Hydrodynamics of inboards

Not an inboard, but I think everyone would be happy with about half what this thing does.

http://m.youtube.com/watch?v=HZ5sLPcWsDY&sns=fb

Those guys will run an automatic transmission which probably takes more Hp to turn and then add in a drive shaft and a drive and a very long prop shaft and you loose a lot more Hp by the time you get to the prop. Also figure that's in some very nasty water where you can't stay on the throttle all the time.

I'm still here, I have been watching this thread and have nothing to add since I really don't know anything. I'm also still trying to muddle through the Savitski papers. Thanks everyone!

Not only is a larger wetted surface advantageous for tracking, but spreading the weight of the boat over the largest possible surface area makes the smallest wake. That sort of design methodology makes for plenty to overcome when it comes to pushing these tugboats faster. Thats one of the reasons the hydrogated 196 (and possibly 206 and 216) offered in the late 2000's have pretty good speed potential- they essentially have removable hook, allowing them to lift the bow at high speeds. They arent small boats and require a lot of hp to push them faster, but there is speed potential there.

If youre using a 2nd gen SN (70-81) as your benchmark hull, 300hp will get you over 50mph, but Im not sure that 400hp will guarantee you see 60mph. Alan's '81 and Hotboat's Martinique were in the 380hp range and were 56-57mph boats. Newer/larger hulls, starting with the BFN and 2001 will require higher power levels to hit those speed numbers. Both of those boats start to reach hull limitations in the mid-upper 50's that require even more hp to push through. Joe's '83 probably is pushing a tad north of 500hp to touch 60mph, and I'm not far behind... though the v-hull BFN does a better job of getting up and out of the water than the flat bottomed 2001.

Bill Burgess shared a few secrets on here as to how he got his '80 SN to run fast (allegedly 72mph on the radar). It included turning a steel speed prop (11x15ish) a lot of RPM, as well as a shallower shaft angle. Not sure what he had for hp, but he did have nitrous on the boat.

It is kind of funny how almost every Fuel boat is either based in TX or has a driver from TX.   It's a pretty big deal locally, I know at least one person who races in every class all the way up to Alcohol Flat, and mr Erlich lives just up the road in Round Rock.

I was trying to keep things pointed in the hull differences that we have, flat and V. The W drive is a whole mother ball game and as far as I know that is a custom piece. Last summer Eddie Knox was going to rebuild one and had every thing ready to crack it open, but unfortunately a guy I work with was on the rope so I had to leave the pits to watch him run. I really want to know what's inside that box, and the next time I get a chance I won't leave.

I think they may have made some quicker and faster runs, but haven't backed them up for an official record. As for the Spirit of TX, I've seen some absolutely amazing driving by Scotty over the years and I know they are the only ones that seem to be able to push Problem Child, unfortunately last year they were so far back all they could do is try to take out PC. They purposely sand bagged qualifying in San Angelo to meet PC in round 1 and ran a quicker time but red lighted. They came back in Marble Falls and qualified 1 and then all hell broke loose on Sunday with the broken drive shaft. Can't wait for things to get started again, another month or so till it's game on.

Problem Child isn't a flat bottom or a v hull, it's a hydro so totally different animal. It's also got a W drive 2 props with 1 motor.

Oh and the 1000ft record is 3.39@258, I was there for that one.    They seem to have that boat dialed in now to run 3.50's at about 250mph, it's very reliable and they still have something left. Spirit of Texas can get into the 2.40's, but it they break a lot of stuff some time though they break Problem Child and get a win.

Gary S wrote: Yet

Pending and I'm sure still in the back of his mind!

SNobsessed wrote: Wow, I wonder how many boat manufacturers did this amount of math.

I'd say not many especially in the early days. Gar Wood for example would design his hulls from his knowledge and experience. It was more of "seat of the pants" engineering.

John,
I've been trying without success to find the patent that was used to design the hull for my X55 Dunphy with the steps. The principal of getting more hull out of the water was an old one but for the X55 it worked. The 55 designation was for them wanting the boat to go 55. Mines close as it's been radar'd at 54. Steps in the hulls go way back to the gentleman's racers and then carried over to to the modern hydros. I remember one comment Reid said way back that he was going to take the chain saw to the bottom of one of his hulls and create steps!! I know he never went that far!

John,

Take a look at anything by Savitsky, he goes well beyond the principles of planing hulls.

Savitsky 1
Savitsky 2

Noel

They sound faster

If I remember correctly Tim, you did 64.X on my iPhone on Green lake with me in the back seat. It was not a real speed run, just a quick roll on with no attempt to shift weight or try different water surfaces. There was some chop so that probably loosened it up a bit.
A couple of the hard to imagine things going on are asymmetric thrust, prop shaft turbulence, and possible rudder stall from being at least partially shielded by the slip stream of the prop shaft and the unequal pressure from the p factor. Sometimes when I try to picture it I envision a condition where one side of the prop is actually producing drag while the other produces thrust. I know it is possible since my friends V drive Cole runs over 100mph in the 1/8 mile at Blarney Island. It is quite a different animal and very dangerous even by my standards.

desertskier wrote: Flat bottom V-drives will easily go over 100mph. A flat bottom DD should be capable of the same. Just put a bigger motor in it and some dry stacks.

Ya might want to do a little more than that, less angle on the drive shaft would be a good place to start, steel running gear/prop, high speed rudder, and less hook on the back would be a minimum if you really want to push it.

more importantly...whats the fastest Tims boat will pull a barefooter?