HYDROFOIL ENHANCED HULL

[Dacon62]

Can a DD boats wake be improved substansially?

Can a V drive throw a tournament level wake?

 

What if you installed 2 (one front, one rear) or 3 (one front, two rear) small, limited lift hydrofoils on a DD or V drive to reduce it's displacement to 2/3 of it's normal weight at slalom speeds. Using a V drive as an example let's say the front foil, maybe attached to the bottom of the front tracking fin, would provide 400 pounds of lift with the transom mounted back foil(s) providing a total of 800 pounds of lift. Maybe the lift would need to be 50/50 (425 lbs front and 425 lbs rear) for a DD or maybe for both. Don't know what the ideal set up would be just figured the V drive is rear heavy and more lift may be needed at the rear than front. That would give approx. 1200 pounds of lift to a 3600 pound 20' V drive and approx. 950 pounds of lift to a 2850 pound DD. I would think that the wake would be much improved in both cases. Could this actually make a V drive a decent slalom boat?

 

Your thoughts......

 

 

 

[Steven_Haines]

That might work for lift but would potentially screw up the handling characteristics of the boat. Don't know for sure, just a w.a.g.!

[eleeski]

Who's stealing my brainstorms? Of course I am planning to add the foils on my ski boat to see if they work well enough to put on my airplane.

Eric

[ForrestGump]

Lift alone can cause significant problems if you don't design the supporting hardware around it. Ask mastercraft. In their testing on their new hull, they created enough lift in the tail to make the boat undriveable. It reduced the effectiveness of the tracking fins and rudder, as well as the efficiency of the drive system(propshaft and prop). At one point they were ordering new castings of rudder and fins that were much deeper in order to test if they could get the tracking back.

[Waternut]

Hydrofoils are really cool but there are some pretty significant drawbacks. In a sailboat or a cruising ship/boat, they are awesome because they smooth out the ride and have less drag. In a water sports application, we are ultimately concerned less with fuel economy and passenger comfort and more concerned with wake characteristics and driveability.

 

The biggest problem with any kind of lifting device is that it doesn't come for free. You either sacrifice wake characteristics for handing or handling for wake. If you start lifting the boat, you start losing the boats ability to track straight. Even a wing 2-3 feet under the water can massively affect the wake back where the skier/wakeboarder is. I'm sure it could be engineered to be behind the skier/wakeboarder but now you're getting complicated and potentially putting a massive spike under your boat that could hit bottom. If you drove a boat with a small wing underneath on a slalom course, you run the chance of slicing your buoy lines too if you get off center.

[BraceMaker]

I would wonder about introducing cavitation to the prop as well.

 

Perhaps you could think about injecting air into the wake to soften the water up. A purposeful cavitation lip on the rear of the hull for use for skiing activities. Dunno if it would work.

[Waternut]

@Bracemaker I think you're on to something with the purposeful cavitation. I do think some of this is already being done with props actually. I think the Nautiques do it already and guys who own mastercrafts have raved about the soft wakes after switching props.

[BraceMaker]

The prop situation I think is different. If you induce cavitation on the prop you don't get efficient transfer of power to the water, there is always going to be some of course, props slip in the water, so the prop has 18" of pitch per rotation, so if it were 100% it would move 18" for every turn, but really it moves forwards less than that. Old boats had 1:1 transmissions with 13" 13 pitch props or similar, and those slipped quite a bit, but turned more times, and I think this gives you that often mentioned bump behind the boat, like a rooster tail.

 

Then those boats went 14X18 with a 1.5:1 prop - those ski pretty darned good, bigger prop, turns slower, but slips less. And designers I believe thought that to be overkill, or perhaps just better engines, because now boats are what 1.23-1? Props are less pitched I believe.

 

Props definately have impact, but I think it is almost more a question of cavitation makes the prop slip which brings up the RPM and pushes a bump to the surface, and I think some of the better machined balanced props slip less, enduce less cavitation, ad keep that bump down in the water till long line.

 

Of course then there's the whole hydrogate/Hull hook/Chine Lock/ TT Rudder flaps. Lots of stuff under boats if you take a moment to crawl under and poke about.

