Top Speed Question/Discussion

[whipper]

Great post Lou! And Erik tell me about it, Im solo most of the time anyway.

Lou I found out the same as you about the engine hight losing speed above the pad. Trophys the most though. They run 2mph or more some times at 1/4 to 1/2 below on my GS also. one of the only props that seems to differ is this 28 drag3 i got. It likes and feels good at even. its faster at even than 1/4 below. one time I was ideling threw shawlow canal to get to another lake with motor jacked as high as it goes and trimmed up just a little. when i got to the other lake i forgot about having the motor so high. I trimmed down and took off wot from idle. As i was ripping across the lake and jumped up on the pad and was doing around 85 I though wow the hull must have found some high test in the tank because i was way higher than normal and accelerating faster than I ever have before with way less trim!! Then it felt hard to control. {that warning sign with the hook devil in the mirror!!haha}} The hull started rising and falling with a little chine walk thrown in for good measure. Then i realized SNAP i have the motor at ONE and 3/4 above still!! OK gently started slowing and lowering the motor to the pad and a bit more then found the right spot on the gauge below 50 then ahhhh made it. That was close!! That got me thinking that for acceleration i could run the motor higher than drop it down a tad on the go before she got unstable for faster ET,s. Then thought. Maybe not such a good practice!! haha
Ive done alot of lip work to my GS but not without talking to Darris with a million phone calls and help from Bill and Chad who have had to do some also. Theres some templates around to follow but still took me many many test days if not weeks to get it so I was happy. Ive redone mine 5 or so times now from hitting sticks I couldnt see at speed. If I never had to touch it again that would be the best thing as its really hard to get it good once ya mess with with it as you said. Just wasn't practical to send it to Darris or I would have!
i turned my seat base side ways a few years ago like a slid steer. That was without a doubt the best thing ive done for ballance I would highly recommend if your the only one driving your XS to do this. I say that because if you only use the reg seat base and not one that actually can go forward and back as well as side to side its stuck in that driving position for you. Someone shorter may find it not as good for them. I was able to ditch 30lbs of counter weight doing this. It takes a few times to get used to driving with the wheel off set to the right a little but now i don't even notice it. Its also great for balancing for passengers. i usually slide it all the way to the right up against the sides and that is good for most sized passengers. You can tweek it were ya need it. Hears a pic of what mine looks like to the side. I was able to to use most of the same mounting holes. i think i only had to drill one or two cant remember any more. i find at wot low 90,s is much more stable and easier to attain than before sitting more centered. It makes me want to make something to go dead center but the way the console is that makes it hard to do and look good. You would need cut the end of the console and add some more material then but the end back on almost a foot over to the left and drill a hole for the steering again. Easier said then done!! Ill bet there's even more speed and stability to be had centred with no counter weight and battery centered ect..
Sorry for the long post also. This would have taken 30 sec to say though.. haha I think i firured out why i always do such long posts!! Im taking out loud to my self as I type..!! yakyakyak!

 

[whipper]

Migiver. She has been one experiment after another. I picked up 4 mph reshaping the gearcase and modifying the cowl for better air delivery and fuel delivery then tweeking the acu to give more fuel and compensate for the lean of the ram air effect I was looking for. Right after I did that was when i hit my fastest top speed of just over 97 mph a few years ago. I cant hit that anymore the motors getting tired after 9 years since the build. Im happy if i can run 93 or so now. Theres 10 holes in the front of the cowl and the two top ones have tubes that flare out to give the intake more air. You reallu feel it from mid range up once you get enough air getting back there. I think a race hatch over the back seats with a Drag cowl at the back like the SS and XR01 etc.. there would be even a little more. Or not...haha When i have more time money and lost my brain im thinking Center Steer ,race hatch and drag cowl to a 300xs 15 inch mid 2.5 gearcase DBR mods 32 Dewalt prop 150 lbs of ballast in a ski locker down the center of the floor deep to the keel, Shave down wind screen low on both sides leaving just the center high and looked finished of course, and a 7000 rpm limiter and let her eat!! haha Be a fun and interesting project I think. If i live it would interesting at the very least. i may have to get another Allison if I destroy mine in the proses. I also think a Hyabusa motor or twin rotor turbo rotory to a surface drive would fit nicely were the gas tank is also. So thats how messed up my trend of thought goes this late at night. Bed time.

