Just read a comparison outboard, sterndive, jet drive.

[tuffr2]

Fishing has never made sense for the cost. But for those that fish the experience is priceless. There is a certain excitment in hitting the throttle.

R&D on Sterndrive boats...sure there has been some. There have been some cool boats made with corvette engines...opps, R&D mostly provided by Chevy. To me, the 4.3 litre, 5.0 litre and 5.7 litre engine blocks with pushrods are all from Chevy. I think I could have bought a carburated sterndrive boat as late as 2014 or 2015. Don't get me started on number of valves per cylinder as 2 seems to be the max...ugh. Those engines have to be 20 years behind in technology. Iron block?? egads.

[Cheechako]

In testing big outboards when I worked for a boat manufacturer, the fuel burn was pretty close regardless of builder. Honda, Evinrude Etec, Suzuki 250 HP were tested. At planing speed, not quite wide open, ~4000 rpm these engines burned about 13.5 gallons per hour. Usually 35 mph or so. Roughly 2.5 miles per gallon.

The trouble with highly tuned multi valve aluminum engines is there is a lot to go wrong. That's one advantage of the old simple V8 iron block. During the mid 2000's time frame we were experiencing a 20% catastrophic engine failure of the 250 HP outboard in one particular brand on new engines. As I mentioned earlier, a GM 350 rebuilt long block runs $1600-1800, pretty hard to beat that.
Outdrives will not clear the water when tilted are not intended to be run tilted either.

[waterman46]

Originally Posted by tuffr2

Glastron now makes a boat with 3 power options. I saw a test of all 3 power options and it proves what I always kinda knew. Outboard power is the best and Jet Drive power the worse. In the test for speed a 150 HP outboard matched 220hp stern drive which was faster than 250hp jet drive.

To be honest I kinda knew this from the old days. Was suprised it is still true in 2018.

The 4 cycle outboard had the best mpg and was also the quietest. Was suprised jet drive finished last again since it has the least amount of underwater drag. They said that in this Glastron set up the jet drive did not have any trim feature. The sterndrive and outboard were able to get more boat out of the water.

They did not talk about jet drive being able to go thru shallow water better.

We try to keep our boats in the water as much as possible!
Suggest you find a more appropriate forum.

[waterman46]

Originally Posted by a64pilot

A four stroke outboard usually doesn’t have good low end grunt like a two stroke does, Mercury Supercharged their Verados to fix that.
Another reason ski boats have big auto motors is mass, a heavy boat isn’t effected much by a skier on a slalom course, where an outboard powered Boat you can feel the skier slow the Boat.

The reason outboards got so popular way back when was because they were light and cheap, they aren’t so light anymore and certainly are not cheap, however you see many big Sportfishermen repowered with multiple 300 HP outboards, which due to their cost, confuses me.
I would expect due to cost to see a resurgence of inboard boats, but logic doesn’t drive what sells, popularity does, or you would not see so many four wheel drive SUV’s on the road, especially say in Florida where snow is unheard of.

My experience is that my 15hp Honda 4 stroke has twice the "grunt" or torque at idle than a similar 2 stroke. Shifting into gear at low idle jumps the RIB from a standstill much more than I like, actually, and RPM doesn't change one bit. A 2 stroke needs to be above a certain rpm to even be in full 2 stroke operation; at idle its often not firing on every cycle, and will slow further when put in gear.

Currently on long tour of SE Asia and we take lots of speedboat trips for snorkeling. All these boats are powered by multiple outboards of insanely high power. It is not uncommon to see 1000hp on a 32 foot boat. The only inboards are on slower larger boats over 40 feet, and in Indonesia where they still only use old wooden boats, open decks, some kind of gasoline inboard which is started by a guy who has to get down beside the engine and touch the starter solenoid to the battery, in absence of a starter switch.

