SCOW; cruiser/racer safety/stability

Dear all.

Recently, we see a growing interest for scow like-hull shapes, like for instance the new mini transat designs. I find this a very interesting development that could work for a new type of cruiser racer as well.

There are a few potential advantages over current cruiser racer designs that a scow could offer. And one very big risk.

pro:
Wide beam gives large interior space.
high stability hull reduces ballast requirement.
wide beam is suitable for waterballast
no keel, just daggerboards means very shallow draft and reduced heeling moment.

con:
negative stability at 90+ degrees.

The ideal boat design can easily adapt to the weather conditions. Waterballast can transform a boat from a lightwind rocket into a brick in the water, reducing the need foor sail changes; spinnakers etc. I light conditions, an unballasted scow would require relatively little sail area to get going and build a little appearent wind. Only lightwind combined with some chop, could hurt the very voluminous hull quite a bit. For cruising purposes ballast tanks on both sides could be filled. For racing ballast can be reduced/ transferred to what the skipper dares to. This system applied in a beamy scow, will replace the need for a ballasted keel completely. except for the safety / stability issue.

The only answer i can come up with is not an elegant one. Bouyancy in the top of the mast. This could be an inflatable bladder of some sort, but this would make the safety of the whole boat rely on a technical system, and it won't make the boat stand up after a capsize.

Who can make this versatile concept a safe one??

 

Versatility comes in several flavors. There's the craft's versatility with respect to weather conditions and venue. The hull plays a roll in that, but usually it is the rig that gets burdened with that responsibility because the effort by the crew has to remain manageable as well, so it is usually better to leave the hull alone and jigger the sails. Boats with water ballast tend to add it quite early, like at ten knots of wind speed. Beyond that, it's back to fiddling with the sails to manage crew effort and tipping moment and drive. So I tend to think of dumping ballast, not adding it, as "normal" is full tanks. I can't think of any examples of boats that add ballast for heavy weather work only. That would make for an unnecessarily heavy boat and rig for 99% of the time. What you do in practice is depower and slow down to manage the loads on the boat.

Then there is the versatility with respect to load conditions. Most scows are not particularly good at this. Their performance tends to be quite sensitive to weight. At least when compared to craft such as sharpies that can vary their displacement by a factor of five and not worry much about the rig they have set. This shouldn't be a big deal for recreational craft, but for small cruisers it is something to consider. They are very sensitive to bow draft, so changes in displacement have to be accommodated by stern trim. This is how sharpies do it, and is somewhat natural to do in an aft cockpit boat anyway. So, easy to do at displacement speeds but not so much at planing speeds where transom immersion must be carefully controlled.

Thirdly, there are boats that accommodate the changes in use of the owner over time or the broad appeal of the boat to many people. Some craft have the reputation of being kept forever - Fischers and Nonsuch, for instance. Others sold by the thousands, such as Hobies and Sunfish. That also reflects a sort of versatility. The ability to remain attractive, ease of maintenance, and generally low owner effort all around tend to help here.

The rig of the scow needs to be set up so the bow height is steady through puffs and at various speeds. The spoon bow helps, but the jib needs to be designed (and sailed) to be neutral through puffs, while the hull is neutral over a wide range of speeds in steady state sailing. So they are jib sensitive in general. I collected about seven different jibs for my 16'er over 25 years of sailing it. Since you really have to manage the jib, a fractional rig and big main tends to work better. Similar to a catamaran in many ways.

You also need to keep in mind that historical scows were the way they were because of a waterline rule and a lake sailing venue, and the modern ones are the way they are due to a box rule and ocean sailing venue. They may both have a spoon bow, but they go about their business in very different ways. The new ones are light and plane flat. The old ones sailed on their ear and were displacement boats. I don't really like calling the new ones scows. They are skiffs that have figured out how to manage the bow draft and are taking advantage of that ability. They can provide a steadier, stiffer boat in pitch as well as in roll. That tends to make the sails more efficient compared to a boat that is bouncing around. The old boats were also extreme attemps at sail plan stability, but it was gust response, not seaway, that was being addressed.

