gearbox ratios

[stevenash]

I have an old seamaster 25 with a Ford 1.8 diesel (from an Orion).
It has a Hurth 2:1 gearbox, and this drives through a V-drive which also has a ratio of 1.4327:1 (don't know why).
Consequently - I have to turn to engine 2.8654 times to turn the prop once. Nearly a 3:1 ratio.

This would explain why I have to scream the nuts of the engine to move the boat. (no insualtion either so getting round from the Medway to the thames was quite painful.

My question is - do I fit a direct drive gearbox, do I convert mine, or should I leave it and somehow the v drive altereed to 1:1.

I would appreciate anyone telling me WHAT to do, and HOW to do it in the most economical way - (I did already consider setting fire to the boat.

 

[alb40]

I think you would find the easiest and cheapest way to solve the proplem is to fit a larger propeller. Speak to SMM propellers at gravesend or Steel developments, and they would be able to calculate what size propeller would be best.

My boat has V drives - 1:1 gearboxes, then 1.5:1 V drives, but my engines are low reving.

If you are not going to come out of the water this winter, the easiest way to replace it would be to dry out on some of the medway's finest mud. I have two boats near rochester, both sit in the mud at all times except high tide. Its very soft, so does no damage to shafts rudders or the boat itself! I can get to my props by hang the back of the boat off the end of the small bank that is built up for the boat to sit on.

 

[oldharry]

I agree, screaming the engine to produce any power - prop much too small.