Swallow Yachts Forum > Technical

1) Mast rake 2) Sprit booms

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Michael Rogers:
Hi, introducing myself, I've had some problems getting onto the forum, now sorted. I'm a long-time Swallowboats fan, building a Storm Petrel in 2004-05 (or was it a year earlier?): she must be from almost the last of the old design kits? She is, nautically speaking, the love of my life, an absolute stunner (as an Italian gentleman with no English said, when he saw her on Lake Garda last summer - "una bella bella barca!!!").

1) This is probably one for Matt? I have wondered off and on, since I built her, whether I have slightly overdone the rake of the mast. It looks - well, splendidly rakish. Questions - i) how can I check? (I've long lost the template I used, but might be able to do another from the instruction manual). ii) From a design point of view, why rake the mast? iii) What effect would  an over-raked mast have on sailing characteristics?

2) This is possibly of general interest. Encouraged by Nick Newland, I made a curved sprit boom. I wasn't entirely happy with it (mainly, the curve was in the wrong place, appearance-wise), although it worked very well. So I did another, and while I was about it I made a full wishbone. Lots of extra problems, but the end result looks very elegant, and sets the sail beautifully. It hasn't been tested in action yet, but I don't foresee problems. I very much doubt whether it will make any measurable difference to performance, but it's fun. If anyone is interested, I can provide more details, and I hope to be at the Swallowboats/Drascombe rally on 28-29 June.

Paul Cross:
Hi
I would be very interested in your wishbone sprit design...I've been thinking along similar lines for our Storm 15.

On the mast rake issue....I would have thought that the more rake you have, the more weather helm you will get! but I'm sure someone will be along soon to give you a full response.

Regards

Paul

Craic:
Paul Cross is right,
the mastrake influences your weather helm. More rake - more helm.

But to be honest, the mastrake alone cannot realistically fully control the weather helm. Even with the mastrake trimmed forward -which looks quite odd-, most boats will still show some weather helm in some gusts.
And quite rightly so, nobody wants a leeward helm, ever.

I suppose there is no general rule, the optimum mast rake must be established through testing.

That is why we are using not the standard rope shrouds on 'Craic' but adjustable bottle screws. In connection with the mast tabernacle they allow the mast rake to be modified quickly, even in mid-race.

But again, there are limits to what the mainmast rake alone can do to the weather helm.

About the curved sprit boom I know too little, except I never missed to have one.
The important thing is to have a mainsail boom, whether or not that is curved is of minor significance.

What would bother me about a curved sprit boom is that one cannot easily to the 'Harbour Furl' of the mainsail.

For a Harbour Furl, the -straight- mainsail boom is taken out of the gooseneck fitting, is tilted upward, and rolled into the mainsail, from clew forward. One cannot do that with a curved boom.

Obviously, I know zilch about the specifics of a Storm Petrel, but I think the above observations would apply there as well.

Michael Rogers:
Thanks to Paul and Claus for their comments.

Mast rake - I am reassured because weather helm is not a problem. It's most pronounced when sailing without the jib, as one would expect, but never excessive. I could fit a mast step which allowed for adjustment (though not under way), but it probably wouldn't be worth it?

Wishbone sprit boom - for Paul (and anyone else interested), bear with me (yes, I know, I did raise the topic in the first place!). I will try to put together a reasonably succinct account for later posting. Some pictures would help, which is where my IT incompetence gets in the way (my 17 year old son can probably help in that area). There are some interesting design and construction challenges.

Harbour furl - interestingly I didn't get this sorted with the original straight boom (obviously simple, as described by Carl), but I have indeed sorted it out (I hope) with the wishbone. It involves a topping lift (4mm braided is ample) through a small masthead cheek block, both ends kept cleated on the mast until used. One end is hooked to the outer end of the boom (I'll go into hooks when I describe the boom), the inner end of the boom is disarticulated from the gooseneck, and the outer end hauled up to the masthead (lengthwise that works well). The clew outhaul is released, and the sail rolled from leech to luff, the furled sail lying neatly against the mast between the two boom members. That's the theory, I am about to test on the water, and will report back. I had this manoeuvre particularly in mind for getting the mainsail out of the way for more comfortable rowing when the wind dies.

Can I wish everyone a really rewarding sailing season this summer.

Michael

Bill Wickett:
Michael,

Nice to hear about your curved sprit and also the full wishbone. We sailed an 18' boat with a full wishbone for 3 seasons. It was a cat rigged vessel, so no headsail. The wishbone carried forward of the mast slightly, so that particular design would not work well with a headsail, as the leech of the headsail would hang up on the forward end of the wishbone.

I am trying to attach some pics of that boat so you can see the set up.

Claus: for furling we just dropped the sail into sling lines (a type of lazy jack) between the 2 arms of the wishbone. With a lug rig I guess this would also hold the upper spar.

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