[Rhodes22-list] Switching from standard mast to IMF

[ROGER PIHLAJA]

Hi All,

It occurs to me that this standard mainsail to IMF mainsail switch is something that other owners might want to do.  We should document the factory forestay lengths to facilitate this switch.  For the record, the pin centerline to pin centerline distance on the forestay on my 1976 standard mainsail Rhodes 22 is 333.625 inches.  Would somebody with a factory installation of the IMF mainsail make the analogous measurement of their forestay?

Roger Pihlaja
S/V Dynamic Equilibrium

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From: Roger Pihlaja<mailto:ROGER_PIHLAJA at MSN.COM>
Sent: Thursday, October 14, 2021 10:40 AM
To: The Rhodes 22 Email List<mailto:rhodes22-list at rhodes22.org>
Subject: Re: [Rhodes22-list] Switching from standard mast to IMF

Mitch and Stephen,

The standard mainsail has more roach vs the IMF mainsail.  If you drew a straight line from the head to the clew on the mainsail, the sail area aft of this line is called the roach.  Roach sail area requires battens to prevent it from curling to leeward.  Since IMF mainsails have no battens, they can’t have much roach.  Since the roach sail area is at the aft edge of the mainsail, it’s presence in the standard mainsail tends to move the Ce of the sail plan aft, thus increasing weather helm.  All else being equal, the IMF mainsail would need to have more mast rake to compensate for the lack of roach and restore neutral helm.  ( i.e. needs a longer forestay )  If you used a standard mainsail forestay with an IMF mainsail, this analysis would predict lee helm, exactly what you experienced.

Roger Pihlaja
S/V Dynamic Equilibrium

Sent from my iPhone

> On Oct 14, 2021, at 8:17 AM, Stephen Staum <snstaum at gmail.com> wrote:
>
> I put the IMF mast from my '87 onto my non IMF '83 back in 2012.  I used
> the shrouds from the '87.  I have learned recently that the forestay was
> too short and the mast did not have the correct rake creating lee helm. I
> would recommend using stainless straps to lengthen the forestay as
> necessary if it is not adjustable.
>
>
> *Thanks and Stay Well,*
>
> *Stephen Staum*
> *s/v Pinafore (formerly Carol Lee 2)*
>
> *Needham, MA*
>
>
>
>> On Wed, Oct 13, 2021 at 3:14 PM Mitch Mitchell <mitchpadl at gmail.com> wrote:
>>
>> I have a 1990 R22 with a standard mast but may soon come into possession of
>> a 1989 IMF mast and wondering if anyone has ever switched and if so what
>> parts I would need to replace such as stays, mast base etc.. Thanks!
>>