But I digress. I suppose these tour operators find total cost of boat, outboard and maintainance to be cheaper than inboards. Certainly safer than a gasoline inboard so maybe that's the reason.

[skipmac]

Originally Posted by waterman46

My experience is that my 15hp Honda 4 stroke has twice the "grunt" or torque at idle than a similar 2 stroke. Shifting into gear at low idle jumps the RIB from a standstill much more than I like, actually, and RPM doesn't change one bit.

The boat speed at idle does not necessarily have a direct relationship with the low end torque of the motor but might be more related to the idle rpm of the motor. Size and pitch of the prop are also a factor.

The only way to get a true and accurate comparison is to put the same HP 2-stroke and 4-stroke motors on identical boat and test.

[skipmac]

Originally Posted by waterman46

We try to keep our boats in the water as much as possible!
Suggest you find a more appropriate forum.

Not sure what you mean by the reference to a more appropriate forum but regarding keeping boats out of the water, on a planing hull boat lifting the max amount of hull out of the water reduces drag, increases speed and thus is a goal in speedboat design.

[valhalla360]

Originally Posted by Cheechako

The problem is a 250 HP outboard is $20k and a V8 I/O almost half that. It is nice having the engine out of the boat, but they are also very hard to work on compared with a simple auto engine. You can get a rebuilt long block for a 350 GM for about $1600-1800 when it comes time to replace. Jets are cool but yeah, inefficient.

The price for high HP engines does favor stern drives but for low HP displacement cruising boats, it flips.

A new 25hp outboard installed is maybe $5-6k. You will be lucky to get the engine for $7-10k and installation will be significant.

[waterman46]

Originally Posted by skipmac

Not sure what you mean by the reference to a more appropriate forum but regarding keeping boats out of the water, on a planing hull boat lifting the max amount of hull out of the water reduces drag, increases speed and thus is a goal in speedboat design.

Sure your question is just fine here since it looks like there is a lot of interest. Just thought there are some powerboating forums out there as well.

[waterman46]

Originally Posted by skipmac

The boat speed at idle does not necessarily have a direct relationship with the low end torque of the motor but might be more related to the idle rpm of the motor. Size and pitch of the prop are also a factor.

The only way to get a true and accurate comparison is to put the same HP 2-stroke and 4-stroke motors on identical boat and test.

I was referring to the dinghy acceleration and motor loading from a standing start, not the dinghy speed at idle. And of course that instant loading on the motor when shifting into gear is very dependent on the prop configuration.

[skipmac]

Originally Posted by waterman46

I was referring to the dinghy acceleration and motor loading from a standing start, not the dinghy speed at idle. And of course that instant loading on the motor when shifting into gear is very dependent on the prop configuration.

Well again to get a truly definitive answer would require a side by side comparison with identical boats but based on my very subjective experience of owning multiple outboard powered ski boats and runabouts from 16' to 22' my very unscientific opinion is 2 strokes are faster to plane than 4 strokes.

One thought I have on the issue, a 2 stroke produces power on every stroke where a 4 stroke only every other. This to me would indicate at lower rpm as the engine starts to rev there will be more power produced at each spin of the engine by 2 strokes and give more power to get on plane. Once at speed and higher rpm the difference is lost.

[valhalla360]

Originally Posted by skipmac

One thought I have on the issue, a 2 stroke produces power on every stroke where a 4 stroke only every other. This to me would indicate at lower rpm as the engine starts to rev there will be more power produced at each spin of the engine by 2 strokes and give more power to get on plane. Once at speed and higher rpm the difference is lost.

All else being equal...that would be true.

20yrs ago there was a lot of truth to this.

