Pol,

now, in haste I traced the original gaff rig, and superimposed it on the junk rig.

I believe, if you get the balance right, with or without the mizzen, then Annie will sail in rings around her gaff-rigged sisters, even with that "little" 51sqm JR. Even more so if you turbocharge that sail by giving it 8, or better 10% camber.

Arne

(See Arnes sketches, Section 2, Photo 10)

David,

thanks for your input. Now, Pol is away on holiday for a little week, so has probably not even seen my suggested mast ( Btw, read Pol's story on building Solitaire's mast, in JRA Magazine 71, p.11).

The reason why I drew up the main mast where I did on Pol’s boat, was that it was easiest for him to install it there. I also knew that Pol was interested in adding a mizzen anyway, since his Annie tended to sail about at anchor with the original rig.

The mast position at 12.5% of the wl. from the end (of wl.) is not that extreme: I just checked the position of Johanna’s mast (11.0%) and Ingeborg (14.0%). I have never had a problem with rising lee helm as I deep-reef these sails, but of course, the wind drag of Johanna’s bare mast could be a challenge in tight harbour manoeuvres (mainly when backing). Johanna’s mast “sail area” is 1.6sqm and its weight is about 3.0% of the boat (on Ingeborg; around 1.18sqm and 2.6%).

It seems that when we build thicker, stronger masts, they gain strength faster than weight, so that is why Annie’s suggested hollow wooden mast will only add 2.4% to her displacement. Moreover, the CG of these masts sits well below the middle of the LAP.

There is another design factor, which I have started to check more frequently on sloop JRs:

The ratio between the sail’s chord and the waterline length.

On Johanna the chord is 83% of the waterline, on Ingeborg it is 80% and on Annie it will be only 74%. Johanna sailed well on all points, but before bearing away after hoisting sail, I had to sheet in the sail and pick up a little speed over 2-3 boatlengths, before she would turn downwind. Ingeborg on the other hand will obey the rudder from the first moment. I therefore think that Annie also will be easy to steer downwind without the need to swing the sail over.

Another thing about that Cornish Crabber design: It appears to have the centreboard quite far aft. Could it be that weather helm will increase if the board is raised? That would be the opposite of what I would want. Does any one of you have experience with this?

Arne

PS: As always, I have suggested to Pol to add endplates near the low end of Annie’s rudder. There is no such thing as too good rudder control.

Michael,

you are right about the windage. That JR mast has 2sqm sail area, as well. This is why I suggest the addition of the 5sqm mizzen.

Arne

Michael,

I think I am well aware of potential problems with the mast right in the bow. However, the mast position I suggest here is not quite in that American Catboat league. Besides, I suggest (and Pol seems keen on) digging out the mast to a wall thickness of just 1/5 of the diameter.

See the mast drawing I have made.

To find its weight, I divide it into 3 section; the upper cut off cone, the mid cylinder, and the lower cut off cone/pyramide.

If my calculations are not completely off, then:

·         the volume of the top section is 303litre (194litre if dug out)

·         the volume of the cylinder section at the partners is 34litre

·         the volume of the bottom section is around 43 litre (approx.)

The total volume of the wood in the solid mast is then 380 litre, while the volume of wood in the hollow mast is 271 litre. Since one litre of water is one kilogram (kg) and since spruce has about half the density of water,

the solid mast should be around 190kg and
the hollow mast should come out at about 136kg. Even if not built with gunsmith’s perfection, that hollow mast should end up well below 150kg.

Compared to the Cornish Crabber 30’s displacement of 14000lbs (6350kg) it will be less than 2.4% of the boat’s displacement. Compared to numbers I have experienced on my own boats, this is very low -  the lowest, actually.

Conclusion: I think that a Cornish Crabber Pilot Cutter 30 will do all right with that mast.

Cheers, Arne

PS: I suggest you double-check my calculations.

PPS: The mast’s diameter was found by using my twisted version of the PJR formula (see Chapter 6 of TCPJR)

Somewhere between these is where the compromise lies I think.

The effect of the tiny mizzen on the CE is amazing! I know it's never going to give much drive but the sketch says something useful to me. I'd like it primarily as a steadying sail at anchor as Annie does sheer about a bit even with her current rig. Practically speaking it can be fitted more or less on top of the rudder post, so the bumkin would not need to be over long.

Thanks, David, for your suggestion of the Gazelle rig with jib. I think if I am converting to JR I'd really like to leave the possibility of even only one flogging headsail to others! 

As for keeping the bowsprit. It would be nice to get rid of that nearly 4m of solid spruce  / 2.7m of overhang off the bow, but could it be handy for an ultra lightweight ghosting sail? We could always make a much lighter timber one since its new duties would require less strength.

Thanks again, Pol.