velvet drive questions

[philcapper]

hope you might be able to answer a couple of questions re: velvet drive 71. No tag on transmission casting numbers 71-1G. it is a reduction unit but no idea what the ratio is. Also, it's supposedly a fresh rebuild which never had oil put in it. Should I be able to turn input/output shaft when it is dry? I am installing in a 24' semi V, 3-4K# boat with a tunnel, and a 200 hp 4.3 GM V6. Comments? what ratio do you think would work best?
thanks, I'm really in the dark here

[BMcF]

The only way to ID the reduction would be from the model number on the brass ID tag...which you say is missing. Unusual, that, because that tag is robustly made and well fastened to those transmissions.

I'll not offer any comment on the 'best' ratio...not near enough information for that.

The velvet drive is hydraulically operated and hence defaults to 'neutral' when the input shaft is not turning and there is no control pressure; you can turn input and output shafts by hand, yes.

[philcapper]

so the fact that i cannot turn he input or output shafts by hand does not bode well for the "rebuild"?

[BMcF]

Originally Posted by philcapper

so the fact that i cannot turn he input or output shafts by hand does not bode well for the "rebuild"?

Cannot turn them at all?..as in appear to be completely stuck?. With new band and clutch pack, all still dry and never oiled up and spun, it could be quite stiff to turn by hand, but should still do so, especially the output side..

[philcapper]

turned output with difficulty can't move input shaft but with bell housing in way, i can't get a good grip on it. i'll fill it ,let it sit for a day and see if it will turn. i've spent years in boats with velvet drives and never paid much attention too the mechanics of the transmission or design of the boat. Is the gear reduction versus a straight drive for use with smaller hp engines or heavier boats? will the propeller dia have to be increased with the use of a 1:1.5 transmission?
thanks

[BMcF]

Originally Posted by philcapper

Is the gear reduction versus a straight drive for use with smaller hp engines or heavier boats?

Yes to both. LOL. Example; My 32' Marinette cabin cruiser runs 1:1 velvets on 225 HP engines (pair) with 14 x 12 props. My buddy's 24' mini-trawler runs a velvet with the reduction gear behind a Pathfinder 74 HP diesel and that is swinging a much larger diameter wheel (18" maybe?) with similar pitch and at lower RPM.

Point being illustrated above is ....without a lot more information on the hull you have, cannot really offer opinions on a suitable prop.

[philcapper]

last question for awhile. Can a reduction transmission be converted to straight drive?

[BMcF]

Originally Posted by philcapper

last question for awhile. Can a reduction transmission be converted to straight drive?

Not any way that I know of.

[philcapper]

A bit of information. this boat is a 1963 Speiglemeyer 24'. semi v, 9'+ beam(precursor to the John Allmand) It has great classic lines and we have gutted the boat, installed new stringers and increased the size of the cuddy. It had a 165 chev in line 6 with a Mercruiser outdrive. Because we will be operating in gulf waters, around the west coast out islands, we are installing a tunnel with an outboard rudder. going to be quite a nice looking boat when done (next year)

[BMcF]

If you are installing a tunnel then that has a lot to do with the prop selection too, diameter especially.

Tunnel configuration issues aside, I see nothing in what you have posted so far that would suggest that a prop could not be selected to match up with that engine and drive, although you will need to determine the final drive ratio, of course. I'm betting its reasonably close to what was in that Merc outdrive, for that matter.

[philcapper]

thanks for all your help. Ill post pix when we are a little further on