Glen-L.com

I am looking for info on the different types of transmissions available. I have read references to V-drives, velvet drives, down angles, direct, reduced etc... What are all these terms? Unfortunately I am a car guy and know little to nothing about boats. Any links to "inboard boat transmissions for dummies?"

I want to build a Barrelback 19' (stretched to 20') with a small block Chevy. What transmission am I going to need? What transmission will keep the engine closer to level and do I have any choices in this regard.

PS.. This is a great site. People seem to be truly interested in helping others. Sorry if this question has been asked but I couldn't find info when I searched.

slow8,



A down angle drive means that the prop shaft is angled down from the engine crank shaft. The boat probably has the shaft angled down about 12 degrees from the motor stringers. An 8 degree down angle will mean the engine would then tilt back 4 degrees.

A straight Velvet Drive the engine would tilt 12 Degrees.

Bill

_________________
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Thanks Bill.

I found some notes here on the Glen L site.

http://www.glen-l.com/inboard-hdw/velvetdrive.html

So it looks like the 71C and 72C are fairly standard.

Any info on the ZF Hurth Trans? Looks like they have the down angle option.

What ratio am I going to need with a 260-280hp engine in a 20' boat? Is the gear ratio an overdrive of crank speed (1.2 ratio would be 1000 rpm at crank = 1,200rpm at prop or vise versa???)

Thanks again!

I'm running a ZF-45A behind a 125 Diesel

Ratio 1.25:1 at 3800 rpm the prop is at 3040 rpm.

Use the how fast chart to determine what speed you can try to get. Then play with gear ratios and prop pitch to try to achieve it.

Bill

_________________
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

for a boat like that, you want as close to a 1:1 ratio as you can get. The 71c and 72c BorgWarner VelvetDrive are not down angle trannys, but they have been the standard bearer for decades, and for good reason. These are old school, cast iron, hydraulic trannys, and accepted as bullit proof. The 71c is good for as much HP as a small block, and the 72c is good for a big block. There is reduction gearing available also; that is a planetary gearset added on to reduce the output RPM to multiply the torque. For your little Barrelback, stay with a 1:1 ratio.
ZF bought out Hurth several years ago; they make the most common down angle trannys, but not in a 1:1 ratio. Most of these are aluminum casings, lightweight, newer technology, and they are good quality. Closest to 1:1 is approx a 1.2:1 as Bill has one of those.
ZF also makes a tranny in similar to the 71c & 72c, but I never seen one.

Can't let Bill and Kens have all the fun, so I'll provide some reading material

The Velvet Drive Installation and Service Manuals contain a wealth of information
(ratios, prop selection, installation, service etc).

Maybe even too much information . . .
__________________
Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod : http://www.boats.chelseacoachworks.com

Thanks for all the info guys.

In my mind mounting an engine at 8° or 12° seems like it would cause oiling and fuel issues...??? Am I being to paranoid?

If I use a Velvet trans can I use a Python or Aqua drive type CV joint to take the angle from the engine to the prop shaft? I think they list up to 8° of deflection for each CV.

I wanted to mount my engine as level as possible for clearance and oiling reasons. Some mfg. say to reduce oil level at 12 to avoid foaming.
I used a Python to split 13 into 6 and 7. The faster the shaft turns the shorter the life at big angles.
I have a 3:1 trans. so my shaft only turns 933 rpm. at cruise.

Carl

_________________
Carl
If not now......When?
http://s270.photobucket.com/albums/jj94/gashog7/boat/
http://www.epoxyworks.com/26/index.html Number26

I also wanted to point out that the Glen-L book Inboard Motor Installations is a wealth of information on the subject. I especially like that it explains so thoroughly the differences between and automotive engine and a marine engine.

Robert

Yes, you are paranoid; inboards have been mounted like that for decades. And yes, there is some oilpans, carburetor wedges, and things to assist the mounted angle. Mine is mounted at 12 degrees without any carb shim and it runs fine.

Durn, I read your replies and now I'm confused and I just got through doing this!! Velvel drives that are plain ol' velvet drives just bolt on and have the same angle as the engine. Borg does make velvet drives with a down angle, cept of course they are V drives with the V drive as part of the transmission, and are significantly different in that they reverse the direction the engine will face, fore or aft. in a straight install, the engine faces forward, with a velvet drive with a down angle v drive it will face backward. These also usually have a different gear ratio than 1 to one. in a normal barrelback, a straight velvet drive with an angled engine is the most common, the engine and tranny will tilt at about 12 degrees. They run like this and have for years. dont worry. I went another direction with a rear mount motor, 71 c velvet to a driveshaft that goes to a v drive in the middle of the boat, that drives a long, 75 inch prop shaft at 9 degrees, rather than 12. I felt that this gave me more room in the boat, a lower shaft angle and a probable performance increase. the penalty of course is weight, complexity, etc. Also, the normal barrelback does not have the fat ass to float a v 8 chevy. you gotta increase flotation to the rear. keep asking questions, you'll get the answers, just as I did. good luck.

I failed to address transmission ratios in my last post. most small boats will use a 1 to l ratio trans mission, that means 1000 crankshaft rpm is 1000 rpm on the output shaft or prop shaft. a 2 to one means the crank is turning 2ooo rpm to the prop shaft turning 1000 rpm. You can do this by using a bigger propeller which has its' advantages and disadvantages. There is a lot written on this. Course to confuse you even more I am using an overdrive in my v drive of 1.1 to 1, which means my prop shaft turns faster than my crankshaft. I am using a smaller prop than normal. To explain a little my v drive is a separate gearbox, not intergal with the velvet drive. This is the set up that V drive drag boats use. They also use huge motors with a gazillion horsepower. I am using 200 horses. I like the idea of the overdrive and a smaller prop, cause of drag, the smaller the prop disc, the lower the drag. there are trade offs here, read up on it.

here is a systen that keeps your engine and tranny level. There are other systems one is named python I think.
http://www.aquadrive.net/

_________________
Wood lasts generations.