Hi Ross, Have really enjoyed the last couple of posts. I like thinking about the laps as spray rails, it added another dimension to what I thought of as simply a nod to tradition. On the matter of fine entry + flare I would like to make an observation - is this discussion of fine entry and flare dependent on hull type? I am thinking of flat bottomed sharpie hulls in particular. These hulls often have nearly plum or vertical sides, but are designed to be sailed with a fair amount of heel, thus introducing a degree of flare. Also, the most successful sharpies have a fair amount of rocker in their flat bottoms, this means that more often than not they carry their stems at or above the waterline. I think that Bolger's Black Skimmer is an excellent example. Are the needs for flare and fine entry different between say, displacement hulls versus planing hulls, or between boats that are designed to be sailed fairly flat versus those with a little heel? cheers, Graham
Yes, the combination of a fine entry (i.e. sharp waterlines in the forward sections, with a half-angle of less than 19 degrees when viewed from above) a flat bottom, adequate rocker, and a boat which sails at an appreciable angle of heel will produce a soft and dry ride in a chop. I lack suitable photos to demonstrate this in decent wind conditions but here are a couple which may help.
|Martin Kortlucke's Folding Schooner designed by Phil Bolger. Once again the wind conditions are light, but you can see the way the chine would work if the boat was heeling more - it would cut like a knife.|
- bottom too wide; and
- not enough bottom rocker
Here are two drawings to give some idea of what I'm talking about. These show the forward hull sections of the design I'm working on, drawn at an angle-of-heel of 25 degrees. For reasons of practicality, the curve of the bottom and the curve of the topsides are not perfectly matched, but you will get some idea of the process involved.
|Forward sections of sharpie heeled at 25 degrees|
|Same drawing, but with only the underwater sections shown. This gives a better visualisation of why properly designed sharpies can work so well, and be so fast.|
Maybe I'll be able to come up with some better way of describing what I mean, but this will have to do for the moment.
Just to get you thinking, I believe that the fastest sharpie would actually be a scow hull, in which case the limitation on breadth of hull is removed. Look at the work of Phil Bolger and Jim Michalak for some clues...