 

[2fast4mom]

Great posts Whipper, we def think along same lines. Maybe we should do an episode on my tv show "Things you should never do to your boat after midnight". But that's an uninterrupted time of day (night) for me and it seems to be when I get the most accomplished.

I'm always intrigued by hearing of things that gain or lose mph, and experience has shown that experimenting usually pays off. Having said that, as tempting as it is to do otherwise, I try to make it an inflexible rule to change just one thing and test, not two or more because then you never really know what caused the performance change.

I loved your great idea of turning the seat base sideways. I'd get away with that if not for my son and I always needing to readjust fore/aft. But yeah if Ya got one driver that's the ticket right there.

Here's something that might really help us or alternatively get us killed (that statement we ought to work into some kind of slogan, lol). Google "Bernoulli Effect" and check out the discovery made in 1738 which is responsible for making airplane wings lift and likewise has tremendous implications for gearcase, lip, hull, prop, and skeg design.

The root discovery is that the side of an object with faster moving liquid will have lower pressure. The converse is true also. So there is an inverse relationship between speed of water and pressure say like on a skeg, which is why torque tabs work. Higher speed of flow = less pressure (port side of skeg) slower speed of flow = more pressure (starboard side of skeg) thus counteracting the torque at speed.

Tremendous implications our friend Bernoulli from 1738 may inspire. Think about it....check out some of the YouTube videos too. The physics of these boats are the most fascinating aspect for me. Although a lot has been tried over the years, there still may be things that have't, and I might have some ideas up my sleeve...but again, one thing at a time.

 

[whipper]

Well then after a little Bernoulli Effect study it can also be said like this. The air flow at the bow is the same as the stern of the hull. The speed of the air is greater through out the length of the hull than fore and aft areas. This would be a low pressure area. The bottom of the hull when trim is applied creates a high pressure area were the top side has lower pressure that allows the hull to maintain that angle of forward thrust relative to the trim applied based on the speed and pitch of prop relative to HP and rpm. As the speed increases the pressure on the underside of the hull creates a higher pressure area that also creates lift freeing up the hull to have less friction of the water or less drag. Because the Design of Allisons are some what symmetrical {top and bottom the same shape from from the front} At slower than pad speeds the pressure differential is not as critical at less than pad speed were the high pressure on the bottom starts to create lift. As more lift is applied with trim the top side pressure area lowers with each bump as does drag. This creates the higher speeds that can only be maintained as log as the bottom of the hull can maintain that higher pressure area than the tops lower pressure in the high pressure area of the length of the hull. Gear cases utilize the same geometry But have a more hydrodynamic effect to relative pressure as there are always parts of it semi submerged. Darris and talked about this with the blunting of the bullet one day. He told me a story about how he had nose cone come right of one day and the boat was faster. That got him thinking and they welded a ball bering to the bullet of another case to study those effects of deflection and blowout. In effect this was the same principle as the hull were as the higher pressure was being applied to the loer section of the gearcase, as the case started getting higher out of the water the bottom of the ball bearing area was less than the top of the bearings mass to relative space creating higher pressure. The over all area of the bullet would determine how far back the high pressure area could be relative to blow out. Ideally you would want the high pressure to end and low pressure to start just before the propeller to avoid cavitation.

So in a nut shell knowing the effects of the pressure differential could possibly over come design limitations in speed to relative thrust if done effectively. Or as you say it could also kill you trying. i think a good slogan could be What doesn't kill you can make you faster.. Or has that already been said.. haha thanks for that physics lesson now im even MORE obsessed. haha Hears cool pic i noticed a while back. it really shows how in the design Darris obviously had intent to create a hull that was as symmetrical as you can an open boat. If you continue the top lines they would match the bottoms vee making it almost Symmetrical . The sides of the XB21 in the pic are same top and bottom also. The XR2001 is the most obvious to that regard.

 

[whipper]

The first 8min are awsome!! From 6min to 8min really applys to Allisons im thinking. Maybe the GS at 106 with its Alpha or angle of Attach reaches stall speed?

