Mastercraft Experiment

[jipster43]

This experiment needs more pics!

 

JP :)

[MCskiFreak]

I still stand by the fact that introducing air in these areas is a bad idea! There is also a problem with the idea of treating a fully submerged propeller like a surface piercing prop. The collapse of the bubbles generates very high local forces and can damage the blade causing it to erode. The only way this can be countered is if a condition can be reached where the propeller is is super cavitating, ie when the cavitation sheet covers the entire prop from tip to root.

 

Yes it is true that MasterCraft as well as the other brands have had some very bad hull designs in the past this is largely due to the fact that most of the engineering departments lack degreed engineers let alone ones with naval architecture/hydrodynamic backgrounds. As it stands MasterCraft is the only one im aware of that employs Naval Architects.

[MCskiFreak]

Real innovation can be made through the use of CFD modeling techniques to both better understand what one of these hulls designs will do as well as improving the efficiency of the hull designs. Just look as the CC 200's hull, from a Naval Architects point of view the thing is atrocious! The amount of power being wasted to move that thing through the water is crazy, while I admit it is an amazing slalom boat, it is not the way forward.

[ForrestGump]

OK, I'll bite. Even though the 200 is the best slalom boat on the planet, it's not the way forward. Why?

[6balls]

Would seem the most efficient hulls are not necessarily the best ski hulls.  If inboard hulls and propulsion were efficient, we should expect far more top end speed from our 350 hp boats.  The Gekko's were fast despite being wide and long(more efficient?), but the wake was mighty stiff.

Have heard CC200 takes more rpm and sucks gas.  Would seem they are pushing an inefficient hull...but I want one.  A naval engineer may not have designed it, but in my limited experience (tourney only), it throws the best slalom wake.  At the end of the day whether we slalom or trick, we want the right wake.

[DW]

To attain a smooth wake, creating lift (or less downward force) at the transom is key.  This is analagous to creating downforce in a road going vehicle which also comes at the expense of drag.  To get more lift (for a ski boat), drag goes up at a cost of fuel economy and top speed since the tools used to do that create drag.  Transom hook, wide chines and reverse deadrise all create more drag than hulls w/o those features.  The actual efficiency is the L/D ratio, but it is very difficult to actually measure other than the feel and perception of the resultant wake.  Since skiers are always in search of the best wake, fuel efficiency will take a back seat.  CFD is certainly a tool that can assist in hull design improvments to assist the engineering staff improve all areas of the hull.

[eleeski]

OK, when I got my new boat I was ready to let the experiment go completely, While the hulls of the 2004 and 2011 look similar, the 2011 has a sweet slalom wake. At 28off and deeper I feel almost nothing at the wake. The pull feels almost the same as the new Nautique pull. I put up good buoy counts behind the boat. And the trick wake is perfect. Fantastic, I thought.

Until Lisa slalomed behind it. She struggled behind the boat. Now this is Lisa's first slalom ride behind ZO - ever (she prefers trick and skis at Stan's and as a guest on tricks). So maybe that is a factor. But the wake felt huge and hard to her. Easy fix, I thought, breaking out the drill.

The 04 test bed ended up with two bubbler holes. One was a 1/2 pipe a little in front of the prop (in the center of the cross member). The other was a  3/4" pipe directly above the prop. The 1/2" pipe did not cause any slippage but had a more subtle effect on the wake. The 3/4" pipe caused a minor annoying slip at startup but was quite effective. After what turned out to be not enough rigorous testing, we ran the boat with both holes open and enjoyed the boat all summer. No prop erosion, no handling issues, just a little catch at startup that felt a bit like weeds on the prop (often there were weeds on the prop also).

So I chose to drill a bubbler for the new boat with the 1/2" pipe a bit forward of the prop. No effect! Still great wakes for me and Lisa still struggled in slalom.

