New Member Mentor Thread


I wanted to start a thread for new members, and old ones too, about the technical aspects of Cor boat racing. Anyone who is about to race, has raced, and even those who know it all might learn something new. Some ground rules first, any question is fair game, there may be some right answers, wrong answers,but lets try to keep the Ego out and the undersanding, underscored. Since I learn the most from people I respect and know their background, I will begin by sharing my background. I have owned R&R Prop Shop for nearly 19 years, and managed to learn a thing or two about high performance propellers and fast boats. The first race boat I ever owned was was a 9 foot Weurly hydro with a 9 hp Wards Sea King, modified by my dad who also raced boats in the '50s. My younger brother and I used to get up early in the morning and tear around a lake called Higgins Lake in Michigan, that was 1967, and I'm still wondering how I survived those years. In the Ninetys, I took up RC boat models and designed and built outrigger hydros, by the late Ninetys I had raced to 3 National Championships in two different classes. In 1999 I bought my first Mod VP boat, a Hydrostream HST with a broken 3.0 liter Johnson on it. About three years after that, Keith Lockliear let me drive his STV, not too much longer after that test drive I was "sniffing around" for a STV and bought a River Rocket from one of my customers who was scared of his. I had owned it for two weeks before I drove it to 111 mph. I started racing COR in 2010, in 2011 and 2012 I won high points honers in this growing class. Maybe the most important thing to share with you is to tell you that there is rarely a Sunday that goes by that you will not find me "on the river" at Willow beach testing something on a fast boat, usually the 234 Stoker, been that way for years. Many of my customers will come into the shop and when they learn of my racing they always say; "Was that you in that yellow boat that passed me? " "How fast does that boat go?"

007's picture

Mike Fjeld is a possible new COR member. We are currently reserving #11 for him as he looks for a boat and set-up that meets his needs. He is a prior APBA competitor in OPC Super Sport.

Propman's picture

Props are a big part of your racing, so I thought I would start with some prop basics. First some terminology, props have some basic characteristics such as diameter, pitch, rake, blade style, blade area, number of blades, cup, not to mention hub styles. Let's start with the simple stuff and work into the more complex. Diameter is the size of the circle that would be traced out by the blade tips as the prop is rotated. Pitch is the distance the propeller would travel in one revolution if water were a solid medium, usually measured in inches, not degrees. Rake is the angle the blade is mounted to the hub. If the blade were mounted perpendicular to the hub/propshaft then it could be said that the propeller has zero rake, more likely on the props you would see on a COR boat, from 10 to 30 degrees, tilted to the aft of the boat.
So if someone has a prop and says it is a 14.5x24, this would indicate it has a diameter of 14.5 inches and a pitch of 24 inches. Blade styles appropriate for COR boats would include Choppers, ET styles, and in some cases cleavers. Most of these propellers would have "tubeless exhaust," that is to say the exhaust of the engine is not directed through the prop, but runs over it. Conventional props such as the Mercury Tempest have a tube the blades are attached to, that directs the exhaust behind the propeller. Probably enough for this post, I'll come back with some discussion of more terms, and then tell you how this works on a Mod VP boat.

Propman's picture

This thread is more involved than you bargained for, but stay with me and I'll cut to the chase sooner than later. Before I do I want to talk about one more term, that is slip, it should be one of your criteria for selecting your race propeller. Slip is the difference between your actual speed and your theoritical speed. Most of us know our actual speed, but haven't a clue about theoritical speed. Theoritical speed can be calculated by knowing our RPM, gear ratio, and propeller pitch. There are slip calculators on the web, Mercury Marine has a good one, to play with so all the math is done for you. Good racers will use the slip calculator to tell how well their propellers, engine, and boat are working together. Lets use an example to illustrate this concept. Suppose I have two propellers, both 24 pitch and I get different actual speeds and RPM's with them, which one is best for my boat? I have used my calculator to determine that my theoritical speed is 80 miles per hour. The first propeller in the test went 72 mph, so 72 divided by 80 is .90---10% less than the Theoritical speed, not bad for a pleasure boat, not so good for a Mod VP boat that is running wide open. The next propeller yields 76 mph at the same rpm, it has an exceptional slip of only 5%---now everyone will say that's the best one. Now here is where we separate the "men" from the 'boys"---Why?--answer that and you move to the front of the pack.
If all I knew was what was stated above, I would guess that the second lifted the boat better than the first, probably because the diameter and the blade area were larger on the second vs the first. Lastly, I would guess that the second propeller had more rake than the first. Pretty good guessin I'd say!*
In the end, if I were to pick propellers to try I would choose ones that looked more like Propeller #2 and less like Propeller #1.
Next on the hit list "Speed.... the holy grail of racers, or is it?

