Without going crazy...

[oldboot]

One fact that many fail to realise is that a long narrow boat and a short fat boat of the same hull shape and the same surface area will have the same righting moment ( stability)

stability = area.

Another problem with our plaining hull speed boats is that they depend for their efficoency on a deep V, the shallower the V the harsher they ride and the less efficient they are.

the longer narrower boats can be every bit as stable....ya just have to look at some of the fishing shows to see how stable thay can be.

Of course the other option is multihull.....which is the way lots of medim sized commercial shipping is going.

There are some incredibly fast displacement hull boats arround these days..and the longer and narrower they can be the faster they can go.

A mate of mine has a sailing cat that is 40 foot and weighs 7 tonnes, and he pushes that allong with 2 x 10Hp diesels.....and can make 7-8 knots with a clean bum and no headwind..I know it isnt fast but it only makes 17-18 knots under full sail and fair wind, before it becomes a serious underpants problem.

If we are talking about environmentaly friendly....if we had long pointy displacement hull cats......we should be able to push them along with 40 to 60 Hp where a square bum speed boat would require 150 to 200HP...ya might not do 40 knots.......but 20-30 and a much smoother ride is a realistic expectation, and running at lower speeds is economical where it isn't in a modern speed boat.

cheers

[FishHunter]

I think the whole thing has to go past the idea of the outboard in it current form or even the power boat in it current form.

There are lots of boats powerd by diesel motors..

I'd even go as far as to say boats were driven by diesel long before they were driven by outboards

lots of those boats in asia driven by stick blender style drives are running diesel motors, and some of them get up and go.

The two issues with diesel are the weight...a diesel motor will always be heavier than an equavalent spark ignition motor, there is simply no way arround that.....and throttle response, diesel in whatever form will always have a slower throttle response than a similar petrol motor ( turbo, supercharged or not)....diesels are at their best pulling steady loads and playing to their torque advantage...this makes them very well adapted to displacement hull boats.

almost all of our "powerboats" are hulls designed to plane, but they function very pooly in displacement and they are horribly inefficient in the transition between displacement and plane.

Look at those asian long boat things, they operate very efficiently in displacement and trasnsition quite smoothly onto the plane with out lugging..they just rise out of the water.

The shape and style of our boats and the expectation of getting up to speed and on the plane quickly, means that the diesel simply wont satisfy this whole
"hole shot mentality"

I am fascinated why you would design a large very expensive boat and then bugger the whole thing up by powering it with an enormous outboard or two.

If the same boat was powered by the same engine but built as an inboard with a straight prop shaft, the weight distribution would have to be better, and transmission efficiency would have to improve because of the removal of a right angle drive.

If the boat was then powered by a diesel rather than a petrol motor there would be no need to have a gear reduction to run the prop......the prop could run at crankshaft speed..because the diesel will be producing maximum power at half the RPM that the current petrol motors require.

The other benifits would be that prop selection would be far less critical as the diesel can produce power and torque over a wider band of RPM..where a petrol outboard relies on being run close to maxumum RPM to achieve maximum power.

I realy think diesel is a very viable power source for boats, but I doubt that it will win favour in the outboard format.

cheers

Turbo diesels have a very narrow powerband in relation to a petrol engine for 2 reasons
1 They cannot rev anywhere near as high
2. The turbo's are very small to reduce turbo lag which also limits the airflow at higher rpm as there are no free lunches.

So yes you have a torque peak at 2000 rpm but it has very little below that point and with the torque falling dramatically from that point on whereas a modern petrol engine could have 85% of its torque curve from 2000 rpm to 6000 rpm with a peak at around 4000 rpm. Try driving a say a Navarra in say 2nd gear at 1500rpm and then floor it and you will feel exactly what I am describing as nothing at all happens till about 2500 rpm and then all hell breaks loose till the party starts to go away from about 3500 and it hits a wall at about 4000rpm.

Superchargers takes power to drive and add considerably to the packaging problems you would have, remember you will have to have some form of charge cooling to get the power required which takes up more space plus then you need particulate filters in the exhaust system to meet the emission requirements.

All of that can be done as a inboard trying to fit that into a outboard will be a difficult and costly exercise.

[stue2]

What would I'd rather have in my Holden 1 tonners??
4 cylinder Corolla engines or 253 V8's from GMH???

The whole diesel is not possible due to weight is getting smaller and smaller in the argument department.
The cook took a 1.6l turbo diesel Hyundi I30 for a drive and it goes like a startled gazelle as compared to the petrol powered 2l engined one.
About 22kgs weight difference in the two cars with the diesel been the heavier of the two.
The torque figures are way different though.
Diesel: 255Nm @1900rpm
Petrol: 186Nm @4500rpm

So when all that is considered there is not much weight difference at all between the two in relation to the extra torque you'll get with the diesels. And torque means giddy up doesn't it??
Only a matter of time I reckon especially for those outboards in the over 150hp range.

I'm with you finga. They will do a good one soon enough. They may even rate them from the Nm they produce. They may not be fast but I bet very efficient cruising motor and no inboard motor cover. Who woulda thought a little car like that would run a diesel that would drag a petrol off 20 years ago

Cheers, Stu

[PinHead]

One fact that many fail to realise is that a long narrow boat and a short fat boat of the same hull shape and the same surface area will have the same righting moment ( stability)

stability = area.

Another problem with our plaining hull speed boats is that they depend for their efficoency on a deep V, the shallower the V the harsher they ride and the less efficient they are.

the longer narrower boats can be every bit as stable....ya just have to look at some of the fishing shows to see how stable thay can be.

Of course the other option is multihull.....which is the way lots of medim sized commercial shipping is going.

There are some incredibly fast displacement hull boats arround these days..and the longer and narrower they can be the faster they can go.

A mate of mine has a sailing cat that is 40 foot and weighs 7 tonnes, and he pushes that allong with 2 x 10Hp diesels.....and can make 7-8 knots with a clean bum and no headwind..I know it isnt fast but it only makes 17-18 knots under full sail and fair wind, before it becomes a serious underpants problem.

If we are talking about environmentaly friendly....if we had long pointy displacement hull cats......we should be able to push them along with 40 to 60 Hp where a square bum speed boat would require 150 to 200HP...ya might not do 40 knots.......but 20-30 and a much smoother ride is a realistic expectation, and running at lower speeds is economical where it isn't in a modern speed boat.

cheers

zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzzzzzzzz..can someone wake me when the dribble stops please.