 

[whipper]

Im chasing the same big top end number Whipper . But don't get your self killed doin it ! Maybe its time to hang a 280 on it and Power your way to triple didgits ! That ol promax maybe tired and If it breaks it wont be pretty . Be safe my friend .

Ya I wont be chasing it anytime soon with my motor. Its more about safety to understand all this stuff at any speed really for me. The more any of us can understand the physics of the dynamics with any fast boat the safer they will be. Its always interests me when, what and why there is any top speed of any hull. The term [Hull speed] can have many meanings from boat to boat. There are guys with heavier boats than Allisons approaching the 120 mark with a single 300xs for instance. Stable at 115. Light some times can be a problem but as Lou and XXXR01 says its all about the Hydrodynamics and Aerodynamics relative to thrust as with anything. Some of those Turbine powered 130mph river racing boats use foils at the bow to control the shape of the hole there punching threw the air and how it shapes across the hulls high pressure area. They have 1300 hp on tap with a hull shaped liked ours. The down force on the bow is so great the foils on either side are like mini wings to help the bow from creating a high pressure area above deck like what guys describe with the GS at 104-106. Todd and Ziemer when there flying there hulls at those speeds have the bow and whole hull up very high. My guess is if you took a measurement from the tip of the bow to the water on any GS going 105 the distance would be very close to the same to keep that air flowing hard enough under the hull to keep the bow from forcing down. If the stern gets so high that the air flows out of from under the hull to fast it would loose that pressure keeping it up. = not so good. Even the SRV at 115 has that high bow and whole hull up attitude. The gearcase design being whats in the water the most has a hudge effect on this both hydrodynamical and for a smaller part aerodynamicly. Beside never driving mine there myself it helps to know the previous owner has had my hull those speeds with my same set-up expect power. But theres also the {other} hulls that are doing 115 and the mythical GS that went 112 and 110 routinely that everyone has a hard time believing. That guy told me it was because of the weight added to the hull to help to stabilize it past 105. Solo past 105 was freeky as hell. Two up way way better. That was 2 240 lb guys at the helm and a 335 hp motor with a messaged gearcase from tooter and giant foil on the gearcase. That motor was 450lbs with gobs of touque. Must like the SRV setups going over 110 today. Whats interesting is those same SRV,s are the same speed or in most cases a little slower than the GS with the same power. But they are able to all do over 110-112 with a 300xs. That is were the dynamics of the relationship to thrust and hull shape have an important roll to over come what it is thats limiting the hulls speed. I want to figure that out. But live in the proses. I have a pretty good idea what it will take other money. Were as the latter is my limiting factor!! haha

 

[whipper]

Whats really funny is a couple of years ago I took my boat to work to lift the engine were we have this giant fan its about 10ft across! i duct taped a bunch of red ribbon to the bow and hull all over the place. and turned on the fan like a sort of make shift wind tunnel in the breeze way. the top ribbons were all flapping around the bottom ones were sticking to the hull more. When i would crank the trailer up you could see what was going on. That was around the time i was asking about the foils on the bow and that river racer type wing. i took some pics with my old phone but the phone broke before I could figure out how to up load anything. The guys at work saw it.haha There all scared to drive with me after that.

i have some drawings of a race hatch for the GS. The large cockpit area sucks the air into it from 50mph up big time as it goes over the top of your head and slams into the back seat then swirls around in a dead zone at the floor up to the back of the front seats. this isnt helping keep the lift as it creats a spot of high pressure toward the mid section on the top of the hull. Imagine the effect on a 747 if the hole back half the fuselage came ripping off at 650mph. Its been done will poor results. So cover that area higher up is a big deal if your looking at having better flow. i keep meaning to talk to Mike Nass about making one out of kevlar with a tail wing at the cowl. I posted a couple of years ago what the dimentions were on the SS and XR02s rear fairing but they would still need modification quite a lot. So figured I may as well wait until I can have one that goes all the way forward. Tuff boats has a nice one that actually will fit pretty good with there 21. I was talking to the owner there about it. BTW he also said he learned alot about how to build the Tuff 21 from Darris. Go figure. Nice guy though and freely shares info.