Break out the drill again and enlarge the hole to 1" pipe. OK this had an effect! Massive slippage! RPMs up to 4500 on startup with a very sluggish acceleration - very uncomfortable to drive. By the 55s the slippage ended and RPMs were normal and the boat drove OK. But instead of knocking down the rooster tail like the old boat, now the roster tail was inflated. It felt a bit softer but it was bigger. As an interesting aside, the trick wake might have gotten better. There is a tiny second wake in the middle of the table - this got smaller. Still, definitely not a recommended modification. My fiberglass skills will be needed to repair this hole. In the mean time, capping the pipe brings the boat back to stock.

My guess as to what happened is that the forward bubbler location drew air into the entire prop surface. It only takes a bit of air to replace the cavitation generated air (why the 1/2" pipe had little effect). The rest of the air interfered with the prop and was just extra volume in the rooster tail. Why did the 3/4" pipe on top of the prop work on the old boat? Perhaps the air was not drawn fully into the prop. That airstream acts as a barrier to the propwash coming to the surface.

Ski boat hydrodynamics is very complex. Design is an art, not a science. Perhaps a naval engineer could model a rectangular block and make some relevant predictions, but the many compound curves and angles of a real ski boat add too many variables. Mastercraft is a great company for evolving their designs. My 2011 is a way better slalom boat than my 2004  and a bit better than Stan's 2008. And at least equal to the Nautique for me.

This board used to be called "slalom tweakers" for people to share the ideas they were trying. This is an experiment in that spirit. Not every experiment is sucessful - but still should be shared. But not every experiment fails either. The experiment will continue. Next is the 3/4" hole over the prop. Who knows, maybe the 2012 MC will have a bubbler that works!

Eric

[A_B]

Hydrodyne use to test some hulls in our lake. One boat had a transluscent hull and no floor boards except for drivers area. There was also a plexiglass section in the floor above the area from rudder to in front of the prop.

They were looking at waterflow through the plexiglas floor.

Maybe you need one of those?

 

To me, start with the 97-01 SN hull and make tweaks to get rid if the dip between the wakes at 38/39 off and that would be close to perfection - without running at 4200 rpm for 34 mph.

[DW]

Eric's experiment is the perfect example to where the application of CFD would be extremely helpful.  The pressure and streamline mapping could show the differences in water flow thus indicating to Eric more accuraltely where to install the bubbler hole and perhaps even help with sizing.  CFD does a great job of painting the picture of what is happening along the surface in question.  Actually, in typical experimentation, a 50% success rate as in Eric's case is pretty damn good.  You might try adding some hook to the transom to see what effect that has on the bubbler system, since you can do that with some shrink tape and small wedges.

[Razorskier1]

For 2011 the MC 197 has a new strut on the shaft that has a sort of "bullet" shape on the front of the strut.  MC has been testing this in side by sides and when they did the skiers universally preferred the wake of the boat with the new strut.  I am sure you can find pictures of it online, and could probably modify your own strut if you were so inclined and save yourself drilling a hole in the boat.  I saw one up at Midwest Mastercraft.  Should create the same effect.  Gives the prop some slip and puts some bubbles in the wake to soften it.  They claim better hole shot, better top end and better wakes -- sounds like a low cost trifecta to me.

JR

[A_B]

High performance I/O drives have bullet tips and they have been known to add mph over standard round nose cones. Not as much drag with the Strut but I'm sure it couldn't hurt.

[Chef23]

While I think it is cool you are trying new things I couldn't bring myself to drill a whole in my brand new Mastercraft

[MCskiFreak]

Shane H.

 

The reason that I do not see the 200's hull design as the way forward is because of its inefficiencies, the design was reactive, something they tried worked, once they found a good slalom wake they stopped. This is the reason I see CFD modeling being so crucial, it allows the user to run many different iterations of a hull designs to find the one that offers the customer the best performance, both from the sport side as well as from an efficiency standpoint.

 

Something that has bothered me for a long time is the shear weight of the hulls from all major manufacturers. There is simply no reason for 20' tournament slalom boat to weigh in at over 3,000lbs. It is time for manufactures to start using closed molding technology!

