Actual boat power

[chrislandy]

Continuing the long winters thought experiments and ponderings,

 

How much of the engines power is used when skiing?

 

So my engine can produce 350lbft between 2700rpm and 4700rpm with peak 370lbft @ around 4100rpm.

 

But that's maximum torque at maximum load typically with wide open throttle, does the loading on the boat ever cause the engine to generate it's maximum power (excluding full throttle power turns)? typically when I'm towing trick it's only doing say 2000rpm on a feather throttle, slalom obviously ups the rpm and throttle but not by that much.

 

So for example, what torque would be used to tow tricks, 36mph @ 12m, mens jump etc

[DW]

Most of the power goes to pushing the hull through the water, lots of surface area compared to the ski (even at a distinct angle to direction). ECU data can be used to calculate the actual power used.

[jpwhit]

I think I recall seeing total power as calculated by the ECM in DIACOM.

 

But if your point is do we really need the power of the larger engine options, I think it's less about absolute max power as opposed to how quickly the larger engines can respond to changes in demand almost instantly. So at any particular RPM, the more torque that can applied almost instantly is what really matters.

 

So maybe what's most interesting is the largest throttle body open percentage during various skiing related activities. I would suspect that would be with Jump. And I seriously doubt it'll ever be 100% for the simple fact that it takes time to open the actuator. But 70% open on a smaller engine will generate less torque than 70% open on a larger engine. And just because you open the throttle body quickly, doesn't mean there isn't time involved in the airflow ramping up....

[Adam Caldwell]

@chrislandy - you can only deliver as much HP/torque as the prop will allow for a given speed. The engine isnt pushing the boat. The prop is.

 

Larger engines that have higher max outpt capacity will more or less just 'last longer' as they are not being asked to run near their max to acheive skiing speeds.

 

Here a couple links for some good info.

https://www.boatdesign.net/attachments/prop-demand-jw-herbert-pdf.66030/

 

https://www.sbmar.com/featured-article/propellers-move-boats-engines-just-turn-them/

[MichaelWiebe]

I would be interested in a ski boat with a turbo V6, assuming zero turbo lag. In cars we see this trend. For example, take the Ford GT. A supercar with supercar performance from a V6.

My thinking is less weight for an even smaller wake, saving space inside the boat, and fuel savings. A win all around. Perhaps the engine wouldn't last as long, as mentioned above.

Maybe I'm off base assuming the skier wouldn't notice the difference during skiing. But I believe the future won't be V8's forever, and all electric seems to be a ways out.

[DW]

The common assumption that a V6 turbo will be a lighter engine may not actually bear fruit. The GM LS V8 tips the scales at the same weight of a few of the V6 turbos on the market, basically 420 +/- lbs. Once installed, those turbo's need to be cooled and they tend to hang off the side so the engine box could be shorter but may not be any narrower. Turbo lag is never going to be zero, particularly from a start, although as the engine speed increases the lag will be reduced, maybe to the point of being acceptable to a skier. I do see the potential of engine placement (fore/aft) moving the CG forward and improving the wake and fuel economy should be improved.

[6balls]

I've never met anyone who regretted selecting the higher power option in a boat or vehicle. I've met people who regretted selecting the lower power option. Unless the lower power option is "more than enough" which sometimes it is, go bigger.

[kurtis500]

"How much of the engines power is used when skiing?"

 

If you havd a dyno sheet, even from the factory, and compared it to the RPM you would be close. A dyno readout would be the closest way to tell what your motor is doing at a certain RPM. There are some boat dyno's that give at the prop HP numbers but they are rare.

[chrislandy]

@adamhcaldwell great links :) That was my thinking and what I was trying to imply, but they explain it in a slightly different and more insightful way.

 

@kurtis500 the torque generated by the engine is a function of the load on it up to the maximum it can produce (which is the dyno plot), so if using the prop drives and the engine turns mantra, if the prop could only turn 200lbft of torque at 3000rpm, no matter how powerful the engine, it will only be producing 200lbft + transmission losses.

 

There are 4 initial thoughts I had

 

1) If you ran the engine at it's optimum efficiency (power, rpm and fuel use), you could use a CVT transmission to vary the prop speed to match the torque from the prop

 

2) A low pressure turbo or supercharger application would work very well as the prop requirements are very little at low rpm and the main power is needed as the prop turns quicker

 

3) An electric motor would be really well matched to the application as the torque delivery can be controlled efficiently

 

4) A variable pitch prop could be good for crossover boats that have different requirements for planing and non planing (surf / wakeboard/ ski) which could enable lower power engines to be used while still getting good low speed performance i.e. low? pitch, high torque at low rpm, then high? pitch at higher rpm to not overload the engine - that way you could prop the boat for say 300lbft from 2000rpm to 5000rpm by varying the pitch

[BraceMaker]

@DW there is also the scarcity of V6s on the market as the options are increasingly I4

 

Indmar as the 2.3 EcoBoost and an all Ford line up. We never seem to discuss them since Penske dropped them

[DW]

@BraceMaker - so before we even get to a turbo V6 as 'latest tech HP' they are absolete!