Actual data from the 234 Stoker Propeller #1 is Mercury small ear Chopper 14x24 16 degrees of rake. Propeller #2 is large ear Mercury Chopper 14.5x24 20 degrees of rake

Propman's picture

Most of the prop testing that is done by the racers in COR is pointed at one thing, how fast did it go, what was the top speed? I would like to expand that criteria list to include some other things, such as; handling, acceleration, slip, ability to avoid blowout/spin, lift (both bow and transom), and durability.
Let's start with handling, what good is a prop that goes fast if it is ill handling? If the boat chine walks, porpoises or spins out easily with this prop on it, don't put it on your boat, put it on Craigslist.
You might think of a lap in a sprint race as a drag race, a turn, another drag race, followed by another turn. Think in those terms, and you might compromise some speed for acceleration.
I talked of slip in the last thread, and I might consider a prop with a moderate slip number, but keep this in mind a prop that slips alot will be more prone to blowout, spinout and probably won't work good in rough water.
Lift is a term in propeller engineer's notebooks that refers to how well the propeller carries the boat. In other words, does the boat run "downhill," does it lift the bow? Does it cause the boat to porpoise? Parameters like rake, cup ,diameter and blade shape all can affect lift. Getting your boat to "fly" over the water and not drag in it should lead you to the checkered flag. This indeed might be the "holy grail" of Mod VP racing.
Last on the list is durability, small, frail, thin propellers may be fast, but I might argue it will be difficult to win a race with only two blades out of three on your propshaft.

So it comes down to this: prop selection is a series of tradeoffs, and a prop whose only redeeming feature is speed wouldn't make it to my race trailer. Lastly, a word about testing, try to change only one thing at a time, use a GPS speedo, the seat of your pants, and some common sense. Try to do your testing away from the race course, if you're testing props or setups during the race my thinking would be you spent too much money to learn something simple about your boat or propeller that you could have learned on your local pond.

Propman's picture

I spoke of getting your boat to fly as one of the keys to having a well set up boat. In the end, the propeller, the engine, and the hull all work together to accomplish "racing." Whoops, I forgot the most important thing, the driver. Even the best boats, cannot win if the driver can't find a good line, can't trim correctly, or overdrives it in the corner. That is another topic. Good prop guys will be able to look at a boat, the trim on the engine, the speed and acceleration and have a reasonably good idea what it might require from a prop standpoint. So let me see if I can share some of the basics. Let's start with porposing, if a boat porposes, it could be a balance issue, overtrimming, undertrimming, or a prop problem. If you find yourself in this boat, try trimming down, and up (within reason) try to make sure that it can't be fixed with the trim button. Next, I would try a high bow lift propeller, such as a Mazco RE3, if this doesn't work go to the opposite end of the spectrum, try a transom lifter such as a cleaver. If all else fails, my best guess would be a balance issue, move one of the "big three" that is the driver, the gas or the motor forward or back. So my "prop" post is morphing into a setup post, and that is a good way to sequence into my next topic...namely setup.

As the owner of a prop shop I have spent years trying to "fix" engines, hulls, drivers and poor setups all with a propeller. Most of the time this is done on the phone, so by comparison, it is easy to accomplish when I get to actually see or drive the boat. Stay tuned for the setup post(s).