Basicly the XR2001 has all the right stuff to go faster than you ever want to go in a 20ft hull with the least amount of power in a Vee hull. So if you can make a GS go 112 then 105 will be a hole lot safer is the relative theory behind this. i know with my 225 even 94 is so trimmed out and that poor little motor stressed to the max isnt as safe as driving 88mph. Its all relative to thrust. Then its all about the hulls speed after you have the thrust to go faster safer. Or I should say as safe as speed is witch is not so safe the faster ya go. I think 80 is a walk in the park and must be for most also. Thats like a good cruising speed with these hulls. Requires very little trim can be done with a 225 easy at anywhere from 1 inch below to 1 inch above with relative safety. Guys with a 260, 280 ,300drags probably feel this about 90-95. Thats just because of the difference in thrust. sorry for the Long post AGAIN. I didnt want to leave much out because i dont want anyone to get the wrong idea and think this is what to expect with there new Allison. Though most of this well documented theres still a long learning curve to get to 80 safely for the first while. After that its all about setup and understanding all this mumbo jumbo that relates to these masterpieces Darris designed for us to play with. God Bless his heart continue to make and come up with the future today. If i think all crazy about this stuff and [Lou] hehe imagine what goes threw Darris mind at night being the creator of all these boats.

 

[1badss]

I have to tell you that the 03 to me is the worst driving A bote I ever had . The next worse was the SS . I love those 02's ! The 02 is the standard to which all A bass boats should be held to . Then again, what do I know ?

 

[whipper]

I have to tell you that the 03 to me is the worst driving A bote I ever had . The next worse was the SS . I love those 02's ! The 02 is the standard to which all A bass boats should be held to . Then again, what do I know ?

Thats what I hear to. Oh i men the 02 part. haha Owning a XB02 is on my bucket list. Ill trade my GS with a tired 225 promax for a XB2002 with a fresh 280 if anyones interested. Have to be straight across. and meet me half way.

 

[2fast4mom]

Hands down, the XB2002 and XR2001 are to me the easiest handling, most forgiving, and fastest hulls currently available new from Allison. However, there is the legendary XR2002, which I just picked up as a project boat. It's a 1985 and will likely become the topic of a new restoration/rigging thread sometime this summer.

Great posts, Whipper! Favor / question: the pics you did with the red curved lines showing symmetry....could you find a pic of an XR2002 at high speed shot from a side view and apply the red line treatment? This could well explain the XR02's status as the fastest top end Allison produced, holding the world speed record for pad vee hulls at 129mph. I theorize the reason after consulting Bernoulli and seeing your posts. What caught my eye was your pic of the XR2001. Now...The bottom of the 01 is either rumored or substantiated to be sort of a direct "lift" from the XR2002..essentially identical. I've got both in the stable right now so I can do some detailed measurements as time allows.

But have a look at an XR2002 running at speed. Remember that the surface with the faster air moving over it will have lower pressure (net effect: less apparent weight and hence lift) and check out XR2002 with XR2001. Use your superimposed red lines. I'm guessing it will be quite easy to see which boat has the fastest air moving over its top cap! This effect is logarithmic with speed. The faster you go, the more it matters.

I was really talking about gearcase design when invoking Bernoulli but the hulls themselves of course fall into the same category of physics. As for the ball bearing nosecone, I've heard the story too but am reserving judgement because I have been told it is possible to make that rounded ball at the nose TOO large in diameter and that this might cause early blowout. Remember that when we talk about high vs low pressure we need to be quite specific if we are referring to the effect relating in the X or Y axis where gearcases and skegs and props are concerned, because the forces at work here are not just up / down (Y axis) as on a hull. With a lower unit you've got up / down (Y axis), sideways torque (X axis), paddle wheel effect of prop (X AND Y axes, and height-dependent), and most relative to your comments, PRESSURE vs. VOLUME of water offered to the propeller.

What does our pal from 1738 say about VOLUME of fluids at fast vs. slow speeds, relative to each other? There will be a quiz at the beginning of the next class, lmao! Hint: directly related and inversely proportional....I think? Ok that's more than a hint.

