MX 14 Fin

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David L Alston
Posts: 72
Joined: 24 Jul 2012, 17:38
Sail number: 3011
Club: Leicestershire RYC UK
Design: Fatboy

MX 14 Fin

Post by David L Alston » 16 Oct 2014, 15:28

I need some help please.

The MX 14 has a rectangular fin box and the fin transitions to rectangle at the hull... Ok

So when I put the fin in the fin box the step of the transition is more or less flush at the front but the is a 2.5 mm step / gap at the rear.

Clearly this is most undesirable and will have an adverse effect on performance and my winning the world championship next year.

So the question is :-
Is the fin box incorrectly fitted and raked forward

At the moment the fin appears to be raked 1.0 mm forward if I use the datum water line as the transom edge and the point on the bow where the bumper ends on the hull.

If I were to correct the fin so it fits flush with the hull - the fin would be raked back about 6mm of vertical for the same water line datum. This process involved filing the fin edge down on one side and filling the other side.


I could leave the rake as it is and simply flare the transition step to meet the hull.

I do not know where the design datum line actually is.

Clearly the boat pitches forward under sail down with but pitches back on the wind - however the bulb position is more or less fixed and the rake will determine where the boat balances on the water.

What do you think ? or better still what did you do ?

They must all be the same or are they ?
.
.

Dave Pickett
Posts: 107
Joined: 18 Oct 2010, 19:33
Sail number: GBR3845
Club: Eastbourne
Design: TS2 and Shiraz

Re: MX 14 Fin

Post by Dave Pickett » 17 Oct 2014, 10:59

David,

Cant help as such, but there is another MX14 in the Eastbourne club which even if not being sailed will be in the clubhouse which you could have a look at. I will be there first thing, will pop along and say hello.........

Colin Helliwell
Posts: 24
Joined: 18 Jun 2014, 18:44
Location: UK

Re: MX 14 Fin

Post by Colin Helliwell » 27 Oct 2014, 17:46

David L Alston wrote:I need some help please.
Yes
A 6mm rake, and after some filing, surely can't be right - that is a lot. Have you checked with them though? It'd surely be weird if this was their normal quality level, so maybe it was just a duff batch? [a Friday afternoon run...?].
It's all small businesses in this kind of sport, so I reckon most are also enthusiasts and will try to rectify a serious customer issue - there can't be any harm in speaking to them? [But btw: if this is MX in Italy - who I just happened to have bought a winch from - then whilst their English is okish, and better than my Italian (mea cupla), I'd advise keep the language/grammar basic and the conversation will go more easily! :) ].
Seems odd that something in production should be so hugely out of kilter - annoying. (Not to mention the vexation of it trashing your Worlds title - but hopefully the SI's will have a clause to claim redress for building your boat wrong? :wink: )

Col

John Hanton
Posts: 2
Joined: 27 Oct 2014, 23:21
Sail number: GBR3115
Club: Norwich
Design: Corbie

Re: MX 14 Fin

Post by John Hanton » 27 Oct 2014, 23:54

Hi David, I would consider 6mm rake at the bottom of the fin to be pretty normal, my home built IOM has this when made to the designers spec. Don't thing the MX14 plans are available to view but the Goth plan certainly shows raked fin. Up to you to decide whether to modify the fin to make it right or ask the builder for advice. My italian is non existant too.
regards,
John.

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