[Dacon62]

@ShaneH Was it lift that rendered the boat undriveable or was the cavitation wash from the prop shooting directly over an inline mounted rudder foil possibly adding to the cavitation problem leading to vague steering input?

If that was the case then mounting two outboard located rudder/foils would put the foils in cleaner undisturbed water.

I agree with @skibrain that running a boat with a configuration like this through a slalom course would be problematic. Let's set that small detail aside for now.

Would the larger dual rudder set up help improve on the tracking and response that is lost due to the lift gained? If so that might check off all 3 items mentioned by @skibrain.

The drawing below is just to illustrate the concept. Many other things would need to be considered to make it function properly.

[Dacon62]

I will give more context.

My original goal is to have the space and convenience of a 20' V drive with the ski wakes of a DD. Have your cake and eat it too kind of situation. It would be very tough to start with a light 20' V drive.

[eleeski]

@Bracemaker Arneson drives are surface piercing props that have become standard on race boats. I added air to my Mastercraft and the boat sped up. Controlled cavitation improves efficiency.

 

@Skibrain is right on. Reduced weight is free improvement of a wake.

 

Hydrofoils are extremely interesting. On the water real world testing will reveal a lot.

 

Eric

[Waternut]

Reduced weight is an awesome concept too and I love how Centurion made the Carbon Pro. They used carbon fiber instead of fiberglass and EVA foam instead of carpet to save weight. However, I couldn't help but notice that the super light Carbon Pro actually weighs quite a bit more than even a similar boat built in the 80's or 90's... Yes it's lighter than today's boats but it kind of shows that luxury is more important than performance.

[eleeski]

@skibrain Malibu wedge! A great idea that works well. Quickly switch from a tiny slalom wake to a big air wake. It might not keep the serious wakeboarder happy (they are pickier than slalom skiers about wakes) but it sure is fun.

 

Eric

[Waternut]

A dual rudder system isn't ideal on a V-hull because in a hard turn, the boat leans over enough to make the other rudder come out of the water. A rudder with more surface area should be sufficient but the hull may need to be reinforced. A wakeplate is a very cheap and cost effective way to create lift on the back of the boat. There are a few guys who have made the wake on a v-drive boat manageable for skiing with wakeplates. Even the 14"x18" wakeplate on my DD boat has the ability to create enough lift to cause tracking issues above 36-37mph...without a skier.

 

Even with a dual rudder, a wing in front of the prop creates an unbalanced flow which is all kinds of bad news.

[Waternut]

There ya go @Rico! New tow boats for 2014 will be submarines with a periscope and a pylon sticking above the water! Softest wake ever...

[BraceMaker]

@eleeski - surface props are far different in design than what's under the MC.

 

How did you introduce the air?

 

I've read about your matte finish on the skis (hand applied) - but would the golf ball dimple hull be beneficial - are gel coat blisters a good thing?

[Dacon62]

@Rico There was an article in Waterski Mag years ago about an underwater track system with an above the water manned pod. Very cool. But yes, no rumbling V8.

@BraceMaker Also remember an interesting thread a while ago were someone had drilled a hole through the hull above the prop, attached a hose to the through hull fitting and introduced air that way to soften the wake.

@skibrain You bet, why just have the foil produce lift? Why not downforce as well?

Just need the hydraulic force on the winglets or a position sensitive linkage to change the angle of the leading and trailing edges and you have wing producing lift or downforce...

 

[BraceMaker]

@dacon62 - part of the question is where the water impacted by those hydrofoils goes.

 

Say you effectively lift the boat but create a depression on either side of the wake, now the wake is effectively larger.

 

For air introduction into wake I would be thinking more like a comb that was mounted on standoffs behind the rear of the hull, with variable angle/depth. The comb teeth could be U shaped if that would introduce air.

[Texas6]

Now one of you really smart guys needs to agree to drill some holes in your boat to give this idea a go for our mutual benefit. I for one am pulling for you, just don't have a spare boat at the moment:)

[ForrestGump]

I know that one of the things that MC experimented with in 2010 was that they created a set of fingers, almost like a long set of fork tines, that they bolted to the back of a 197 to aerate the wake. They stuck down below the transom a small amount. It softened the wake considerably they told us.