007's picture

Any thoughts on trim tabs and how they might change the handling of a boat?

Propman's picture

First, lets get the terminology correct, I assume you are refering to "tunnel tabs" not trim tabs, as trim tabs would normally contact the water and be like extensions of the bottom. Tunnel Tabs would be like extensions of the tunnels. The Stoker comes with these built in, and adjustable turnbuckles to change the angle just like the trim tabs. To understand what is going on we'll have to get into how a tunnel boat works. Tunnel boats funnel air underneth the boat and compress it, this compressed air in turn presses up on the bottom of the boat and creates lift. Non-tunnel boats as well as tunnel boats also get lift from hydrodynamic sources such as the center pad and the outer sponsons. This "hydrodynamic" lift allows the boat to plane on top of the water, and as the boat goes faster and faster the hull weight will be supported on an ever smaller "patch" of hull. The real problem with this type of lift is drag, the hull touching the water drags the hull back and tends to slow it down. When you are driving along at steady speeds most (almost all) of the horsepower that your engine produces is used to overcome this drag. Now the more technical of you might say "What about the aerodynamic drag?" That is the drag created by the air "rubbing" on the hull. It is safe to say that the aerodynamic drag is much, much smaller than the hydrodynamic drag even though the part dragging in the water may be small by comparison. So now we can get back to tunnel boats, if we can reduce wetted surface dragging the hull by lifting the boat with air then we drag less in air than water and can go faster with the same amount of horsepower. Now here is a fact that might help you comprehend this better. Say your COR boat weighs 1550 lbs and you are flying along the river, the hydrodynamic lift and the aerodynamic lift equal 1550 lbs. Now imagine the situation where the driver could trim it out until the hull barely touches the water. At this point most of the lift is generated by the air and very little by the water. A little more trim and it would be easy to generate more than 1550 lbs of lift by aerodynamic sources and now what was a COR boat is now a "COR airplane." Emilio are you paying attention?

So now we have enough background information to talk about tunnel tabs. Tunnel tabs are like a valve on a compressor, if they are lowered, they restrict the opening and create higher pressure or compression, on the hull and this higher pressure pushes on all those square inches on the top of the tunnel and gives you more aerodynamic lift, wonderful right? .....Well let me tell you a story. Some time ago I rigged up adjustable trim tabs on the Stoker in place of the existing tunnel tabs. I knew that if I could go just a little bit faster, I could climb on that "magic cushion of air" and I would be the "King of the river" It did work, though not nearly as well as I had hoped. I would zip along, foot on the wood, trimmed out and operate the tabs up and down and nothing would happen. Finally, I was frustrated, so I ran them all the way down, lo and behold the back end popped up and I had another couple of miles an hour. So there I was, all full of myself, everywhere I went the trim tabs all the way down. After an hour or so of riding my "magic cushion" I happened across a wake, not too big, but perhaps I shoud have given it more respect, the boat popped up like it normally did, but when that wave encountered the trim tab all the way down, it drove the back of the boat up and the front down.. hard......after I emptied the water out of my helmet, I remember thinking: "That's dangerous as "h*&%."
In my defense, I did learn a thing or two. Tunnel tabs can be used to vary the amount of aerodynamic lift, but it is not a big difference, not enough to overcome a poorly balanced boat or a bottom that is not true. They also increase the tunnel length and the boat will act "aerodynamically "longer"....well, just say it will be somewhat more stable. Lastly, I have heard that boats that porpose at speed may respond well to the addition of tunnel tabs. I would also ask you to be careful with this idea.
Especially you Emilio!

I have thoroughly enjoyed reading your posts. Although I'm fairly knowledgeable on these subjects as well, I commend you on taking the time and effort to do this good deed. Your articles can be very beneficial to those who are new COR racers or to those who may not fully understand propeller theory and boat design.

