But Bryan y'all forgot the most important part.... it just looks shippier, may be because of the aditional height and extra feet.
Anyway mate whats the story on the fancy formular for HP/Speed. Is it applicable to the GA, am I way off track, is it anuther innernet (praise be to Al Gore) spoof, does that only apply to the Northern Hemisphere with its floating on top of the world lighter water or what. Ed seems to be rethinking fitting a huge 300hp firebreathing supertanker engine as a result and I dont want to be the one responsible for putting him crook. Roughly (educated guess) what HP do you reccomend to get his 20Knots.... of course there are variables like gearbox and prop bite but could it be done with say ..... 100hp?
Thanks
Muzza.
Shippier, eh? OK ...I like that. It definitely looks "shippier" when you're standing under the bow and looking up at it...
As far as speed predictions go, there are many methods available and several calculators online. Most will not be accurate, but all will be within a reasonable doubt of reality. That said, I would suggest taking it a step further if you want more accurate speed predictions. The attached spreadsheet contains Savitsky's methods along with later refinements (Blount, Lee, etc) and is pretty good ...but keep in mind that it does not take into consideration things like the parasitic drag from outboard skegs, strakes on the bottom of the boat, imperfections in the surface, humps and hollows, propeller efficiencies or the lack thereof (slip) etcetera and it DOES assume that the boat has a traditional drive shaft and rudder. These models tend to be more accurate on heavier, beamier, boats than on lighter and relatively narrower boats such as the Great Alaskan.
What I did for speed prediction (and I'll need to dig up my hydrodynamics results for you after I get home from work), was to use the Savitsky+ analysis in RhinoMarine, an add-on for my Rhino 3D CAD program that I used for modeling the Great Alaskan. Again, all the little things that take away from speed (parasitic drag and imperfections) are not considered, so even those results need to be modified. I originally modeled a 22' Tolman Jumbo and came up with a scaling factor to make the results match up with reality, then I modeled a 26' Great Alaskan (modest load) and multiplied the results by the same scaling factor. To take a guess at how Ed's boat will perform, I would predict the same 26' Great Alaskan with the attached spreadsheet, then modify the numbers to model Ed's boat, and then derive a scaling factor between the two. Once there, you can use that scaling factor to adjust the speed and power predictions from the 26' boat to Ed's football-field-length (haha) boat and you'd be in the right ballpark.
If you want to keep it simple, figure 40# per horsepower as the minimum and 25# per horsepower maximum and go pick your motor and prop. This would result in about a 150 hp minimum sized outboard and a 250 hp maximum if you assume 6150# (that's the number you used, right). I think in reality that you will be surprised at how this boat moves easily and I'd probably limit Ed's boat's horsepower to something more like 200 or 225 hp. With this horsepower, I would expect the boat to move along in the mid-thirty knot range or possibly faster. Anything above 40 knots or so starts to become an inaccurate prediction in my book because minor hull variations (humps, hollows, etc) start coming into play more as the boat goes faster.
Brian
