Sprit Rig Design

Just a brief qualitative observation form me... The fore mast seems placed too forward, the CE appears too much ahead of CLP. Overall it gives me an impression of a boat which might have too much lee helm.
But I guess you have already considered that, in which case I will apologise for the intrusion

 

No intrusion, Daiquiri,

If I didn't want comments I'd just hide in a hole somewhere.

I've been working the numbers and 50% mizzen and 100% foresail I'm sitting at 15% lead. Using full sail area, I come in at 5% lead that is typical of how schooner type rigs are balanced, at least according to Skene. I think that I am in the ballpark. I am can relocate of the bilge boards a bit more forward and extend the clews aft a couple of feet if it comes to it.

Unfortunately, in a vessel this size, accomodations have a large effect on rig design. The slab reef option has opened up the door for a bit more sail area that I what to use to pull things aft a bit.

Thanks for your interest.

 

Don't forget the possibility of adjusting the rake of the mast...this can be used to fine tune CE and even adjust for slightly differing sail sizes.

 

Good call, Steve,

I was saving that one for sea trials. Found some disparities between the model and the drawings. Found a couple of percentage points error with the C/E and CLR, thanks to Daiquiri's prompting. I'm working through things and will hope to post an update in the next couple of days.

At one point, I was beginning to think the sprit-rig wasn't going to work and was starting to delve into a balanced lug rig. Those masts, at least the fore mast, would have to be raked.

 

sprits in denmark

The trad Danish small fishing boat sprit rigs are very square with clew higher than tack, with many even having the luff a little taller than the peak, leech close to vertical, (fore often overlapping the main a little to give a "slot"). This makes it so they don't twist much, and the sprit is short. 2 slab reefs, with the heel of the sprit about the height of the first reef when under full sail, there's enough room between tack and deck to accommodate reef #2. This means a little longer mast, shorter sprit. (from "Danske Fiskerbade" -Andreas Laursen, Host & Sons, Kobenhavn, 1972).
For wonderful information on sprit rigs see "Wooden Boat Designs" Christian Nielsen, Scribner's, NY, 1980, a smothering plethora of detail. See Pete Culler's books too for excellent snotter design and much sprit info. Only sailed sprit maybe 100 hours total myself so am not expert.

 

Updated sailplan and keel.

Cleaned up things a bit. Settled (for now) on the sprit placement and brought the keel forward. Nice aspect on the keel change is that it lowers the ballast a bit.

Bataan, if you hade to choose the most informative book, would you choose Nielson's or Culler's book? If heard Culler's name before and wish I could purchase every book I ever wanted.

 

I have to ask if you have sailed a traditional sprit rig with the loose foot before. Such a sail does not trim well other than close hauled to windward and the sheet loads are very high. Traditional sprits'ls were made this way for a reason. They were easy to brail up on the fishing, crabbing and oyster tonging grounds. There was no boom to hit the often single fisherman in the head or get in the way of work. Having sailed boomless sprits'ls many times, I would not have one for other than historical reasons.

Booms are effective in controlling sail shape on all courses and are much easier on the crew because of he much lower sheet loads.

 

Sprit Reference

It would probably be Culler's fairly new reprint of several of his books under one soft cover and I think it's called "Pete Culler's Boats". I don't have a copy in front of me but it covers things quite well, with a lot of material on sprit. My preference for small boats is standing lug, easier to drop in a big hurry, and 90% of the UK small boat fishing fleet used it. Inshore and river craft were often sprit, but almost all the boats that went to sea used lug, not necessarily because it was more efficient or anything, just easier to handle. A lug sail with simple lazyjacks is a very easy thing, while the sprit is harder to furl and stow. My boat BERTIE (see antique tech thread in monohulls or page 5 of Spray thread) has a large standing lug mizzen sail that I find almost perfect.

 

follow up

I totally agree about the boom. A loose footed sail is used in the front of a cat rigged schooner or ketch so it can be larger and will overlap the boomed after sail and form a slot like a modern headsail, plus the stated reasons that it can be gotten out of the way for fishing or other work. BERTIE's boomed lug mizzen is a very simple and reliable thing, and long ago when I was an apprentice I rigged several cheap vessels under 20 feet with WW2 surplus lifeboat masts and sails, again lug, but that was back when you could get a whole rig for $50. For absolute blinding efficiency, but difficult handling, a dipping lug has to be experienced to be believed. In the '70s had a nicely shaped 18' 1880s ship's jolly boat that I rigged like a Dover Beach Punt with a big light dipping lug main, standing lug mizzen and stone ballast that would out-point most average marconi boats and consistently beat Cal 20s on all points of sail.

 

Tom,

Thanks for the input. I was wondering about sheeting loads and sailing off the wind. From what Bataan has just said, I have probably removed any advantage to this style of rig since I've removed any overlap to allow for accommodations. I'm leaving the option open for a forward boom.

Bataan,

Thanks for the follow up. I've Culler's book on my wish list. Your comments on the the lug sail are most welcome. I have come very close several times to changing the sailplan to a balance lug. Everything I'v read or come across says good things about them. The only drawback that I know of is sail shape on the wrong tack, but then, I'm already dealing with that in the sprit rig.

 

Reply to LP

Balance lug needs battens, at least 3 or so, then you can get the panels flat and the mast doesn't screw up the shape so much. Much experimenting was done in the late 1800s with balance lug small boats. Standing lug, with a boom like a gaff and very little overlap aloft, doesn't seem much different on either tack. Gaspe' schooners were cat rigged gaff and the throat stayed aloft, the peak being eased until the gaff was vertical down the back of the mast then sail furled to mast. Chinese is good but heavy for the sail area and needs a stiff hull to accommodate. I like Chinese lug for above 500 sq ft, gaff for 150 to 500 sq ft, standing lug for small sails. All these are long and low so you get fore and aft changes when reefing so take best to vessels with longish keels and tolerance for these changes.

 

hi LP.
how goes it with this boat!!??
i am most fascinated with sprits on larger boats, i just love the idea of the simplicity of unstayed masts,- an ideal set up for trailer sailers, and the ability to fly a jib on an unstayed mast.
The sprits seem to be surprising performers
kindest regards
wayne

 

Hey, Wayne.

It's been a while since looked at this thread. After discussions on sprit rigs, I chose to go a different route. The vessel has gone through many iterations and I have settle on the attached balance lug rig. I've started building some componentry for the boat, but have not started the all out build, yet.

I have a several threads going regarding different aspects of it's design and build.

This one regarding balance lug ideas.

http://www.boatdesign.net/forums/sailboats/balance-lug-design-ideas-47677.html

This regarding the general design.

http://www.boatdesign.net/forums/boat-design/blackrock-24-a-46525.html

And this one that follows the build.

http://www.boatdesign.net/forums/wooden-boat-building-restoration/blackrock-24-build-46526.html

Thanks for your interest. I hope the new rig peaks your interest.

 

i sure would like to chat to you in greater detail.
i too am looking at a build here- its all still in the formative stages yet- mentally!!
just ideas and thoughts-and lots of sketches, before i start talking to an architect.
i have a very clearly defined set of use parameters that i need/have to fulfill- so that does make the job a bit easier.

a lot of write ups i read, put the sprit as a higher performer than the lugs etc, and even better when a headsail was added- but the balanced lugs are possibly a bit easier to manage and reef etc i guess
i would love to chat more about this concept, and hear about your decision change etc etc, do you have an e mail add
mine is mwnicol@qcislands.net
kindest regards
wayne