Propman's picture

If you want to do some more "heavy reading" look into Jim Russell's tunnel boat design software. About 15 years ago I bought this software from him, I have spoke with him on the phone and he is the "Guru" of tunnel boats. The software is somewhat difficult to employ. But if you read the book that comes with it you will come away with this great understanding of how tunnel boats work.

05's picture

Pushing it to the extreme is the way to go and learn, but it is safer to read and learn than from someone else mishap's, thank you Kevin for taking the time to write and share all that knowledge.

WALTHOLLIS's picture

I like your route instead Emelio, just pin it until it becomes airborne and then back off just a bit :)

Propman's picture

Perhaps I should have titled this post "everything you forgot in Physics Class." I have been working on Greg's boat and this topic was mentioned, so me thinks it makes a great topic for my posts. First some physics, then on to boat balance, how it affects lift and the best use of horsepower. Suppose you decided to lift your boat, but you forgot all but one of your lifting straps. If you have enough time, you might eventually be able to lift the entire boat with one strap by moving the strap back and fourth until you are able to balance it on the strap. If you were able to do this and sit in the driver's seat at the same time, you would have found the center of gravity of your boat. If you were to able to do this on all the COR boats and drivers you might find measurements from as low as 35 inches from the transom to as high as 60 inches. Now suppose we switched drivers in the same boat and went from a light driver to a heavy driver we might find that the center of gravity would have moved forward. Likewise, if we decided the the boat needed more engine setback and we added setback we would find the balance point (center of gravity) would move back. Physics guys like to do this kind of measurement because it is easy to predict how bodies in motion (boats) react to forces applied to them. (propeller thrust) A simple way to think of this is imagine your boat like a teeter totter that has its' point of rotation around the trailing edge of the center sponson. Now most kids can tell you that biggest kid can be balanced out by the smallest one if the big kid moves towards the center of rotation (I always had to move in) and the small one moves as far away as he can sit from the center. If the two can balance the teeter totter they both have the same "moment arm" about the center of the teeter. Now imagine the engine which weighs 425 lbs hanging on the setback bracket 28 inches behind the sponson edge being balanced by Jonney Sories (140 lbs) 75 inches in front of the trailing edge. This is an over simplification of what is actually going on, but it is important to think in these terms. If we take all the forces acting on the boat and add them up, we would like to balance the "teeter totter" until the boat neither falls down on the front nor rolls over backwards (blows over).
I used a term; "moment arm" without an explanation. If I took the weight and multiplied the distance from the point of rotation, I would have the moment arm of that weight at that distance. Let's use the example of Jonney and the outboard. Jonney's weight of 140 lbs times 6.1 feet leads to moment arm of 854 ft-lbs. The engine weight of 425 lbs x 2.33 feet from the sponson equals a moment arm of 990 ft-lbs. So if we don't want Jonney to blow over (imagine that) we could move the seat forward to 7.07 feet from the trailing edge, (7.07ft x 140lbs = 990 ft-lbs) now Jonney and the outboard both have the same moment arm and the boat is perfectly balanced. Isn't it ironic: Here you thought in high school "I'm never gonna use this crap" and now you need to balance your race boat--turns out Mrs. London was right after all.

Now for the "TOP SECRET STUFF" from Team 234's super secret vault. Look at my avatar picture, it is a picture of Keith doing testing at Willow Beach. It shows all the right stuff; that is a boat that is both fast and very stable, yet it appears to hanging on the smallest possible patch of sponson. There is no spray comming off the sides, the only spray is behind the boat, the motor is completely level with the water, and thus the direction of travel. All of the thrust generated by the propeller is directed forward, not being used to lift the bow or transom. There is a "low and heavy" roostertail. It is a thing of beauty to anyone who knows these boats.

