40+ reversing

[Charles uk]

Sandro edit your details so we know where you are.

[Rex NZ]

Sandro

The reverse bucket idea has alot of merit
* no restarts req
* well proven on jetboats
* the propshaft thrust is maintained in the same direction, could be an issue otherwise on a clutch drive.
* simple to setup, follow links below

A slide might be likely to jam. I'd go with a pivoted bucket that folds upwards out of the water. A propane gas bottle or pipe bend would make a good donor for a nice piece of compound curved steel.

http://www.google.co.nz/imgres?q=jet+ou ... -AQ&zoom=1

http://t2.gstatic.com/images?q=tbn:ANd9 ... JdDKrkB2Vj

http://www.google.co.nz/search?q=jet+ou ... 80&bih=935

Rex

[Keith.P]

You could always redesign the gearbox.
Its very easy, this short video will help you understand the principals involved. http://www.wimp.com/buildit/
Off you go.

[electrosys]

Excellent !

But of course what he was really describing - at some length - was the ACME Industries Infinite Improbability Drive.

But then - you knew that really ...

[Sandro_Picchio]

Thank you RexNZ,

What I am thinking of is something lighter than the gas bottle.

I don't yet know how to insert a sketch in a post, anyway the spoiler should be made of galvanized or ss sheet, stiffened by a heavvyer frame. Its shape thus should be developable, i.e. bent from a flat sheet.

Two possible ways:

1- Spoiler shaped as a rounded bottom W or as a 3, placed vertically behind the propellor, tall as the diameter and well wider of it, dividing the water jet and redirecting it forwards each side of the prop.

2- Spoiler U shaped, diameter almost twice the propeller's, placed horizontally behind the prop, reaching deeper than it, redirecting the water jet forwards under the prop.

The spoiler 1 has the advantages of a draft not deeper than the prop and of being streamlined if immersed by the boat rocking when motoring forward.

The spoiler would be hinged as you said above the propellor, swinging out of the water.

It would not be very difficult had the motor being hanging really outboard of the transom, but in my instance the Seagull is in a well to port of the keel, ahead of a sloping transom.

The spoiler hinge could be fitted to the hull instead of the motor leg, applyng the backwards pull directly to the boat and avoiding pulling the motor out of the water when reversing. Of course steering in reverse with the motor would not be possible.
But the bottom end of the spoiler is also to be held firmly forwards when reversing and a strong point must be found, eventually not on the gearbox.

Moreover, the motor must be free of tilting, prodding the gearbox out through the transom higher than water level.
A few space overcrowding problems are still unsolved.

We'll see.

Sandro

[david]

Thanks for that electrosys, I was most of the way through building it when my shed filled up with bowls of petunias.

[Horsley-Anarak]

Thanks for that electrosys, I was most of the way through building it when my shed filled up with bowls of petunias.

"Forty-two,"

H-A

[david]

Yes, but has Benji got his question?

[Horsley-Anarak]

Yes, but has Benji got his question?

Not sure give me 7½ million years and I will let you know.

H-A

[Buzzook]

Clearly this question requires Deep Thought.....

[Rex NZ]

Sandro

Maybe have a scavenge thru some wrecked jet units or jetskis for some bits.

This might provide some useful linkages or bucket/scoop.

Rex

[Collector Inspector]

Welcome Sandro, just back from the bush and happy new year to everyone aye?

I am afraid that you lost me with your 4Hp (E4BRHCRM), for example with a clutch?

Also what you followed up with is, while a converstaion starter/keep it going, has...............flumaxed me?

Maybe B is snarky for 2012, let us see aye?

Anzani Rock!

B

[electrosys]

Hi Sandro

Couple of thoughts re: the reversing 'bucket'.

If you adopt system 1 (i.e. the '3' shape), then with the bucket attached to the drive tube (say), should the reverse thrust stream not be absolutely equal on both sides, then you'll have created a steering moment. Which could be fun, until you get used to it.

However, if the bucket is attached directly to the transom, then this effect could actually be employed to provide steering - by directing more thrust through one side than the other. Such thrust will have the 'reverse-tiller' effect of course: moving the Seagull's tiller across to s/board will cause an increased thrust from the port side of the bucket, which will push the reversing transom towards s/board. But - it shouldn't take too long to get used to that.

With system 2 (the under-slung bucket), the horizontal diameter really only needs to be that of the prop, plus (say) an inch on either side. The vertical height could be reduced by having the under-slung portion a rectangular shape - same width as the upper bucket, but with less height - which suggests the use of a more 'mouldable' material than steel plate - say GRP (suitably reinforced with s/s straps) - presumably built-up over a mould ?
From the rear it would look not unlike an old-fashioned diver's helmet - rounded top with a flat base.


Ok - here's a question for the academics ...
A Seagull driving forwards (i.e. normally) - in deep water - does not require a kick-up preventer, as the drive shaft is being pressed towards the transom. Ok.

Now - let's say I fit a reversing bucket to the Seagull's drive leg, which has 75% efficiency, and I now drive the Seagull with the reversing bucket engaged.


Case 1: Regardless of what's happening behind it, the propellor continues to press the drive shaft towards the transom, so a kick-up preventer is NOT required.

Case 2: From a 'complete system point of view' there is a net force directed backwards, so a kick-up preventer IS required to keep the drive shaft in place.

Case 3: The propellor is driving the drive shaft forwards with a strength of 1 unit, whereas the reversing bucket is creating a pull in the reverse direction of 0.75 units, so a kick-up preventer is NOT required.

Ok - any takers ?

[Charles uk]

To provide enough thrust to move the boat backwards the forward push from the motor has to be less than the redirected thrust pushing it backwards so the motor will self tilt unless restrained.

This only applies if the reversing bucket is attached to the leg if the bucket is hung from the transom this would not apply, you would have to hope enough water was directed back towards the bow to overcome the water that was bypassing your deflector, Perhaps a GRP one cast on a ladies bare bum would be the best shape, & there are a lot of different patterns to choose from, I can't help you there as all the ones I know, would be more suitable for the 60 hp version.

[charlesp]

....'cast on a ladies bare bum'

Funnily enough I'm up your way on the day you rub on the releasing agent, so I can give you a hand! (Or two..)