (that I have left !!!) are 45 mm diameter at the boom cut out.... There is just no way a 45mm dia mast will go fully into my North clamp... Anybody using North booms I suggest you check your mast diameter. To be fair clamp is extremely well made;strong;easy to use but IMHO just does not fit normal (???) SDM`s. Any comments any body...(Besides stick to carbon booms...but the nort uses same clamp !)
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i believe SDM are about 48mm inside diameter at the base.
Couldn't say at the boom position - but will vary depending on the height you set your mast.
Saying that - if your mast does not fit completely and firmly into the head, then (as you have experienced) you are at risk of breaking the mast.
There is a fair amount of pressure delivered though the boom head so having the maximum possible connecting surface area is crucial to reducing point pressure on the mast.
I think you are right about the 48mm diameter at base but I believe (its case with mine) that in cut out area mast is virtually constant diameter... The point loading issue is exactly what I think caused breakage on 100%...the 75% I used previuosly (in rougher conditions) coped... Spoke to didtributor he suggested/implied the North at cut out is much thinner and fits into cup fully...Thats fair enough an we all know by rights we should stick to one brand to avoid these issues ,having said that surely there is some responsibility on North to say on boom info..."not to be used on mast diameters over (I`d guess) 42mm"..( All my SDM`s are 45mm outside diameter at cutout,including my 430`s and 400`s )
Speaking to retailer it seems the industry are sneaking another "problem" in for us... The majority of his "SDM`s" were what a few years ago would have been called "drops" or even Hybrids...( ie 48 mm base but tapering quickly) Apparently all my masts are now old fashioned ???? The IMCS rating is a sham...and we seem to be getting further away from "industry" standards...on back of development but in essence to promote sales of new kit...
I now have a boom which I have lost all confidence in using...answer from retailer ...change all my masts ????
North seem reluctant to comment. (Asked elsewhere)
I,ve tidied broken mast up so gap between mast and boom front can be seen...problem is shown in side view picture..The mast contacts the boom on a very small area and on to a hrad plastic solid part of boom...as far as I can tell this is exactly where mast broke..it even shows impact damage of same size to area around hinge of boom.
Yeah that looks to be designed for the North drop shape SDM's
they should tell you it is not for use on normal masts. I'd be p!ssed too 
Select to expand quoteMark _australia said..
Yeah that looks to be designed for the North drop shape SDM's
they should tell you it is not for use on normal masts. I'd be p!ssed too
Cheers Mark...Emailed North with the pics and complaint...no reply as yet...old story ...Buyer Beware...thought clamp looked great in shop...didnt check after purchase...windy when rigging....straight out...400 yard swim in...... We live and learn...
Yeah, that's a rubbish fit. They should make it clear that its not for most SDM masts. I'd be annoyed if I had bought it and at the least take it back for a refund. Masts are not meant to be loaded like that.
I don't even use RDMs without a shim, even in booms that are meant to be able to handle a RDM without a shim. The shims spread the load and are good at preventing slip without requiring too much pressure.
Select to expand quoteFormulaNova said..
I don't even use RDMs without a shim, even in booms that are meant to be able to handle a RDM without a shim. The shims spread the load and are good at preventing slip without requiring too much pressure.
I second that Formula. Ever since changing over from SDM to RDM's I've had no issues and I put that down to the two things you mentioned plus the fact the RDM wall thickness is almost twice that of an SDM. When still occasionally using an SDM I use a 1.5mm thick rubber sheet to minimise clamp tension on mast.
Even though somewhat of an oldschool design I think the Maui sails is one of the best boom heads for fitting any mast and spreading the load equally and over a larger area - I know there's a lot that don't like it but IMHO I'm yet to find a better one on the market.
If you clamp a cylinder, having 3 points of contact is pretty good.. I reckon that's how it's supposed to clamp the mast..
Surly someone out there has a North mast they're willing to chuck inside their iFront. See it there's a gap at the front (my bet is there is)
Seabreeze 2014 Angry Mob
Barn,
Those 3 points of load are exactly that - a point load. These vertical point loads to the side of the mast when loaded would easily stress the mast wall beyond the point of failure i.e. imagine Jennifer Lawrence &/or Sofia Vergara standing on you with only the points of her/their high heels or Clive Palmer in some crosby loafers eating a bucket of KFC with Jacqui Lambie on his shoulders. I know which one I'd choose but it'd cause a lot more damage physically (although I'd die smiling). The other whilst not as physically damaging would mentally scar you for life. 