 

Hi Phil, good toughts, i agree that reefing or changing sails will always be necesary. I think that a twin cat rig with wishboom would work.

http://solarwindboats.com/wp-content/uploads/2012/04/homepic2.jpg

this type or rig keeps the center of effort relatively low making it easyer to control the trim. Also managing the jib as you mentioned will be easy because the sheet loads are very low due to the wishbones

for racing, the boat should sail upwind with increasing amount of ballast upto 40 % of its total displacement. downwind the boat should be empty.

perhaps I should not call this a scow concept. see enclosed j peg.

L.O.A = 38 ft
beam= 13.3ft

I am not sure if this design could evolve into a pitch stable craft like you described

what's your take on the capsizing and safety issue?

 

Why not look up the A-scow and E-scow designs and start from there. An E-scow is 29ft LoA.

 

Having owned an Inland Lakes M-16 scow that I sailed on Choctawhatchee Bay, I can add one more con: scows pound in a seaway. I mean, knock-the-fillings-out-of-your-mouth pounding. They also require heavier scantlings for the same reason - my 16 ft scow had a minimum weight of 450 lb.

 

It seems to me that its sensitivity to pounding would make it unsuitable as an off shore design. Day use dingys and inland waters no problem, but this is a very serious disadvantage for long open water crossings.

 

I think the idea of a 'race cruiser scow' has a bit of conflict. The idea that it will get performance from form stability rather than ballast is at odds with the fact that cruising wants to carry heavy accommodations that take away that performance. It won't get performance by planing when sailed upright because it is too heavy and it pounds. I don't think that 'sail it on it's ear' works for cruising sailors either -if they would put up with it it would still take active management they don't want to provide continuously.

If you look at the pro's listed by the OP they are not exclusive to the scow. A wide transom gets the job done and it doesn't have the negatives the wide bow does because it's in the bows wake. If you have dagger boards you can toe them in to better match the submerged profile and the triangle has longer sides than the rectangle of the same length on deck. Lift forward is the last benefit scows have and a better solution for that is DSS.

 

Tom, your M16 was a heavyweight slug if it weighed that much. My M20s weighed less than 300 fully rigged. Neither the M20 or the E scow was a bad pounder. Scows are presumed to sail in heeled attitude wherin there is a pretty fine waterline and the entry is not bulbous either. I agree, if sailed flat it'll pound your fillings out.

Chocktawotchee bay? as in Florida's Choctawatchee? If so You are a long way from home.

 

My understanding is that the scow Mini worked because it exploited the rating rule. It was bigger and more powerful than the other Minis.

Does this rule interpretation make the hull form a good candidate for racer cruiser ?

 

thanks for al the interesting feedback from everybody.

However, I am looking for a solution that will make this a safer design. And possibly self righting.

 

My feelings about scows is they are larger boats with the ends loped off because there was some major limitation on length and the ends were up out of the water most of the time anyway. In very small lightweight boats I find transoms weaken the structure so much of what gets cut off is added back to stiffen and strengthen. Clipping the front is worse.

In light weight racers with huge rigs they can sail at great heal and get a catamaran in what passes for a monohull. Or when there is enough wind they can use their large flat surface to plane sooner than other designs.

Cruisers have no artificial constraints so they would prefer the real catamaran, or triangle.

 

My M16 was a late 1960's pre-fire vintage wooden Melges. It was built to the minimum weight, and had a lead corrector weight under the foredeck. 450 lb was the minimum weight for the class. If you check the ILYA pages, you'll see the M16 is no longer shown, but the MC (basically the same hull) has a weight of 420 lb.

Yes, Choctawatchee Bay in NW Florida. I took the boat with me when I was stationed at Eglin AFB, then sold it in Dallas (White Rock had a fleet of M16s) when I was transferred to the Mohave Desert. I had to have the boards and rudders annodized to handle the salt water. The waves there were a lot bigger than the chop on Lake Okoboji.

If I heeled the boat up just right, it would sort of tiptoe over the waves, and it felt great when it was in the groove. However, every so often, a wave would hit it wrong, and there'd be a big BANG. There's no way you'd be able to avoid pounding in an ocean seaway when cruising with a scow.

 

The Sonders, which were basically scows, were known to pound the caulking out of their seams in Marblehead Harbor (ca. 1910)

Cheers,

Earl