[Texas6]

@ShaneH, they tested the fingers and they did what they were designed to do BUT......?? What was the drawback? Handling I presume?

[ForrestGump]

No, they didn't indicate any drawbacks. It was just an experiment to see what aerating the wake behind the boat would do.

[Texas6]

Interesting. Can't wait to see where they ended up on their new boat

[DW]

Can a DD wake be improved, yes, as noted reducing weight helps a significant amount (depends on one's definition of significant of course). Altering the CG also can offer noticible improvements. I have done a bit of both and noticed the positive changes. It is relatively easy for a single consumer to customize their own boat, as I have done, but more of a challenge to make it commercially viable. There is not really a very big market for a single purpose slalom boat, Eric should chime in as his ideal includes trick which needs significantly different characteristics out of the same boat so that shrinks the market potential.

[rodltg2]

@rico, great concept but can you imgine the amount of spray that would come off the pole!

 

My idea would be two sets of tracks. One on each side of the lake . Then a beam going across the lake connecting them. In the center a set of bleacher type seating so lots of people could watch the action!

[Dacon62]

I envision a lot of beer being spilled by the spectators.

[BraceMaker]

@rodltg2 - I think the moving mass is the big issue. Whenever I've thought about this the conclusion I have come to is that you need a guide rail underwater with a light weight streamlined torpedo that runs through the water, the pylon would come up with a wing shape to minimize spray/resistance to the water.

 

But I think the whole thing would be pulled through the water by an overhead cable park system - giving you the option to disconnect the pylon, and attach a tow rope to the cable park.

 

The pylon's main purpose then is to remove the sway/motion of the overhead system and provide an "on water" pull point that doesn't move left and right, as such the track system would dampen oscillations in the system.

 

If you wanted a gantry crane it would probably need to be far narrower, so the cart is not so heavy, and overhead with a drop to skier height.

[BraceMaker]

@shaneH @texas6 - After posting that I was thinking a draw back would simply be that it would tend to pick up junk from the lake and or be damaged. Ideally the fingers would be fairly fine - which would yield easy damage.

 

@skibrain - one direction we don't see in current boats is to do DD with lower profile engines such that the engine cover is less obnoxious. Perhaps a flat 8 instead of a V-8? Production costs on that strategy would be high I am sure - but you could lower the effective engine height and with the high freeboard on many boats I am sure you could make it blend.

 

We need the central pylons however - so slalom kills having passangers.

[DW]

@Shane: any pictures or more specific description of the MC wake device. Sounds very interesting.

[Dacon62]

Don't think a flat 6 would fit between the stringers and it may not be as tall but it will likely take up more width while probably being at least 1.5 feet above the floor so don't know if you really gain anything. The area between the motor box and gunnel would be more cramped. Also, either your intake or exhaust would be in the bilge area...not ideal.

[BraceMaker]

I came to similar conclusions and have since moved on to visualizing shallow angle V engines, or inlines....

[Dacon62]

Lets get nuts here for a second...Stuff 2 vertically positioned inline 4's into the gunnels. One starboard, one port then come off each shaft with a 90 (have to run through the stringers, don't know if that would work) so that both shafts run into a low profile transmission in the area that it is typically located now. Ideally the transmission could be made to fit under the floor completely and the motors would be tucked away while still acheiving basically the same balance and center of gravity.

[rodltg2]

I think that it's cool that our sport requires the motorized element . There is nothing else like it. Sure the Olympics won't accept it. Too me having a boat provides family fun , and exploring , houseboat trips and course skiing, I couldn't ask for a better time. I say let us have our ski tugs and hope they sell enough wake makers to so they keep making them.

[allycat]

yep

 

[Dacon62]

Thanks eveyone for your thoughts on this.

If anyone out there gets the guts to drill some holes do some fabricating and experiment with this keep us in the loop.

[Johnbrad]

Hull may be the best wake for wakeboarding!

 

_______________

Small Fishing Boat

[ForrestGump]

@allycat Punctuation is your friend.

[allycat]

not wrong there @ShaneH think the beers got me on that post