So here are the measurements: with me in the seat, the center of gravity is 52 inches from the transom, 46 inches from the trailing edge of the sponson. (The sponson ends 6 inches forward of the transom.) 12 inches of actual engine setback. The fuel tank is centered on the CG at 46"

By way of comparison, the numbers for Greg's Sleekcraft are:
Greg in the seat, CG is 58 inches from the transom which is also the trailing edge of the sponson. 12 inches of actual setback. Fuel tank on the CG at 58 inches

Keep in mind that boats are different and you might have different "ideal" measurements than me on a different boat, but you now have a starting point. You also have a way of figureing out how far you need to move any weight to move the CG with the moment arm calculations. Or you might call me for a little Physics lesson.

Very interesting formula you have there. Again, thank you for your input.

Propman's picture

In the last post, I had you imagine your boat like a teeter totter and I showed you how to balance it hanging on a single sling. This would allow you to find the center of gravity, more correctly this is know as the static CG, meaning sitting still, I always thought my boat was more fun to drive when it was moving, but understanding that requires more thinking. There is a vertical CG as well as the horizontal CG which I talked about in the last post. In our boats it is usually within 20 inches (up) from the bottom. It depends on how high the driver sits from the bottom, the height of the fuel tank, the size (20 inches or 15 inches) of the mid-section. It affects how the boat handles and the stability of the hull, There is some simple advice I might offer here: Keep all the heavy things in your boat as low as practically possible.
So your boat has a vertical and horizontal CG and the point where these two dimensions intersect is known as the static CG. Imagine a point approximately 43 inches forward from the transom and 18 inches off the bottom and you wouldn't be too far off on a COR boat. Now imagine as you accellerate your boat you also have a Dynamic CG. The Dynamic CG is the sum of the forces acting on the boat as it is moving. Forces such as propeller thrust, aerodynamic drag, hydrodynamic drag, aerodynamic lift, hydrodynamic lift. I know this is a hard one to get your mind around, but think of the static cg and the forces like weight applying a moment arm to the boat and pulling the bow or transom down depending on far they are from the point of rotation. The dynamic CG is like that but in a vertical sense, the forces could be up or down or back and forth. Some examples would be water dragging on the hull, it tends to slow the boat, it also has a moment arm about the vertical CG, in our example 18 inches. Another example would be the forward thrust of the propeller, it would tend to accelerate the boat, it too has a moment arm in the vertical direction. If we assume that this force is applied at the center of the prop shaft, and the center of a COR boat's propshaft is 1 inch below the bottom, the moment arm length is 1 inch plus the 18 inches from the bottom to the vertical CG. Now let's say you are making a long run in your boat and you have achieved a steady speed, you are neither accelarating or slowing down. At this point the propeller thrust equals all the drag forces slowing the hull. Just like Jonney and the outboard balance each other, the thrust is equal to the drag, and they "balance" each other back and forth. I always like to use the analogy of the "giant cresent wrench," imagine your engine is a like a giant cresent wrench attached to the rear of your boat, now imagine the prop depth is like the length of the handle of this wrench. Now if the prop is 1 inch below the bottom and the point of rotation is the bottom, then the thrust and the drag are applied at nearly the same vertical point. Now imagine that you lower the engine to 8 inches propshaft to bottom. You now have a longer moment arm, the length of the wrench is longer, and if the same amount of thrust is applied the boat will rotate, lifting the bow up, and we all know if the bow goes up so does the speedo. The problem here is when we lowered the gearcase, we also caused more gearcase drag. So it is not always a bust, but sometimes by raising the bow we reduce hull drag but add gearcase drag, now if the net sum of the two drags is less you might go faster, if the sum is more than you probably have slowed down.

So we learned that the boat is like a teeter totter both in the horizontal and the vertical directions. We have learned that driving and setting up a boat is like doing a balancing act, balancing weight fore and aft and matching trim, drag and thrust to come to the best use of the limited HP to maximize speed. It is very complex in the details and elegantly simple in the application. In my time doing this I have been baffled and amazed, dragged down and bouyed up.

