Why is the Sharpie Sharp?

[alkorn]

Pretty much all the experts agree that flat-bottomed centerboard sailboats (skiffs, sharpies, garveys) need to have a high length-to-beam ratio to perform well.

What happens to a flat-bottom centerboard sailboat when it's too broad? Is it simply that the accepted problems of flat-bottomed hulls - pounding, bad in a chop, weather helm in strong winds - get worse? Or do other problems, such as a squirrely helm, crop up?

And - to take this one step farther - how wide can a flat-bottomed boat be before all these problems get too bad? (Obviously some subjectivity here.)

[donald branscom]

Pretty much all the experts agree that flat-bottomed centerboard sailboats (skiffs, sharpies, garveys) need to have a high length-to-beam ratio to perform well.

What happens to a flat-bottom centerboard sailboat when it's too broad? Is it simply that the accepted problems of flat-bottomed hulls - pounding, bad in a chop, weather helm in strong winds - get worse? Or do other problems, such as a squirrely helm, crop up?

And - to take this one step farther - how wide can a flat-bottomed boat be before all these problems get too bad? (Obviously some subjectivity here.)

I do not think all experts agree.
The original sharpies had a 4:1 beam to length ratio.
Modern sailboats have beam to length ratios of 3:1 , almost exclusively.

When a flat bottom boat is under sail it does not pound because when it is healed over the underwater shape is a "V".
When "modified" sharpies were tried the underwater shape was more flat. than a "V" so in was not "improved"at all.

Modern racing boats are almost the same as a sharpie really. There has not been much "improvement" in the hull shape. The chines are slightly more rounded is all. Most of the improvement has been with rudders, keels, and rigging and hardware.

The fatter boats may have been influenced by the fact that slips are charged for BY THE FOOT. Buyers want comfort.

The wider boat has a little more form stability.
The thing that i always wonder about is that almost all modern boats are 3:1 beam to length ratios and the sharpies were 4:1 but why did no one try 3.5:1???? Bunch of sheep mentality if you ask me.
Sailing is full of fashion and fads.

Below is my model of Howard Chappele's modified sharpie.
3 ft. long model. From page 56 of his book "Boatbuilding"
http://i10.tinypic.com/688rpk6.jpg
<a href="http://tinypic.com" target="_blank"><img src="http://i10.tinypic.com/688rpk6.jpg" border="0" alt="Image and video hosting by TinyPic"></a>

[donald branscom]

This is another of Howard chappelle's boats in his book "Boatbuilding"
It is 22 feet and the model is 22 inches.
The bottom is flat BUT the bilges are more rounded than a sharpie.
The rudder and centerboard are much improved.
http://i17.tinypic.com/67rjbtk.jpg
<a href="http://tinypic.com" target="_blank"><img src="http://i17.tinypic.com/67rjbtk.jpg" border="0" alt="Image and video hosting by TinyPic"></a>

[johnw]

According to Chapelle, the reason the boats were made narrow was that the fat ones didn't carry their way through a tack well. Many sharpies were built by the fishermen who owned them, so long and narrow wasn't such a big problem for cost. V-bottomed boats are generally wider, and when Thomas Clapham wanted sharpies that could carry more weight, he introduced V into th ends (the Nonpariel type, he called them.)

[merlinron]

is it possible that thier shape stems from the type of waters they were most commonly sail in... namely shallow?.

i wonder if the under water shape of a heeled sharpie's 4:1 hull ratio presents a relatively efficient foil to windward considering the lack of efficiency of it's centerboard( or none there of) in the shallows. the 4:1 ratio being a better compromise in shape between performance and windward ability. as foils improved, comfort(roominess) could be afforded by increasing beam to 3:1 without too big a loss in performance.

[Thorne]

Yep, that and the fact that the design was pre-internal combustion engine -- when you HAD to sail it or not make port, efficiency becomes just a tad more important...

;0 )

My favorite comment on this comes from Chapelle in his American Small Boats, where he describes the antics of the Italian feluccas hooking the anchor chains of the ferries in SF Bay to get a free ride -- with fishermen and ferrymen tossing various objects at each other. The joys of pre-motorized boat operation....

[ahp]

I have wondered the same thing. The Lightning is certainly a good sailing boat,15,000 cannot be wrong. It is a modified sharpie with an ark bottom, yes? The bean is 6 ft 6 in. and the length 19 ft, beamier than the traditional sharpie. I have wondered if the Lightning with a sharpie rig would work well.

