A single screw

[Guest]

With engines becoming smaller and produceing more Hp, is there an arguement for one engine, in traditional twin screw boats up to 40ft. Obvious savings on fuel , maintanence , space etc. some manouverabilty would be lost but fitted with thrusters as standard would help in this matter. I make these comments after having to buy everything twice which hurts after a while.

 

[Chris_d]

Re: Its a Brit thing

In Scandinavia lots of boats in this range only have one engine, likewise
in the rest of europe, I think the twin screw thing is a very british, something to do with a culture of Bristol and Mosquito bombers from the war I think!.
As you say twins cost more and are less efficent and heavier, at least up to 40ft.
I would happily put up with a single screw ( !!! ), never found handling that much of a problem.

 

[kimhollamby]

Yes, there are major plusses and it is only market forces now that keep such things from happening.

Big capacity single diesels could be quite a fun fit; slower revving, less noisy, lots more maintenance room, hydrodynamically more efficient. Just seen a pair of the new Cummins QSM11s in action on a Hatteras 53; one of those at 660hp/2300rpm could do at lot for something in the 35ft-40ft range. Double up on water intakes and fuel filters and the whole thing starts to look very exciting indeed. As you say bow and stern thrusters can do a lot of those who don't like the thought of single engine slow speed stuff; add a trolling valve to the gearbox and it will go as slow as you want too.

Bit of an issue on how to make a single shaft and huge prop work on a vee hull with no keel; suspect some poor handling characteristics. Perhaps a waterjet would be the answer, although that might cause some inefficiency. For a semi-displacement hull with a deepish keel it's a no-brainer.

Only signficant risk then is prop fouling. But a lot of owners in this range also fit decent genset, so how about some kind of diesel electric auxiliary for get-you-home and river cruising or fish trolling?

kim_hollamby@ipcmedia.com<P ID="edit"><FONT SIZE=-1>Edited by kimhollamby on 11/10/2002 13:32 (server time).</FONT></P>

 

[Divemaster1]

Would seriously consider this as an option for the obvious reasons that Kim stated below. And when looking at efficiency, you get better fuel economy, thus range and lower overall running cost. Would consider surface drive on a fast planning hull (sensitive to weight at stern I am lead to believe), but still have some problems finding a properly engineered fix on the aux. propulsion issue, without affecting the boat's performance (drag etc.).

Single engine could be OK, but need an alternative propulsion (shaft or whatever) for safety.


AHM

 

[tripleace]

Single Diesel driving hydraulic pump.

props driven by Hyd, which could also drive generator, bow truster and stern thruster

you could also have a second much smaller say 10-15 hp engine again driving hyd, which would be used for low speed work, standby or combined to add extra power. It would also drive gen.

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[hlb]

Too enefficiant. But could have one engine driving two shafts and even have one prop going Folwards whilst the other goes back. So no need for bow thrusters.

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Haydn

 

[jfm]

Not hydraulic motors

Discussed before. 600hp hydraulic pump hugely inefficient, and all crew wd need ear defenders

 

[qsiv]

Re: Not hydraulic motors

Pardon?

 

[hlb]

Re: Not hydraulic motors

HE SAID. (In a loud voice.)

Discussed before. 600hp hydraulic pump hugely inefficient, and all crew wd need ear defenders.





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Haydn

 

[Duncan_Hamble]

Regarding strange handling characteristics with a deep V hull with no keel I don't remember the Fairey Huntress having any particular problems.

In addition getting a smooth water flow to a propeller behind a keel on a high speed boat would be a problem.

A water jet probably wouldn't help handling, especially at low speed as it has no rudder - you would need to have some thrust to be able to steer. Have you tried driving a jet ski slowly?

Anyway, single engines are a good idea but require Owners to maintain them well. In my experience maintainance is often lacking.

 

[wakeup]

Oh Man, Wait till Gludy see this nm!

.

yada yada..

 

[qsiv]

Re: Not hydraulic motors

I agree ...

I know it's a long, long time ago but in WW II my old man had a 'special' Petrol-Electric (only the Americans had big diesels, Brits just burned in pools of petrol) MGB.

Having tooled around in a normal triple ( or were they quad) engine version he had the centre engine(s) replaced with electrics plus a silenced genset. He used this toys to land resistance workers and spies in Holland. Apparently they quite liked his delivery service - if conditions were 'right' (vile weather, fog etc) rather than having them put ashore in rubber dinghies he dropped them off against the quay in Schevingen - so much nicer not to get wet feet, they said.

 

[kimhollamby]

Okay, agreed waterjet intakes on vee hulls not the easiest to sort. But what I was thinking about was the necessary single shaft configuration on a keel-less hull which is going to place the prop a long way down on a 40-footer and make it vulnerable, unless the designer can incorporate some kind of semi-tunnel and not lose efficiency (or in fact gain some thanks to shallower shaft angle) which might be possible. Still quite difficult on a big prop I suspect.

Two badly maintained engines not much better than one I'm afraid, especially as the inexperienced owner might be tempted to push a sole remaining engine hard in case of failure of the other one with consequential problems. Singles arguably concentrate the mind somewhat and at least you can get to both sides easily...unless the interior designer has a field day and slaps quarter berths and the like alongside, which is not unknown.

Speaking from a degree of experience, having run a single-engined boat at sea for a couple of seasons. One failure; fuel filter problem due to bad diesel which was relatively easily solved without external assistance because the fuel filter had lots of space around it.

kim_hollamby@ipcmedia.com

 

[kimhollamby]

Hey, how about electric auxiliary drive that actually lifts clear of the water (or at least the planing surface) when not needed? In fact, that sounds pretty much like some stern thruster arrangements, albeit it would need to be able to swing through 90° to perform both duties, be a bit more powerful and be continuous rated. That might in fact point to hydraulics, would allow a feed to be taken from genset or main engine.

You only need enough horsepower to make hull speed of boat, say about 7 knots or so, for it to do the job, so quite low horsepower requirement.

Better this than going for second shaft in water in my book.

kim_hollamby@ipcmedia.com

 

[hlb]

So whats up with my one engine and two shaft design. Nowt needs to change, cept stick one big engine in the middle, running two gear boxes side by side. Simple easy and no hastle.

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Haydn

 

[kimhollamby]

Too much drag and inefficient in terms of power train losses. Much better to channel the main power source down the centreline and do something different for the get-you-home bit, at least in my opinion.

kim_hollamby@ipcmedia.com

 

[hlb]

Yes but you have not answered how you get a bloody great prop under the center line. My answer is simple.

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Haydn

 

[tripleace]

recap then

One bloody big engine, driving a water jet, in a tunnel.

Both bow and stern thrusters driven by hydraulics which are powered by a second smaller engine which drives the hydraulic motor and which in fact also drives the generator.

oh yes the stern truster turns 90% and is continously rated

I'm down to halfords to get the bits to do it tommorow....

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[hlb]

Re: recap then

How about an electric motor and a long flex!

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Haydn

 

[Guest]

Re: recap then

........... better still a pair of oars ........... I said OARS.............
cheaper still.........

JR