Capnzee88's picture

Kevin, your articles provide great reading material. When you refer to a teeter tooter, would you by chance mean the old teeter totters that are now considered too dangerous for most modern day play grounds? I did take the time to look up teeter tooter and found it to be relative to a test tube. This sent not to be critical but in jest. Your articles are very informative. Rod

Especially on vertical CG. I have a question for you. Would the position of 6 inches in height on a 11 gallon fuel tank from the bottom of a boat make a significant difference in vertical CG? Thank you.

I should have said, would the "difference" of 6 inches make a considerable impact on vertical CG. If I'm following you on this, if the tank is in a higher position from the bottom it would create more natural leverage towards the back of the boat, yes? Or would it be just the opposite?

Propman's picture

I knew it didn't look right, but I couldn't think of a way to look it up. I didn't know that you couldn't find one on every school playground, how are our children ever going to understand physics if they can't bust their tail bone when the guy on the other end jumps off when you are not looking? I think us "old farts" have an advantage when we are building our race boats, we grew up climbing trees, building forts and treehouses. We played football without padding, we rode bikes without helmets, if we got too dirty playing in the mud, my mother would tell us to take the hose and squirt each other off before we could come inside. We had hard heads, we knew if you spun out on your bike it was gonna hurt, and the faster you went the more it was gonna hurt if you got thrown off. I learned, way too early in life, that if you didn't build things sturdy enough, they wouldn't support your weight the very first trip off the roof. How we ever survived is still a mystery to me.

Propman's picture

To answer the question of weather the 6 inches will make a significant difference on 11 gallons of fuel plus tank I would say no, but you are right in that the effect of raising it will create a longer moment arm, and the propshaft will have more leverage on the vertical CG. I don't know if you will able to detect any change in the straight away speed or bow lift. I would be more concerned about what will happen when you try to turn sharply. The slightly higher CG, along with the 72 lbs of fuel sloshing toward the outside of the turn will create a moment arm that will tend to roll the inside sponson up and the outside sponson down, this in turn will increase your chances of spinning out. Even though this is a small thing, if you could turn even slightly better on every turn it could end up a big difference after 20 turns. Bunky Hunt said it best: "A million here, a million there, pretty soon it adds up to some real money." Keep all the weight as low as practically possible.

Thank you for your response. I never knew about the theory of vertical CG until now. Thank you!

757 team

After thinking about vertical CG, I should have realized in one sense I knew of vertical CG, but never heard it used in that term. In car racing when applying lead weight at a asphalt track, one puts lead weight towards the rear and left of center plus low as possible (help lessen roll over) while conversely on a dirt track, one puts added weight to the right of center and on the high side of chassis (more roll and side bite). Anyway, I lowered the fuel tank.

Looking forward to this upcoming season. See ya' at one of the races!

After viewing the list on "Drivers and Boats", I noticed we weren't listed. I can only assume you don't consider us COR members. That's OK, we'll come race anyway, that is, if you'll have us.

757 Team

007's picture

You just need to send me your info: Of course, you are recognized as COR members and boat owners. You are invited to all meetings and races.

flying finn's picture

I dropped off the #128 COR boat at the show Wed. It is there to show off COR to everyone. Feel free to come anytime and hang out at the boat, bring your pictures, videos, chairs etc. any time. I will be there Saturday only so come then or Friday or Sunday.

Propman's picture

Attached is a picture of me finding the CG on the Stoker. I am completely off the trailer.

R&R Prop Shop
Propman's picture

Emilio can fly his boat, even without water. Under the scale at R&R Prop Shop

Capnzee88's picture

When designing and then building an aircraft, the CG is a required element. The CG must "come in" within a few inches plus or minus or the aircraft will be uncontrollable. Therefore, flying an aircraft that is out side of the CG limits is dangerous. Depending upon the design of the wing, most conventional type aircraft demand that the CG be roughly 1/3 of the way back of the leading edge of the wing. How would this knowledge be applied to the CG on a boat or could it? If not, where would you suggest placing the CG and why? On most small race boats, the drivers will move their body forward and back (depending upon their speed and water conditions) as much as several feet there by moving the CG considerably. In their case, the driver can make up as much as 50 per cent of the entire weight. Therefore, finding the proper CG on a boat where all weights are fixed is a matter of testing and will ultimately be dependent upon design of that boat and the speed at which it will be travelling. Knowing the CG of your boat is only good for one thing and that is "hoisting". Knowing where the CG should be is an entirely different subject. JMT

I would assume the majority of the COR boats are running "approximately" the same main jet size, therefore my question is, how many gallons of fuel does a 2.0 burn in one heat race, let's say at Puddingstone?

