inboard engine-outboardor propeller?

[dionysis]

Is it possible to have an inboard engine, with a demountable or tilting outboard, electric or hydrolic propeller unit with wires or hoses leading forward to the engine? So that when away from land the boat does not suffer from added resistance etc., and there is no hole in the hull. Is this realistic?

Cheers dionysis

[George99]

What is the size of the boat?
What is the engine HP needed?
What is the use of the boat? Pleasure? Ocean going?

Give me some hints to come up with a practical solution

George99

[gonzo]

It's easy. Either use an electric motor connected to a generator, or a hydraulic motor connected to a pump.

[dionysis]

Hi George99 and Gonzo.

The boat will be about 60 ft lwl, and 20 tons, ocean going sloop. For a proper auxiliary, tables say about 100 hp, but I think this is too much.

I think that something of the order of 30 to 50 hp would be enough for an emergency, and for docking in close quarters.

I know this is rather small, but I hate the thought of such a big motor, with all it's attendant maintenance. What do you say?

I agree, your suggestion Gonzo, is the way to go. Air cooled too.

cheers and thanks for the replies. dionysis.

[gonzo]

30 to 50 seems OK. Bow thrusters on boats that size are about 10-15 HP.

[ongolo]

Hi Dionis,

why not put an air cooled diesel in. There is no other maintenance than oil changes, and whether you have an air colled diesel of 30 or 100hp its still only an oil change,

I have a 4 cyl 912 deutz in my 55ft schooner with 22t displacement by a narrow beam of only 12 ft.

the engine can dev a max of 80 hp at 3000rpm but only 65 at 2300 rpm and about 50 at 1800rpm which I will normaly run at.

regards ongolo

[dionysis]

Air cooled is the way to go ongolo, and I am glad that you agree gonzo, that say 50 hp is allright in this sze boat.

Bow thrusters? hmm... seems more trouble than they are worth. Why are they important?

Check out this new kind of propeller:

hubner-braun propeller

What do you think?

cheers, dionysis

[gonzo]

In the US where marinas are overcrowded, there is little space to maneuver. Even twin screw boats can have a hard time docking. In these conditions, a bow thruster may be necessary.

[dionysis]

This is well worth considering. Thanks for the pointer gonzo.

dionysis

[gonzo]

That propeller looks interesting. Do they give efficiency comparisons to standard propellers? I had a 34' catamaran with an outboard in a central pod. It worked, somewhat, to move the boat sideways. The lateral movemant produces huge eddies that make the propeller cavitate.

[dionysis]

Info on website says same efficiencies as a normal propeller.

Cavitation going sideways makes sense, since there would be a lot of resistance, just as there would be a lot of resistance initially when moving off from a mooring say.

I like the idea because you can get retractable ones.

By the way this kind of propeller, according to the website, is used on tug boats, so would be ideal for going sideways, really good for manouvering in confined situations.

cheers

[Doug Carlson]

Its a very interesting system. I wonder about durability and maintenance in that it appears to be significantly more complex than a fixed blade, folding, or even a variable pitch (feathering) propellor. Pitch is altered on every rotation. Helicopter complexity.

[yipster]

Its a very interesting system. I wonder about durability and maintenance in that it appears to be significantly more complex than a fixed blade, folding, or even a variable pitch (feathering) propellor. Pitch is altered on every rotation. Helicopter complexity.

ánd it leaves a hole in the hull...
i posted a webcam pic of myself on the pc here with a RC heli hanging over my head but toke it off again, think for a boat prop i agree with Doug, still its a interesting idea!

[gonzo]

One concern is that it has not protection from impact.

[SailDesign]

These "props". like the Voith-Schneiders used on tugs, are much slower-turning than "real" props, so the impact thing is not such a problem. Believe me, if they were painful to deal with, or un-reliable in debris-filled water, they would not be put on harbour tugs ;-))
Yes, they are more complex, though.
Steve