Happy Bernoulli-ing! Lol

 

[2fast4mom]

Whipper I just watched your video from the Dharma Initiative and despite its antiquity, obviously the rules don't change from then til now!

Great stuff and it got me thinking....At around ten minutes they start talking about "stalling" an airfoil. Could what many have ASSUMED to be "prop blowout" over the years at high speeds, in actuality be an aerodynamic STALL of the hull, produced by too much trim and resulting in too high of an angle of attack?

 

[whipper]

Whipper I just watched your video from the Dharma Initiative and despite its antiquity, obviously the rules don't change from then til now!

Great stuff and it got me thinking....At around ten minutes they start talking about "stalling" an airfoil. Could what many have ASSUMED to be "prop blowout" over the years at high speeds, in actuality be an aerodynamic STALL of the hull, produced by too much trim and resulting in too high of an angle of attack?

Thats what I was eluding to in post #25 ,yes that could very well be a contributing factor. Also the faster you go the more the bullet would be pointier that rounder. The SM when not above the pad could contribute to blow out at above 106 on our hulls because we tend to have them still touching the surface as posed to a tunnel hull that raises there case more having a lesser effect on the {bubble} vs gearcase length to prop. Then there is thrust to over come the effect of stall. It would take more HP to run with less trim at the same speed. A good example was Helmuts 152mph run in an STV. He was useing a SSM case that has a pointier bullet more slender design and a very small two blade prop with well over 300hp. There are not to many setups like his in pleasure boats there for most guys with STV run 110-130 tops. His setup was 152! I would be surprised if anyone ran 130+ with a STV on a stock SM. All the 160-200 mph hulls have massive thrust and very long gearcases with sharp bullets for this reason. David ran his 02 122+ lots with over 300hp and a very high gearcase hight bullet probably wasnt in the water... If his case hight was lower the bullet would be sending air to the prop and there wouldnt be enough thrust to propel the 02 to those speeds. The 112mph GS had 335+ hp with massive touque. He utilized wedges to stay neutral trim allowing a better angle of attach. The lift would have been created from the velocity more than trim hence over coming the stall situation with less power and more trim at 106 most guys set-ups discover. He also had wieght forward more keeping the bow down as without got flighty. {stall?} There is something i have noticed about all of the vee hulls that go over 110 that are shaped like the Grand Sport and are 950-1100 lbs. They all have 335+hp and massive torque engines and worked gearcases. The same doesnt apply to the same extent on the XB02,XR01 &02 and lesser extent the SS because they are all Narrower and Shallower hulls that also are much lighter. So they can achieve speeds over 110 with a good angle of attach much easier than the XB&XS03 can with the same power.

i would have to think that in order to setup a GS to go over 110 you will need a few things. A lower angle of attach to maintain a high pressure area under the hull with just the right amount of low pressure consistent above. It will take 335hp min motor with good touque. A 32 pitch prop mated to a elongated gearcase with a more pointed bullet than a stock SM and at least 7000 rpm but 7500 would be better so you wouldnt need more pitch than 32. 3deg wedge,race hatch for better air stream and a burning desire to even attempt this. The XR 2002 isnt a boat its an arrow!!

 

[TBuck2003]

Whippy you need to become an Author bro' !!! Tons of good points on this topic but I will give you my thoughts and some of them or most may have been covered. Talking to Darris he told me that the GSE develops 5-600 lbs. of down force on the deck at 95 plus... Regardless of horsepower the faster you go, the worse it becomes. Obviously faster with more h.p. until you hit the wall. I believe I found the wall on my GSE to be 105-107 ish. You were talking about running bigger wheels to get more speed. Here is my thoughts on that. First you have to prop where the power band is of the motor. Of the motors mentioned you have to be 7500+ on a 260 and on a 280 possibly a bit more. The S3000 or Drag makes peak power over 9,000 rpm's. Yes Shook ran a 29p prop but a lot of set up and motor height goes into that equation. Don't you think he would of run a 32 if it produced more speed?? That was with I believe a small gear case also. The other factor of more pitch is the torque loading factor that happens with said prop. Instead of the prop screwing forward on a horizontal plane the prop climbs to the surface because of the torque reaction trying to turn more pitch. Combine that with down force on the deck, and you have a tail lifting nightmare, that usually does not end well... That is why the guys you mentioned run 26-27p props at a high rpm. I can tell you first hand there is a major difference between my XR 2002 and my GSE at similar speeds. With Xr I could talk on the phone at 106-107... MY .02