Last time I went down south, I brought way too much fuel (unneeded weight and space in tow vehicle). Last race at Salt Springs, I forgot to calculate our fuel consumption.

An answer of a roundabout figure would be greatly appreciated. Thank you!

Capnzee88's picture

My memory could be off but it seems I burned about 20 gals. the last time at Puddingstone. I'm sure someone else will chime in on this one. I think we are running 4 heats of 8 laps each. The course is about 1 mile around so we would run approx. 32 miles plus warm up and testing.

So approximately in "miles per gallon", maybe 2 miles per gallon at wide open throttle. About the same as my family Sleekcraft tunnel with a modified Evinrude XP 200 had gotten years back before I sold it.

Rod, do you happen to know the approximate distance of the course at Long Beach Marine Stadium? If so, please let me know. Thanks! I think it would be about 1/2 to 3/4 of a mile course.

Propman's picture

My boat is different than Rod's so my numbers are somewhat different. I measured Long Beach a couple of years ago and it was just less than a mile around it. With a six gallon tank I had to add between 2.5 to 3 gallons between heats and those were 5 laps per heat, perhaps a total of 7 to 8 laps plus some to get to and from the ramp. The first year I ran Puddingstone we ran 15 lap heats, and I ran out of gas at the finish line perhaps a total of 17 laps of at least 1.25 miles all on six gallons of fuel. Of course it is always considered "bad form" to run out of gas during the race. Fill up your tank of 11 gallons and run the first heat, measure how much you used to fill it back up, give yourself a small cushion and use that amount for each heat. Remember that this year the boat w/o fuel must weigh 1550 lbs. including the driver.

Thank you for your input. Now assuming you used your 6 gallon tank at Long Beach then you were able to finish the 20 lap race on Sunday, correct? If that is correct, then I shouldn't have any problem with my 11 gallon tank for that 20 lap race. Yes?

flying finn's picture

At Puddingstone, it has been decided that we will run 4 races of 8 laps each over two days on a coarse of 1 to 1.25 miles long.

Capnzee88's picture

Years ago I was "politicking" for APBA aproval of a 1 kilo course, single pin turn for records. This was not approved however I did put a 1 kilo course in for local records at Long Beach. The kilo markers (5/8 of a mile) were not that far apart from where we are currently running. We could not get a one mile course buoy to buoy. I would guess that the current markers are little more than 3/4 of a mile apart, however when you drive around a single pin you add to the distance around the course effectively making it longer--therefore, distance depends upon how you run the course. I believe I would stick closely to what you figured for your for your family Sleek. If you are figuring it that close, you are figuring it too close. Some times they wave off the start several times and you need a little "reserve" for just those times. Another way to figure is by the hour. If you burn 24 gals. per hour and you are on the water for approximately 15 minutes for a closed course race you wll most likely burn around 6 gals. with no reserve-not smart and not worth it. Carry a reserve "be happy" & don't over engineer. Rod

Thank you for filling me on what you know about the course at Long Beach.

Propman's picture

I found that my mileage varies greatly by speed, during racing/turning I use much more than on the long run. Also the faster you go the less fuel you use per mile. During the Enduro we averaged just over 4 mpg. A typical test day for me I will average 2.88 mpg over 52 miles. Unless you could tell me an average speed I don't think I could even come close to a number in gals/hour. Last year Keith drove the boat at Long Beach and we used the 31 gal tank, so I don't know exactly how much we used in the 20 lapper. At Lake Ming we used app. 7.5 gallons in the 20 lapper and something less than 5 for the ten lapper. Rod is right carry a reserve, remember all sorts of things can happen, like restarts, and all manner of "horsing" around.