[ReallyGottaSki]

Perhaps, make new ski boats less bloated and less draggy like say 20 years ago

[ALPJr]

Will be interesting to see the impacts on boating and tow boats in the next decade or so considering GM and Ford’s commitment to transitioning to EVs.

[DW]

@ALPJr - it will, but consider that the boat mfg's scrounged like crazy to acquire all the old style (Gen 1) iron small block GM engines when it was announced they were stopping the manufacture of them. They were assembled in Mexico and were crate and industrial engines, none being used in vehicles as they had been phased out long before. Point being - there will be a considerable phase lag in general adoption of new technology power units (in my opinion based on history) and a lot is based on cost. Electric power band is ideal for a ski/wake/surf boat so an innovative company may capitalize on it.

[kurtis500]

A variable pitch prop would be nice if they could ever get them to fit on a 1" or 1 1/8" shaft/strut setup.

 

A low pressure supercharger does wonders at all rpms. Pulls out of the hole better than a turbo and higher torque/hp across the board. Just have to watch the gas gauge closely.. Boats could use more efficient transmissions to convert the power. Mine has a tranny in it and a few friends have them as well. (Turbo 400) With a midship engine I dont see anywhere to put a transmission in the tournament boats unles the made the v-drive/direct drive and tranny in one unit. The CVT would work imo

[TEL]

Do we really need more power? The current engines work fine, I do not think I have used full throttle to pull any one up at sea level in Florida. Most of the boats I drive have 5.7L and 6L's

[BraceMaker]

@DW Yup - basically.

 

Other than VR6's you've got all the added complexity of having 2 heads, if you want modern DOHC set ups then you have engines like the VW EA837 - which is both not compact and not inexpensive.

 

The auto industry is going to 4 bangers - and interestingly many companies are moving back to inline 6's with formats where the inline 4 and inline 6 will be extremely similar power plants.

 

Which honestly an inline 6 would be awesome for ski boats - particularly a slant configuration which most people I don't think would complain if they had a slightly longer but narrower engine box and solves many of the issues for space that you'd need for turbo.

[DW]

@BraceMaker - There's always this: https://www.hemmings.com/stories/article/chrylsers-slant-six

 

[ReallyGottaSki]

I suspect the GM Atlas 4.2 could power a decent budget 'skier' . 290hp@6000 (later ones)

and a 12p prop could be a good combo

[Fastguy888]

As the owner of www.ev-mods.com It is very interesting to see the development of the NAUTIQUE-gs22e It seems a well developed electric drive train would be ideal for 3 event lakes: less noise = more ski sites, instant torque = instant speed control. Surprised the GS22 (never mind the price) seems underpowered. At 5,900 lbs and 265hp 325 tq. Consider a standard Tesla Model 3 is 3,552 lbs with 346hp 389 tq. Seems the issue is the constant draw of a boat direct drive vs a car that can coast and convert brake energy. I don't think the tech is there now for a cost effective electric 3 event boat but expect my daughter will see them.

[DW]

@ReallyGottaSki - unfortunately the less bloated ones don't seem to sell. Given the small demand and niche market for a lightweight ski tug, the burden appears to fall on the individual to create their own. Not that difficult to nick away if one wants to expend some elbow grease, time and effort to toss a few pounds in the trash can. FYI - results can be pretty damn good if one is willing to go down that path.

[kurtis500]

@fastguy888 that is a heavy boat but good for surfing or wakeboarding I guess. You're right to point out the boat has no way to regenerate power, that only draws power. Add in the obnoxious steroes... I wouldnt venture out on lake Powell with it.

 

of topic question...Taycan good or so so?

[Fastguy888]

@kurtis500 I could land a Tesla on top of my 400hp 454 EFI Tige SLM 2000 Comp that is under 3k lbs and weigh about the same as the NAUTIQUE GS22e. With that said I appreciate NAUTIQUE pushing the idea. Pure performance Tesla Better than Taycan, Build quality the Taycan wins. Lucid Air will be a great car and Rivan T1 Truck would be an awesome way to tow the boat to the lake.