Modern engines, they've done a lot work on 4 strokes to match the 2 stroke low end performance.
- Cam shafts, stroke length and other engine geometrics can be modified to provide more low end torque.
- In larger engines, there are enough cylinders that there is always a cylinder on the power stroke. It's not like an old 1 cylinder lawnmower engine that has to coast thru 3 strokes before reaching the next power stroke, so it needs to build up a good amount of momentum to generate much torque thru all 4 strokes.
- Some of the larger 4 strokes use forced induction which is also known to significantly boost low end torque.
- Does idle torque really matter that much? Unlike a car where your tires increase their RPM directly proportional to the acceleration of the car (assuming you don't spin the wheels which doesn't help acceleration anyway). A prop particularly on hard acceleration from a standstill will spin and slip before the boat acceleration catches up with the prop speed. Too much torque at the very bottom end, doesn't add much acceleration. It just adds more slippage. After a second or so, the 4stroke RPM is up in the range where the engine is putting out good torque, so you may not see any performance gains in normal usage.

[ZULU40]

Originally Posted by valhalla360

Too much torque at the very bottom end, doesn't add much acceleration. It just adds more slippage.

bunk...

[ranger58sb]

Originally Posted by waterman46

Suggest you find a more appropriate forum.

??

This forum is named "Powered Boats."

-Chris

[Colin A]

Originally Posted by skipmac

Well again to get a truly definitive answer would require a side by side comparison with identical boats but based on my very subjective experience of owning multiple outboard powered ski boats and runabouts from 16' to 22' my very unscientific opinion is 2 strokes are faster to plane than 4 strokes.

One thought I have on the issue, a 2 stroke produces power on every stroke where a 4 stroke only every other. This to me would indicate at lower rpm as the engine starts to rev there will be more power produced at each spin of the engine by 2 strokes and give more power to get on plane. Once at speed and higher rpm the difference is lost.

The line in the industry was that a two stroke was better power wise in the mid range to middle high range. In general every test I have read puts the two stoke at an acceleration advantage.

[Colin A]

Originally Posted by ZULU40

I just dont think stern drives have reached the same levels of sophistication. Back when they started inboards were regarded as more reliable and more fuel efficient, now these margins are less clear.

Stern drives never enjoyed the sale ability that outboards have and likely never will, so they havent had the benefit of R&D that would have pointed them to sophistications like casting/machining the drive out of the same block of alloy.

New outboards seem to come around every few years from one direction or another, but genuinely new inboard engines suitable for stern drives are somewhat rarer.

Plus they require a huge hole in your boat to accept the drive package, and designed in water tight integrity that makes them neither suited to hulls designed for outboards, or inboards.

Their specialness will prevent them ever penetrating the market in the same way, so the R&D will always be dulled and behind that of outboards in particular.

Here in the US from the late 80's thru the early 2000's Sterndrive sales sometimes exceeded outboards. There were tons of them sold during that period. One of the main reasons was cost they were fairly cheap thanks to using cast iron blocks etc. They also made good power for a price on heavier boats. They still sell a fair amount of them but outboards have pushed forward and become more fuel efficient cleaner quieter and lower maintenance (particularly in salt water ) then their sterndrive counter parts. I think the type of boats has also helped the shift. Fisherman have always preferred outboards and with the huge growth of the center console market outboards pulled further ahead.

While parts for the engine half of a stern drive are cheap the drive and transom assy are not, they are also labor intensive to repair when something goes wrong which dosen't help. Replacing Manifolds gimbal bearings boots and bellows on a regular basis gets tiring and or expensive. While a freshwater sterndrive boats lasts about equally well as a freshwater outboard once your using them in salt it's really not a contest when I was a tech fixing these things we were replacing long blocks and drive units on the sterndrives far quicker then we had issues with outboards. Mind you there are exceptions to this as everyone builds a clunker know and then.

For me an outboard has several big advantages. For one no giant hole in the transom (I have seen a shockingly large number of boats sink from bellows and drive shaft failures) More room inside the boat, and when something does need to be worked on I can haul the boat out on the trailer and stand next to the engine while I tear it down instead of hanging upside down in an engine room.

As for jets the main reason I find them attractive is simplicity.