Reduction gearbox

[martinwill]

I have a 2:1 reduction hurth gearbox, but is not suitable for my boat according to various prop calculators, it needs to be more towards 1:1, can the gearbox ratios be changed by changing the internal gears ? or is it a new box or higher reving engine

[gonzo]

What model is it?

[martinwill]

Its a HBW10-2R its the external same dimmensions as a HBW150/ZF15M which come in a 1.6:1 reduction.
Also the HBW100 comes in a 1.48:1 reduction which should fit my adaptor plate
Will purchase one of the above (2nd hand) if one turns up as i have been told it would be cheaper than replacing gears.All this just to get the right prop for the boat as the prop calculators available on the net surjest a 5 blade prop.
Its a 17 foot full displacement fishing boat, waterline 16 foot, weight about 1 ton, 2000 max rpm, 16.5hp, 2:1 reduction(at present) with a max diameter prop of 13.5 inches.
Any help appreciated

[alan white]

Dunno if a 1:1 tranny is direct (as opposed to going through a layshaft), but if so, it would be more efficient (10-15%) by virtue of the direct shafting alone.
More reason then to search for a 1:1 ratio. Five blades seems unnecessary with 1:1, or did you mean with your current 2:1 set-up?

Alan

[martinwill]

Yes Alan the 5 blade prop would be needed with its current box at 2:1 (according to prop calculator at castlemarine.co.uk) , with a 1.5:1 reduction i can run a 13.5x11.75 3 blade prop 64%DAR (disc area ratio), i would rather change the ratio in my current box but will purchase a new one at a push and will stick to hurth so i dont have to change the mounting plate, which would be hard to get for my old Petter PH2W
I need to know if hbw150 or hbw100 parts fit my hbw10-2r or are any other make boxes interchangable with hurth mountings

[mike price]

Hi Does Anyone Have Any Experienc With A Hbw 100 Box Lagging When Engaging Gear Please. It Is In A Narrow Boat Paired To A Betamarine 2cyl. When Either Foreward Or Reverse Is Engaged There Is A Delay Before Take Up . Sometimes It Takes 3 To 6 Seconds To Change,, Thanks Mike

[Jango]

Martinwill, Most Gearboxes, other than 1:1, have an extension containing the reduction gears. In order to go to 1:1, you would need to remove the Extension and most likely install a rear seal, Thrust Bearings and Hub. Probably alot easier and less expensive to change Gear ratios, if you have access to inexpensive gears.

Jango

[mike price]

Thank you jango. i am not sure i know what you mean , i will try and find a manual on the net somewhere,

[Jango]

Mike, unless you are also Martinwill, You should start a New trend with your questions. Makes it kind of confusing.

[martinwill]

Thanks for that Jango, (Martinwill here this time !!) i have never been inside a hurth box, but i will certainly look into going to a 1:1 reduction as that would suit my boat fine.
I have not got access to cheap parts but will search suppliers, for the parts you mentioned, seal, thrust bearing and hub, any other thoughts please contact me and thanks.