[chrislandy]

Another idea that came to me was to do a hybrid, you could have an efficient, smaller engine for the 80% of the time with an electric motor for the more demanding or pootling around bits, then the motor could also be used to help charge the batteries when not using it - akin to regen braking

[BraceMaker]

@chrislandy part of the hybrid equation is if it is useful to different markets. If you were only pulling slalom skiers down the course to both ends you have a pretty defined amount of capacity that the boat needs per pass to go 0 to 36 to 0 over 2000 feet skier in tow. The engine could go right on running to power up essentially a capacitor for the next pass.

 

But that would be worthless for me because we also take out boat on around the lake 20 mile ski attempts so it would be all engine all the time after that first 2000 feet.

 

Goes back to the original power question then add in time and it's a how much work does a ski boat engine do

[chrislandy]

@BraceMaker it's also a question going around in aeronautical fields too, I understand there is a plane in development that uses an electric motor to assist at takeoff to enable a smaller more efficient turbine engine to be used for cruising. Apparently this is because the turbine engine has to be sized for takeoff as this is the most power required, but then has to trade off to a non optimal size for cruising.

 

But also, taking your 20 mile ski attempts as an example, you wouldn't be running at 36mph for 20 miles would you? More like 25-28mph I would have thought, so if you have a more efficient engine at that speed / load.

 

For non tournament you could have something like: motor + engine to plane, engine to 30, then engine + motor for 30-45+

 

 

So, if the prop can only turn 200lbft, why have an engine that could do 350lbft at the same rpm as it will only ever generate 200lbft

[BraceMaker]

Speed varies but often so does number of skiers I am using the slalom course as more of a static definable event point A to point B with enough juice to run the boat properly on a smaller power plant like your plane take off example.

 

When you sell that same boat after its no longer on the private ski lake you have to accommodate variable use - 20 miles going 27-30 with 2 or 3 skiers at once is a very different use of the boat and power. But presumably the market for a 2022 prostar assumes someone other than a tournament lake user is going to buy the boat eventually and want to use it like a boat not like a tournament pass.

[chrislandy]

That's the US model I suppose, but say here in the UK, there are no big lakes and most tournament boats end up on private tournament sized lakes.

 

I also ski on a lake in France, but that is considered "large" with a 3km (1.8mile) ski zone and the remainder all <5kph / 3mph

[ReallyGottaSki]

@DW i concur, yeah we've both tinkered heavily, with great results

 

Satisfied my parts combination created a relatively efficient old boat. With a +/-6 gal jug four of us ski, , three skiers ski hard at 34mph, four 1 mile lengths each, about 30 cuts fit in a length. the fourth skis light at 8 1-mile lengths at 30 mph. Sums 20 miles total in a morning. a gph meter for more tuning and more objective numbers is a consideration!

 

I've picked up a low miles LM4 all aluminum 5.3 for a future project, just have to find a neglected doner hull, I have one particular in mind for its ski performance and efficiency

 

Such a great time for hobbying, all-aluminum engines can now be gotten at the boneyard for 500 bucks, get some before they are soda cans!

[DW]

@ReallyGottaSki - 6 GPH is darn good for a ski tug, nice. Interestingly, the larger engine I built up improved fuel efficiency, a nice add for the additional Hp it has over the previous combination. A few caveats, boat is lighter (aluminum engine), reciprocating mass is less even with a longer stroke, combustion chamber is probably more efficient and I can spin it slower at the same Hp level.

[ReallyGottaSki]

@DW i believe it, you got a great combo!

I don't think i have a true hour at-speed, but four long sessions for 1 jug , happy with that.

 

Prior I used to be touching into the secondaries with a boatful compensating for slalom 36mph, making compensation response really dull.

Now after mods its not even close, can do 44 mph on just the primaries and minute compensation is so responsive.

Even my daughter remarked it holds speed really well, almost set it and forget it.

I'm going to do some monitoring of manifold vacuum this season, then may consider msd programmable * Edit 6530 to further dial in the timing. One can also use it with a map sensor to add just a little advance when loaded lighter, partial throttle while manifold vacuum is higher then make it fade as approaching WOT. Just a few degrees at partial throttle cruise could really drop gph i think, my experiments adding in more initial demonstrated much less throttle needed for 30mph -34 mph cruise. Full mapping sounds like good clean hobbying

[DW]

FWIW - Saw a data snapshot of some MEFI data pulling a skier = throttle position 32-38% oscillating as the skier pulls, right at 10 GPH fuel consumption. This being a Monsoon FI engine. Running fuel consumption is pretty interesting as typical overall consumption is reported to be in the ballpark of 5 GPH, just shows how much time spent at idle.