 

[whipper]

Whippy you need to become an Author bro' !!! Tons of good points on this topic but I will give you my thoughts and some of them or most may have been covered. Talking to Darris he told me that the GSE develops 5-600 lbs. of down force on the deck at 95 plus... Regardless of horsepower the faster you go, the worse it becomes. Obviously faster with more h.p. until you hit the wall. I believe I found the wall on my GSE to be 105-107 ish. You were talking about running bigger wheels to get more speed. Here is my thoughts on that. First you have to prop where the power band is of the motor. Of the motors mentioned you have to be 7500+ on a 260 and on a 280 possibly a bit more. The S3000 or Drag makes peak power over 9,000 rpm's. Yes Shook ran a 29p prop but a lot of set up and motor height goes into that equation. Don't you think he would of run a 32 if it produced more speed?? That was with I believe a small gear case also. The other factor of more pitch is the torque loading factor that happens with said prop. Instead of the prop screwing forward on a horizontal plane the prop climbs to the surface because of the torque reaction trying to turn more pitch. Combine that with down force on the deck, and you have a tail lifting nightmare, that usually does not end well... That is why the guys you mentioned run 26-27p props at a high rpm. I can tell you first hand there is a major difference between my XR 2002 and my GSE at similar speeds. With Xr I could talk on the phone at 106-107... MY .02

Agree 100% on all points Todd. Author haha I know im sorry. Mind you it got you to write the longest post ive ever seen you write. I as always VALUE your opinion as you are one of the guys i always refer to as the fast guys who knows there setup obviously. i know your opinion and do agree about the big wheels. I was more referring to the SRV guys running them with the DBR 300XS motors. Thats the only way they can get up to those speeds there running with the rpm limited even with the DBR stage 11. BUT I cant help but always wonder about the guy with the 335 hp 300PM that did 110-112? That always sticks in my mind. Then the SRV guys running the 300XS over 112 also with hulls that are normally slower than the GS with the same power. Its hard to not wonder about that. But would agree the smaller wheel the better the handling besides that. To have the rpm and run a smaller wheel i also think is way safer. I wont bother even turning a a 30 anymore. i have the revs and my 28 basicly does just as good only better down low. For 1 or 2 mph its not worth less performance every wear else. 27 is the majic number i think also. Ive said that lots but finding one like yours is what I want. Not the knob but the actual T3Xsport

 

[jay j]

I have had 3 grand sports and to say the least they were very fun boats to 90 -95 mph. I talked to Dewitt Deweese in length about the setup and he took a gs to 114 with a drag motor and only did it once. After he did that he took the motor off and never attempted a top end run again with the gs. Not only was it a handful getting over the 105 range but was a hairy ride back down. I had a boatworks 260 on one of mine and ran 99 and change but never wanted to go beyond that, of course i'm a big guy and the counter weight only helps so much. This has been a good read. Thanks for reminding me of some lost thoughts.

 

[mikesufka]

114 mph in a Grandsport? Wow!!!!!

 

[Lotus 50]

I've been following this with interest. I've wondered before about the SRV vs the GS. The SRV is a pretty big boat, and Ken is at 114 with a modified 300XS.

But 500-600 lb of downforce is a lot. I think that negates the hull as wing theory of lift. Sorry Bernoulli. The downforce has to be overcome by the prop. Lower prop = more leverage = more lift. But lower prop = more hydrodynamic drag, which is probably more important than aero drag, as water is 784 X more dense. Or prop lift could be increased with trim, but if the propshaft is angled relative to the direction of flow, there is a greater chance of flow separating, ie blowout.

My related question is SS vs GS speed. I think they should be about the same with a stock 225 PM. Would either redline a 30" wheel? That's about as big a prop as I'd want to drive with.