EDIT - beat ya Mark 
^^ and if you spread the same load evenly around the same cylinder it is less pressure. C'mon Barn you know, psi and stuff....
So if all that curve mated against the mast perfectly (ie: any other boom on any other mast) it would have muchly reduced point loading.
My MSPaint crashed so I can't show a diagram.
What about 4 points of contact.. The front and back points receive most of the load, while the outer points contribute to very little.
Even if you found a perfectly fitting mast, the 'psi and stuff' of the clamping force will still focus on a few areas...
The cup for that mast doesn't even look round.. Maybe Floyd can use the rest of the mast and find the diameter where it actually sits 'perfectly' in the front..
Just to counterpoint: My 2014 North Silver on a NP RDM fits like a glove, no Jlaw point loading, just smooth pressure wrapped around that sensual cylinder.
I have a north silver as well, and am here to defend it! (cause I love it) Below you can see that the boom has this inside bit that moves with the whole hinge of the boom clamp.
Looks like the mast might fit in there pretty well aye?
Well it does, snug as a bug.
And when you clamp it closed, even though there may be a gap at the front of the clamp the mast is still supported by the inside bit (dont know the technical term).
If you look REALLY closely (on both my picture and the one provided by FloydVaughn) you can just make out that supporting inside bit holding the mast nicely. This picture is not taken with a north mast - it is in fact a Severne 460 SDM.
Any way, thats my 2 cents, love my north boom and would recommend it to many!
Barn those 5JLaws would not be, they are tangential to the mast so your 100 JLaws on the rope does not equate to the 90 + 5 +5. 5JLaws tangentially, but the actual radial force exerted more like 3 or 4.
Sorry.
But yes, of course no boom fits like a glove. However the point loading there does seem extreme as the mast dia is nothing like the boom head dia.
Unless what JockyC shows is correct, if that inside bit is rigid and offers support then it is a good fit. Looks like it would not, but you can't say until you swing off it :)
Select to expand quoteJockyC said..
I have a north silver as well, and am here to defend it! (cause I love it) Below you can see that the boom has this inside bit that moves with the whole hinge of the boom clamp.
Looks like the mast might fit in there pretty well aye?
I believe this inside bit is only there to close the clamp (to avoid putting your hands in the luff of the sail trying to close it) but doesn't provide any support.
IMO only the Mauisails and Streamlined offer perfect contact.
The section of mast in earlier pictures is where boom goes. (45 mm outside diameter) I cut broken section off and tidied edges for examing /showing clamp...
Current photo shows mast OD of 41 mm (I slid tapered top section in) This is as fit should be..I would assume the Northy mast is around 41 mm diametewr at boom cut out. ???
Thanks for interest everybody...
To be fair retailer was good...didnt acknowledge fault as being with boom but heavily discounted next purchase...(you,ve guessed, a mast and boom, oh and a new board)
From my limited knowledge...carbon fibre will not tolerate any sort of point loading, be it single or as in some diagrams 3..or is it 5 ??
There will be instances when all force is on one of the single points...it was telling that mast broke on tack that would have loaded the mast onto harder section of boom, I`d gybed on other tack (loading rubber block) no problems...
Think its fairly obvious now boom simply does not fit this diameter mast...A point North/Retailer will not acknowledge. But I should have checked... So ultimately its my resposibility...
Still awaiting reply from importer..he isnt returning calls now....Blamed mast on first conversation. Think I`ll modify boom ????
PS Anybody using Silverline boom on standard SDM`s check inside of your clamp. You will see a small area up one side of clamp marked in black from mast abrasion (on opposite side to rubber block)..This represents the small area actually in contact with your mast. Think if you are on 75% and below there`s no problem but there is no way I would use a 100% mast in there again...likely scenario ??? Mast breaks..retailer blames mast and sell you a North...thay dont suit your sails perfectly...so then next sail change you buy North sails ??? Might be cynical but it would be so easy to make this cup fit "standard" SDM`s... Would be even easier to tell folk its not designed for masts over 41 mm or so. (at cut out)
