Going forward in reverse

[jubro]

A friend has just fitted a new propellor, only to discover she (gentlemen please be civil) ordered it wrongly handed. Sorting this out properly will entail more cost and fiddling about (ie. hauling the boat out again), so we're trying to decide if there's any good reason why she shouldn't spend this year using reverse gear to go forward, and vica-versa? The engine is a Volvo 20hp (probably a 2002 by the age of the boat) driving a conventional propshaft. We think that it could even be good for the gearbox, as the reverse cone is likely to be much less worn than the forward one, so it might even extend its life a bit. Any thoughts?

 

[sarabande]

ahead and astern ratios are usually (???) different. Possibly gearboxes aren't designed to spend their working life in astern.

There might also be accidental selection of the wrong direction under manoeuvering stress, which might entail a bit of an explanation to the insurance company.


Perhaps buy a secondhand one for this year?


Why won't the supplier take it about against an order for the proper one ?

 

[jubro]

I wasn't sure about the ratios thing. On my boat, with a Yanmar saildrive, it feels like I have the same 'push' in astern as I do in forward, but I have no idea if the ratios are actually the same. Can anyone confirm whether astern is usually a different ratio to forward?

I think the issue with getting the correct prop is mainly to do with having to haul the boat out again to do it, and that my friend is a keen racer and usually has a busy programme of events, so won't want to have the boat out of commission if she can help it. The other issue is that the prop came from Australia, so switching it for the other handed version could take a while...

I completely take your point about illogical control arrangements leading to mishaps under stress. I watched a friend bring his boat alongside a few years ago for craning out, when at the last moment it accelerated and hit the boat in front hard. It had an athwartship gear lever mounted at the back of the cockpit. The following year, this had gained big labels for FORWARD and ASTERN. As he's a boatbuilder, this accident cost him nothing but a little time and a lot of embarrasment!

 

[scottie]

Move the gear cable on the control to the other side and get used to the prop wash going he other way
The box Will run ok in reverse it's designed that way when wanted for twin screw.
Disregards comments about other set ups as you do not have them!

 

[Woodlouse]

What Scottie says. Open the morse control and move the gear cable to the other side. Problem solved.

 

[jubro]

Thank you both - the bits about twin screws and two sides to the morse lever rings bells and makes perfect sense. I'll pass these pearls on.

 

[Hoolie]

What Scottie says. Open the morse control and move the gear cable to the other side. Problem solved.

Temporarily maybe - but you're still left with the ratio problem. Normally about 2:1 difference fwd/astern.

 

[Woodlouse]

Temporarily maybe - but you're still left with the ratio problem. Normally about 2:1 difference fwd/astern.

Really? I'd have thought marine engines would have the same ratio for forwards and backwards. Otherwise companies would have to supply different gearboxes for those with two engines. Also you'd generally want just as much power to the prop going backwards as forwards.

 

[sarabande]

Some gearboxes do have differing ratios...

 

[VicS]

What is all this about a ratio problem.

If its a Volvo 2002 I think you will find that it has a MS2 gear box !

I think you will find that the gear ratio is the same forwards and reverse.

Look at the design of the box and how it works .. it cannot be different!

 

[Hoolie]

Really? I'd have thought marine engines would have the same ratio for forwards and backwards. Otherwise companies would have to supply different gearboxes for those with two engines. Also you'd generally want just as much power to the prop going backwards as forwards.

Well, my Hurth gearbox has about 2:1 difference between astern and forward, as has been implied by other posts on this thread.

 

[VicS]

Well, my Hurth gearbox has about 2:1 difference between astern and forward, as has been implied by other posts on this thread.

So it may have . But this is almost ceratinly an MS2

 

[sarabande]

the different ratios issue was raised as a general, not a particular comment, to consider potential problems of running astern.

And other manufacturers do have different ratios. e.g.

http://www.thameswaymarineproducts.co.uk/transtyp.htm

 

[Norman_E]

Aside from any ratio issue, it usually requires one more gear wheel to be engaged to run in reverse, and that may not be designed as suitable for continuous use.

 

[Tranona]

Two issues. First the ratio. Many boxes have different ratios forward and astern. Yanmar for example have a fixed astern ratio but a choice of three different forward ratios. Think Vic is right and the MS2 box is probably the same for each. Second is whether the box is designed to run continuously in either directions. Some are so that they can be used in handed applications, but I would be wary doing it with a box that is set up normally for only one direction of prop. Need to check with the manufacturer.

 

[VicS]

Aside from any ratio issue, it usually requires one more gear wheel to be engaged to run in reverse, and that may not be designed as suitable for continuous use.

No if its a MS2 the same gears are engaged .
Look at the diagram also the video posted on this thread http://www.ybw.com/forums/showthread.php?t=312148

 

[Martin_J]

and looking at the diagram just now (thanks VicS).. it's actually the same part number for the gear above the cone as it is for the one below #8
Cool..

Talking of reversing.. Many years ago I met a French boat that had their wheel gear reversed.. Skipper said he felt happier that it felt more like a tiller when steering!

 

[VicS]

and looking at the diagram just now (thanks VicS).. it's actually the same part number for the gear above the cone as it is for the one below #8
Cool..

Talking of reversing.. Many years ago I met a French boat that had their wheel gear reversed.. Skipper said he felt happier that it felt more like a tiller when steering!

To a small extent i can understand that. Ive only ever sailed one wheel steered boat and found no problem. After all it steers like a car.

BUT we had one person on the YM course I did who had only ever sailed with wheel steering. He found it difficult to get used to the way a tiller operated.. Some interesting consequences!

 

[nigelmercier]

Reminds me of the scene in the alien ship from Independence Day:

Captain Steven Hiller: [after reversing into the rear wall] Oops.
David Levinson: W-what do you mean, oops?
Captain Steven Hiller: Some jerk put this...
[Turns the piece of paper round]
Captain Steven Hiller: the wrong way round.

 

[Martin_J]

Still trying to figure out what I video'd and how exactly it works... What does part #46 in that diagram do? I'll wait until morning before wanting to understand the answer.