[johnw]

There's a reason racing boats carry the rigs they do. I love the sharpie rig, but it won't go to windward with a marconi sloop.

[ahp]

I agree, having sailed briefly in a 30 Square Meter, never-the-less...

[Woxbox]

When a flat-bottomed boat has a wide beam, the chines create huge turbulance because the curvature of the sides is far different from the curvature of the bottom. The skinnier the boat, the less this becomes a problem. The water wants to and does flow down and under the chine, creating a vortex.
Phil Bolger's many sharpies have more rocker than most -- he says he's found that this reduces the turbulence as the two curves are a closer match--producing a noticeably faster boat. I beleive he's done a couple of them where the curves are identical.
It's been my experience that beamier, flat-bottomed boats develop a very strong weather helm as they heel -- so you wind up fighting this with more rudder, which increases drag. I'm not sure why this is, but I strongly suspect it's forced by the irregular flow of water around a bottom that, below the waterline, is highly asymetrical.

[alkorn]

When a flat-bottomed boat has a wide beam, the chines create huge turbulance because the curvature of the sides is far different from the curvature of the bottom. The skinnier the boat, the less this becomes a problem. The water wants to and does flow down and under the chine, creating a vortex.
Phil Bolger's many sharpies have more rocker than most -- he says he's found that this reduces the turbulence as the two curves are a closer match--producing a noticeably faster boat. I beleive he's done a couple of them where the curves are identical.
It's been my experience that beamier, flat-bottomed boats develop a very strong weather helm as they heel -- so you wind up fighting this with more rudder, which increases drag. I'm not sure why this is, but I strongly suspect it's forced by the irregular flow of water around a bottom that, below the waterline, is highly asymetrical.
What you say about matching the rocker to the side curvature seems to show up in Karl Stambaugh's Catbird 18: it's a very beamy sharpie (18' LOA x 8' beam) but has lots of rocker:
http://www.cmdboats.com/images/catbird_18.jpg

[donald branscom]

WOW ! 2:25 beam to length ratio. Fat little boat.
8 feet wide takes up a full lane of traffic

I almost built that boat too! Did not notice the top view.
I only was looking at the side view.
It would not have fit in my garage.
The one i am building is 7 feet wide and I only have a foot to squeeze by on each side. I am concerned because i am ready to put a rub rail on each side that is 1.5 inches wide added onto each side.
That would have been a serious prOblema.

[Woxbox]

The Catbird is so beamy the weather beam might well be in the water a good deal of the time, which is not desirable.

I think some would argue that Catbird is too beamy to even be called a sharpie. Chapelle describes traditional sharpies as adhering to these rules:

1: Beam on the bottom is about 1/6th overall length.
2: Flare amidships 3 1/2 to 4 inches perfoot -- less for speed, more for seaworthiness
3: Low freeboard, strong sheer.
4: Displacement as light as possible.
5: The chine line, in elevation must appear as follows: the heel of the stem should be above the waterline; the chine runs straight for about one-third of the overall length of the abaft the stem, sloping downwards toward the midsection. The chine then curves gently to the point of greatest draft, and runs upward to the stern in a flat, gentle curve. A long run is important.
6: A light rig is necessary for safety.

He goes on to describe modications to make beamier boats work, which notably require some deadrise aft. These types became known as the nonpareil sharpies or flatties.

In any event, a wide flat bottom that runs all the way to the transom is unusual. Heel just a little bit and the leeward quarter digs in and drags. That aside, the Catbird is an attractive boat -- anybody out there sailed one?

[Steve Paskey]

Wm. and John Atkin designed some surprisingly wide flat-bottomed sailing skiffs:

Shore Liner, 24' LOA x 9' at the sheer
Mother Hubbard, 19' LOA x 7'6"
James Samuel Jr., 17'1" x 7'1"

I don't know the width of these boats at the bottom, but none have an extreme amount of flare ... Judging from the drawings online I'd guess that they're wider on the bottom than 1/4 the length ... and some may be close to 1/3 the length.

I've always wondered how well they sailed ... Shore Liner seems to have been fairly popular in her day, with at least 60 boats built IIRC.

[alkorn]

...... He goes on to describe modications to make beamier boats work, which notably require some deadrise aft.

According to the Boat Design Quarterly article on the Catbird 18, Stambaugh shows curving the transom bottom to produce an arc bottom aft as a construction option.