[A_B]

Agree with the 200 going in the wrong direction. I am a CC guy always had one and thought I always would, but, the 200 seems to be going in the wrong direction in hull/engine efficiency.

 

We need a v6 powered ski boat not a v10.

[MCskiFreak]

That is my feeling exactly! Unfortunately the mentatlity at the big three seems to be if you can afford a $50K + boat you can afford the gas

[thager]

Bring back the 196! While they're at it bring back the dealerships that were stabbed in the back.

[Mateo_Vargas]

I also saw the new MC bullet strut on some boats that arrived last week. Couldn't take a picture because the card wasn't in my phone. I might be able to get a photo this week.

[kona]

http://www.mastercraft.com/teamtalk/attachment.php?attachmentid=62641&stc=1&d=1288385651

[skibug]

And what is the pitch for the bullet strut?

[Jody_Seal]

Mark my words: They will break a few struts between the barrel and the web. Not enough material to sustain structural integrity with the amount of Torque and HP now available in these boats. A lot of inboard racers cringe when they are told these ski boats are running in excess of 400HP and still utilizing a brass- Nibral strut over Stainless Steel. Talk about an in efficient drag on a boat this thing will take 1-2 mph right of the top over a standard type strut, Butt!! I would assume it aids in tracking and may have some impact on the wake. Another thing that strikes me is the amount of space between the hub of the propeller and barrel of the strut again not an efficient condition for an inboard. looking at the picture the shaft may be not attached to the motor hence the large gap between the two.

[DW]

Very interesting idea.  The bullet nose is actually quite common on newer design cruise ships, it aids in drag reduction and vastly improves the stability for the boat itself.  It will be very interesting to see the characteristics this provides.  Also looks to be a retrofitable modification to older MC's. 

Nice to see innovations coming in the newer boats particularly for the slalom junkies after being abandoned for about 10 years during the wakeboard explosion in popularity

[MCskiFreak]

From what I have heard there is almost no reduction in the top speed of the boats with these struts. The whole idea is to soften the wakes that bulb is designed to be directly in front of the water flow going to the prop at the boats optimum trim angle. The 300 uses that same strut design and it has actually increased the boats efficiency due to the reduction in air bubbles.

[jipster43]

I have no idea what I'm talking about here, but if there is question about the structural integrity of the brass strut, why not make 'em out of stainless steel as Jody mentioned? I'm still waiting for the video of Eric drilling into his new Tournament Team! JP :)

[MCskiFreak]

It is not a difficult process to calc. the stresses that are going to be induced so if the engineers at MC and the supplier are competent they will have done the calculation to ensure the product can handle normal working loads.

[DW]

The loads based on the power output of the engine should not be transmitted to the strut as in theory it really acts as only a bearing housing unless there is enough torque to actually bend the shaft in acceleration as opposed to a slight twist in the shaft due to the acceleration loads.  What will increase loads to the strut would be an increase in engine speed as that will accentuate any balance issues with the system and if the prop or shaft are out of balance or bent.  There probably will be some increase in loading due to the bullet nose when there is non symmetric flow across the rudder housing, perhaps in the turn around island.  An impact will always have that negative effect.

[Jody_Seal]

Back when this thred started I cautioned Eric on his experimentation concerning introducing air to the prop and rudder area of his MasterCraft. Their is probably no one on this forum that has worked in development of inboard specific boats including the Engineers that arm chair their Theory and calculation ideas and process here on this site. They also have never been tossed out nor had an Inboard on top of them and swimming out from under an upside down one. Inboards are finicky beasts and the slightest over look of under water appendages can cause catastrophic consequences. Most of the Inboards we use today are barrel sided hulls That under the right circumstances can find and alternative surface to run on, This is not a good situation to be in. even today their are tournament boats that under the right condition will not go where the driver intends them to go under power. As for the new Strut That MC has come out with it looks like they have another gimmick (as do all the manufacturers) to add an increase in the price of their product. I am sure that their are benefits to the device but again I would have utilize more material on the web between the base and the barrel. Hopefully MC did a full battery of testing and this has had many many hours of R&D under as many a condition that can be thought of! Then again it is the unknown that causes problems.