 

[whipper]

I couldnt red line a 30 stock but could after some mods barley. JR could a few years ago with his 225SS with a Brucato acu and heads. Thats why i did the same. When my limitter was 6750 I couldnt but when my limiter was 7500 with 33cc heads I could. it sounds strange but thats what happen. Also I raised my motor witch probably had more to do with it. I find it easier to spin a 28 to 7300 than a 30 to 6750. Ive only had one 30 that I could do that with and it broke, it was so thin. The other 2 I couldnt get past 6600 or so. Im quite happy turning 28 pitch to higher rpm even though my motor is side pinned its lasted a long time. the Brucato acu and tighter heads were great mods. I would add SVS and change my fuel to prostock also and those mods turn a promax from mild to wild. I did a poor mans fuel system for more direct flow. But what a difference even that made! You just have to know the gas is good with no water or run aces as insurance. 40/1 for 9 years and counting . jinks

There is a few guys with healthy promax builds than can turn a 30 with a GS to 6750+ at sea level but not many that ive heard of. Your SS should run 5mph+ faster than a GS with a 225 promax. The more power after that a little bigger differential like with a 260 +. It all depends on the boat, power, the driver and setup though really. No two boats are the same and motors especially!! If I had a motor that guy my size could run 100 with his GS and put that motor on my GS on that same body of water I should be able to run 100 as well with the same setup, prop shaft height and trim. I wish i has some of those motors i hear about or lost 100lbs..

 

[2fast4mom]

Thank you Whipper for post 33, your superimposed red lines as requested for the XR2002 speak volumes. As suspected, it's quite easy to see which surface will have the faster air movement at speed and it's the top cap--ensuring an area of low pressure with high pressure building under the hull, for lift just like an airplane wing. In fact, the red drawing around the XR2002 even resembles the profile of an aircraft wing more closely than any other hull I've seen from Allison.

Todd, points well taken however I tend towards skepticism regarding that "500 to 600 lb down force" on the nose of the GS at speed. Think about it. That's over the weight of the outboard! If there were that much downforce, the bow would simply plow, not lift, let alone pick the whole boat up out of the water so it's level on the pad....I think those numbers might be off by a factor of ten....then again, what's a decimal point amongst friends? Lol

 

[whipper]

No problem Lou. But i was looking how I drew than and went to the top of the fairing. If i just did the Top of the hull the lines would be very symmetrical. Thats Chummy get her done with a 200xs.. Theres alot of changes to the low pressure area after the wind screen. If you did this profile to all the fastest Allison's against the rest of them descending to the XB21 as far as power to weight and windscreen size. My guess is the Fastest Allison's have the smallest windscreen and as the screens get bigger the hulls are slower. It would go like this. XR2001 and XR2002 close to the same both capable of 130. Then the XB2002 122 but Shook has gone as fast as a XR with his but safe to say the XR is the hull you would rather want to be in over 125. Then Super Sport 110-115 and a few faster. Then GS and XB03 close to the same in that 105-107 with only two Ive heard of faster 112 with the 300 simon motor and the one jay just said with the S3000 114. I can believe it with a S3000 but must have been a death wish ride. haha Then the XB21 not only has a large screen for protection but power to weight plays in more also so 100 is a few guys with a 300xs I belive if heard of. These speeds represent the fastest internet top speeds that guys have heard about or seen but other than Glen and Shooks speeds that have been extensively documented. The 105-107 XS XB 03 speeds have been well documented like Todd and Ziemers but the 112 and 114 have no pics or GPS readings. To be fare the 112 GS and above were probably a little before we had snap shot pics from out phones and posting with a camera as easy as we can today. i know for me if i ever decide to do a run that will be faster than anyone has ever heard of i will make sure the camera is on the GPS the whole time. We have that technology now quite readily. so unless I see it its hard to believe if the speeds are extraordinary. Not calling anyone a lire but you see the point im sure. i was watching a guy do 122 the other day with the camera on the GPS. i was like wow thats what he did alright. 300X clamshell screen . think it was a Lanier LCB, Is this a tunnel or a vee hull?? Bow looks vee but maybe a Stoker type tunnel?? The way he is steering says Tunnel hull no balancing just steering. Watch this.