You've answered what I needed to know. Thank you!

Propman's picture

On the CG questions Rod posed, Knowing where your CG is important because it greatly affects speed and handling. Whenever, I don't know something in racing, I will try to copy someone else's ideas, preferably someone ahead of me, or more experienced than me. I have offered specific measurements from my boat, that took years to figure out and test. There is some evidence that this boat handles well and goes fast. So if I can't figure how to rig and setup my boat, even if my boat is different, I might start with someone else's ideas and work from there. I guess you could always spend years figuring it out on your own. I have been forthright with this information, and I would ask anyone interested to contact me and I will offer you my best and honest advice. I am sincerely interested in helping new racers become better racers.

Capnzee88's picture

Having some idea of the importance of CG I would think that a "builder/racer" would attempt to move weight aft until the bow begins to lift excessively (with neutral trim) and the planing surface of the boat starts digging into the water causing excessive drag. The high angle of attack is increasing the drag through the air and the planing surface "pushing" water are both causing drag. You can tell when you have over reached the lift/drag (sweet spot)component when you see a nose high boat pushing a lot of water out the sides of the boat = time to start moving weight forward. Didn't mean to hi jack-Kevin's post on CG. He has a very informative "school" going and I hated to see it go dormant! I add one more thought, each boat has it's own "sweet-spot" (CG) for the speed it is travelling. As the speed increases with horsepower, air pressure becomes more effective and there is a good chance weight will need to be moved forward as the speed increases-2.0 versus 2.5 or 85 mph versus 95 mph (or more). I believe most COR boats were originally designed for around 95 mph. conclusion: COR boats, (that were originally designed for more powerful engines) move weight back then test again. Rod

007's picture

We have another new potential COR boat. 20' 2" pointy nose STV, (only one of a few).

007's picture

Eddie has his COR 2.0 Sleekcraft running finally. He sent it this video with a message,"he is gunning for us".

DaBull's picture

pictures, we need pictures. I would like to see just what APBA has mandated. I`m not against it just would like to see what it looks like. Would one out of a Texas tri-hull racer work?

007's picture

Sep 12-14 -- San Diego Bayfair (SCSC)
Sept 27-28 -- Copperopolis CA - Salt Springs Reservoir
Oct 4-5 -- Lake Ming, Bakersfield, CA (SCSC)
Oct 24-25 -- Parker 336 Enduro (RDP) Div 2 Race

Roll bar pics to follow shortly.

It's been approximately 3 months since the new rules were imposed by APBA. I would think by now at least one ardent member of COR would have installed a roll bar. Has anybody really installed one? And, if somebody has, how much trouble is it to take a picture and put it on this website so others may know what a "roll bar" would really look like on a tunnel boat? At this point, curiosity has gotten the better part of me.

franky's picture

a lanyard and a life vest.....just saying...

007's picture

John Soares is working on a bar for Keith Bandy. Material has been ordered, and are now on hand... enough to make a few bars. I believe Kevin Taylor is also working on one.

I am a newbie to the go fast boating scene.I have had many types of boats in the past(not a young whippersnapper).I have just got my hand on an Allison GT-20 with a 225 Merc.The boat and motor are both `81 yr models.I am trying to put together a hyd. steering system.So far I have a Teleflex Pro helm.My problem is that I cannot find a match for the helm or the boat.Surely there is something that will be compatible so as I can "tighten" up the steering.thanx in advance for any suggestions.BTW this merc only has one hole one the steering arm.


007's picture

If I understand your question right, in addition to the helm you will need a front mounted cylinder and a set of hoses from seastar. It should mount throughout the 1981 Mercury 225 tilt tube and will bolt to the hole in the tiller arm. You can find the part number by calling Teleflex. They also make a special ARP bolt to go through the single bolt hole on the tiller arm. If you by the cylinder new, it will come with the recommended bolt.