[Mateo_Vargas]

I think the chicks will dig it.  Kinda like hanging bull nuts on the back of your pickup.

[Steven]

You're right Mateo, those "Bull Nutz" really get the women going!

[Jody_Seal]

I had a set hanging under the platform of my 09 6 liter Nautique (Great jump boat).

[Steven]

U probably couldn"t keep the women away could u?!

[MCskiFreak]

The idea behind this strut is not to introduce any amount of air to "soften" the wake, but to provide a cleaner less turbulent flow of water to the propeller, the end goal is the same as Eric's idea but without the chance for catastrophic reaction to the modification.

[Mateo_Vargas]

So Eric wanted an innie.  MasterCraft went with the outtie.

[ForrestGump]

Not the first time that MC has gone with an outie appendage on their running gear. Anyone remember the 98 190 that would chine lock without the winged rudder?

[Dirt]

Take it easy shane, I have one in my driveway. Any new stories

[MCskiFreak]

The design has been proven elsewhere in the marine industry as well as on the 300 as a way to improve the efficiency of the propeller and is an enhancement over the existing hull design not a necessity as the winged rudder was on the 98. For any detractors of the design the strut was designed by there Naval Architect, the only one in the inboard industry I might add, who understands the hydrodynamics of the hull, underwater appendages and propeller better than 99% of the people on this site.

[skibug]

Yes, but is this Naval Architect a skier and how long has he been at MC?  I have an 09 197 MC TT (first MC I owned).  The wakes at 22-28 are quite a bit worse than any other ski boats I have skied behind in recent years ('03 Malibu RLX, '10 Malibu LXi, '05 196, '06 196, '07 196).

[MCskiFreak]

I do not know if he is a skier or not, but he has been with MC since '08. The '09 TT 197 hull has not been changed since MC got the hull dialed in like 2005, so he had no hand in the design of that hull. The 197 does have a pronounced hump up to 28, and just the nature of hand laid fiberglass construction lends itself to large variation in both tolerances and weight, this could be an underlying issue with your particular boat. Hopefully he is a skier to help better understand customer needs but at the end of the day if he understands fluid flow and planning hull hydrodynamics (he should since he was a nav arch. for Fountain powerboats), a good hull design will come out of that knowledge whether or not he skis.

[MCskiFreak]

After speaking with one of my professors today whose specializes in high speed planing craft, and theoretical hydrodynamics he verified the legitimacy of the new strut as a way to both improve the wakes and efficiency. This is the case because of the nature of the flow around the shaft and strut. With this new strut having the projection causes the water to be broken up in a less destructive manner by the shaft and strut. This makes the propeller operate more efficiently because it is not experiencing fluctuation in loading. The strut also has the welcome side effect of reducing the vibrations imparted on the system.

[eleeski]

As a mechanical engineer who took a few fluids classes, fluid dynamics is exteremely complex. Making design features that perform based solely on fluid dynamics is going to be pretty random. Tried and true experimentation will prove to be much more valueable - especially when you are looking for subjective feel improvements.

Today's boats are designed to optimize skiing characteristics. Efficiency is ignored. So many other critical factors for boat design are not relevant to the skier. Tweaking a good design is the most reliable way to make a better ski boat.

MCskifreak is right about the weight. Advances in materials and molding techniques should be able to significantly lower the weight (and hopefully the materials costs) in a proven hull. Ballast if the weight is needed for skiing but keep it light so we can tow our boats with a mini (like in Europe).

I love my new 11 MC but I'm going to buy a strut!

Eric

[kona]

So why not a strut with a wing to generate lift. ale-hydrofoil ?

[MCskiFreak]

The idea is based on the solid principles of wake field distributions and how they flow around a body, pick up any intro to Naval Architecture book, and you will see where the idea is based.

 

Unfortunately the material cost remain about the same for open mold vs. vacuum bagging. The only way to save money is to get the line workers proficient at the process and thus reduce labor costs.